Creational Patterns: Object Pool

Properties:

-          When cost of creating an object from scratch is high it might be a good idea to reuse already created objects.

-          Identified by a pool class that objects are retrieved from and then released back to.

Implementation:

-          Reused objects might be wrapped by another object.

-          Pool class keeps created objects.

-          Client requests a new object instance from pool when it needs a new object. After client is done with object instance it releases the object, so that the object can be reused again.

Java Example Usage:

-          com.mchange.v2.c3p0.ComboPooledDataSource

Example Usage:

// create connection pool

ComboPooledDataSource dataSource = new ComboPooledDataSource();

dataSource.setDriverClass( "org.mysql.Driver" );            

dataSource.setJdbcUrl( "jdbc:mysql://localhost/testdb" );

dataSource.setUser("user");                                 

dataSource.setPassword("password");                                 

   

dataSource.setMinPoolSize(5);                                    

dataSource.setAcquireIncrement(5);

dataSource.setMaxPoolSize(20);

   

Connection conn = null;

Statement stmt = null;

ResultSet resultSet = null;

   

try {

    conn = dataSource.getConnection();// get a connection from pool

    stmt = conn.createStatement();

    resultSet = stmt.executeQuery("SELECT * FROM Person");

    int numcols = resultSet.getMetaData().getColumnCount();

    while(resultSet.next()) {

        for(int i=1;i<=numcols;i++) {

            System.out.print(resultSet.getString(i));

        }

    }

} catch(SQLException e) {

    e.printStackTrace();

} finally {

    try { if (resultSet != null) resultSet.close(); } catch(Exception e) { }

    try { if (stmt != null) stmt.close(); } catch(Exception e) { }

    try { if (conn != null) conn.close(); } catch(Exception e) { } // Release connection back to pool

}