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 <chapter id="jdbc">
  <title><acronym>JDBC</acronym> Interface</title>

  <note>
   <title>Author</title>
   <para>
    Originally written by Peter T. Mount (<email>peter@retep.org.uk</email>), 
    the original author of the <acronym>JDBC</acronym> driver.
   </para>
  </note>

  <para>
   <acronym>JDBC</acronym> is a core <acronym>API</acronym> of Java 1.1 and later.
   It provides a standard set of
   interfaces to <acronym>SQL</acronym>-compliant databases.
  </para>

  <para>
   <productname>PostgreSQL</> provides a <firstterm>type
   4</firstterm> <acronym>JDBC</acronym> Driver.  Type 4 indicates
   that the driver is written in Pure Java, and communicates in the
   database system's own network protocol. Because of this, the driver
   is platform independent; once compiled, the driver can be used on
   any system.
  </para>

  <para>
   This chapter is not intended as a complete guide to
   <acronym>JDBC</acronym> programming, but should help to get you
   started. For more information refer to the standard
   <acronym>JDBC</acronym> <acronym>API</acronym> documentation.
   Also, take a look at the examples included with the source. The
   basic example is used here.
  </para>

 <sect1 id="jdbc-setup">
  <title>Setting up the <acronym>JDBC</acronym> Driver</title>

  <sect2 id="jdbc-build">
   <title>Getting the Driver</title>

   <para>
    Precompiled versions of the driver can be downloaded from
    the <ulink
    url="http://jdbc.postgresql.org"><productname>PostgreSQL</productname>
    <acronym>JDBC</acronym> web site</ulink>.
   </para>

   <para>
    Alternatively you can build the driver from source, but you
    should only need to do this if you are making changes to the
    source code.  For details, refer to the PostgreSQL installation
    instructions.  After installation, the driver should be found in
    <filename><replaceable>PREFIX</>/share/java/postgresql.jar</filename>.
    The resulting driver will be built for the version of Java you are
    running.  If you build with a 1.1 JDK you will build a version
    that supports the JDBC 1 specification, if you build with a Java 2
    JDK (e.g., JDK 1.2 or JDK 1.3) you will build a version that
    supports the JDBC 2 specification.
   </para>
  </sect2>

  <sect2 id="jdbc-classpath">
   <title>Setting up the Class Path</title>

   <para>
    To use the driver, the JAR archive (named
    <filename>postgresql.jar</filename> if you built from source, otherwise
    it will likely be named <filename>jdbc7.2-1.1.jar</filename> or 
    <filename>jdbc7.2-1.2.jar</filename> for the JDBC 1 and JDBC 2 versions
    respectively)
    needs to be included in the
    class path, either by putting it in the <envar>CLASSPATH</envar>
    environment variable, or by using flags on the
    <command>java</command> command line.
   </para>

    <para>
     For instance, I have an application that uses the
     <acronym>JDBC</acronym> driver to access a large database
     containing astronomical objects. I have the application and the
     <acronym>JDBC</acronym> driver installed in the <filename
     class="directory">/usr/local/lib</filename> directory, and the
     Java <acronym>JDK</acronym> installed in
     <filename>/usr/local/jdk1.3.1</filename>.  To run the
     application, I would use:
<programlisting>
export CLASSPATH=/usr/local/lib/finder.jar<co id="co.jdbc-finder">:/usr/local/pgsql/share/java/postgresql.jar:.
java Finder
</programlisting>
     <calloutlist>
      <callout arearefs="co.jdbc-finder">
       <para>
        <filename>finder.jar</filename> contains the Finder application.
       </para>
      </callout>
     </calloutlist>
    </para>

    <para>
     Loading the driver from within the application is covered in
     <xref linkend="jdbc-use">.
    </para>
  </sect2>

  <sect2 id="jdbc-prepare">
   <title>Preparing the Database for <acronym>JDBC</acronym></title>

   <para>
    Because Java only uses TCP/IP connections, the
    <application>PostgreSQL</application> server must be configured to
    accept TCP/IP connections.  This can be done by setting 
    <literal>tcpip_socket = true</literal> in the 
    <filename>postgresql.conf</filename> file or by supplying the
    <option>-i</option> option flag when starting
    <command>postmaster</command>.
   </para>

   <para>
    Also, the client authentication setup in the
    <filename>pg_hba.conf</filename> file may need to be configured.
    Refer to the <citetitle>Administrator's Guide</citetitle> for
    details.  The <acronym>JDBC</acronym> Driver supports the trust,
    ident, password, md5, and crypt authentication methods.
   </para>
  </sect2>
 </sect1>

 <sect1 id="jdbc-use">
  <title>Using the Driver</title>

  <sect2 id="jdbc-import">
   <title>Importing <acronym>JDBC</acronym></title>

   <para>
    Any source that uses <acronym>JDBC</acronym> needs to import the
    <literal>java.sql</literal> package, using:

<programlisting>
import java.sql.*;
</programlisting>

    <important>
     <para>
      Do not import the <literal>org.postgresql</literal> package. If
      you do, your source will not compile, as
      <command>javac</command> will get confused.
     </para>
    </important>
   </para>
  </sect2>

  <sect2 id="jdbc-load">
   <title>Loading the Driver</title>

   <para>
    Before you can connect to a database, you need to load the
    driver. There are two methods available, and it depends on your
    code which is the best one to use.
   </para>

   <para>
    In the first method, your code implicitly loads the driver using the
    <function>Class.forName()</function> method.
    For <productname>PostgreSQL</>, you would use:

<programlisting>
Class.forName("org.postgresql.Driver");
</programlisting>

    This will load the driver, and while loading, the driver will automatically
    register itself with <acronym>JDBC</acronym>.

    <note>
     <para>
      The <function>forName()</function> method can throw a
      <classname>ClassNotFoundException</classname> if the driver is
      not available.
     </para>
    </note>
   </para>

   <para>
    This is the most common method to use, but restricts your code to
    use just <productname>PostgreSQL</productname>.  If your code may
    access another database system in the future, and you do not use
    any <productname>PostgreSQL</productname>-specific extensions, then
    the second method is advisable.
   </para>

   <para>
    The second method passes the driver as a parameter to the
    <acronym>JVM</acronym> as it starts, using the <option>-D</option>
    argument. Example:
<programlisting>
java -Djdbc.drivers=org.postgresql.Driver example.ImageViewer
</programlisting>
    In this example, the <acronym>JVM</acronym> will attempt to load
    the driver as part of its initialization. Once done, the
    <classname>ImageViewer</classname> is started.
   </para>

   <para>
    Now, this method is the better one to use because it allows your
    code to be used with other database packages without recompiling
    the code. The only thing that would also change is the connection
    <acronym>URL</acronym>, which is covered next.
   </para>

   <para>
    One last thing: When your code then tries to open a
    <classname>Connection</classname>, and you get a <errorname>No
    driver available</errorname> <classname>SQLException</classname>
    being thrown, this is probably caused by the driver not being in
    the class path, or the value in the parameter not being correct.
   </para>
  </sect2>

  <sect2 id="jdbc-connect">
   <title>Connecting to the Database</title>

   <para>
    With <acronym>JDBC</acronym>, a database is represented by a
    <acronym>URL</acronym> (Uniform Resource Locator).  With
    <application>PostgreSQL</application>, this takes one of the
    following forms:

    <itemizedlist>
     <listitem>
<synopsis>
jdbc:postgresql:<replaceable class="parameter">database</replaceable>
</synopsis>
     </listitem>

     <listitem>
<synopsis>
jdbc:postgresql://<replaceable class="parameter">host</replaceable>/<replaceable class="parameter">database</replaceable>
</synopsis>
     </listitem>

     <listitem>
<synopsis>
jdbc:postgresql://<replaceable class="parameter">host</replaceable>:<replaceable class="parameter">port</replaceable>/<replaceable class="parameter">database</replaceable>
</synopsis>
     </listitem>
    </itemizedlist>

    where:

    <variablelist>
     <varlistentry>
      <term>
       <replaceable class="parameter">host</replaceable>
      </term>
      <listitem>
       <para>
        The host name of the server. Defaults to <literal>localhost</literal>.
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>
       <replaceable class="parameter">port</replaceable>
      </term>
      <listitem>
       <para>
        The port number the server is listening on. Defaults to the
        <productname>PostgreSQL</productname> standard port number (5432).
       </para>
      </listitem>
     </varlistentry>

     <varlistentry>
      <term>
       <replaceable class="parameter">database</replaceable>
      </term>
      <listitem>
       <para>
        The database name.
       </para>
      </listitem>
     </varlistentry>
    </variablelist>
   </para>

   <para>
    To connect, you need to get a <classname>Connection</classname> instance from 
    <acronym>JDBC</acronym>. To do this,
    you would use the <function>DriverManager.getConnection()</function> method:

<programlisting>
Connection db = DriverManager.getConnection(url, username, password);
</programlisting>
   </para>
  </sect2>

  <sect2 id="jdbc-disconnect">
   <title>Closing the Connection</title>

   <para>
    To close the database connection, simply call the
    <function>close()</function> method to the <classname>Connection</classname>:
<programlisting>
db.close();
</programlisting>
   </para>
  </sect2>
 </sect1>


  <sect1 id="jdbc-query">
   <title>Issuing a Query and Processing the Result</title>

   <para>
    Any time you want to issue <acronym>SQL</acronym> statements to
    the database, you require a <classname>Statement</classname> or 
    <classname>PreparedStatement</classname> instance. Once you have 
    a <classname>Statement</classname> or 
    <classname>PreparedStatement</classname>, you can use issue a
    query. This will return a <classname>ResultSet</classname>
    instance, which contains the entire result.  <xref
    linkend="jdbc-query-example"> illustrates this process.
   </para>

   <example id="jdbc-query-example">
    <title>Processing a Simple Query in <acronym>JDCB</acronym></title>

    <para>
     This example will issue a simple query and print out the first
     column of each row using a <classname>Statement</classname>.
<programlisting>
Statement st = db.createStatement();
ResultSet rs = st.executeQuery("SELECT * FROM mytable where columnfoo = 500");
while(rs.next()) {
    System.out.print("Column 1 returned ");
    System.out.println(rs.getString(1));
}
rs.close();
st.close();
</programlisting>
    </para>

    <para>
     This example will issue the same query as before using 
     a <classname>PreparedStatement</classname>
     and a bind value in the query.
<programlisting>
int foovalue = 500;
PreparedStatement st = db.prepareStatement("SELECT * FROM mytable where columnfoo = ?");
st.setInt(1, foovalue);
ResultSet rs = st.executeQuery();
while(rs.next()) {
    System.out.print("Column 1 returned ");
    System.out.println(rs.getString(1));
}
rs.close();
st.close();
</programlisting>
    </para>
   </example>

   <sect2>
    <title>Using the <classname>Statement</classname> or <classname>
    PreparedStatement</classname> Interface</title>

    <para>
     The following must be considered when using the
     <classname>Statement</classname> or 
     <classname>PreparedStatement</classname> interface:

     <itemizedlist>
      <listitem>
       <para>
        You can use a single <classname>Statement</classname> instance
        as many times as you want. You could create one as soon as you
        open the connection and use it for the connection's
        lifetime. But you have to remember that only one
        <classname>ResultSet</classname> can exist per
        <classname>Statement</classname> or 
        <classname>PreparedStatement</classname> at a given time.
       </para>
      </listitem>

      <listitem>
       <para>
        If you need to perform a query while processing a
        <classname>ResultSet</classname>, you can simply create and
        use another <classname>Statement</classname>.
       </para>
      </listitem>

      <listitem>
       <para>
        If you are using threads, and several are using the database,
        you must use a separate <classname>Statement</classname> for
        each thread. Refer to <xref linkend="jdbc-thread"> if you are
        thinking of using threads, as it covers some important points.
       </para>
      </listitem>

      <listitem>
       <para>
        When you are done using the <classname>Statement</classname>
        or <classname>PreparedStatement</classname>
        you should close it.
       </para>
      </listitem>
     </itemizedlist>
    </para>
   </sect2>

   <sect2>
    <title>Using the <classname>ResultSet</classname> Interface</title>

    <para>
     The following must be considered when using the
     <classname>ResultSet</classname> interface:

     <itemizedlist>
      <listitem>
       <para>
        Before reading any values, you must call
        <function>next()</function>. This returns true if there is a
        result, but more importantly, it prepares the row for
        processing.
       </para>
      </listitem>

      <listitem>
       <para>
        Under the <acronym>JDBC</acronym> specification, you should
        access a field only once. It is safest to stick to this rule,
        although at the current time, the
        <productname>PostgreSQL</productname> driver will allow you to
        access a field as many times as you want.
       </para>
      </listitem>

      <listitem>
       <para>
        You must close a <classname>ResultSet</classname> by calling
        <function>close()</function> once you have finished using it.
       </para>
      </listitem>

      <listitem>
       <para>
        Once you make another query with the
        <classname>Statement</classname> used to create a
        <classname>ResultSet</classname>, the currently open
        <classname>ResultSet</classname> instance is closed
        automatically.
       </para>
      </listitem>

      <listitem>
       <para>
        <classname>ResultSet</classname> is currently read only.
        You can not update data through the <classname>ResultSet</classname>.
        If you want to update data you need to do it the old fashioned way
        by issuing a <acronym>SQL</acronym> update statement.  This is 
        in conformance with the <acronym>JDBC</acronym> specification 
        which does not require drivers to provide this functionality.
       </para>
      </listitem>
     </itemizedlist>
    </para>
   </sect2>
  </sect1>

  <sect1 id="jdbc-update">
   <title>Performing Updates</title>

   <para>
    To change data (perform an insert, update, or delete) 
    you use the <function>executeUpdate()</function> method.
    <function>executeUpdate()</function> is similar to the
    <function>executeQuery()</function> used to issue a select,
    however it doesn't return a <classname>ResultSet</classname>,
    instead it returns the number of records affected by the insert,
    update, or delete statement.
   </para>

  <example id="jdbc-delete-example">
   <title>Simple Delete Example</title>
   <para>
     This example will issue a simple delete and print out the number
     of rows deleted.
<programlisting>
int foovalue = 500;
PreparedStatement st = db.prepareStatement("DELETE FROM mytable where columnfoo = ?");
st.setInt(1, foovalue);
int rowsDeleted = st.executeUpdate();
System.out.println(rowsDeleted + " rows deleted");
st.close();
</programlisting>
   </para>
  </example>
  </sect1>

  <sect1 id="jdbc-ddl">
   <title>Creating and Modifying Database Objects</title>

   <para>
    To create, modify or drop a database object like a table or view
    you use the <function>execute()</function> method.
    <function>execute</function> is similar to the
    <function>executeQuery()</function> used to issue a select,
    however it doesn't return a result.
   </para>

  <example id="jdbc-drop-table-example">
   <title>Drop Table Example</title>
   <para>
     This example will drop a table.
<programlisting>
Statement st = db.createStatement();
ResultSet rs = st.executeQuery("DROP TABLE mytable");
st.close();
</programlisting>
   </para>
  </example>
  </sect1>

 <sect1 id="jdbc-binary-data">
  <title>Storing Binary Data</title>

  <para>
    <application>PostgreSQL</application> provides two distinct ways to 
    store binary data.  Binary data can be stored in a table using 
    <application>PostgreSQL's</application> binary data type 
    <type>bytea</type>, or by using the <firstterm>Large Object</firstterm>
    feature which stores the binary data in a separate table in a special 
    format, and refers to that table by storing a value of type 
    <type>OID</type> in your table.
  </para>

  <para>
    In order to determine which method is appropriate you 
    need to understand the limitations of each method.  The 
    <type>bytea</type> data type is not well suited for storing very 
    large amounts of binary data.  While a column of type 
    <type>bytea</type> can hold upto 1Gig of binary data, it would 
    require a huge amount of memory (<acronym>RAM</acronym>) to 
    process such a large value.  The Large Object method for 
    storing binary data is better suited to storing very large values, 
    but it has its own limitations.  Specifically deleting a row 
    that contains a Large Object does not delete the Large Object.
    Deleting the Large Object is a separate operation that needs to
    be performed.  Large Objects also have some security
    issues since anyone connected to the database case view 
    and/or modify any Large Object, even if they don't have 
    permissions to view/update the row containing the Large Object.
  </para>

  <para>
    7.2 is the first release of the <acronym>JDBC</acronym> Driver 
    that supports the <type>bytea</type> data type.  The introduction of 
    this functionality in 7.2 has introduced a change in behavior 
    as compared to previous releases.  In 7.2 the methods 
    <function>getBytes()</function>, <function>setBytes()</function>, 
    <function>getBinaryStream()</function>, and 
    <function>setBinaryStream()</function> operate on 
    the <type>bytea</type> data type.  In 7.1 these methods operated 
    on the <type>OID</type> data type associated with Large Objects.  
    It is possible to revert the driver back to the old 7.1 behavior 
    by setting the <parameter>compatible</parameter> property on 
    the <classname>Connection</classname> to a value of 
    <literal>7.1</literal>
  </para>

  <para>
    To use the <type>bytea</type> data type you should simply use 
    the <function>getBytes()</function>, <function>setBytes()</function>,
    <function>getBinaryStream()</function>, or 
    <function>setBinaryStream()</function> methods.
  </para>

  <para>
    To use the Large Object functionality you can use either the 
    <classname>LargeObject</classname> <acronym>API</acronym>
    provided by the <application>PostgreSQL</application> 
    <acronym>JDBC</acronym> Driver, or by using the 
    <function>getBLOB()</function> and <function>setBLOB()</function>
    methods.
  </para>

  <important>
   <para>
    For <application>PostgreSQL</application>, you must access Large
    Objects within an <acronym>SQL</acronym> transaction.  You would
    open a transaction by using the
    <function>setAutoCommit()</function> method with an input
    parameter of <literal>false</literal>.
   </para>
  </important>

  <note><para>In a future release of the
      <acronym>JDBC</acronym> Driver, the <function>getBLOB()</function>
      and <function>setBLOB()</function> methods may no longer 
      interact with Large Objects and will instead work on 
      <type>bytea</type> data types.  So it is recommended that you 
      use the <classname>LargeObject</classname> <acronym>API</acronym> 
      if you intend to use Large Objects.
  </para></note>


  <example id="jdbc-binary-data-example">
   <title>Binary Data Examples</title>

   <para>
    For example, suppose you have a table containing the file name of
    an image and you also want to store the image in a <type>bytea</type>
    column:
<programlisting>
CREATE TABLE images (imgname text, img bytea);
</programlisting>
   </para>

   <para>
    To insert an image, you would use:
<programlisting>
File file = new File("myimage.gif");
FileInputStream fis = new FileInputStream(file);
PreparedStatement ps = conn.prepareStatement("INSERT INTO images VALUES (?, ?)");
ps.setString(1, file.getName());
ps.setBinaryStream(2, fis, file.length());
ps.executeUpdate();
ps.close();
fis.close();
</programlisting>

    Here, <function>setBinaryStream()</function> transfers a set number
    of bytes from a stream into the column of type <type>bytea</type>.
    This also could have been done using the <function>setBytes()</function>
    method if the contents of the image was already in a 
    <classname>byte[]</classname>. 
   </para>

   <para>
    Retrieving an image is even easier.  (We use
    <classname>PreparedStatement</classname> here, but the
    <classname>Statement</classname> class can equally be used.)

<programlisting>
PreparedStatement ps = con.prepareStatement("SELECT img FROM images WHERE imgname=?");
ps.setString(1, "myimage.gif");
ResultSet rs = ps.executeQuery();
if (rs != null) {
    while(rs.next()) {
        byte[] imgBytes = rs.getBytes(1);
        // use the stream in some way here
    }
    rs.close();
}
ps.close();
</programlisting>
   </para>

   <para>
    Here the binary data was retrieved as an
    <classname>byte[]</classname>.  You could have used a 
    <classname>InputStream</classname> object instead.  
   </para>

   <para>
    Alternatively you could be storing a very large file and want to use
    the <classname>LargeObject</classname> <acronym>API</acronym> to 
    store the file:
<programlisting>
CREATE TABLE imagesLO (imgname text, imgOID OID);
</programlisting>
   </para>

   <para>
    To insert an image, you would use:
<programlisting>
// All LargeObject API calls must be within a transaction
conn.setAutoCommit(false);

// Get the Large Object Manager to perform operations with
LargeObjectManager lobj = ((org.postgresql.Connection)conn).getLargeObjectAPI();

//create a new large object
int oid = lobj.create(LargeObjectManager.READ | LargeObjectManager.WRITE);

//open the large object for write
LargeObject obj = lobj.open(oid, LargeObjectManager.WRITE);

// Now open the file
File file = new File("myimage.gif");
FileInputStream fis = new FileInputStream(file);

// copy the data from the file to the large object
byte buf[] = new byte[2048];
int s, tl = 0;
while ((s = fis.read(buf, 0, 2048)) > 0)
{
	obj.write(buf, 0, s);
	tl += s;
}

// Close the large object
obj.close();

//Now insert the row into imagesLO
PreparedStatement ps = conn.prepareStatement("INSERT INTO imagesLO VALUES (?, ?)");
ps.setString(1, file.getName());
ps.setInt(2, oid);
ps.executeUpdate();
ps.close();
fis.close();
</programlisting>
</para>
   <para>
    Retrieving the image from the Large Object:

<programlisting>
// All LargeObject API calls must be within a transaction
conn.setAutoCommit(false);

// Get the Large Object Manager to perform operations with
LargeObjectManager lobj = ((org.postgresql.Connection)conn).getLargeObjectAPI();

PreparedStatement ps = con.prepareStatement("SELECT imgOID FROM imagesLO WHERE imgname=?");
ps.setString(1, "myimage.gif");
ResultSet rs = ps.executeQuery();
if (rs != null) {
    while(rs.next()) {
	//open the large object for reading
	int oid = rs.getInt(1);
	LargeObject obj = lobj.open(oid, LargeObjectManager.READ);

	//read the data
	byte buf[] = new byte[obj.size()];
	obj.read(buf, 0, obj.size());
	//do something with the data read here

	// Close the object
	obj.close();
    }
    rs.close();
}
ps.close();
</programlisting>
   </para>

  </example>
 </sect1>


 <sect1 id="jdbc-ext">
  <title><application>PostgreSQL</application> Extensions to the
    <acronym>JDBC</acronym> <acronym>API</acronym></title>

  <para>
   <productname>PostgreSQL</productname> is an extensible database
   system.  You can add your own functions to the backend, which can
   then be called from queries, or even add your own data types.  As
   these are facilities unique to <productname>PostgreSQL</productname>,
   we support them from Java, with a set of extension
   <acronym>API</acronym>'s. Some features within the core of the
   standard driver actually use these extensions to implement Large
   Objects, etc.
  </para>

  <sect2>
   <title>Accessing the Extensions</title>

   <para>
    To access some of the extensions, you need to use some extra
    methods in the <classname>org.postgresql.Connection</classname>
    class. In this case, you would need to case the return value of
    <function>Driver.getConnection()</function>.  For example:
<programlisting>
Connection db = Driver.getConnection(url, username, password);
// ...
// later on
Fastpath fp = ((org.postgresql.Connection)db).getFastpathAPI();
</programlisting>
   </para>

   <sect3>
    <title>Class <classname>org.postgresql.Connection</classname></title>

<synopsis>
public class Connection extends Object implements Connection

java.lang.Object
   |
   +----org.postgresql.Connection
</synopsis>

    <para>
     These are the extra methods used to gain access to
     <productname>PostgreSQL</productname>'s extensions. Methods
     defined by <classname>java.sql.Connection</classname> are not
     listed.
    </para>

    <sect4>
     <title>Methods</title>

     <itemizedlist>
      <listitem>
<synopsis>
public Fastpath getFastpathAPI() throws SQLException
</synopsis>
       <para>
        This returns the Fastpath <acronym>API</acronym> for the
        current connection.  It is primarily used by the Large Object
        <acronym>API</acronym>.
       </para>

       <para>
        The best way to use this is as follows:
<programlisting>
import org.postgresql.fastpath.*;
...
Fastpath fp = ((org.postgresql.Connection)myconn).getFastpathAPI();
</programlisting>
        where <varname>myconn</> is an open <classname>Connection</> to <productname>PostgreSQL</productname>.
       </para>

       <formalpara>
        <title>Returns:</title>
        <para>
         Fastpath object allowing access to functions on the
         <productname>PostgreSQL</productname> backend.
        </para>
       </formalpara>

       <formalpara>
        <title>Throws:</title>
        <para>
         SQLException by Fastpath when initializing for first time
        </para>
       </formalpara>
      </listitem>

      <listitem>
       <para>
<synopsis>
public LargeObjectManager getLargeObjectAPI() throws SQLException
</synopsis>
        This returns the Large Object <acronym>API</acronym> for the
        current connection.
       </para>

       <para>
        The best way to use this is as follows:
<programlisting>
import org.postgresql.largeobject.*;
...
LargeObjectManager lo = ((org.postgresql.Connection)myconn).getLargeObjectAPI();
</programlisting>
        where <varname>myconn</> is an open <classname>Connection</> to
        <productname>PostgreSQL</productname>.
       </para>

       <formalpara>
        <title>Returns:</title>
        <para>
         <classname>LargeObject</classname> object that implements the <acronym>API</acronym>
        </para>
       </formalpara>

       <formalpara>
        <title>Throws:</title>
        <para>
         <classname>SQLException</classname> by <classname>LargeObject</classname> when initializing for first time
        </para>
       </formalpara>
      </listitem>

      <listitem>
       <para>
<synopsis>
public void addDataType(String type, String name)
</synopsis>
        This allows client code to add a handler for one of
        <productname>PostgreSQL</productname>'s more unique data types. Normally, a data type not
        known by the driver is returned by <literal>ResultSet.getObject()</literal> as a
        <classname>PGobject</> instance.  This method allows you to write a class
        that extends <classname>PGobject</>, and tell the driver the type name, and
        class name to use. The down side to this, is that you must
        call this method each time a connection is made.
       </para>

       <para>
        The best way to use this is as follows:
<programlisting>
 ...
((org.postgresql.Connection)myconn).addDataType("mytype","my.class.name");
 ...
</programlisting>
        where <varname>myconn</varname> is an open <classname>Connection</> to
        <productname>PostgreSQL</productname>.  The handling class must
        extend <classname>org.postgresql.util.PGobject</classname>.
       </para>
      </listitem>
     </itemizedlist>
    </sect4>
   </sect3>


   <sect3>
    <title>Class <classname>org.postgresql.Fastpath</classname></title>

<synopsis>
public class Fastpath extends Object

java.lang.Object
   |
   +----org.postgresql.fastpath.Fastpath
</synopsis>

    <para>
     <classname>Fastpath</classname> is an <acronym>API</acronym> that
     exists within the <application>libpq</application> C interface, and allows a client machine
     to execute a function on the database backend.  Most client code
     will not need to use this method, but it is provided because the
     Large Object <acronym>API</acronym> uses it.
    </para>

    <para>
     To use, you need to import the
     <classname>org.postgresql.fastpath</classname> package, using the
     line:
<programlisting>
import org.postgresql.fastpath.*;
</programlisting>
     Then, in your code, you need to get a
     <classname>FastPath</classname> object:
<programlisting>
Fastpath fp = ((org.postgresql.Connection)conn).getFastpathAPI();
</programlisting>
     This will return an instance associated with the database
     connection that you can use to issue commands. The casing of
     <classname>Connection</classname> to
     <classname>org.postgresql.Connection</classname> is required, as
     the <function>getFastpathAPI()</function> is an extension method,
     not part of <acronym>JDBC</acronym>.  Once you have a
     <classname>Fastpath</classname> instance, you can use the
     <function>fastpath()</function> methods to execute a backend
     function.
    </para>

    <formalpara>
     <title>See Also:</title>
     <para>
      <classname>FastpathFastpathArg</classname>, <classname>LargeObject</classname>
     </para>
    </formalpara>

    <sect4>
     <title>Methods</title>

     <itemizedlist>
      <listitem>
<synopsis>
public Object fastpath(int fnid,
                       boolean resulttype,
                       FastpathArg args[]) throws SQLException
</synopsis>
       <para>
        Send a function call to the <productname>PostgreSQL</productname> backend.
       </para>

       <formalpara>
        <title>Parameters:</title>
        <para>
                <parameter>fnid</> - Function id
                <parameter>resulttype</> - True if the result is an integer, false 
for
                other results
                <parameter>args</> - <classname>FastpathArguments</classname> to pass to fastpath
        </para>
       </formalpara>

       <formalpara>
        <title>Returns:</title>
        <para>
         null if no data, Integer if an integer result, or byte[]
         otherwise
        </para>
       </formalpara>
      </listitem>

      <listitem>
<synopsis>
public Object fastpath(String name,
                       boolean resulttype,
                       FastpathArg args[]) throws SQLException
</synopsis>
       <para>
        Send a function call to the <productname>PostgreSQL</productname> backend by name.
       </para>

       <note>
        <para>
         The mapping for the procedure name to function id needs to
         exist, usually to an earlier call to <function>addfunction()</function>. This is
         the preferred method to call, as function id's can/may change
         between versions of the backend. For an example of how this
         works, refer to org.postgresql.LargeObject
        </para>
       </note>

       <formalpara>
        <title>Parameters:</title>
        <para>
                <parameter>name</> - Function name
                <parameter>resulttype</> - True if the result is an integer, false 
for
                other results
                <parameter>args</> - <classname>FastpathArguments</classname> to pass to fastpath
        </para>
       </formalpara>

       <formalpara>
        <title>Returns:</title>
        <para>
         null if no data, Integer if an integer result, or byte[]
         otherwise
        </para>
       </formalpara>

       <formalpara>
        <title>See Also:</title>
        <para><classname>LargeObject</classname></para>
       </formalpara>
      </listitem>

      <listitem>
<synopsis>          
public int getInteger(String name,
                      FastpathArg args[]) throws SQLException
</synopsis>
       <para>
        This convenience method assumes that the return value is an Integer
       </para>

       <formalpara>
        <title>Parameters:</title>
        <para>
                <parameter>name</parameter> - Function name
                <parameter>args</parameter> - Function arguments
        </para>
       </formalpara>

       <formalpara>
        <title>Returns:</title>
        <para>integer result</para>
       </formalpara>

       <formalpara>
        <title>Throws:</title>
        <para>
         <classname>SQLException</classname> if a database-access error occurs or no result
        </para>
       </formalpara>
      </listitem>

      <listitem>
<synopsis>
public byte[] getData(String name,
                      FastpathArg args[]) throws SQLException
</synopsis>
       <para>
        This convenience method assumes that the return value is binary
        data.
       </para>

       <formalpara>
        <title>Parameters:</title>
        <para>
                <parameter>name</parameter> - Function name
                <parameter>args</parameter> - Function arguments
        </para>
       </formalpara>

       <formalpara>
        <title>Returns:</title>
        <para>byte[] array containing result</para>
       </formalpara>

       <formalpara>
        <title>Throws:</title>
        <para>
         <classname>SQLException</classname> if a database-access error occurs or no result
        </para>
       </formalpara>
      </listitem>

      <listitem>
<synopsis>
public void addFunction(String name,
                        int fnid)
</synopsis>
       <para>
        This adds a function to our look-up table.  User code should
        use the <function>addFunctions</function> method, which is based upon a query,
        rather than hard coding the oid. The oid for a function is not
        guaranteed to remain static, even on different servers of the
        same version.
       </para>
      </listitem>

      <listitem>
<synopsis>
public void addFunctions(ResultSet rs) throws SQLException
</synopsis>
       <para>
        This takes a <classname>ResultSet</classname> containing two columns. Column 1
        contains the function name, Column 2 the oid.  It reads the
        entire <classname>ResultSet</classname>, loading the values into the function table.
       </para>

       <important>
        <para>
         Remember to <function>close()</function> the
         <classname>ResultSet</classname> after calling this!
        </para>
       </important>

       <note>
        <title>Implementation note about function name look-ups</title>

        <para>
         <productname>PostgreSQL</productname> stores the function id's and their corresponding
         names in the <classname>pg_proc</> table. To speed things up locally,
         instead of querying each function from that table when
         required, a <classname>Hashtable</classname> is used. Also, only the function's
         required are entered into this table, keeping connection
         times as fast as possible.
        </para>

        <para>
         The <classname>org.postgresql.LargeObject</classname> class
         performs a query upon its start-up, and passes the returned
         <classname>ResultSet</classname> to the
         <function>addFunctions()</function> method here.  Once this
         has been done, the Large Object <acronym>API</acronym> refers
         to the functions by name.
        </para>

        <para>
         Do not think that manually converting them to the OIDs will
         work. OK, they will for now, but they can change during
         development (there was some discussion about this for V7.0),
         so this is implemented to prevent any unwarranted headaches
         in the future.
        </para>
       </note>

       <formalpara>
        <title>See Also:</title>
        <para>
         <classname>LargeObjectManager</classname>
        </para>
       </formalpara>
      </listitem>

      <listitem>
<synopsis>
public int getID(String name) throws SQLException
</synopsis>
       <para>
        This returns the function id associated by its name If
        <function>addFunction()</function> or <function>addFunctions()</function> have not been called for this
        name, then an <classname>SQLException</classname> is thrown.
       </para>
      </listitem>
     </itemizedlist>
    </sect4>
   </sect3>


   <sect3>
    <title>Class <classname>org.postgresql.fastpath.FastpathArg</classname></title>

<synopsis>
public class FastpathArg extends Object

java.lang.Object
   |
   +----org.postgresql.fastpath.FastpathArg
</synopsis>

    <para>
     Each fastpath call requires an array of arguments, the number and
     type dependent on the function being called.  This class
     implements methods needed to provide this capability.
    </para>

    <para>
     For an example on how to use this, refer to the
     <classname>org.postgresql.LargeObject</classname> package.
    </para>

    <formalpara>
     <title>See Also:</title>
     <para>
      <classname>Fastpath</classname>, <classname>LargeObjectManager</classname>, <classname>LargeObject</classname>
     </para>
    </formalpara>

    <sect4>
     <title>Constructors</title>

     <itemizedlist>
      <listitem>
<synopsis>
public FastpathArg(int value)
</synopsis>
       <para>
        Constructs an argument that consists of an integer value
       </para>

       <formalpara>
        <title>Parameters:</title>
        <para>
         value - int value to set
        </para>
       </formalpara>
      </listitem>

      <listitem>
<synopsis>
public FastpathArg(byte bytes[])
</synopsis>
       <para>
        Constructs an argument that consists of an array of bytes
       </para>

       <formalpara>
        <title>Parameters:</title>
        <para>
         bytes - array to store
        </para>
       </formalpara>
      </listitem>

      <listitem>
<synopsis>
public FastpathArg(byte buf[],
                   int off,
                   int len)
</synopsis>
       <para>
        Constructs an argument that consists of part of a byte array
       </para>

       <formalpara>
        <title>Parameters:</title>
        <para>
         <variablelist>
          <varlistentry>
           <term><parameter>buf</></term>
           <listitem>
            <simpara>source array</simpara>
           </listitem>
          </varlistentry>

          <varlistentry>
           <term><parameter>off</parameter></term>
           <listitem>
            <simpara>offset within array</simpara>
           </listitem>
          </varlistentry>

          <varlistentry>
           <term><parameter>len</parameter></term>
           <listitem>
            <simpara>length of data to include</simpara>
           </listitem>
          </varlistentry>
         </variablelist>
        </para>
       </formalpara>
      </listitem>

      <listitem>
<synopsis>
public FastpathArg(String s)
</synopsis>
       <para>
        Constructs an argument that consists of a String.
       </para>
      </listitem>
     </itemizedlist>
    </sect4>
   </sect3>
  </sect2>


  <sect2>
   <title>Geometric Data Types</title>

   <para>
    <productname>PostgreSQL</productname> has a set of data types that
    can store geometric features into a table. These include single
    points, lines, and polygons.  We support these types in Java with
    the org.postgresql.geometric package.  It contains classes that
    extend the org.postgresql.util.PGobject class.  Refer to that
    class for details on how to implement your own data type handlers.
   </para>

<programlisting>
Class org.postgresql.geometric.PGbox

java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.postgresql.geometric.PGbox

   public class PGbox extends PGobject implements Serializable, 
Cloneable

   This represents the box data type within <productname>PostgreSQL</productname>.

Variables

 public PGpoint point[]

          These are the two corner points of the box.

Constructors

 public PGbox(double x1,
              double y1,
              double x2,
              double y2)

        Parameters:
                x1 - first x coordinate
                y1 - first y coordinate
                x2 - second x coordinate
                y2 - second y coordinate

 public PGbox(PGpoint p1,
              PGpoint p2)

        Parameters:
                p1 - first point
                p2 - second point

 public PGbox(String s) throws SQLException
                            
        Parameters:
                s - Box definition in <productname>PostgreSQL</productname> syntax

        Throws: SQLException
                if definition is invalid
                
 public PGbox()

          Required constructor
              
Methods

 public void setValue(String value) throws SQLException
                
          This method sets the value of this object. It should be 
overridden, but still called by subclasses.
                            
        Parameters:
                value - a string representation of the value of the 
object
        Throws: SQLException
                thrown if value is invalid for this type

        Overrides:
                setValue in class PGobject

 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with
                
        Returns:
                true if the two boxes are identical
          
        Overrides:
                equals in class PGobject

 public Object clone()
        
          This must be overridden to allow the object to be cloned

        Overrides:
                clone in class PGobject
   
 public String getValue()
        
        Returns:
                the PGbox in the syntax expected by <productname>PostgreSQL</productname>

        Overrides:
                getValue in class PGobject

<!-- **************************************************************** -->
Class org.postgresql.geometric.PGcircle

java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.postgresql.geometric.PGcircle
        
   public class PGcircle extends PGobject implements Serializable, 
Cloneable
               
   This represents <productname>PostgreSQL</productname>'s circle data type, consisting of a point 
and a radius

Variables

 public PGpoint center
           
          This is the center point
 
 double radius
           
          This is the radius
   
Constructors   

 public PGcircle(double x,
                 double y,
                 double r)
          
        Parameters:
               x - coordinate of center
                y - coordinate of center
                r - radius of circle

 public PGcircle(PGpoint c,
                 double r)
          
        Parameters:
                c - PGpoint describing the circle's center
                r - radius of circle

 public PGcircle(String s) throws SQLException

        Parameters:
                s - definition of the circle in <productname>PostgreSQL</productname>'s syntax.

        Throws: SQLException
                on conversion failure

 public PGcircle()

          This constructor is used by the driver.
            
Methods   

 public void setValue(String s) throws SQLException

        Parameters:
                s - definition of the circle in <productname>PostgreSQL</productname>'s syntax.

        Throws: SQLException
                on conversion failure

        Overrides:
                setValue in class PGobject

 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with
            
        Returns:
                true if the two circles are identical

        Overrides:
                equals in class PGobject

 public Object clone()

          This must be overridden to allow the object to be cloned

        Overrides:
                clone in class PGobject

 public String getValue()

        Returns:
                the PGcircle in the syntax expected by <productname>PostgreSQL</productname>
        
        Overrides:
                getValue in class PGobject

<!-- **************************************************************** -->
Class org.postgresql.geometric.PGline

java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.postgresql.geometric.PGline

   public class PGline extends PGobject implements Serializable, 
Cloneable

   This implements a line consisting of two points. Currently line is 
not yet implemented in the backend, but this class ensures that when 
it's done were ready for it.

Variables
   
 public PGpoint point[]
     
          These are the two points.

Constructors

 public PGline(double x1,
               double y1,
               double x2,
               double y2)

        Parameters:
                x1 - coordinate for first point
                y1 - coordinate for first point
                x2 - coordinate for second point
                y2 - coordinate for second point

 public PGline(PGpoint p1,
               PGpoint p2)
     
        Parameters:
                p1 - first point
                p2 - second point

 public PGline(String s) throws SQLException
               
        Parameters:
                s - definition of the line in <productname>PostgreSQL</productname>'s syntax.

        Throws: SQLException
                on conversion failure

 public PGline()

          required by the driver
               
Methods

 public void setValue(String s) throws SQLException

        Parameters:
                s - Definition of the line segment in <productname>PostgreSQL</productname>'s 
syntax

        Throws: SQLException
                on conversion failure

        Overrides:
                setValue in class PGobject
                
 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with
               
        Returns:
                true if the two lines are identical
   
        Overrides:
                equals in class PGobject

 public Object clone()
        
          This must be overridden to allow the object to be cloned

        Overrides:
                clone in class PGobject

 public String getValue()
   
        Returns:
                the PGline in the syntax expected by <productname>PostgreSQL</productname>
        
        Overrides:
                getValue in class PGobject

<!-- **************************************************************** -->
Class org.postgresql.geometric.PGlseg
             
java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.postgresql.geometric.PGlseg
          
   public class PGlseg extends PGobject implements Serializable, 
Cloneable
 
   This implements a lseg (line segment) consisting of two points

Variables

 public PGpoint point[]
           
          These are the two points.

Constructors
   
 public PGlseg(double x1,
               double y1,
               double x2,
               double y2)
     
        Parameters:

                x1 - coordinate for first point
                y1 - coordinate for first point
                x2 - coordinate for second point
                y2 - coordinate for second point

 public PGlseg(PGpoint p1,
               PGpoint p2)
           
        Parameters:
                p1 - first point
                p2 - second point
   
 public PGlseg(String s) throws SQLException

        Parameters:
                s - Definition of the line segment in <productname>PostgreSQL</productname>'s syntax.

        Throws: SQLException
                on conversion failure

 public PGlseg()

          required by the driver
               
Methods    
   
 public void setValue(String s) throws SQLException
   
        Parameters:
                s - Definition of the line segment in <productname>PostgreSQL</productname>'s 
syntax

        Throws: SQLException
                on conversion failure
     
        Overrides:
                setValue in class PGobject
                
 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with
               
        Returns:
                true if the two line segments are identical
   
        Overrides:
                equals in class PGobject
   
 public Object clone()

          This must be overridden to allow the object to be cloned

        Overrides:
               clone in class PGobject

 public String getValue()

        Returns:
                the PGlseg in the syntax expected by <productname>PostgreSQL</productname>
        
        Overrides:
                getValue in class PGobject

<!-- **************************************************************** -->
Class org.postgresql.geometric.PGpath
                                
java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.postgresql.geometric.PGpath
          
   public class PGpath extends PGobject implements Serializable, 
Cloneable
               
   This implements a path (a multiply segmented line, which may be 
closed)
           
Variables

 public boolean open
               
          True if the path is open, false if closed

 public PGpoint points[]

          The points defining this path

Constructors   

 public PGpath(PGpoint points[],
               boolean open)
          
        Parameters:
                points - the PGpoints that define the path
                open - True if the path is open, false if closed

 public PGpath()

          Required by the driver

 public PGpath(String s) throws SQLException

        Parameters:
                s - definition of the path in <productname>PostgreSQL</productname>'s syntax.

        Throws: SQLException
                on conversion failure

Methods

 public void setValue(String s) throws SQLException
   
        Parameters:
                s - Definition of the path in <productname>PostgreSQL</productname>'s syntax
           
        Throws: SQLException
                on conversion failure

        Overrides:
                setValue in class PGobject

 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with

        Returns:
                true if the two pathes are identical

        Overrides:
                equals in class PGobject

 public Object clone()

          This must be overridden to allow the object to be cloned

        Overrides:
                clone in class PGobject

 public String getValue()

          This returns the path in the syntax expected by 
<productname>PostgreSQL</productname>

        Overrides:
                getValue in class PGobject

 public boolean isOpen()

     This returns true if the path is open

 public boolean isClosed()

     This returns true if the path is closed

 public void closePath()

     Marks the path as closed

 public void openPath()

     Marks the path as open

<!-- **************************************************************** -->
Class org.postgresql.geometric.PGpoint
                                
java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.postgresql.geometric.PGpoint
          
   public class PGpoint extends PGobject implements Serializable, 
Cloneable

   This implements a version of java.awt.Point, except it uses double 
to represent the coordinates.

   It maps to the point data type in <productname>PostgreSQL</productname>.

Variables

 public double x

          The X coordinate of the point

 public double y

          The Y coordinate of the point

Constructors

 public PGpoint(double x,
                double y)

        Parameters:
                x - coordinate
                y - coordinate

 public PGpoint(String value) throws SQLException
     
          This is called mainly from the other geometric types, when a 
point is embedded within their definition.
             
        Parameters:
                value - Definition of this point in <productname>PostgreSQL</productname>'s 
syntax
   
 public PGpoint()
          
          Required by the driver

Methods

 public void setValue(String s) throws SQLException

        Parameters:
                s - Definition of this point in <productname>PostgreSQL</productname>'s syntax

        Throws: SQLException
                on conversion failure

        Overrides:
                setValue in class PGobject
          
 public boolean equals(Object obj)

        Parameters:
                obj - Object to compare with

        Returns:
                true if the two points are identical

        Overrides:
                equals in class PGobject

 public Object clone()
                
          This must be overridden to allow the object to be cloned

        Overrides:
                clone in class PGobject
          
 public String getValue()       
    
        Returns:
                the PGpoint in the syntax expected by <productname>PostgreSQL</productname>

        Overrides:
                getValue in class PGobject
          
 public void translate(int x,
                       int y)

          Translate the point with the supplied amount.

        Parameters:
                x - integer amount to add on the x axis
                y - integer amount to add on the y axis

 public void translate(double x,
                       double y)
          
          Translate the point with the supplied amount.
 
        Parameters:
                x - double amount to add on the x axis
                y - double amount to add on the y axis

 public void move(int x,
                  int y)
                
          Moves the point to the supplied coordinates.

        Parameters:
                x - integer coordinate
                y - integer coordinate

public void move(double x,
                  double y)
          
          Moves the point to the supplied coordinates.

        Parameters:
                x - double coordinate
                y - double coordinate

 public void setLocation(int x,
                         int y)

          Moves the point to the supplied coordinates. refer to
          java.awt.Point for description of this

        Parameters:
                x - integer coordinate
                y - integer coordinate

        See Also:
                Point

 public void setLocation(Point p)

          Moves the point to the supplied java.awt.Point refer to
          java.awt.Point for description of this

        Parameters:
                p - Point to move to

        See Also:
                Point

<!-- **************************************************************** -->
Class org.postgresql.geometric.PGpolygon
                                
java.lang.Object
   |
   +----org.postgresql.util.PGobject
           |
           +----org.postgresql.geometric.PGpolygon

   public class PGpolygon extends PGobject implements Serializable, 
Cloneable
               
   This implements the polygon data type within <productname>PostgreSQL</productname>.

Variables

 public PGpoint points[]

          The points defining the polygon
                                
Constructors

 public PGpolygon(PGpoint points[])

          Creates a polygon using an array of PGpoints

        Parameters:
                points - the points defining the polygon

 public PGpolygon(String s) throws SQLException
                 
        Parameters:
                s - definition of the polygon in <productname>PostgreSQL</productname>'s syntax.

        Throws: SQLException
                on conversion failure

 public PGpolygon()

          Required by the driver

Methods

 public void setValue(String s) throws SQLException

        Parameters:
                s - Definition of the polygon in <productname>PostgreSQL</productname>'s syntax

        Throws: SQLException
                on conversion failure

        Overrides:
                setValue in class PGobject

 public boolean equals(Object obj)
     
        Parameters:
                obj - Object to compare with
                                
        Returns:
                true if the two polygons are identical

        Overrides:
                equals in class PGobject

 public Object clone()
        
          This must be overridden to allow the object to be cloned

        Overrides:
                clone in class PGobject
                 
 public String getValue()

        Returns:
                the PGpolygon in the syntax expected by <productname>PostgreSQL</productname>

        Overrides:
                getValue in class PGobject
</programlisting>
  </sect2>


  <sect2>
   <title>Large Objects</title>

   <para>
    Large objects are supported in the standard
    <acronym>JDBC</acronym> specification.  However, that interface is
    limited, and the <acronym>API</acronym> provided by <productname>PostgreSQL</productname> allows for random
    access to the objects contents, as if it was a local file.
   </para>

   <para>
    The org.postgresql.largeobject package provides to Java the <application>libpq</application>
    C interface's large object <acronym>API</acronym>. It consists of
    two classes, <classname>LargeObjectManager</classname>, which deals with creating,
    opening and deleting large objects, and <classname>LargeObject</classname> which deals
    with an individual object.
   </para>

   <sect3>
    <title>Class <classname>org.postgresql.largeobject.LargeObject</classname></title>

<synopsis>
public class LargeObject extends Object

java.lang.Object
   |
   +----org.postgresql.largeobject.LargeObject
</synopsis>

    <para>
     This class implements the large object interface to
     <productname>PostgreSQL</productname>.
    </para>

    <para>
     It provides the basic methods required to run the interface, plus
     a pair of methods that provide <classname>InputStream</classname> and <classname>OutputStream</classname>
     classes for this object.
    </para>

    <para>
     Normally, client code would use the methods in 
     <classname>BLOB</classname> to access large objects.
    </para>

    <para>
     However, sometimes lower level access to Large Objects is
     required, that is not supported by the <acronym>JDBC</acronym>
     specification.
    </para>

    <para>
     Refer to org.postgresql.largeobject.LargeObjectManager on how to
     gain access to a Large Object, or how to create one.
    </para>

    <formalpara>
     <title>See Also:</title>
     <para><classname>LargeObjectManager</classname></para>
    </formalpara>

    <sect4>
     <title>Variables</title>

     <variablelist>
      <varlistentry>
       <term>public static final int SEEK_SET</term>
       <listitem>
        <para>Indicates a seek from the beginning of a file</para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>public static final int SEEK_CUR</term>
       <listitem>
        <para>Indicates a seek from the current position</para>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>public static final int SEEK_END</term>
       <listitem>
        <para>Indicates a seek from the end of a file</para>
       </listitem>
      </varlistentry>
     </variablelist>
    </sect4>

    <sect4>
     <title>Methods</title>

     <itemizedlist>
      <listitem>
<synopsis>
public int getOID()
</synopsis>
       <para>
        Returns the OID of this <classname>LargeObject</classname>
       </para>
      </listitem>

      <listitem>
<synopsis>
public void close() throws SQLException
</synopsis>
       <para>
        This method closes the object. You must not call methods in
        this object after this is called.
       </para>
      </listitem>

      <listitem>
<synopsis>
public byte[] read(int len) throws SQLException
</synopsis>
       <para>
        Reads some data from the object, and return as a byte[] array
       </para>
      </listitem>

      <listitem>
<synopsis>
public int read(byte buf[],
                 int off,
                 int len) throws SQLException
</synopsis>
       <para>
        Reads some data from the object into an existing array
       </para>

       <formalpara>
        <title>Parameters:</title>
        <para>
         <variablelist>
          <varlistentry>
           <term>buf</term>
           <listitem>
            <simpara>destination array</simpara>
           </listitem>
          </varlistentry>

          <varlistentry>
           <term>off</term>
           <listitem>
            <simpara>offset within array</simpara>
           </listitem>
          </varlistentry>

          <varlistentry>
           <term>len</term>
           <listitem>
            <simpara>number of bytes to read</simpara>
           </listitem>
          </varlistentry>
         </variablelist>
        </para>
       </formalpara>
      </listitem>

      <listitem>
<synopsis>
public void write(byte buf[]) throws SQLException
</synopsis>
       <para>
        Writes an array to the object
       </para>
      </listitem>

      <listitem>
<synopsis>
public void write(byte buf[],
                  int off,
                  int len) throws SQLException
</synopsis>
       <para>
        Writes some data from an array to the object
       </para>

       <formalpara>
        <title>Parameters:</title>
        <para>
         <variablelist>
          <varlistentry>
           <term>buf</term>
           <listitem>
            <simpara>destination array</simpara>
           </listitem>
          </varlistentry>

          <varlistentry>
           <term>off</term>
           <listitem>
            <simpara>offset within array</simpara>
           </listitem>
          </varlistentry>

          <varlistentry>
           <term>len</term>
           <listitem>
            <simpara>number of bytes to write</simpara>
           </listitem>
          </varlistentry>
         </variablelist>
        </para>
       </formalpara>
      </listitem>

<!--
 public void seek(int pos,
                  int ref) throws SQLException

          Sets the current position within the object.

          This is similar to the fseek() call in the standard C 
library.It allows you to have random access to the large object.

        Parameters:
                pos - position within object
                ref - Either SEEK_SET, SEEK_CUR or SEEK_END
        Throws: SQLException
                if a database-access error occurs.

 public void seek(int pos) throws SQLException

          Sets the current position within the object.

          This is similar to the fseek() call in the standard C 
library.It allows you to have random access to the large object.

        Parameters:
                pos - position within object from begining

        Throws: SQLException
                if a database-access error occurs.

 public int tell() throws SQLException

        Returns:
                the current position within the object

        Throws: SQLException
                if a database-access error occurs.

 public int size() throws SQLException

          This method is inefficient, as the only way to find out the 
size of the object is to seek to the end, record the current position, 
then return to the original position.

          A better method will be found in the future.

        Returns:
                the size of the large object

        Throws: SQLException
                if a database-access error occurs.

 public InputStream getInputStream() throws SQLException

          Returns an InputStream from this object.

          This InputStream can then be used in any method that 
requires an InputStream.

        Throws: SQLException
                if a database-access error occurs.

 public OutputStream getOutputStream() throws SQLException

          Returns an OutputStream to this object

          This OutputStream can then be used in any method that 
requires an OutputStream.

        Throws: SQLException
                if a database-access error occurs.
-->
     </itemizedlist>
    </sect4>
   </sect3>


   <sect3>
    <title>Class <classname>org.postgresql.largeobject.LargeObjectManager</classname></title>

<synopsis>                                
public class LargeObjectManager extends Object

java.lang.Object
   |
   +----org.postgresql.largeobject.LargeObjectManager
</synopsis>

    <para>
     This class implements the large object interface to
     <productname>PostgreSQL</productname>.  It provides methods that
     allow client code to create, open and delete large objects from
     the database. When opening an object, an instance of
     <classname>org.postgresql.largeobject.LargeObject</classname> is
     returned, and its methods then allow access to the object.
    </para>

    <para>
     This class can only be created by org.postgresql.Connection.  To
     get access to this class, use the following segment of code:
<programlisting>
import org.postgresql.largeobject.*;
Connection  conn;
LargeObjectManager lobj;
// ... code that opens a connection ...
lobj = ((org.postgresql.Connection)myconn).getLargeObjectAPI();
</programlisting>
    </para>

    <para>
     Normally, client code would use the <classname>BLOB</classname>
     methods to access large objects.  However, sometimes
     lower level access to Large Objects is required, that is not
     supported by the <acronym>JDBC</acronym> specification.
    </para>

    <para>
     Refer to org.postgresql.largeobject.LargeObject on how to
     manipulate the contents of a Large Object.
    </para>

    <sect4>
     <title>Variables</title>

     <variablelist>
      <varlistentry>
       <term>public static final int WRITE</term>
       <listitem>
        <simpara>This mode indicates we want to write to an object.</simpara>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>public static final int READ</term>
       <listitem>
        <simpara>This mode indicates we want to read an object.</simpara>
       </listitem>
      </varlistentry>

      <varlistentry>
       <term>public static final int READWRITE</term>
       <listitem>
        <simpara>This mode is the default. It indicates we want read and write access to a large object.</simpara>
       </listitem>
      </varlistentry>
     </variablelist>
    </sect4>

    <sect4>
     <title>Methods</title>

     <itemizedlist>
      <listitem>
<synopsis>
public LargeObject open(int oid) throws SQLException
</synopsis>
       <para>
        This opens an existing large object, based on its OID. This
        method assumes that READ and WRITE access is required (the
        default).
       </para>
      </listitem>

      <listitem>
<synopsis>
public LargeObject open(int oid,
                        int mode) throws SQLException
</synopsis>
       <para>
        This opens an existing large object, based on its OID, and
        allows setting the access mode.
       </para>
      </listitem>

      <listitem>
<synopsis>
public int create() throws SQLException
</synopsis>
       <para>
        This creates a large object, returning its OID.
        It defaults to READWRITE for the new object's attributes.
       </para>
      </listitem>

      <listitem>
<synopsis>
public int create(int mode) throws SQLException
</synopsis>
       <para>
        This creates a large object, returning its OID, and sets the
        access mode.
       </para>
      </listitem>

      <listitem>
<synopsis>
public void delete(int oid) throws SQLException
</synopsis>
       <para>          
        This deletes a large object.
       </para>
      </listitem>

      <listitem>
<synopsis>
public void unlink(int oid) throws SQLException
</synopsis>
       <para>
        This deletes a large object.  It is identical to the delete
        method, and is supplied as the C <acronym>API</acronym> uses
        <quote>unlink</quote>.
       </para>
      </listitem>
     </itemizedlist>
    </sect4>
   </sect3>
  </sect2>

 </sect1>


 <sect1 id="jdbc-thread">
  <title>Using the driver in a multithreaded or a servlet environment</title>

  <para>
   A problem with many <acronym>JDBC</acronym> drivers is that only
   one thread can use a <classname>Connection</classname> at any one
   time -- otherwise a thread could send a query while another one is
   receiving results, and this would be a bad thing for the database
   engine.
  </para>

  <para>
   The <productname>PostgreSQL</productname> <acronym>JDBC</acronym> Driver
   is thread safe.
   Consequently, if your application uses multiple threads then you do
   not have to worry about complex algorithms to ensure that only one
   uses the database at any time.
  </para>

  <para>
   If a thread attempts to use the connection while another one is
   using it, it will wait until the other thread has finished its
   current operation.  If it is a regular <acronym>SQL</acronym>
   statement, then the operation consists of sending the statement and
   retrieving any <classname>ResultSet</classname> (in full).  If it
   is a <classname>Fastpath</classname> call (e.g., reading a block
   from a <classname>LargeObject</classname>) then it is the time to
   send and retrieve that block.
  </para>

  <para>
   This is fine for applications and applets but can cause a
   performance problem with servlets.  With servlets you can have a
   heavy load on the connection. If you have several threads
   performing queries then each but one will pause, which may not be what
   you are after.
  </para>

  <para>
   To solve this, you would be advised to create a pool of
   connections.  When ever a thread needs to use the database, it asks
   a manager class for a <classname>Connection</classname>. The
   manager hands a free connection to the thread and marks it as
   busy. If a free connection is not available, it opens one.  Once
   the thread has finished with it, it returns it to the manager who
   can then either close it or add it to the pool. The manager would
   also check that the connection is still alive and remove it from
   the pool if it is dead.
  </para>

  <para>
   So, with servlets, it is up to you to use either a single
   connection, or a pool. The plus side for a pool is that threads
   will not be hit by the bottle neck caused by a single network
   connection. The down side is that it increases the load on the
   server, as a backend process is created for each
   <classname>Connection</classname>.  It is up to you and your
   applications requirements.
  </para>
 </sect1>


 <sect1 id="jdbc-reading">
  <title>Further Reading</title>

  <para>
   If you have not yet read it, I'd advise you read the
   <acronym>JDBC</acronym> <acronym>API</acronym> Documentation
   (supplied with Sun's <acronym>JDK</acronym>), and the
   <acronym>JDBC</acronym> Specification.  Both are available from
   <ulink
   url="http://java.sun.com/products/jdbc/index.html">http://java.sun.com/products/jdbc/index.html</ulink>.
  </para>

  <para>
   <ulink
   url="http://jdbc.postgresql.org">http://jdbc.postgresql.org</ulink>
   contains updated information not included in this document, and
   also includes precompiled drivers.
  </para>
 </sect1>
</chapter>

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