hibernate annotation方式实现属性级延迟加载

1.在POJO文件需要延迟加载的属性上加“ @Basic(fetch = FetchType.LAZY) ”

2、借助类增强器对二进制Class文件进行强化处理（buildtime bytecode instrumentation)。通过ANT调用Hibernate类增强器对.class文件进行强化处理。

build_instrument.xml

<project name="工程名" default="instrument" basedir=".">
  <property name="lib.dir" value="./WebContent/WEB-INF/lib"/>
  <property name="classes.dir" value="./WebContent/WEB-INF/classes"/>
  
  <path id="lib.class.path">
     <fileset dir="${lib.dir}">
         <include name="**/*.jar"/>
     </fileset>
  </path>
  <target name="instrument">
     <taskdef name="instrument"
         classname="org.hibernate.tool.instrument.javassist.InstrumentTask">

        <classpath path="${classes.dir}"/>
        <classpath refid="lib.class.path"/>
     </taskdef>
        
     <instrument verbose="true">
        <fileset dir="${classes.dir}/com/model/book">
           <include name="BookChapter.class"/><!--需要增强处理的文件-->
        </fileset>
     </instrument>
  </target>
</project>

3.执行ant的脚本，对classes文件进行增强处理。启动tomcat，居然报异常了

ERROR 2008-11-08 12:57:58,796 [main] org.springframework.web.context.ContextLoader.initWebApplicationContext(204) | Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.hibernate.MappingException: Could not determine type for: org.hibernate.bytecode.javassist.FieldHandler, for columns: [org.hibernate.mapping.Column(fieldHandler)]
Caused by: 
org.hibernate.MappingException: Could not determine type for: org.hibernate.bytecode.javassist.FieldHandler, for columns: [org.hibernate.mapping.Column(fieldHandler)]
 at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:266)
 at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:253)
 at org.hibernate.mapping.Property.isValid(Property.java:185)
 at org.hibernate.mapping.PersistentClass.validate(PersistentClass.java:440)
 at org.hibernate.mapping.RootClass.validate(RootClass.java:192)
 at org.hibernate.cfg.Configuration.validate(Configuration.java:1102)
 at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1287)
 at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:915)
 at org.springframework.orm.hibernate3.LocalSessionFactoryBean.newSessionFactory(LocalSessionFactoryBean.java:805)
 at org.springframework.orm.hibernate3.LocalSessionFactoryBean.buildSessionFactory(LocalSessionFactoryBean.java:745)
 at org.springframework.orm.hibernate3.AbstractSessionFactoryBean.afterPropertiesSet(AbstractSessionFactoryBean.java:134)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1203)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1172)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:427)
 at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:249)
 at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:155)
 at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:246)
 at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:160)
 at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:285)
 at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:352)
 at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:246)
 at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:189)
 at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:49)
 at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3830)
 at org.apache.catalina.core.StandardContext.start(StandardContext.java:4337)
 at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
 at org.apache.catalina.core.StandardHost.start(StandardHost.java:719)
 at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
 at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
 at org.apache.catalina.core.StandardService.start(StandardService.java:516)
 at org.apache.catalina.core.StandardServer.start(StandardServer.java:710)
 at org.apache.catalina.startup.Catalina.start(Catalina.java:566)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
 at java.lang.reflect.Method.invoke(Unknown Source)
 at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:288)
 at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:413)
2008-11-8 12:57:58 org.apache.catalina.core.StandardContext listenerStart
严重: Exception sending context initialized event to listener instance of class org.springframework.web.context.ContextLoaderListener
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is org.hibernate.MappingException: Could not determine type for: org.hibernate.bytecode.javassist.FieldHandler, for columns: [org.hibernate.mapping.Column(fieldHandler)]
Caused by: org.hibernate.MappingException: Could not determine type for: org.hibernate.bytecode.javassist.FieldHandler, for columns: [org.hibernate.mapping.Column(fieldHandler)]
 at org.hibernate.mapping.SimpleValue.getType(SimpleValue.java:266)
 at org.hibernate.mapping.SimpleValue.isValid(SimpleValue.java:253)
 at org.hibernate.mapping.Property.isValid(Property.java:185)
 at org.hibernate.mapping.PersistentClass.validate(PersistentClass.java:440)
 at org.hibernate.mapping.RootClass.validate(RootClass.java:192)
 at org.hibernate.cfg.Configuration.validate(Configuration.java:1102)
 at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1287)
 at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:915)
 at org.springframework.orm.hibernate3.LocalSessionFactoryBean.newSessionFactory(LocalSessionFactoryBean.java:805)
 at org.springframework.orm.hibernate3.LocalSessionFactoryBean.buildSessionFactory(LocalSessionFactoryBean.java:745)
 at org.springframework.orm.hibernate3.AbstractSessionFactoryBean.afterPropertiesSet(AbstractSessionFactoryBean.java:134)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1203)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1172)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:427)
 at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:249)
 at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:155)
 at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:246)
 at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:160)
 at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:285)
 at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:352)
 at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:246)
 at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:189)
 at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:49)
 at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3830)
 at org.apache.catalina.core.StandardContext.start(StandardContext.java:4337)
 at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
 at org.apache.catalina.core.StandardHost.start(StandardHost.java:719)
 at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
 at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
 at org.apache.catalina.core.StandardService.start(StandardService.java:516)
 at org.apache.catalina.core.StandardServer.start(StandardServer.java:710)
 at org.apache.catalina.startup.Catalina.start(Catalina.java:566)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
 at java.lang.reflect.Method.invoke(Unknown Source)
 at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:288)
 at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:413)
2008-11-8 12:57:58 org.apache.catalina.core.StandardContext start

4.原来annotation写在field上，hibenate默认就是认为是访问方式是“field”，如果写在getMethod上，访问方式是“property”。将注释修改到属性上后问题解决。

 @Id 
 @AccessType(value = "property")
 @GeneratedValue(strategy = GenerationType.IDENTITY)
 private Long id;
 private String name; 
 @Basic(fetch = FetchType.LAZY)
 private String content;
.......