How to Create an External Connection Pool

The use of external connection pools is available from 3.0MP32

Introduction

Openbravo uses connection pools to reuse existing connections/prepared statements, avoiding the cost of initiating a connection, parsing SQL etc. By default Openbravo uses two different connection pools:

• Hibernate default connection pool for DAL-related queries
• Apache DBCP for the connections provided by the ConnectionProviderImpl.

From 3.0MP32 it is possible to specify an external connection provider to replace these two connection pools. Openbravo provides a free commercial module that implements the Tomcat JDBC Connection Pool, but it is possible for developers to publish a module implement their own connection pool.

ExternalConnectionPool abstract class

In order to implement an external connection pool, developers must subclass the ExternalConnectionPool abstract class. This class has three methods:

/**
   * 
   * @param externalConnectionPoolClassName
   *          The full class name of the external connection pool
   * @return An instance of the external connection pool
   */
public final synchronized static ExternalConnectionPool getInstance(
      String externalConnectionPoolClassName) throws InstantiationException,
      IllegalAccessException, ClassNotFoundException;

The getInstance method is in charge of instantiating the external connection pool. The name of the class that implements the connection pool is passed as a parameter, its value is taken from the db.externalPoolClassName property of Openbravo.properties.

/**
   * @return A Connection from the external connection pool
   */
public abstract Connection getConnection()

This is the main method that should be overwritten by all external connection providers. It takes no arguments, and it should return a connection that has been borrowed from the pool.

/**
   * If the external connection pool supports interceptors this method should be overwritten
   * 
   * @param interceptors
   *          List of PoolInterceptorProvider comprised of all the interceptors injected with Weld
   */
public void loadInterceptors(List<PoolInterceptorProvider> interceptors)

This method should be overwritten if the connection pool supports interceptors and allows custom interceptors to be instantiated using dependency injection. A list of PoolInterceptorProvider will be passed as an arguments, containing the full class name of the interceptors.

Design Considerations

• Include a configuration file so that users can customize the external connection pool to meet their needs.
• If the pool needs to execute some initialization code, place it in the getConnection method and make sure that is only executed the first time that method is invoked.
• For all connection returned by the pool:
  • SessionInfo.setDBSessionInfo(Connection conn, String rdbms) must be executed
  • The sql query included in the bbdd.sessionConfig property must be executed using that connection.
• Take into account that these two operations must be executed on the returned connection only when the connection is actually created, not every time it is returned from the pool.