java - hibernate : load and LazyInitializationException

Question

根据教程:http://jpa.ezhibernate.com/Javacode/learn.jsp?tutorial=27hibernateloadvshibernateget ,

If you initialize a JavaBean instance with a load method call, you can only access the properties of that JavaBean, for the first time, within the transactional context in which it was initialized.

If you try to access the various properties of the JavaBean after the transaction that loaded it has been committed, you'll get an exception, a LazyInitializationException, as Hibernate no longer has a valid transactional context to use to hit the database.

但是根据我的实验，使用 hibernate 3.6 和 postgres 9，它根本不会抛出任何异常。我错过了什么吗？

这是我的代码:

import org.hibernate.Session;


public class AppLoadingEntities {
    /**
    * @param args
    */
    public static void main(String[] args) {
        HibernateUtil.beginTransaction();
        Session session = HibernateUtil.getSession();
        
        EntityUser userFromGet = get(session);
        EntityUser userFromLoad = load(session);
        
        // finish the transaction
        session.getTransaction().commit();
        
        // try fetching field value from entity bean that is fetched via get outside transaction, and it'll be okay
        System.out.println("userFromGet.getId() : " + userFromGet.getId());
        System.out.println("userFromGet.getName() : " + userFromGet.getName());
        
        // fetching field from entity bean that is fetched via load outside transaction, and it'll be errornous
        // NOTE : but after testing, load seems to be okay, what gives ? ask forums
        try {
            System.out.println("userFromLoad.getId() : " + userFromLoad.getId());
            System.out.println("userFromLoad.getName() : " + userFromLoad.getName());
        } catch(Exception e) {
            System.out.println("error while fetching entity that is fetched from load : " + e.getMessage());
        }
    }

    private static EntityUser load(Session session) {
        EntityUser user = (EntityUser) session.load(EntityUser.class, 1l);
        return user;
    }

    private static EntityUser get(Session session) {
        // safe to set it to 1, coz the table got recreated at every run of this app
        EntityUser user = (EntityUser) session.get(EntityUser.class, 1l);
        return user;
    }

}

这是输出:

82 [main] INFO org.hibernate.annotations.common.Version - Hibernate Commons Annotations 3.2.0.Final
87 [main] INFO org.hibernate.cfg.Environment - Hibernate 3.6.0.Final
87 [main] INFO org.hibernate.cfg.Environment - hibernate.properties not found
90 [main] INFO org.hibernate.cfg.Environment - Bytecode provider name : javassist
92 [main] INFO org.hibernate.cfg.Environment - using JDK 1.4 java.sql.Timestamp handling
132 [main] INFO org.hibernate.cfg.Configuration - configuring from resource: /hibernate.cfg.xml
132 [main] INFO org.hibernate.cfg.Configuration - Configuration resource: /hibernate.cfg.xml
172 [main] WARN org.hibernate.util.DTDEntityResolver - recognized obsolete hibernate namespace http://hibernate.sourceforge.net/. Use namespace http://www.hibernate.org/dtd/ instead. Refer to Hibernate 3.6 Migration Guide!
189 [main] INFO org.hibernate.cfg.Configuration - Configured SessionFactory: null
228 [main] INFO org.hibernate.cfg.AnnotationBinder - Binding entity from annotated class: EntityUser
254 [main] INFO org.hibernate.cfg.annotations.EntityBinder - Bind entity EntityUser on table MstUser
285 [main] INFO org.hibernate.cfg.Configuration - Hibernate Validator not found: ignoring
287 [main] INFO org.hibernate.cfg.search.HibernateSearchEventListenerRegister - Unable to find org.hibernate.search.event.FullTextIndexEventListener on the classpath. Hibernate Search is not enabled.
291 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - Using Hibernate built-in connection pool (not for production use!)
291 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - Hibernate connection pool size: 20
291 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - autocommit mode: false
300 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - using driver: org.postgresql.Driver at URL: jdbc:postgresql://localhost:5432/hibernate
300 [main] INFO org.hibernate.connection.DriverManagerConnectionProvider - connection properties: {user=sofco, password=****}
369 [main] INFO org.hibernate.cfg.SettingsFactory - Database ->
       name : PostgreSQL
    version : 9.0.1
      major : 9
      minor : 0
369 [main] INFO org.hibernate.cfg.SettingsFactory - Driver ->
       name : PostgreSQL Native Driver
    version : PostgreSQL 9.0 JDBC4 (build 801)
      major : 9
      minor : 0
386 [main] INFO org.hibernate.dialect.Dialect - Using dialect: org.hibernate.dialect.PostgreSQLDialect
395 [main] INFO org.hibernate.engine.jdbc.JdbcSupportLoader - Disabling contextual LOB creation as createClob() method threw error : java.lang.reflect.InvocationTargetException
396 [main] INFO org.hibernate.transaction.TransactionFactoryFactory - Transaction strategy: org.hibernate.transaction.JDBCTransactionFactory
397 [main] INFO org.hibernate.transaction.TransactionManagerLookupFactory - No TransactionManagerLookup configured (in JTA environment, use of read-write or transactional second-level cache is not recommended)
397 [main] INFO org.hibernate.cfg.SettingsFactory - Automatic flush during beforeCompletion(): disabled
397 [main] INFO org.hibernate.cfg.SettingsFactory - Automatic session close at end of transaction: disabled
397 [main] INFO org.hibernate.cfg.SettingsFactory - JDBC batch size: 15
397 [main] INFO org.hibernate.cfg.SettingsFactory - JDBC batch updates for versioned data: disabled
397 [main] INFO org.hibernate.cfg.SettingsFactory - Scrollable result sets: enabled
397 [main] INFO org.hibernate.cfg.SettingsFactory - JDBC3 getGeneratedKeys(): enabled
397 [main] INFO org.hibernate.cfg.SettingsFactory - Connection release mode: auto
398 [main] INFO org.hibernate.cfg.SettingsFactory - Default batch fetch size: 1
398 [main] INFO org.hibernate.cfg.SettingsFactory - Generate SQL with comments: disabled
398 [main] INFO org.hibernate.cfg.SettingsFactory - Order SQL updates by primary key: disabled
398 [main] INFO org.hibernate.cfg.SettingsFactory - Order SQL inserts for batching: disabled
398 [main] INFO org.hibernate.cfg.SettingsFactory - Query translator: org.hibernate.hql.ast.ASTQueryTranslatorFactory
398 [main] INFO org.hibernate.hql.ast.ASTQueryTranslatorFactory - Using ASTQueryTranslatorFactory
399 [main] INFO org.hibernate.cfg.SettingsFactory - Query language substitutions: {}
399 [main] INFO org.hibernate.cfg.SettingsFactory - JPA-QL strict compliance: disabled
399 [main] INFO org.hibernate.cfg.SettingsFactory - Second-level cache: enabled
399 [main] INFO org.hibernate.cfg.SettingsFactory - Query cache: disabled
399 [main] INFO org.hibernate.cfg.SettingsFactory - Cache region factory : org.hibernate.cache.impl.NoCachingRegionFactory
399 [main] INFO org.hibernate.cfg.SettingsFactory - Optimize cache for minimal puts: disabled
399 [main] INFO org.hibernate.cfg.SettingsFactory - Structured second-level cache entries: disabled
401 [main] INFO org.hibernate.cfg.SettingsFactory - Echoing all SQL to stdout
402 [main] INFO org.hibernate.cfg.SettingsFactory - Statistics: disabled
402 [main] INFO org.hibernate.cfg.SettingsFactory - Deleted entity synthetic identifier rollback: disabled
402 [main] INFO org.hibernate.cfg.SettingsFactory - Default entity-mode: pojo
402 [main] INFO org.hibernate.cfg.SettingsFactory - Named query checking : enabled
402 [main] INFO org.hibernate.cfg.SettingsFactory - Check Nullability in Core (should be disabled when Bean Validation is on): enabled
424 [main] INFO org.hibernate.impl.SessionFactoryImpl - building session factory
548 [main] INFO org.hibernate.impl.SessionFactoryObjectFactory - Not binding factory to JNDI, no JNDI name configured
Hibernate: select entityuser0_.id as id0_0_, entityuser0_.name as name0_0_, entityuser0_.password as password0_0_ from MstUser entityuser0_ where entityuser0_.id=?
Hibernate: select entityuser0_.id as id0_0_, entityuser0_.name as name0_0_, entityuser0_.password as password0_0_ from MstUser entityuser0_ where entityuser0_.id=?
userFromGet.getId() : 1
userFromGet.getName() : Albert Kam xzy
userFromLoad.getId() : 1
userFromLoad.getName() : Albert Kam xzy

Answer 1

您没有看到该异常，因为在您的 load(...) 方法中，您有以下 System.out

System.out.println("user fetched with 'load' inside transaction : " + user);

正如您所看到的，您通过调用 toString() 来打印“用户”(这是自动调用的)。在日志中，我看到正在打印以下内容，这意味着您已经覆盖了 toString() 方法，该方法在内部调用每个给定属性的 getter 方法。由于这一切都是在事务仍然打开时发生的(您在调用 load(...) 方法后提交事务)，因此您不会看到此异常。

user fetched with 'load' inside transaction : 1:Albert Kam xzy:abc