Spring中的经典疑问： Error creating bean with name 'urlMapping' ...
问题描述：
正在学习spring的多动作控制器，然而配置完成运行后，出现了这样的错误信息，我估计很多老鸟见过，如下：
Error creating bean with name 'urlMapping' defined in ServletContext resource [/WEB-INF/classes/applicationContext.xml]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'multiController' defined in ServletContext resource [/WEB-INF/classes/applicationContext.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.page.NewIndexShowListController]: Constructor threw exception; nested exception is java.lang.NullPointerException
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:521)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:450)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:290)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:287)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:189)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:562)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:871)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:423)
at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:443)
at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:459)
at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:340)
at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:307)
at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:127)
at javax.servlet.GenericServlet.init(GenericServlet.java:212)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1161)
at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:981)
at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:4042)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4348)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:791)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:771)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:525)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:920)
at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:883)
at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:492)
at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1138)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:311)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:117)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1053)
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(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:288)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:413)
我查过好多网上信息，都没有解决，再看我的applicationContent.xml配置
<bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="mappings">
<props>
<prop key="/*Page.htm">multiController</prop>
</props>
</property>
</bean>
<bean id="propMethodResolver"
class="org.springframework.web.servlet.mvc.multiaction.PropertiesMethodNameResolver">
<property name="mappings">
<props>
<prop key="/nextPage.htm">nextPage</prop>
<prop key="/previousPage.htm">previousPage</prop>
<prop key="/firstPage.htm">firstPage</prop>
<prop key="/lastPage.htm">lastPage</prop>
<prop key="/getPage.htm">getPage</prop>
</props>
</property>
</bean>
<bean id="multiController" class="com.page.NewIndexShowListController">
<property name="methodNameResolver">
<ref bean="propMethodResolver"/>
</property>
<property name="myuserDAO">
<ref bean="MyuserDAO"/>
</property>
</bean>
以及 web.xml配置
<servlet>
<servlet-name>dispatcher</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/classes/applicationContext.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcher</servlet-name>
<url-pattern>*.do,*.htm</url-pattern>
</servlet-mapping>
<filter>
<filter-name>encodingFilter</filter-name>
<filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>GBK</param-value>
</init-param>
<init-param>
<param-name>forceEncoding</param-name>
<param-value>true</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>encodingFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
前台的简单代码：
<body>
<a href="nextPage.htm">下一页</a>
<a href="previousPage.htm">前一页</a>
<a href="firstPage.htm">首页</a>
<a href="lastPage.htm">尾页</a>
<a href="getPage.htm">某页</a>
</body>
后台的代码：
public class NewIndexShowListController extends MultiActionController{
private MyuserDAO myuserDAO;
Map map=new HashMap();
@SuppressWarnings("unchecked")
List<Myuser> userList=myuserDAO.findAllOrderByTime();
PageModel pageModel=new PageModel(userList, 5);
int pageCount=pageModel.getTotalPages();
public ModelAndView nextPage(HttpServletRequest req,HttpServletResponse res)throws Exception
{
System.out.println("将显示下一页");
List sublist=pageModel.getNextPage();
for(int i = 0; i < sublist.size(); i++)
{
System.out.println(sublist.get(i));
}
map.put("sublist",sublist);
return new ModelAndView("success","map",map);
}
public ModelAndView previousPage(HttpServletRequest req,HttpServletResponse res)throws Exception
{
System.out.println("将显示前一页");
List sublist=pageModel.getPreviousPage();
for(int i = 0; i < sublist.size(); i++)
{
System.out.println(sublist.get(i));
}
map.put("sublist",sublist);
return new ModelAndView("success","map",map);
}
public ModelAndView firstPage(HttpServletRequest req,HttpServletResponse res)throws Exception
{
System.out.println("将显示首页");
List sublist=pageModel.getFirstPage();
for(int i=0;i<sublist.size();i++)
{
System.out.println(sublist.get(i));
}
map.put("sublist",sublist);
return new ModelAndView("success","map",map);
}
public ModelAndView lastPage(HttpServletRequest req,HttpServletResponse res)throws Exception
{
System.out.println("将显示尾页");
List sublist=pageModel.getLastPage();
for(int i=0;i<sublist.size();i++)
{
System.out.print(sublist.get(i));
}
map.put("sublist",sublist);
return new ModelAndView("success","map",map);
}
public ModelAndView getPage(HttpServletRequest req,HttpServletResponse res)throws Exception
{
int pagenum=Integer.parseInt(req.getParameter("pagenum"));
List sublist=pageModel.getObjects(pagenum);
for(int i = 0; i < sublist.size(); i++)
{
System.out.println(sublist.get(i));
}
map.put("sublist",sublist);
return new ModelAndView("success","map",map);
}
public void setMyuserDAO(MyuserDAO myuserDAO)
{
this.myuserDAO=myuserDAO;
}
public MyuserDAO getMyuserDAO()
{
return this.myuserDAO;
}
}
控制器代码继承了MuitiActionCotroller，不明白报这样的错误说明了什么，哪里出了错误？虚心求教，感激不尽～
答
404? 额，这。。可能是地址出问题。。哈哈，等于没回答。。。
答
[code="java"]org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.page.NewIndexShowListController]: Constructor threw exception; nested exception is java.lang.NullPointerException[/code]
这个应该是在调用NewIndexShowListController父类MultiActionController的构造方法中出现空指针导致，请检查该构造方法。
答
public class NewIndexShowListController extends MultiActionController{
private MyuserDAO myuserDAO;
Map map=new HashMap();
@SuppressWarnings("unchecked")
List userList=myuserDAO.findAllOrderByTime();
PageModel pageModel=new PageModel(userList, 5);
int pageCount=pageModel.getTotalPages();
这一段就有问题了
myuserDAO是通过spring注入进来的，注意类初始化顺序
你的很多操作，在构造函数运行前运行。。
答
之前也有这个问题。我的问题出在：在一个model类中声明了另一个类的变量，没有指定这两个类的关系。spring不知道怎么装载吧，估计是