MVC Spring实现-错误:java.lang.NullPointerException
我有一个MVC Spring控制器,在Imp文件中,我有:MVC Spring实现-错误:java.lang.NullPointerException,java,spring-mvc,Java,Spring Mvc,我有一个MVC Spring控制器,在Imp文件中,我有: import com.ish.system.dao.UserDAO; public class CustomImpl implements CustomService { UserDAO userDAO = null; public UserDAO getUserDAO() { return userDAO; } public void setUserDAO(UserDAO userDAO) { this.userD
import com.ish.system.dao.UserDAO;
public class CustomImpl implements CustomService {
UserDAO userDAO = null;
public UserDAO getUserDAO() {
return userDAO;
}
public void setUserDAO(UserDAO userDAO) {
this.userDAO = userDAO;
}
public String ServiceType(userId) {
User user = userDAO.findById(userId);
...
以下是控制台中的错误:
SEVERE: Servlet.service() for servlet dispatcherServlet threw exception
java.lang.NullPointerException
at com.ish.smdb.service.impl.CustomImpl.ServiceType(CustomImpl.java:142)
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.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:309)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
这是控制器:
@RequestMapping(value="/ServiceType", method=RequestMethod.GET)
public @ResponseBody String ServiceType(
Locale locale,
Model model) {
String result = custom.ServiceType();
return result;
}
下面是bean:
<bean id="Custom" parent="baseTransactionProxy">
<property name="target">
<bean id="CustomImpl" class="com.is.sm.service.impl.CustomImpl">
<property name="userDAO" ref="UserDAO" />
</bean>
</property>
</bean>
确保userDAO为null。但我没有找到原因。我怎么了 customimplbean依赖于UserDAO,因此必须将userdaobean注入customimplbean, 请发布您的xml配置文件,您已经在其中定义了bean 更新: 下面是一个解决方案,您可以使用spring注释进行注入: 在UserDAOImpl Cals(UserDAO接口实现)中,使用: 然后在CustomImpl类中:
@Autowired
UserDAO userDAO ;
你能发布你的完整的stacktrace吗?你能告诉我那是什么吗?我只是通过输出打印跟踪代码。你能发布你的控制器代码吗?你是如何调用ServiceType的,你是如何初始化userDAO的?上面说的,你说确定userDAO为空,这是你的错误。它是空的。。您的类是如何初始化的?当然userDAO必须设置在某个地方或注入。我刚刚发布了我的控制器。您能告诉我如何初始化它吗?下面是我定义的bean:
@Autowired
UserDAO userDAO ;