Because Hibernate is designed to operate in many different environments, there are a large number of configuration parameters. Fortunately, most have sensible default values and Hibernate is distributed with an example hibernate.properties file in etc/ that shows the various options. Just put the example file in your classpath and customize it. An instance of org.hibernate.cfg.Configuration represents an entire set of mappings of an application's Java types to an SQL database. The Configuration is used to build an (immutable) SessionFactory. The mappings are compiled from various XML mapping files. You may obtain a Configuration instance by instantiating it directly and specifying XML mapping documents. If the mapping files are in the classpath, use addResource(): An alternative (sometimes better) way is to specify the mapped class, and let Hibernate find the mapping document for you: Then Hibernate will look for mapping files named /org/hibernate/auction/Item.hbm.xml and /org/hibernate/auction/Bid.hbm.xml in the classpath. This approach eliminates any hardcoded filenames. A Configuration also allows you to specify configuration properties: This is not the only way to pass configuration properties to Hibernate. The various options include: Pass an instance of java.util.Properties to Configuration.setProperties(). Place hibernate.properties in a root directory of the classpath. Set System properties using java -Dproperty=value. Include <property> elements in hibernate.cfg.xml (discussed later). hibernate.properties is the easiest approach if you want to get started quickly. The Configuration is intended as a startup-time object, to be discarded once a SessionFactory is created. When all mappings have been parsed by the Configuration, the application must obtain a factory for Session instances. This factory is intended to be shared by all application threads: Hibernate does allow your application to instantiate more than one SessionFactory. This is useful if you are using more than one database. Usually, you want to have the SessionFactory create and pool JDBC connections for you. If you take this approach, opening a Session is as simple as: As soon as you do something that requires access to the database, a JDBC connection will be obtained from the pool. For this to work, we need to pass some JDBC connection properties to Hibernate. All Hibernate property names and semantics are defined on the class org.hibernate.cfg.Environment. We will now describe the most important settings for JDBC connection configuration. Hibernate will obtain (and pool) connections using java.sql.DriverManager if you set the following properties: Property name Purpose hibernate.connection.driver_class jdbc driver class hibernate.connection.url jdbc URL hibernate.connection.username database user hibernate.connection.password database user password hibernate.connection.pool_size maximum number of pooled connections Hibernate's own connection pooling algorithm is however quite rudimentary. It is intended to help you get started and is not intended for use in a production system or even for performance testing. You should use a third party pool for best performance and stability. Just replace the hibernate.connection.pool_size property with connection pool specific settings. This will turn off Hibernate's internal pool. For example, you might like to use C3P0. C3P0 is an open source JDBC connection pool distributed along with Hibernate in the lib directory. Hibernate will use its C3P0ConnectionProvider for connection pooling if you set hibernate.c3p0.* properties. If you'd like to use Proxool refer to the packaged hibernate.properties and the Hibernate web site for more information. Here is an example hibernate.properties file for C3P0: For use inside an application server, you should almost always configure Hibernate to obtain connections from an application server Datasource registered in JNDI. You'll need to set at least one of the following properties: Propery name Purpose hibernate.connection.datasource datasource JNDI name hibernate.jndi.url URL of the JNDI provider (optional) hibernate.jndi.class class of the JNDI InitialContextFactory (optional) hibernate.connection.username database user (optional) hibernate.connection.password database user password (optional) Here's an example hibernate.properties file for an application server provided JNDI datasource: JDBC connections obtained from a JNDI datasource will automatically participate in the container-managed transactions of the application server. Arbitrary connection properties may be given by prepending "hibernate.connnection" to the property name. For example, you may specify a charSet using hibernate.connection.charSet. You may define your own plugin strategy for obtaining JDBC connections by implementing the interface org.hibernate.connection.ConnectionProvider. You may select a custom implementation by setting hibernate.connection.provider_class. There are a number of other properties that control the behaviour of Hibernate at runtime. All are optional and have reasonable default values. Warning: some of these properties are "system-level" only. System-level properties can be set only via java -Dproperty=value or hibernate.properties. They may not be set by the other techniques described above. Property name Purpose hibernate.dialect The classname of a Hibernate Dialect which allows Hibernate to generate SQL optimized for a particular relational database. eg. full.classname.of.Dialect hibernate.show_sql Write all SQL statements to console. eg. true | false hibernate.default_schema Qualify unqualified tablenames with the given schema/tablespace in generated SQL. eg. SCHEMA_NAME hibernate.default_catalog Qualify unqualified tablenames with the given catalog in generated SQL. eg. CATALOG_NAME hibernate.session_factory_name The SessionFactory will be automatically bound to this name in JNDI after it has been created. eg. jndi/composite/name hibernate.max_fetch_depth Set a maximum "depth" for the outer join fetch tree for single-ended associations (one-to-one, many-to-one). A 0 disables default outer join fetching. eg. recommended values between 0 and 3 hibernate.default_batch_fetch_size Set a default size for Hibernate batch fetching of associations. eg. recommended values 4, 8, 16 hibernate.default_entity_mode Set a default mode for entity representation for all sessions opened from this SessionFactory dynamic-map, dom4j, pojo hibernate.order_updates Force Hibernate to order SQL updates by the primary key value of the items being updated. This will result in fewer transaction deadlocks in highly concurrent systems. eg. true | false hibernate.generate_statistics If enabled, Hibernate will collect statistics useful for performance tuning. eg. true | false hibernate.use_identifer_rollback If enabled, generated identifier properties will be reset to default values when objects are deleted. eg. true | false hibernate.use_sql_comments If turned on, Hibernate will generate comments inside the SQL, for easier debugging, defaults to false. eg. true | false Property name Purpose hibernate.jdbc.fetch_size A non-zero value determines the JDBC fetch size (calls Statement.setFetchSize()). hibernate.jdbc.batch_size A non-zero value enables use of JDBC2 batch updates by Hibernate. eg. recommended values between 5 and 30 hibernate.jdbc.batch_versioned_data Set this property to true if your JDBC driver returns correct row counts from executeBatch() (it is usually safe to turn this option on). Hibernate will then use batched DML for automatically versioned data. Defaults to false. eg. true | false hibernate.jdbc.factory_class Select a custom Batcher. Most applications will not need this configuration property. eg. classname.of.Batcher hibernate.jdbc.use_scrollable_resultset Enables use of JDBC2 scrollable resultsets by Hibernate. This property is only necessary when using user supplied JDBC connections, Hibernate uses connection metadata otherwise. eg. true | false hibernate.jdbc.use_streams_for_binary Use streams when writing/reading binary or serializable types to/from JDBC (system-level property). eg. true | false hibernate.jdbc.use_get_generated_keys Enable use of JDBC3 PreparedStatement.getGeneratedKeys() to retrieve natively generated keys after insert. Requires JDBC3+ driver and JRE1.4+, set to false if your driver has problems with the Hibernate identifier generators. By default, tries to determine the driver capabilites using connection metadata. eg. true|false hibernate.connection.provider_class The classname of a custom ConnectionProvider which provides JDBC connections to Hibernate. eg. classname.of.ConnectionProvider hibernate.connection.isolation Set the JDBC transaction isolation level. Check java.sql.Connection for meaningful values but note that most databases do not support all isolation levels. eg. 1, 2, 4, 8 hibernate.connection.autocommit Enables autocommit for JDBC pooled connections (not recommended). eg. true | false hibernate.connection.release_mode Specify when Hibernate should release JDBC connections. By default, a JDBC connection is held until the session is explicitly closed or disconnected. For an application server JTA datasource, you should use after_statement to aggressively release connections after every JDBC call. For a non-JTA connection, it often makes sense to release the connection at the end of each transaction, by using after_transaction. auto will choose after_statement for the JTA and CMT transaction strategies and after_transaction for the JDBC transaction strategy. eg. on_close (default) | after_transaction | after_statement | auto hibernate.connection.<propertyName> Pass the JDBC property propertyName to DriverManager.getConnection(). hibernate.jndi.<propertyName> Pass the property propertyName to the JNDI InitialContextFactory. Property name Purpose hibernate.cache.provider_class The classname of a custom CacheProvider. eg. classname.of.CacheProvider hibernate.cache.use_minimal_puts Optimize second-level cache operation to minimize writes, at the cost of more frequent reads. This setting is most useful for clustered caches and, in Hibernate3, is enabled by default for clustered cache implementations. eg. true|false hibernate.cache.use_query_cache Enable the query cache, individual queries still have to be set cachable. eg. true|false hibernate.cache.use_second_level_cache May be used to completely disable the second level cache, which is enabled by default for classes which specify a <cache> mapping. eg. true|false hibernate.cache.query_cache_factory The classname of a custom QueryCache interface, defaults to the built-in StandardQueryCache. eg. classname.of.QueryCache hibernate.cache.region_prefix A prefix to use for second-level cache region names. eg. prefix hibernate.cache.use_structured_entries Forces Hibernate to store data in the second-level cache in a more human-friendly format. eg. true|false Property name Purpose hibernate.transaction.factory_class The classname of a TransactionFactory to use with Hibernate Transaction API (defaults to JDBCTransactionFactory). eg. classname.of.TransactionFactory jta.UserTransaction A JNDI name used by JTATransactionFactory to obtain the JTA UserTransaction from the application server. eg. jndi/composite/name hibernate.transaction.manager_lookup_class The classname of a TransactionManagerLookup - required when JVM-level caching is enabled or when using hilo generator in a JTA environment. eg. classname.of.TransactionManagerLookup hibernate.transaction.flush_before_completion If enabled, the session will be automatically flushed during the before completion phase of the transaction. (Very useful when using Hibernate with CMT.) eg. true | false hibernate.transaction.auto_close_session If enabled, the session will be automatically closed during the after completion phase of the transaction. (Very useful when using Hibernate with CMT.) eg. true | false Property name Purpose hibernate.query.factory_class Chooses the HQL parser implementation. eg. org.hibernate.hql.ast.ASTQueryTranslatorFactory or org.hibernate.hql.classic.ClassicQueryTranslatorFactory hibernate.query.substitutions Mapping from tokens in Hibernate queries to SQL tokens (tokens might be function or literal names, for example). eg. hqlLiteral=SQL_LITERAL, hqlFunction=SQLFUNC hibernate.hbm2ddl.auto Automatically export schema DDL to the database when the SessionFactory is created. With create-drop, the database schema will be dropped when the SessionFactory is closed explicitly. eg. update | create | create-drop hibernate.cglib.use_reflection_optimizer Enables use of CGLIB instead of runtime reflection (System-level property). Reflection can sometimes be useful when troubleshooting, note that Hibernate always requires CGLIB even if you turn off the optimizer. You can not set this property in hibernate.cfg.xml. eg. true | false You should always set the hibernate.dialect property to the correct org.hibernate.dialect.Dialect subclass for your database. If you specify a dialect, Hibernate will use sensible defaults for some of the other properties listed above, saving you the effort of specifying them manually. RDBMS Dialect DB2 org.hibernate.dialect.DB2Dialect DB2 AS/400 org.hibernate.dialect.DB2400Dialect DB2 OS390 org.hibernate.dialect.DB2390Dialect PostgreSQL org.hibernate.dialect.PostgreSQLDialect MySQL org.hibernate.dialect.MySQLDialect MySQL with InnoDB org.hibernate.dialect.MySQLInnoDBDialect MySQL with MyISAM org.hibernate.dialect.MySQLMyISAMDialect Oracle (any version) org.hibernate.dialect.OracleDialect Oracle 9i/10g org.hibernate.dialect.Oracle9Dialect Sybase org.hibernate.dialect.SybaseDialect Sybase Anywhere org.hibernate.dialect.SybaseAnywhereDialect Microsoft SQL Server org.hibernate.dialect.SQLServerDialect SAP DB org.hibernate.dialect.SAPDBDialect Informix org.hibernate.dialect.InformixDialect HypersonicSQL org.hibernate.dialect.HSQLDialect Ingres org.hibernate.dialect.IngresDialect Progress org.hibernate.dialect.ProgressDialect Mckoi SQL org.hibernate.dialect.MckoiDialect Interbase org.hibernate.dialect.InterbaseDialect Pointbase org.hibernate.dialect.PointbaseDialect FrontBase org.hibernate.dialect.FrontbaseDialect Firebird org.hibernate.dialect.FirebirdDialect If your database supports ANSI, Oracle or Sybase style outer joins, outer join fetching will often increase performance by limiting the number of round trips to and from the database (at the cost of possibly more work performed by the database itself). Outer join fetching allows a whole graph of objects connected by many-to-one, one-to-many, many-to-many and one-to-one associations to be retrieved in a single SQL SELECT. Outer join fetching may be disabled globally by setting the property hibernate.max_fetch_depth to 0. A setting of 1 or higher enables outer join fetching for one-to-one and many-to-one associations which have been mapped with fetch="join". See for more information. Oracle limits the size of byte arrays that may be passed to/from its JDBC driver. If you wish to use large instances of binary or serializable type, you should enable hibernate.jdbc.use_streams_for_binary. This is a system-level setting only. The properties prefixed by hibernate.cache allow you to use a process or cluster scoped second-level cache system with Hibernate. See the for more details. You may define new Hibernate query tokens using hibernate.query.substitutions. For example: hibernate.query.substitutions true=1, false=0 would cause the tokens true and false to be translated to integer literals in the generated SQL. hibernate.query.substitutions toLowercase=LOWER would allow you to rename the SQL LOWER function. If you enable hibernate.generate_statistics, Hibernate will expose a number of metrics that are useful when tuning a running system via SessionFactory.getStatistics(). Hibernate can even be configured to expose these statistics via JMX. Read the Javadoc of the interfaces in org.hibernate.stats for more information. Hibernate logs various events using Apache commons-logging. The commons-logging service will direct output to either Apache Log4j (if you include log4j.jar in your classpath) or JDK1.4 logging (if running under JDK1.4 or above). You may download Log4j from http://jakarta.apache.org. To use Log4j you will need to place a log4j.properties file in your classpath, an example properties file is distributed with Hibernate in the src/ directory. We strongly recommend that you familiarize yourself with Hibernate's log messages. A lot of work has been put into making the Hibernate log as detailed as possible, without making it unreadable. It is an essential troubleshooting device. The most interesting log categories are the following: Category Function org.hibernate.SQL Log all SQL DML statements as they are executed org.hibernate.type Log all JDBC parameters org.hibernate.tool.hbm2ddl Log all SQL DDL statements as they are executed org.hibernate.pretty Log the state of all entities (max 20 entities) associated with the session at flush time org.hibernate.cache Log all second-level cache activity org.hibernate.transaction Log transaction related activity org.hibernate.jdbc Log all JDBC resource acquisition org.hibernate.hql.ast.AST Log HQL and SQL ASTs during query parsing org.hibernate.secure Log all JAAS authorization requests org.hibernate Log everything (a lot of information, but very useful for troubleshooting) When developing applications with Hibernate, you should almost always work with debug enabled for the category org.hibernate.SQL, or, alternatively, the property hibernate.show_sql enabled. The interface org.hibernate.cfg.NamingStrategy allows you to specify a "naming standard" for database objects and schema elements. You may provide rules for automatically generating database identifiers from Java identifiers or for processing "logical" column and table names given in the mapping file into "physical" table and column names. This feature helps reduce the verbosity of the mapping document, eliminating repetitive noise (TBL_ prefixes, for example). The default strategy used by Hibernate is quite minimal. You may specify a different strategy by calling Configuration.setNamingStrategy() before adding mappings: org.hibernate.cfg.ImprovedNamingStrategy is a built-in strategy that might be a useful starting point for some applications. An alternative approach to configuration is to specify a full configuration in a file named hibernate.cfg.xml. This file can be used as a replacement for the hibernate.properties file or, if both are present, to override properties. The XML configuration file is by default expected to be in the root o your CLASSPATH. Here is an example: java:/comp/env/jdbc/MyDB org.hibernate.dialect.MySQLDialect false org.hibernate.transaction.JTATransactionFactory java:comp/UserTransaction ]]> As you can see, the advantage of this approach is the externalization of the mapping file names to configuration. The hibernate.cfg.xml is also more convenient once you have to tune the Hibernate cache. Note that is your choice to use either hibernate.properties or hibernate.cfg.xml, both are equivalent, except for the above mentioned benefits of using the XML syntax. With the XML configuration, starting Hibernate is then as simple as You can pick a different XML configuration file using Hibernate has the following integration points for J2EE infrastructure: Container-managed datasources: Hibernate can use JDBC connections managed by the container and provided through JNDI. Usually, a JTA compatible TransactionManager and a ResourceManager take care of transaction management (CMT), esp. distributed transaction handling across several datasources. You may of course also demarcate transaction boundaries programatically (BMT) or you might want to use the optional Hibernate Transaction API for this to keep your code portable. Automatic JNDI binding: Hibernate can bind its SessionFactory to JNDI after startup. JTA Session binding: The Hibernate Session may be automatically bound to the scope of JTA transactions if you use EJBs. Simply lookup the SessionFactory from JNDI and get the current Session. Let Hibernate take care of flushing and closing the Session when your JTA transaction completes. Transaction demarcation is declarative, in EJB deployment descriptors. JMX deployment: If you have a JMX capable application server (e.g. JBoss AS), you can chose to deploy Hibernate as a managed MBean. This saves you the one line startup code to build your SessionFactory from a Configuration. The container will startup your HibernateService, and ideally also take care of service dependencies (Datasource has to be available before Hibernate starts, etc). Depending on your environment, you might have to set the configuration option hibernate.connection.aggressive_release to true if your application server shows "connection containment" exceptions. The Hibernate Session API is independent of any transaction demarcation system in your architecture. If you let Hibernate use JDBC directly, through a connection pool, you may begin and end your transactions by calling the JDBC API. If you run in a J2EE application server, you might want to use bean-managed transactions and call the JTA API and UserTransaction when needed. To keep your code portable between these two (and other) environments we recommend the optional Hibernate Transaction API, which wraps and hides the underlying system. You have to specify a factory class for Transaction instances by setting the Hibernate configuration property hibernate.transaction.factory_class. There are three standard (built-in) choices: org.hibernate.transaction.JDBCTransactionFactory delegates to database (JDBC) transactions (default) org.hibernate.transaction.JTATransactionFactory delegates to container-managed transaction if an existing transaction is underway in this context (e.g. EJB session bean method), otherwise a new transaction is started and bean-managed transaction are used. org.hibernate.transaction.CMTTransactionFactory delegates to container-managed JTA transactions You may also define your own transaction strategies (for a CORBA transaction service, for example). Some features in Hibernate (i.e. the second level cache, automatic JTA and Session binding, etc.) require access to the JTA TransactionManager in a managed environment. In an application server you have to specify how Hibernate should obtain a reference to the TransactionManager, since J2EE does not standardize a single mechanism: Transaction Factory Application Server org.hibernate.transaction.JBossTransactionManagerLookup JBoss org.hibernate.transaction.WeblogicTransactionManagerLookup Weblogic org.hibernate.transaction.WebSphereTransactionManagerLookup WebSphere org.hibernate.transaction.WebSphereExtendedJTATransactionLookup WebSphere 6 org.hibernate.transaction.OrionTransactionManagerLookup Orion org.hibernate.transaction.ResinTransactionManagerLookup Resin org.hibernate.transaction.JOTMTransactionManagerLookup JOTM org.hibernate.transaction.JOnASTransactionManagerLookup JOnAS org.hibernate.transaction.JRun4TransactionManagerLookup JRun4 org.hibernate.transaction.BESTransactionManagerLookup Borland ES A JNDI bound Hibernate SessionFactory can simplify the lookup of the factory and the creation of new Sessions. Note that this is not related to a JNDI bound Datasource, both simply use the same registry! If you wish to have the SessionFactory bound to a JNDI namespace, specify a name (eg. java:hibernate/SessionFactory) using the property hibernate.session_factory_name. If this property is omitted, the SessionFactory will not be bound to JNDI. (This is especially useful in environments with a read-only JNDI default implementation, e.g. Tomcat.) When binding the SessionFactory to JNDI, Hibernate will use the values of hibernate.jndi.url, hibernate.jndi.class to instantiate an initial context. If they are not specified, the default InitialContext will be used. Hibernate will automatically place the SessionFactory in JNDI after you call cfg.buildSessionFactory(). This means you will at least have this call in some startup code (or utility class) in your application, unless you use JMX deployment with the HibernateService (discussed later). If you use a JNDI SessionFactory, an EJB or any other class may obtain the SessionFactory using a JNDI lookup. Note that this setup is not neccessary if you use the HibernateUtil helper class introduced in chapter one, which acts as a Singleton registry. However, HibernateUtil is more common in a non-managed environment. For non-managed environments we suggested HibernateUtil with a static SessionFactory, and ThreadLocal management of the Hibernate Session. This approach isn't easy to use in an EJB environment, as several EJB's may execute inside the same transaction but not the same thread. We recommend that you bind the SessionFactory to JNDI in a managend environment. Instead of rolling your own ThreadLocal utility, use the getCurrentSession() method on the SessionFactory to obtain a Hibernate Session. If there is no Hibernate Session in current JTA transaction, one will be started and assigned. Both the hibernate.transaction.flush_before_completion and hibernate.transaction.auto_close_session configuration option, will be set automatically for every Session you retrieve with getCurrentSession(), so they will also be flushed and closed automatically when the container ends the JTA transactions. If you, for example, use the DAO design pattern to write your persistence layer, all DAO's lookup the SessionFactory when needed and open the "current" Session. There is no need to pass instances of SessionFactory or Session around between controlling code and DAO code. The line cfg.buildSessionFactory() still has to be executed somewhere to get a SessionFactory into JNDI. You can do this either in a static initializer block (like the one in HibernateUtil) or you deploy Hibernate as a managed service. Hibernate is distributed with org.hibernate.jmx.HibernateService for deployment on an application server with JMX capabilities, such as JBoss AS. The actual deployment and configuration is vendor specific. Here is an example jboss-service.xml for JBoss 4.0.x: jboss.jca:service=RARDeployer jboss.jca:service=LocalTxCM,name=HsqlDS java:/hibernate/SessionFactory java:HsqlDS org.hibernate.dialect.HSQLDialect org.hibernate.transaction.JTATransactionFactory org.hibernate.transaction.JBossTransactionManagerLookup true true 5 true org.hibernate.cache.EhCacheProvider true true auction/Item.hbm.xml,auction/Category.hbm.xml ]]> This file is deployed in a directory called META-INF and packaged in a JAR file with the extension .sar (service archive). You also need to package Hibernate, its required third-party libraries, your compiled persistent classes, as well as your mapping files in the same archive. Your enterprise beans (usually session beans) may be kept in their own JAR file, but you may include this EJB JAR file in the main service archive to get a single (hot-)deployable unit. Consult the JBoss AS documentation for more information about JMX service and EJB deployment.