一个简单的登陆页面，登陆的时候抛出异常。
严重: Servlet.service() for servlet action threw exception
java.lang.NullPointerException
at com.grace.studentGradeManage.action.StudentAction.loginAction(StudentAction.java:43)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:280)
at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:216)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:291)
at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:877)
at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:594)
at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1675)
at java.lang.Thread.run(Thread.java:619)
web.xml 配置：
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/classes/applicationContext.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
applicationContext.xml配置：
<bean id="studentDao" class="com.grace.studentGradeManage.dao.StudentDao">
<property name="sessionFactory">
<ref bean="sessionFactory"/>
</property>
</bean>
<bean id="studentService" class="com.grace.studentGradeManage.service.StudentService">
<property name="studentDao">
<ref bean="studentDao"/>
</property>
</bean>
<bean name="/studentAction" class="com.grace.studentGradeManage.action.StudentAction">
<property name="studentService">
<ref bean="studentService"/>
</property>
</bean>
------解决方案--------------------
你把/WEB-INF/classes/applicationContext.xml改为classpath:applicationContext.xml试一试，还有就是你得测试下你的studentDAO是否为null,再判断是否注入，到底是没有注入还是你的action自己写得有问题，里面是有有set方法！！。
------解决方案--------------------
<action path="/studentAction" type="org.springframework.web.struts.DelegatingActionProxy"></action>
检查一下你的struts文件是不是这样配的,
你的ssh集成时，struts文件有没有这个配置：
<plug-in className="org.springframework.web.struts.ContextLoaderPlugIn">
<set-property property="contextConfigLocation" value="你的spring文件路径(多个文件用逗号隔开)"/>
</plug-in>
自己再检查一下