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This is a simple readme describing how to compile and use the jdbc driver.
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This file was amended on January 17 2001 to reflect the changes made in the 7.1
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This isn't a guide on how to use JDBC - for that refer to Javasoft's web site:
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http://www.javasoft.com/
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For problems with this driver, then refer to the postgres-jdbc email
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http://www.postgresql.org/
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The Driver's home page is:
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http://jdbc.postgresql.org/
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or http://www.retep.org.uk/postgresql/
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NB: They are both the same physical directory so both will always be in sync
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(unless the laws of physics break down ;-) )
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To compile you will need to have ANT installed. To obtain ant go to
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http://jakarta.apache.org/ant/index.html and download the binary. Being pure
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java it will run on virtually all java platforms. If you have any problems
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please email the jdbc list.
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Once you have ANT, run the configure script in the top-level directory with
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the --with-java option. Then proceed with 'make' and 'make install' as
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usual. This will compile the correct driver for your JVM, and build a .jar
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file (Java ARchive) called postgresql.jar. The file will be installed in
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the directory PREFIX/share/java.
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That jar file will contain the driver for _your_ version of the JDK.
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Note: As of 7.1, you can build from the top-level directory or from
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REMEMBER: Once you have compiled the driver, it will work on ALL platforms
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that support that version of the API. You don't need to build it for each
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That means you don't have to compile it on every platform. Believe me, I
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still hear from people who ask me "I've compiled it ok under Solaris, but it
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won't compile under Linux" - there's no difference.
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Don't try to run javac directly. Don't try to run ant directly. Neither
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You may see a message similar to:
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postgresql/Driver.java:87: interface java.sql.Connection is an interface. It can't be instantiated.
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return new Connection (host(), port(), props, database(), url, this);
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This is caused by not having the current directory in your CLASSPATH. Under
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Linux/Solaris, unset the CLASSPATH environment variable, and rerun ant.
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If you are still having problems, I keep a copy of the driver (for different
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versions of the backend) on my web site http://www.retep.org.uk/postgres/
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or http://jdbc.postgresql.org/
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More details are in the Implementation file src/interfaces/jdbc/Implementation
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To install the driver, the .class files have to be in the classpath.
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ie: under LINUX/SOLARIS (the example here is my linux box):
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export CLASSPATH=.:/usr/local/pgsql/share/java/postgresql.jar
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Please don't be tempted to extract the files from the .jar file. There are a
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lot of files in there, and you may break the Exception handling.
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To use the driver, you must introduce it to JDBC. Again, there's two ways
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This method hardcodes your driver into your application/applet. You
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introduce the driver using the following snippet of code:
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Class.forName("org.postgresql.Driver");
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} catch(Exception e) {
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// your error handling code goes here
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Remember, this method restricts your code to just the postgresql database.
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However, this is how most people load the driver.
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This method specifies the driver from the command line. When running the
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application, you specify the driver using the option:
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-Djdbc.drivers=org.postgresql.Driver
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eg: This is an example of running one of my other projects with the driver:
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java -Djdbc.drivers=org.postgresql.Driver uk.org.retep.finder.Main
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note: This method only works with Applications (not for Applets).
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However, the application is not tied to one driver, so if you needed
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to switch databases (why I don't know ;-) ), you don't need to
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recompile the application (as long as you havent hardcoded the url's).
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The driver recognises JDBC URL's of the form:
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jdbc:postgresql:database
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jdbc:postgresql://host/database
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jdbc:postgresql://host:port/database
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Also, you can supply both username and passwords as arguments, by appending
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jdbc:postgresql:database?user=me
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jdbc:postgresql:database?user=me&password=mypass
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1) If you are connecting to localhost or 127.0.0.1 you can leave it out of the
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URL. ie: jdbc:postgresql://localhost/mydb can be replaced with
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2) The port defaults to 5432 if it's left out.
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That's the basics related to this driver. You'll need to read the JDBC Docs
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on how to use it. However, there are some examples included in the example
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directory. To build, type: make examples
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To run them, they follow the same syntax. For example, the basic example shows
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how to insert data, and perform queries:
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java example.basic jdbc:postgresql:test user password
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A "feature" of PostgreSQL is that access to LargeObjects is only permitted
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within a Transaction. Because of this, any use of LargeObjects (also known
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as Blobs) requires that the Connection.setAutoCommit() method be called
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disabling the autocommit feature.
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Connection db; // open the connection here
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db.setAutoCommit(false); // Turn off AutoCommit
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Most of the time, you can use the getBytes()/setBytes() methods to read and
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write small Large Objects. However, PostgreSQL's own internal api's are
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available. These allow you to access the object as if it was a file.
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The first thing you need to do is to open the LargeObjectManager. This class
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handles the opening of existing objects, and creating new ones. To do this,
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you use the following line of code:
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LargeObjectManager lobj;
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lobj = ((org.postgresql.Connection)db).getLargeObjectAPI();
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where db is a reference to an open Connection object.
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Once that is done, you can use the API for the lifetime of that Connection.
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To create an object, you call the create() method. This takes an argument
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with the file modes you intend to use. The following line is normally
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int oid = lobj.create(LargeObjectManager.READ|LargeObjectManager.WRITE);
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Here, lobj is the LargeObjectManager we have opened earlier, and oid is the
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Large Object's oid in the database.
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To open an existing object, you use the open() method. This takes an oid, and
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the file permissions. It then returns a LargeObject object.
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LargeObject obj = lobj.open(oid,LargeObjectManager.WRITE);
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Once the LargeObject is open, you can call methods to read, write, seek etc.
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Here's the supported methods:
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int oid = obj.getOID(); Return the objects oid
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obj.close(); Close the object
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byte data[] = obj.read(int len); Read len bytes
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onj.read(byte data[],int off,int len); Read into data[off] len bytes
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obj.write(byte data[]); Write the array data
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obj.write(byte data[],int off,int len); Write len bytes from data[off]
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obj.seek(int pos,int ref); As fseek in C.
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obj.seek(int pos); Move to pos (from the begining)
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int pos = obj.tell(); Returns the current position
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int size = obj.size(); Returns the objects size
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Caveat: If you commit(), rollback() a transaction, or turn on autocommit whilst
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an object is open PostgreSQL will close it. You will need to reopen the object
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before using it again. Using the existing LargeObject will cause an
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SQLException to be thrown.
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The driver now issues the "show datestyle;" query when it first connects, so
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any call to ResultSet.getDate() how returns the correct date.
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One caveat though: if you change the datestyle from within JDBC, you must also
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issue the "show datestyle" query. Without this, the driver will not know of
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Statement s = db.createStatement();
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s.executeUpdate("set datestyle='european'");
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s.executeUpdate("show datestyle");
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Please note: This may change later, so that the driver uses the same format
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internally (similar to how the ODBC driver works).
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JDBC supports database specific data types using the getObject() call. The
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following types have their own Java equivalents supplied by the driver:
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box, circle, line, lseg, path, point, polygon
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When using the getObject() method on a resultset, it returns a PG_Object,
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which holds the postgres type, and its value. This object also supports
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methods to retrive these types.
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Eg: column 3 contains a point, and rs is the ResultSet:
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PG_Object o = (PG_Object)rs.getObject(3);
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PGpoint p = o.getPoint();
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System.out.println("point returned x="+p.x+", y="+p.y);
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Also, when using these classes, their toString() methods return the correct
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syntax for writing these to the database.
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Peter T Mount, December 29 1998
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home email: peter@retep.org.uk http://www.retep.org.uk
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work email: petermount@it.maidstone.gov.uk or peter@taer.maidstone.gov.uk
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PS: Please use the home email whenever possible. If you must contact me at work
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then please cc my home one at the same time.
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src/interfaces/jdbc/README
