由动态代理引起的空指针

来源：互联网发布：seo岗位职责编辑：程序博客网时间：2024/05/22 05:16

这个问题困扰我很长时间，而且我两次跌倒在这个坑里，所以我决定把它记录下来（虽然它的改动很简单）

java.lang.NullPointerException
at gov.gfmis.fap.util.dao.springdao.GeneralDAO.getSession(GeneralDAO.java:59)
at gov.gfmis.fap.workflow.service.WorkFlowDesignImplBO.getBytes(WorkFlowDesignImplBO.java:328)
at gov.gfmis.fap.workflow.service.WorkFlowDesignImplBO.getWorkFlow(WorkFlowDesignImplBO.java:250)
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.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:287)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.j
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:148)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:170)
at org.springframework.aop.framework.adapter.ThrowsAdviceInterceptor.invoke(ThrowsAdviceInterceptor.java:118
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:170)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:176)
at $Proxy83.getWorkFlow(Unknown Source)
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.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:287)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.j
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:148)
at org.springframework.remoting.support.RemoteInvocationTraceInterceptor.invoke(RemoteInvocationTraceInterce
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:170)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:176)
at $Proxy83.getWorkFlow(Unknown Source)
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 com.caucho.hessian.server.HessianSkeleton.invoke(HessianSkeleton.java:157)
at org.springframework.remoting.caucho.HessianServiceExporter.handleRequest(HessianServiceExporter.java:91)
at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:723)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:663)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:394)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:358)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

原来要代理的bean的配置：

<bean id="generalDAO" class="gov.gfmis.fap.util.dao.springdao.GeneralDAO">     <property name="sessionFactory" ref="mysessionFactory"/>   </bean>

GeneralDAO有这样的代码代码：

public final Session getSession() {return getSession(this.hibernateTemplate.isAllowCreate());}private Session getSession(boolean allowCreate) {return (!allowCreate ? SessionFactoryUtils.getSession(getSessionFactory(), false) : SessionFactoryUtils.getSession(getSessionFactory(), this.hibernateTemplate.getEntityInterceptor(), this.hibernateTemplate.getJdbcExceptionTranslator()));}public final void setSessionFactory(SessionFactory sessionFactory) {this.hibernateTemplate = createHibernateTemplate(sessionFactory);}protected HibernateTemplate createHibernateTemplate(SessionFactory sessionFactory) {return new HibernateTemplate(sessionFactory);}public final void closeSession(Session s) {try {boolean existingTransaction = SessionFactoryUtils.isSessionTransactional(s, getSessionFactory());if (existingTransaction == false) {SessionFactoryUtils.releaseSession(s, getSessionFactory());}} catch (HibernateException e) {e.printStackTrace();}}public final SessionFactory getSessionFactory() {return (this.hibernateTemplate != null ? this.hibernateTemplate.getSessionFactory() : null);}public final void setHibernateTemplate(HibernateTemplate hibernateTemplate) {this.hibernateTemplate = hibernateTemplate;}public final HibernateTemplate getHibernateTemplate() {return hibernateTemplate;}

加上代理的配置如下：

<bean id="generalDAOImpl" class="gov.gfmis.fap.util.dao.springdao.GeneralDAO">     <property name="sessionFactory" ref="mysessionFactory"/>   </bean>     <bean  class="org.springframework.aop.framework.ProxyFactoryBean"  id="generalDAO" >   <property name="target">    <ref bean="generalDAOImpl"/>   </property>   <property name="interceptorNames">    <list>     <value>aopMethod</value>    </list>   </property></bean><bean  class="org.springframework.aop.support.NameMatchMethodPointcutAdvisor"  id="aopMethod" >      <property name="advice">         <bean  class="gov.gfmis.epay.sql.interceptor.EPaySqlMethodBefore" />      </property>      <property name="mappedName">          <value>*</value>      </property>    </bean>

再次启动服务就报了上面的空指针了，

原来setSessionFactory、getSession()、getSessionFactory()、setHibernateTemplate方法都是final类型的。所以不能被继承的类重写。所以代理类实例化这个类的时候无法注入这些属性。

使用final的意思是不让重写这些方法，但是这些方法真的有必要被禁止重写，这个是按照spring代码的写法来写的。但是代码在没有变得像spring代码

那么精致之前，不应该不允许被重写，实际上final我觉得用的意义真不大，看不出来有什么作用。所以果断去掉就好了。

前人挖坑，后人填坑。这次记录下来这个坑是怎么造成的。

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