struts2 Action 中 ，ActionContext 不可以作为成员变量哦

问题出在：

     Action对象是在 ActionContext 容器对象之前创建的，ActionContext 作为成员变量，还没有轮到创建它哦，

所以NullPointerExcetion.

     这个问题，烦扰了我很久：

     同样的Action改了个名字，原来是JoinAction 后来 独立出来 MemberAction（由JoinAction 复制而来）

     中间改过代码，把ActionContext作为了MemberAction成员变量了，之后，JoinAction可以访问，但MemberAction总是500错误。

     一直怀疑是applicationContent.xml出错，共用了一个singleton的service，怎么改都不成功。

    经过梳理，觉得，问题不是出在这里，因为 在Action里调用singleton 或prototype service 的代码，之前都写过，这个有问题就麻烦了。折腾了几次重启tomcat，才排除。这个原因。

    改成之前错误代码，重现下给大家看看：

    ==========错误的代码：============================================如下：

 

   public class MemberAction extends ActionSupport {

    private static final long serialVersionUID = 1L;

    Member member;
    MemberService service;
    HttpSession session = ServletActionContext .getRequest().getSession();
    /**
     * ========== 初始化:mofidyMe.jsp ==========
     */
    public String initModifyMe() {}

....

}

 

========== applicationContent.xml 配置： ============如下：

    <!-- 以下注入是Member Table 开始于 55555 结束于55555 -->
    <bean id="memberDao" class="db.dao.impl.MemberDaoImpl" scope="singleton">
        <property name="sessionFactory" ref="sessionFactory"></property>
    </bean>
    <bean id="memberService" class="marego.service.impl.MemberServiceImpl" scope="singleton">
        <property name="memberDao" ref="memberDao"></property>
    </bean>
    <bean id="joinAction" class="marego.action.JoinAction" scope="prototype">
        <property name="service" ref="memberService"></property>
    </bean>
   
    <!-- 以下注入是Member Table 开始于 66666 结束于66666 -->
    <bean id="memberAction" class="marego.action.MemberAction" scope="prototype">
        <property name="service" ref="memberService"></property>
    </bean>

 

 

重启，不报错,ok。

输入本地Url：http://127.0.0.1:8088/wyweb/marego/modifyMe

HTTP Status 500 -

Apache Tomcat/6.0.20 - Error report<!--H1 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:22px;} H2 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:16px;} H3 {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;font-size:14px;} BODY {font-family:Tahoma,Arial,sans-serif;color:black;background-color:white;} B {font-family:Tahoma,Arial,sans-serif;color:white;background-color:#525D76;} P {font-family:Tahoma,Arial,sans-serif;background:white;color:black;font-size:12px;}A {color : black;}A.name {color : black;}HR {color : #525D76;}-->

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

Unable to instantiate Action, memberAction,  defined for 'modifyMe' in namespace '/marego'Error creating bean with name 'memberAction' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [marego.action.MemberAction]: Constructor threw exception; nested exception is java.lang.NullPointerException
	com.opensymphony.xwork2.DefaultActionInvocation.createAction(DefaultActionInvocation.java:306)
	com.opensymphony.xwork2.DefaultActionInvocation.init(DefaultActionInvocation.java:387)
	com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:186)
	org.apache.struts2.impl.StrutsActionProxy.prepare(StrutsActionProxy.java:61)
	org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:39)
	com.opensymphony.xwork2.DefaultActionProxyFactory.createActionProxy(DefaultActionProxyFactory.java:47)
	org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:458)
	org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:395)

 

root cause

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'memberAction' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [marego.action.MemberAction]: Constructor threw exception; nested exception is java.lang.NullPointerException
	org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:451)
	org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:268)
	org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:160)
	org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:757)
	com.opensymphony.xwork2.spring.SpringObjectFactory.buildBean(SpringObjectFactory.java:126)
	com.opensymphony.xwork2.ObjectFactory.buildBean(ObjectFactory.java:139)
	com.opensymphony.xwork2.ObjectFactory.buildAction(ObjectFactory.java:109)
	com.opensymphony.xwork2.DefaultActionInvocation.createAction(DefaultActionInvocation.java:287)
	com.opensymphony.xwork2.DefaultActionInvocation.init(DefaultActionInvocation.java:387)
	com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:186)
	org.apache.struts2.impl.StrutsActionProxy.prepare(StrutsActionProxy.java:61)
	org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:39)
	com.opensymphony.xwork2.DefaultActionProxyFactory.createActionProxy(DefaultActionProxyFactory.java:47)
	org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:458)
	org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:395)

 

root cause

org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [marego.action.MemberAction]: Constructor threw exception; nested exception is java.lang.NullPointerException
	org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:100)
	org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:61)
	org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:757)
	org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:722)
	org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:386)
	org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:268)
	org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:160)
	org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:757)
	com.opensymphony.xwork2.spring.SpringObjectFactory.buildBean(SpringObjectFactory.java:126)
	com.opensymphony.xwork2.ObjectFactory.buildBean(ObjectFactory.java:139)
	com.opensymphony.xwork2.ObjectFactory.buildAction(ObjectFactory.java:109)
	com.opensymphony.xwork2.DefaultActionInvocation.createAction(DefaultActionInvocation.java:287)
	com.opensymphony.xwork2.DefaultActionInvocation.init(DefaultActionInvocation.java:387)
	com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:186)
	org.apache.struts2.impl.StrutsActionProxy.prepare(StrutsActionProxy.java:61)
	org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:39)
	com.opensymphony.xwork2.DefaultActionProxyFactory.createActionProxy(DefaultActionProxyFactory.java:47)
	org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:458)
	org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:395)

 

root cause

java.lang.NullPointerException
	marego.action.MemberAction.<init>(MemberAction.java:36)
	sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
	sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
	java.lang.reflect.Constructor.newInstance(Constructor.java:513)
	org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:85)
	org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:61)
	org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:757)
	org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:722)
	org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:386)
	org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:268)
	org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:160)
	org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:757)
	com.opensymphony.xwork2.spring.SpringObjectFactory.buildBean(SpringObjectFactory.java:126)
	com.opensymphony.xwork2.ObjectFactory.buildBean(ObjectFactory.java:139)
	com.opensymphony.xwork2.ObjectFactory.buildAction(ObjectFactory.java:109)
	com.opensymphony.xwork2.DefaultActionInvocation.createAction(DefaultActionInvocation.java:287)
	com.opensymphony.xwork2.DefaultActionInvocation.init(DefaultActionInvocation.java:387)
	com.opensymphony.xwork2.DefaultActionProxy.prepare(DefaultActionProxy.java:186)
	org.apache.struts2.impl.StrutsActionProxy.prepare(StrutsActionProxy.java:61)
	org.apache.struts2.impl.StrutsActionProxyFactory.createActionProxy(StrutsActionProxyFactory.java:39)
	com.opensymphony.xwork2.DefaultActionProxyFactory.createActionProxy(DefaultActionProxyFactory.java:47)
	org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:458)
	org.apache.struts2.dispatcher.FilterDispatcher.doFilter(FilterDispatcher.java:395)

 

note The full stack trace of the root cause is available in the Apache Tomcat/6.0.20 logs.

---

Apache Tomcat/6.0.20

错误出来了。

 

  改正：

  去掉 之后初始化的成员变量，再输入刚那个Url，OK，可以访问了。