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Hibernate is designed to operate in many different environments and, as such, there is a broad range of configuration parameters. Fortunately, most have sensible default values and Hibernate is distributed with an example hibernate.properties file in etc/ that displays the various options. Simply put the example file in your classpath and customize it to suit your needs.
Configuration cfg = new Configuration() .addResource("Item.hbm.xml") .addResource("Bid.hbm.xml");
Configuration cfg = new Configuration() .addClass(org.hibernate.auction.Item.class) .addClass(org.hibernate.auction.Bid.class);
A org.hibernate.cfg.Configuration also allows you to specify configuration properties. For example:
Configuration cfg = new Configuration() .addClass(org.hibernate.auction.Item.class) .addClass(org.hibernate.auction.Bid.class) .setProperty("hibernate.dialect", "org.hibernate.dialect.MySQLInnoDBDialect") .setProperty("hibernate.connection.datasource", "java:comp/env/jdbc/test") .setProperty("hibernate.order_updates", "true");
If you want to get started quicklyhibernate.properties is the easiest approach.
Session session = sessions.openSession(); // open a new Session
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 org.hibernate.connection.C3P0ConnectionProvider for connection pooling if you set hibernate.c3p0.* properties. If you would like to use Proxool, refer to the packaged hibernate.properties and the Hibernate web site for more information.
The following is an example hibernate.properties file for c3p0:
hibernate.connection.driver_class = org.postgresql.Driver hibernate.connection.url = jdbc:postgresql://localhost/mydatabase hibernate.connection.username = myuser hibernate.connection.password = secret hibernate.c3p0.min_size=5 hibernate.c3p0.max_size=20 hibernate.c3p0.timeout=1800 hibernate.c3p0.max_statements=50 hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect
For use inside an application server, you should almost always configure Hibernate to obtain connections from an application server javax.sql.Datasource registered in JNDI. You will need to set at least one of the following properties:
表 3.2. Hibernate数据源属性
| 属性名 | 用途 |
|---|---|
| hibernate.connection.datasource | 数据源JNDI名字 |
| 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 is an example hibernate.properties file for an application server provided JNDI datasource:
hibernate.connection.datasource = java:/comp/env/jdbc/test
hibernate.transaction.factory_class = \
org.hibernate.transaction.JTATransactionFactory
hibernate.transaction.manager_lookup_class = \
org.hibernate.transaction.JBossTransactionManagerLookup
hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect从JNDI数据源获得的JDBC连接将自动参与到应用程序服务器中容器管理的事务(container-managed transactions)中去.
Arbitrary connection properties can be given by prepending "hibernate.connection" to the connection property name. For example, you can specify a charSet connection property using hibernate.connection.charSet.
You can define your own plugin strategy for obtaining JDBC connections by implementing the interface org.hibernate.connection.ConnectionProvider, and specifying your custom implementation via the hibernate.connection.provider_class property.
java -Dproperty=value or hibernate.properties. They cannot be set by the other techniques described above.表 3.4. Hibernate JDBC和连接(connection)属性
| 属性名 | 用途 |
|---|---|
| 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. e.g. recommended values between |
| hibernate.jdbc.batch_versioned_data | Set this property to true if your JDBC driver returns correct row counts from executeBatch(). Iit is usually safe to turn this option on. Hibernate will then use batched DML for automatically versioned data. Defaults to false. e.g. |
| hibernate.jdbc.factory_class | Select a custom org.hibernate.jdbc.Batcher. Most applications will not need this configuration property. e.g. |
| 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. e.g. |
| hibernate.jdbc.use_streams_for_binary | Use streams when writing/reading binary or serializable types to/from JDBC. *system-level property* e.g. |
| hibernate.jdbc.use_get_generated_keys | Enables 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, it tries to determine the driver capabilities using connection metadata. e.g. |
| hibernate.connection.provider_class | The classname of a custom org.hibernate.connection.ConnectionProvider which provides JDBC connections to Hibernate. e.g. |
| hibernate.connection.isolation | Sets the JDBC transaction isolation level. Check java.sql.Connection for meaningful values, but note that most databases do not support all isolation levels and some define additional, non-standard isolations. e.g. |
| hibernate.connection.autocommit | Enables autocommit for JDBC pooled connections (it is not recommended). e.g. |
| hibernate.connection.release_mode | Specifies 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, 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. e.g. This setting only affects |
| hibernate.connection.<propertyName> | Pass the JDBC property <propertyName> to DriverManager.getConnection(). |
| hibernate.jndi.<propertyName> | Pass the property <propertyName> to the JNDI InitialContextFactory. |
表 3.5. Hibernate缓存属性
| 属性名 | 用途 |
|---|---|
hibernate.cache.provider_class
| The classname of a custom CacheProvider. e.g. |
hibernate.cache.use_minimal_puts
| Optimizes 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. e.g. |
hibernate.cache.use_query_cache
| Enables the query cache. Individual queries still have to be set cachable. e.g. |
hibernate.cache.use_second_level_cache
| Can be used to completely disable the second level cache, which is enabled by default for classes which specify a <cache> mapping. e.g. |
hibernate.cache.query_cache_factory
| The classname of a custom QueryCache interface, defaults to the built-in StandardQueryCache. e.g. |
hibernate.cache.region_prefix
| A prefix to use for second-level cache region names. e.g. |
hibernate.cache.use_structured_entries
| Forces Hibernate to store data in the second-level cache in a more human-friendly format. e.g. |
表 3.6. Hibernate事务属性
| 属性名 | 用途 |
|---|---|
hibernate.transaction.factory_class
| The classname of a TransactionFactory to use with Hibernate Transaction API (defaults to JDBCTransactionFactory). e.g. |
jta.UserTransaction
| A JNDI name used by JTATransactionFactory to obtain the JTA UserTransaction from the application server. e.g. |
hibernate.transaction.manager_lookup_class
| The classname of a TransactionManagerLookup. It is required when JVM-level caching is enabled or when using hilo generator in a JTA environment. e.g. |
hibernate.transaction.flush_before_completion
| If enabled, the session will be automatically flushed during the before completion phase of the transaction. Built-in and automatic session context management is preferred, see 第 2.5 节 “Contextual sessions”. e.g. |
hibernate.transaction.auto_close_session
| If enabled, the session will be automatically closed during the after completion phase of the transaction. Built-in and automatic session context management is preferred, see 第 2.5 节 “Contextual sessions”. e.g. |
表 3.7. 其他属性
| 属性名 | 用途 |
|---|---|
hibernate.current_session_context_class
| Supply a custom strategy for the scoping of the "current" Session. See 第 2.5 节 “Contextual sessions” for more information about the built-in strategies. e.g. |
hibernate.query.factory_class
| Chooses the HQL parser implementation. e.g. |
hibernate.query.substitutions
| Is used to map from tokens in Hibernate queries to SQL tokens (tokens might be function or literal names, for example). e.g. |
hibernate.hbm2ddl.auto
| Automatically validates or exports 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. e.g. |
hibernate.cglib.use_reflection_optimizer
| Enables the use of CGLIB instead of runtime reflection (System-level property). Reflection can sometimes be useful when troubleshooting. Hibernate always requires CGLIB even if you turn off the optimizer. You cannot set this property in hibernate.cfg.xml. e.g. |
The properties prefixed by hibernate.cache allow you to use a process or cluster scoped second-level cache system with Hibernate. See the 第 19.2 节 “二级缓存（The Second Level Cache）” for more information.
You can define new Hibernate query tokens using hibernate.query.substitutions. For example:
hibernate.query.substitutions true=1, false=0
hibernate.query.substitutions toLowercase=LOWER
Hibernate utilizes Simple Logging Facade for Java (SLF4J) in order to log various system events. SLF4J can direct your logging output to several logging frameworks (NOP, Simple, log4j version 1.2, JDK 1.4 logging, JCL or logback) depending on your chosen binding. In order to setup logging you will need slf4j-api.jar in your classpath together with the jar file for your preferred binding - slf4j-log4j12.jar in the case of Log4J. See the SLF4J documentation for more detail. To use Log4j you will also need to place a log4j.properties file in your classpath. An example properties file is distributed with Hibernate in the src/ directory.
It is recommended 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:
在使用Hibernate开发应用程序时, 你应当总是为org.hibernate.SQL 开启debug级别的日志记录,或者开启hibernate.show_sql属性。
org.hibernate.cfg.NamingStrategy接口允许你为数据库中的对象和schema 元素指定一个“命名标准”.
SessionFactory sf = new Configuration() .setNamingStrategy(ImprovedNamingStrategy.INSTANCE) .addFile("Item.hbm.xml") .addFile("Bid.hbm.xml") .buildSessionFactory();
org.hibernate.cfg.ImprovedNamingStrategy是一个内建的命名策略, 对 一些应用程序而言，可能是非常有用的起点.
另一个配置方法是在hibernate.cfg.xml文件中指定一套完整的配置. 这个文件可以当成hibernate.properties的替代。 若两个文件同时存在，它将覆盖前者的属性.
<?xml version='1.0' encoding='utf-8'?> <!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD//EN" "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> <hibernate-configuration> <!-- a SessionFactory instance listed as /jndi/name --> <session-factory name="java:hibernate/SessionFactory"> <!-- properties --> <property name="connection.datasource">java:/comp/env/jdbc/MyDB</property> <property name="dialect">org.hibernate.dialect.MySQLDialect</property> <property name="show_sql">false</property> <property name="transaction.factory_class"> org.hibernate.transaction.JTATransactionFactory </property> <property name="jta.UserTransaction">java:comp/UserTransaction</property> <!-- mapping files --> <mapping resource="org/hibernate/auction/Item.hbm.xml"/> <mapping resource="org/hibernate/auction/Bid.hbm.xml"/> <!-- cache settings --> <class-cache class="org.hibernate.auction.Item" usage="read-write"/> <class-cache class="org.hibernate.auction.Bid" usage="read-only"/> <collection-cache collection="org.hibernate.auction.Item.bids" usage="read-write"/> </session-factory> </hibernate-configuration>
With the XML configuration, starting Hibernate is then as simple as:
SessionFactory sf = new Configuration().configure().buildSessionFactory();
You can select a different XML configuration file using:
SessionFactory sf = new Configuration() .configure("catdb.cfg.xml") .buildSessionFactory();
There are three standard, or built-in, choices:
You can also define your own transaction strategies (for a CORBA transaction service, for example).
The easiest way to handle Sessions and transactions is Hibernate's automatic "current" Session management. For a discussion of contextual sessions see 第 2.5 节 “Contextual sessions”. Using the "jta" session context, if there is no Hibernate Session associated with the current JTA transaction, one will be started and associated with that JTA transaction the first time you call sessionFactory.getCurrentSession(). The Sessions retrieved via getCurrentSession() in the"jta" context are set to automatically flush before the transaction completes, close after the transaction completes, and aggressively release JDBC connections after each statement. This allows the Sessions to be managed by the life cycle of the JTA transaction to which it is associated, keeping user code clean of such management concerns. Your code can either use JTA programmatically through UserTransaction, or (recommended for portable code) use the Hibernate Transaction API to set transaction boundaries. If you run in an EJB container, declarative transaction demarcation with CMT is preferred.
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