Connection Pooling with C3P0 ComboPooledDataSource

JDBC for Oracle - Herong's Tutorial Examples

∟Connection Pooling with C3P0 ComboPooledDataSource

This section provides a tutorial example that shows you how to use the C3P0 ComboPooledDataSource class to manage the connection pool with JavaBean style properties.

The easiest way to use C3P0 package for connection pooling is to use the com.mchange.v2.c3p0.ComboPooledDataSource class. It implements the standard JDBC javax.sql.DataSource interface to manage the connection pool with JavaBean style properties.

The ComboPooledDataSource class uses set*() and get*() methods to configure and manage the connection pool. Here is my sample Java program, C3p0ComboPooledDataSourceExample.java against my local Oracle server.

/* C3p0ComboPooledDataSourceExample.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import javax.sql.DataSource;
import com.mchange.v2.c3p0.ComboPooledDataSource;

public class C3p0ComboPooledDataSourceExample {
  static java.io.PrintStream out = System.out;

  public static void main(String[] args) throws Exception {
    String url 
      = "jdbc:oracle:thin:Herong/TopSecret@//localhost:1521/XE";

    // Get a DataSource with pooled connections
    DataSource ds = getDataSource(url);

    // Get a pooled connection
    Connection con = ds.getConnection();
    checkDataSource(ds);

    // Verify the pooled connection
    DatabaseMetaData meta = con.getMetaData();
    out.println();
    out.println("Database Connection Info: ");
    out.println("   Server name: "+meta.getDatabaseProductName());
    out.println("   Server version: "+meta.getDatabaseProductVersion());
    out.println("   Driver name: "+ meta.getDriverName());
    out.println("   Driver version: "+ meta.getDriverVersion());
    out.println("   JDBC major version: "+ meta.getJDBCMajorVersion());
    out.println("   JDBC minor version: "+ meta.getJDBCMinorVersion());

    // Close the pooled connection
    con.close();

    // Wait for 3 minutes to check the server side
    out.println();
    out.println("Go and count connections on the database server ...");
    Thread.sleep(3*60*1000);

    // Close the DataSource
    closeDataSource(ds);
  }

  public static DataSource getDataSource(String url) throws Exception {
    ComboPooledDataSource cpds = new ComboPooledDataSource();
    cpds.setJdbcUrl(url);
    cpds.setInitialPoolSize(10);
    DataSource ds = (DataSource) cpds;
    return ds;
  }

  public static void closeDataSource(DataSource ds) throws Exception {
    ComboPooledDataSource cpds = (ComboPooledDataSource) ds;
    cpds.close();
  }

  public static void checkDataSource(DataSource ds) throws Exception {
    ComboPooledDataSource cpds = (ComboPooledDataSource) ds;
    out.println();
    out.println("C3P0 ComboPooledDataSource Info: ");
    out.println("   Total Connections: "+cpds.getNumConnections());
    out.println("   Busy Connections: "+cpds.getNumBusyConnections());
    out.println("   Idle Connections: "+cpds.getNumIdleConnections());
    out.println("   Connection URL: "+cpds.getJdbcUrl());
    out.println("   User Name: "+cpds.getUser());
    out.println("   Password: "+cpds.getPassword());
  }
}

To run this test program, I need both Oracle JDBC and C3P0 JAR files. See other tutorials to download them.

c3p0-0.9.5.5.jar - To provide JDBC connection pooling.
ojdbc11.jar - To provide JDBC driver for Oracle server.

Let's run it:

herong> java -cp .:\
  c3p0-0.9.5.5.jar:\
  ojdbc11.jar \
  C3p0ComboPooledDataSourceExample.java

8:37:33 PM com.mchange.v2.log.MLog
INFO: MLog clients using java 1.4+ standard logging.
8:37:38 PM com.mchange.v2.c3p0.C3P0Registry
INFO: Initializing c3p0-0.9.5.5 [built 11-December-2019 22:07:46 ...]
8:37:38 PM com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource
INFO: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource
  [ acquireIncrement -> 3,
    acquireRetryAttempts -> 30,
    ...
  ]

C3P0 ComboPooledDataSource Info:
   Total Connections: 3
   Busy Connections: 1
   Idle Connections: 2
   Connection URL: jdbc:oracle:thin:Herong/TopSecret@//localhost:1521/XE
   User Name: null
   Password: null

Database Connection Info:
   Server name: Oracle
   Server version: Oracle Database 21c Express Edition Release ...
   Driver name: Oracle JDBC driver
   Driver version: 21.4.0.0.0
   JDBC major version: 4
   JDBC minor version: 3

Go and count connections on the database server ...

On the Oracle server, log in as "root". I see 10 connections:

SQL> SELECT sid, SUBSTR(username,0,8) FROM v$session 
       WHERE username IS NOT NULL;

       SID SUBSTR(USERNAME,0,8)
---------- --------------------------------
        12 HERONG
       137 HERONG
       263 HERONG
       379 SYS
       380 HERONG
       506 HERONG
       507 HERONG
       623 HERONG
       750 HERONG
       751 HERONG
       874 HERONG

11 rows selected.

So, what we can see from this tutorial:

C3P0 ComboPooledDataSource class nicely hides the connection pool in a standard JDBC DataSource object. Once created, it can be used in your application to perform normal JDBC operations.
I asked to initialize 10 connections, and I see 10 connections on Oracle server. But the ComboPooledDataSource class only reports 3 connections. Not sure why.
You can easily change the connection URL to test C3P0 for connection pooling with MySQL or SQL Server.