c# print document barcode Starting a project in Java

Generator Quick Response Code in Java Starting a project

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With no application server to provide a connection pool, an application either implements its own pooling algorithm or relies on a third-party library such as the open source C3P0 connection pooling software. Without Hibernate, the application code calls the connection pool to obtain a JDBC connection and then executes SQL statements with the JDBC programming interface. When the application closes the SQL statements and finally closes the connection, the prepared statements and connection aren t destroyed, but are returned to the pool. With Hibernate, the picture changes: It acts as a client of the JDBC connection pool, as shown in figure 2.3. The application code uses the Hibernate Session and Query API for persistence operations, and it manages database transactions (probably) with the Hibernate Transaction API. Hibernate defines a plug-in architecture that allows integration with any connection-pooling software. However, support for C3P0 is built in, and the software comes bundled with Hibernate, so you ll use that (you already copied the c3p0.jar file into your library directory, right ). Hibernate maintains the pool for you, and configuration properties are passed through. How do you configure C3P0 through Hibernate

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One way to configure the connection pool is to put the settings into your hibernate.cfg.xml configuration file, like you did in the previous section. Alternatively, you can create a hibernate.properties file in the classpath root of the application. An example of a hibernate.properties file for C3P0 is shown in listing 2.5. Note that this file, with the exception of a list of mapping resources, is equivalent to the configuration shown in listing 2.4.

hibernate.connection.driver_class = org.hsqldb.jdbcDriver hibernate.connection.url = jdbc:hsqldb:hsql://localhost hibernate.connection.username = sa hibernate.dialect = org.hibernate.dialect.HSQLDialect

hibernate.c3p0.min_size = 5 hibernate.c3p0.max_size = 20 hibernate.c3p0.timeout = 300 hibernate.c3p0.max_statements = 50 hibernate.c3p0.idle_test_period = 3000

This is the minimum number of JDBC connections that C3P0 keeps ready at all times. This is the maximum number of connections in the pool. An exception is thrown at runtime if this number is exhausted. You specify the timeout period (in this case, 300 seconds) after which an idle connection is removed from the pool. A maximum of 50 prepared statements will be cached. Caching of prepared statements is essential for best performance with Hibernate. This is the idle time in seconds before a connection is automatically validated. Specifying properties of the form hibernate.c3p0.* selects C3P0 as the connection pool (the c3p0.max_size option is needed you don t need any other switch to enable C3P0 support). C3P0 has more features than shown in the previous example; refer to the properties file in the etc/ subdirectory of the Hibernate distribution to get a comprehensive example you can copy from. The Javadoc for the class org.hibernate.cfg.Environment also documents every Hibernate configuration property. Furthermore, you can find an up-to-date table with all Hibernate configuration options in the Hibernate reference

documentation. We ll explain the most important settings throughout the book, however. You already know all you need to get started.

Can I supply my own connections Implement the org.hibernate.connection.ConnectionProvider interface, and name your implementation with the hibernate.connection.provider_class configuration option. Hibernate will now rely on your custom provider if it needs a database connection.

Now that you ve completed the Hibernate configuration file, you can move on and create the SessionFactory in your application. Handling the SessionFactory In most Hibernate applications, the SessionFactory should be instantiated once during application initialization. The single instance should then be used by all code in a particular process, and any Session should be created using this single SessionFactory. The SessionFactory is thread-safe and can be shared; a Session is a single-threaded object. A frequently asked question is where the factory should be stored after creation and how it can be accessed without much hassle. There are more advanced but comfortable options such as JNDI and JMX, but they re usually available only in full Java EE application servers. Instead, we ll introduce a pragmatic and quick solution that solves both the problem of Hibernate startup (the one line of code) and the storing and accessing of the SessionFactory: you ll use a static global variable and static initialization. Both the variable and initialization can be implemented in a single class, which you ll call HibernateUtil. This helper class is well known in the Hibernate community it s a common pattern for Hibernate startup in plain Java applications without Java EE services. A basic implementation is shown in listing 2.6.