Any source that uses JDBC needs to import the java.sql package, using:
Important: Do not import the org.postgresql package. If you do, your source will not compile, as javac will get confused.
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.
In the first method, your code implicitly loads the driver
For PostgreSQL, you would
This will load the driver, and while loading, the driver will automatically register itself with JDBC.
forName()method can throw a
ClassNotFoundExceptionif the driver is not available.
This is the most common method to use, but restricts your code to use just PostgreSQL. If your code may access another database system in the future, and you do not use any PostgreSQL-specific extensions, then the second method is advisable.
The second method passes the driver as a parameter to the
JVM as it starts, using the
-D argument. Example:
java -Djdbc.drivers=org.postgresql.Driver example.ImageViewer
In this example, the JVM
will attempt to load the driver as part of its initialization.
Once done, the
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 URL, which is covered next.
One last thing: When your code then tries to open a
Connection, and you get a
No driver available
SQLException being thrown, this is probably
caused by the driver not being in the class path, or the value
in the parameter not being correct.
With JDBC, a database is represented by a URL (Uniform Resource Locator). With PostgreSQL, this takes one of the following forms:
The host name of the server. Defaults to localhost.
The port number the server is listening on. Defaults to the PostgreSQL standard port number (5432).
The database name.
To connect, you need to get a
Connection instance from JDBC. To do this, you would use the
Connection db = DriverManager.getConnection(url, username, password);
To close the database connection, simply call the
close() method to the
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