最近一直在弄WebWork，Struts都快忘了。今天又自己小试了一下SSH，结果每次都是报空指针异常，经过一番研究，发现，如果不把action的type改成
org.springframework.web.struts.DelegatingActionProxy
的话，就会报这个
java.lang.NullPointerException
com.test.struts.action.UserAction.show(UserAction.java:46)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
java.lang.reflect.Method.invoke(Method.java:597)
org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:274)
org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:194)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:419)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:224)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
解决办法：
1.在struts-config.xml的action把type改成org.springframework.web.struts.DelegatingActionProxy，例如：
<action attribute="userForm" input="/index.jsp" name="userForm"
parameter="param" path="/user" scope="request"
type="org.springframework.web.struts.DelegatingActionProxy"
validate="false">
<forward name="success" path="/success.jsp" />
</action>
2.在spring的配置文件(applicationContext.xml)里添加一些代码：
<bean id="transactionManager"
class="org.springframework.orm.hibernate3.HibernateTransactionManager">
<property name="sessionFactory">
<ref bean="sessionFactory" />
</property>
</bean>
给DAO加上代理
<bean id="UserDAOIProxy"
class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean">
<property name="transactionManager">
<ref bean="transactionManager" />
</property>
<property name="target">
<ref bean="UserDao" />
</property>
<property name="transactionAttributes">
<props>
<prop key="create*">PROPAGATION_REQUIRED</prop>
<prop key="update*">PROPAGATION_REQUIRED</prop>
<prop key="delete*">PROPAGATION_REQUIRED</prop>
<prop key="get*">PROPAGATION_REQUIRED,readOnly</prop>
</props>
</property>
</bean>
3.更改Service的引用
<bean name="UserService"
class="com.test.service.impl.UserServiceImpl">
<property name="userDao">
<ref bean="UserDAOIProxy" />
</property>
</bean>
这样就不会报那个异常了，测试通过^_^
我的配置文件代码：
applicationContext.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
<bean id="dataSource"
class="org.apache.commons.dbcp.BasicDataSource">
<property name="driverClassName"
value="oracle.jdbc.driver.OracleDriver">
</property>
<property name="url"
value="jdbc:oracle:thin:@192.192.192.19:1521:orcl">
</property>
<property name="username" value="sunyu"></property>
<property name="password" value="19830317"></property>
</bean>
<bean id="sessionFactory"
class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
<property name="dataSource">
<ref bean="dataSource" />
</property>
<property name="hibernateProperties">
<props>
<prop key="hibernate.dialect">
org.hibernate.dialect.Oracle9Dialect
</prop>
<prop key="hibernate.show_sql">true</prop>
</props>
</property>
<property name="mappingResources">
<list>
<value>com/test/model/TestUser.hbm.xml</value>
</list>
</property>
</bean>
<bean id="transactionManager"
class="org.springframework.orm.hibernate3.HibernateTransactionManager">
<property name="sessionFactory">
<ref bean="sessionFactory" />
</property>
</bean>
<bean name="UserDao" class="com.test.dao.impl.UserDaoImpl">
<property name="sessionFactory">
<ref bean="sessionFactory" />
</property>
</bean>
<bean id="UserDAOIProxy"
class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean">
<property name="transactionManager">
<ref bean="transactionManager" />
</property>
<property name="target">
<ref bean="UserDao" />
</property>
<property name="transactionAttributes">
<props>
<prop key="create*">PROPAGATION_REQUIRED</prop>
<prop key="update*">PROPAGATION_REQUIRED</prop>
<prop key="delete*">PROPAGATION_REQUIRED</prop>
<prop key="get*">PROPAGATION_REQUIRED,readOnly</prop>
</props>
</property>
</bean>
<bean name="UserService"
class="com.test.service.impl.UserServiceImpl">
<property name="userDao">
<ref bean="UserDAOIProxy" />
</property>
</bean>
<bean name="/user" class="com.test.struts.action.UserAction">
<property name="userService">
<ref bean="UserService" />
</property>
</bean>
</beans>
struts-config.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts-config PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 1.2//EN" "http://struts.apache.org/dtds/struts-config_1_2.dtd">
<struts-config>
<data-sources />
<form-beans>
<form-bean name="userForm" type="com.test.struts.form.UserForm" />
</form-beans>
<global-exceptions />
<global-forwards />
<action-mappings>
<action attribute="userForm" input="/index.jsp" name="userForm"
parameter="param" path="/user" scope="request"
type="org.springframework.web.struts.DelegatingActionProxy"
validate="false">
<forward name="success" path="/success.jsp" />
</action>
</action-mappings>
<message-resources parameter="com.test.struts.ApplicationResources" />
<plug-in
className="org.springframework.web.struts.ContextLoaderPlugIn">
<set-property property="contextConfigLocation"
value="/WEB-INF/applicationContext.xml" />
</plug-in>
</struts-config>
------------------------------------------
第二种方法，如果在struts-config.xml里面加上
<controller>
<set-property property="processorClass"
value="org.springframework.web.struts.DelegatingRequestProcessor" />
</controller>
这样action就不需要type属性了
----------------------------------------------