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Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Developer's Guide

Chapter 11 Using the JDBC API for Database Access

This chapter describes how to use the JavaTM Database Connectivity (JDBCTM) API for database access with the Sun Java System Application Server. This chapter also provides high level JDBC implementation instructions for servlets and EJBTM components using the Application Server. The Application Server supports the JDBC 3.0 API, which encompasses the JDBC 2.0 Optional Package API.

The JDBC specifications are available at http://java.sun.com/products/jdbc/download.html.

A useful JDBC tutorial is located at http://java.sun.com/docs/books/tutorial/jdbc/index.html.

For explanations of two-tier and three-tier database access models, see the Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Administration Guide.

Note –

The Application Server does not support connection pooling or transactions for an application’s database access if it does not use standard J2EETM DataSource objects.

This chapter discusses the following topics:

General Steps for Creating a JDBC Resource

To prepare a JDBC resource for use in J2EE applications deployed to the Application Server, perform the following tasks:

For information about how to configure some specific JDBC drivers, see the Configurations for Specific JDBC Drivers.

Integrating the JDBC Driver

To use JDBC features, you must choose a JDBC driver to work with the Application Server, then you must set up the driver. This section covers these topics:

Supported Database Drivers

Supported JDBC drivers are those that have been fully tested by Sun. For a list of the JDBC drivers currently supported by the Application Server, see the Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Release Notes. For configurations of supported and other drivers, see Configurations for Specific JDBC Drivers.

Note –

Because the drivers and databases supported by the Application Server are constantly being updated, and because database vendors continue to upgrade their products, always check with Sun technical support for the latest database support information.

Making the JDBC Driver JAR Files Accessible

To integrate the JDBC driver into a Application Server domain, copy the JAR files into the domain-dir/lib/ext directory, then restart the server. This makes classes accessible to any application or module across the domain. For more information about Application Server classloaders, see Classloaders.

Creating a Connection Pool

When you create a connection pool that uses JDBC technology (a JDBC connection pool) in the Application Server, you can define many of the characteristics of your database connections.

You can create a JDBC connection pool in one of these ways:

Testing a Connection Pool

You can test a JDBC connection pool for usability in one of these ways:

Both these commands fail and display an error message unless they successfully connect to the connection pool.

For information about how to tune a connection pool, see the Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Performance Tuning Guide.

Creating a JDBC Resource

A JDBC resource, also called a data source, lets you make connections to a database using getConnection(). Create a JDBC resource in one of these ways:

Creating Applications That Use the JDBC API

An application that uses the JDBC API is an application that looks up and connects to one or more databases. This section covers these topics:

Sharing Connections

When multiple connections acquired by an application use the same JDBC resource, the connection pool provides connection sharing within the same transaction scope. For example, suppose Bean A starts a transaction and obtains a connection, then calls a method in Bean B. If Bean B acquires a connection to the same JDBC resource with the same sign-on information, and if Bean A completes the transaction, the connection can be shared.

Connections obtained through a resource are shared only if the resource reference declared by the J2EE component allows it to be shareable. This is specified in a component’s deployment descriptor by setting the res-sharing-scope element to Shareable for the particular resource reference. To turn off connection sharing, set res-sharing-scope to Unshareable.

For general information about connections and JDBC URLs, see the Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Administration Guide.

Obtaining a Physical Connection from a Wrapped Connection

The DataSource implementation in the Application Server provides a getConnection method that retrieves the JDBC driver’s SQLConnection from the Application Server’s Connection wrapper. The method signature is as follows:

public java.sql.Connection getConnection(java.sql.Connection con) 
throws java.sql.SQLException

For example:

InitialContext ctx = new InitialContext();
com.sun.appserv.DataSource ds = (com.sun.appserv.DataSource) 
   ctx.lookup("jdbc/MyBase");
Connection con = ds.getConnection();
Connection drivercon = ds.getConnection(con);
// Do db operations.
con.close();

Using Non-Transactional Connections

The DataSource implementation in the Application Server provides a getNonTxConnection method, which retrieves a JDBC connection that is not in the scope of any transaction. There are two variants, as follows:

public java.sql.Connection getNonTxConnection() throws java.sql.SQLException
public java.sql.Connection getNonTxConnection(String user, String password) 
throws java.sql.SQLException

Another way to get a non-transactional connection is to create a resource with the JNDI name ending in __nontx. This forces all connections looked up using this resource to be non transactional.

Typically, a connection is enlisted in the context of the transaction in which a getConnection call is invoked. However, a non-transactional connection is not enlisted in a transaction context even if a transaction is in progress.

The main advantage of using non-transactional connections is that the overhead incurred in enlisting and delisting connections in transaction contexts is avoided. However, use such connections carefully. For example, if a non-transactional connection is used to query the database while a transaction is in progress that modifies the database, the query retrieves the unmodified data in the database. This is because the in-progress transaction hasn’t committed. For another example, if a non-transactional connection modifies the database and a transaction that is running simultaneously rolls back, the changes made by the non-transactional connection are not rolled back.

Here is a typical use case for a non-transactional connection: a component that is updating a database in a transaction context spanning over several iterations of a loop can refresh cached data by using a non-transactional connection to read data before the transaction commits.

Using JDBC Transaction Isolation Levels

For general information about transactions, see Chapter 12, Using the Transaction Serviceand the Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Administration Guide. For information about last agent optimization, which can improve performance, see Transaction Scope.

Not all database vendors support all transaction isolation levels available in the JDBC API. The Application Server permits specifying any isolation level your database supports. The following table defines transaction isolation levels.

Table 11–1 Transaction Isolation Levels

Transaction Isolation Level  

Description  

TRANSACTION_READ_UNCOMMITTED

Dirty reads, non-repeatable reads and phantom reads can occur. 

TRANSACTION_READ_COMMITTED

Dirty reads are prevented; non-repeatable reads and phantom reads can occur. 

TRANSACTION_REPEATABLE_READ

Dirty reads and non-repeatable reads are prevented; phantom reads can occur. 

TRANSACTION_SERIALIZABLE

Dirty reads, non-repeatable reads and phantom reads are prevented. 

Note that you cannot call setTransactionIsolation() during a transaction.

You can set the default transaction isolation level for a JDBC connection pool. For details, see Creating a Connection Pool.

To verify that a level is supported by your database management system, test your database programmatically using the supportsTransactionIsolationLevel() method in java.sql.DatabaseMetaData, as shown in the following example:

java.sql.DatabaseMetaData db;
if (db.supportsTransactionIsolationLevel(TRANSACTION_SERIALIZABLE)
   { Connection.setTransactionIsolation(TRANSACTION_SERIALIZABLE); }

For more information about these isolation levels and what they mean, see the JDBC 3.0 API specification.

Note –

Applications that change the isolation level on a pooled connection programmatically risk polluting the pool, which can lead to errors.

Configurations for Specific JDBC Drivers

Application Server 8.1 is designed to support connectivity to any database management system with a corresponding JDBC driver. The following JDBC driver and database combinations are supported. These combinations have been tested with Application Server 8.1 and are found to be J2EE compatible. They are also supported for CMP.

For an up to date list of currently supported JDBC drivers, see the Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Release Notes.

Other JDBC drivers can be used with Application Server 8.1, but J2EE compliance tests have not been completed with these drivers. Although Sun offers no product support for these drivers, Sun offers limited support of the use of these drivers with Application Server 8.1.

For details about how to integrate a JDBC driver and how to use the Administration Console or the command line interface to implement the configuration, see the Sun Java System Application Server Enterprise Edition 8.1 2005Q2 Administration Guide.

Note –

An Oracle database user running the capture-schema command needs ANALYZE ANY TABLE privileges if that user does not own the schema. These privileges are granted to the user by the database administrator. For information about capture-schema, see Using the capture-schema Utility.

PointBase Type 4 Driver

The PointBase JDBC driver is included with the Application Server by default, except for the Solaris bundled installation, which does not include PointBase. Therefore, unless you have the Solaris bundled installation, you do not need to integrate this JDBC driver with the Application Server.

PointBase is intended for evaluation use only, not for production or deployment use.

The JAR file for the PointBase driver is pbclient.jar.

Configure the connection pool using the following settings:

Sun Java System JDBC Driver for DB2 Databases

The JAR files for this driver are smbase.jar, smdb2.jar, and smutil.jar. Configure the connection pool using the following settings:

Sun Java System JDBC Driver for Oracle 8.1.7 and 9.x Databases

The JAR files for this driver are smbase.jar, smoracle.jar, and smutil.jar. Configure the connection pool using the following settings:

Sun Java System JDBC Driver for Microsoft SQL Server Databases

The JAR files for this driver are smbase.jar, smsqlserver.jar, and smutil.jar. Configure the connection pool using the following settings:

Sun Java System JDBC Driver for Sybase Databases

The JAR files for this driver are smbase.jar, smsybase.jar, and smutil.jar. Configure the connection pool using the following settings:

IBM DB2 8.1 Type 2 Driver

The JAR files for the DB2 driver are db2jcc.jar, db2jcc_license_cu.jar, and db2java.zip. Set environment variables as follows:

LD_LIBRARY_PATH=/usr/db2user/sqllib/lib:${j2ee.home}/lib
DB2DIR=/opt/IBM/db2/V8.1
DB2INSTANCE=db2user
INSTHOME=/usr/db2user
VWSPATH=/usr/db2user/sqllib
THREADS_FLAG=native

Configure the connection pool using the following settings:

JConnect Type 4 Driver for Sybase ASE 12.5 Databases

The JAR file for the Sybase driver is jconn2.jar. Configure the connection pool using the following settings:

Inet Oraxo JDBC Driver for Oracle 8.1.7 and 9.x Databases

The JAR file for the Inet Oracle driver is Oranxo.jar. Configure the connection pool using the following settings:

Inet Merlia JDBC Driver for Microsoft SQL Server Databases

The JAR file for the Inet Microsoft SQL Server driver is Merlia.jar. Configure the connection pool using the following settings:

Inet Sybelux JDBC Driver for Sybase Databases

The JAR file for the Inet Sybase driver is Sybelux.jar. Configure the connection pool using the following settings:

Oracle Thin Type 4 Driver for Oracle 8.1.7 and 9.x Databases

The JAR file for the Oracle driver is ojdbc14.jar. Configure the connection pool using the following settings:

OCI Oracle Type 2 Driver for Oracle 8.1.7 and 9.x Databases

The JAR file for the OCI Oracle driver is ojdbc14.jar. Make sure that the shared library is available through LD_LIBRARY_PATH and that the ORACLE_HOME property is set. Configure the connection pool using the following settings:

IBM Informix Type 4 Driver

Configure the connection pool using the following settings:

MM MySQL Type 4 Driver

Configure the connection pool using the following settings:

CloudScape 5.1 Type 4 Driver

The JAR files for the CloudScape driver are db2j.jar, db2jtools.jar, db2jcview.jar, jh.jar, db2jcc.jar, and db2jnet.jar. Configure the connection pool using the following settings: