Spring aop 出错。Exception in thread "main" java.lang.NullPointerException

package com.model;

public class User {
	private String name;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	private String password;

}

package com.dao;

import com.model.User;

public interface UserDAO {

	public void save(User user);
}

package com.imp;
import com.dao.UserDAO;
import com.model.User;

public class UserDAOimp implements UserDAO{

	public void save ( User user) {

		System.out.println("user is saved");
	}

}

package com.service;
import com.dao.UserDAO;
import com.model.User;

public class UserService {

	private UserDAO userDAO;

	public void add(User user){

		userDAO.save(user);
	}

	public UserDAO getUserDAO() {
		return userDAO;
	}

	public void setUserDAO(UserDAO userDAO) {
		this.userDAO = userDAO;
	}
}

package com.service;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.model.User;

public class UserServiceTest {

	public static void main(String[] args) {

		ApplicationContext acx = new ClassPathXmlApplicationContext("bean.xml");

		UserService u = (UserService) acx.getBean("userService");

		u.add(new User());
	}

}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:context="http://www.springframework.org/schema/context"
     xmlns:aop="http://www.springframework.org/schema/aop"
     xsi:schemaLocation="http://www.springframework.org/schema/beans
         http://www.springframework.org/schema/beans/spring-beans-3.1.xsd
         http://www.springframework.org/schema/context
         http://www.springframework.org/schema/context/spring-context-3.1.xsd
         http://www.springframework.org/schema/aop
         http://www.springframework.org/schema/aop/spring-aop-3.1.xsd">

    <context:annotation-config/>
    <context:component-scan base-package="com"/>
    <aop:aspectj-autoproxy/>
    <bean id="log" class="com.aop.Log"/>
    <bean id="userService" class="com.service.UserService"/>
    
</beans>

jar 包:commons-logging-1.1.1.jar  aopalliance-1.0.jar  aspectjrt-1.5.0.jar  aspectjweaver-1.5.0.jar

报错：
七月 09, 2012 10:01:58 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@3f32ca2b: startup date [Mon Jul 09 22:01:58 CST 2012]; root of context hierarchy
七月 09, 2012 10:01:58 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [bean.xml]
七月 09, 2012 10:01:58 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory registerBeanDefinition
信息: Overriding bean definition for bean 'log': replacing [Generic bean: class [com.aop.Log]; scope=singleton; abstract=false; lazyInit=false; autowireMode=0; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=null; initMethodName=null; destroyMethodName=null; defined in file [D:\myeclipse10\MyEclipse 10  workspace\Spring\bin\com\aop\Log.class]] with [Generic bean: class [com.aop.Log]; scope=; abstract=false; lazyInit=false; autowireMode=0; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=null; initMethodName=null; destroyMethodName=null; defined in class path resource [bean.xml]]
七月 09, 2012 10:01:58 下午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
信息: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@57a40a9f: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,log,org.springframework.aop.config.internalAutoProxyCreator,userService,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0]; root of factory hierarchy
Exception in thread "main" java.lang.NullPointerException
at com.service.UserService.add(UserService.java:11)
at com.service.UserServiceTest.main(UserServiceTest.java:14)

5 个解决方案

#1

你的UserDAO 没注入到UserService里面
所在UserService里面UserDAO 对象还是没初始化，为null的，那么后面这样子调用userDAO.save(user);就会出错了

#2

有了
<context:component-scan base-package="com"/>
就不需要
<context:annotation-config/>

不知道是不是这个原因。

#3

引用 1 楼  的回复:

你的UserDAO 没注入到UserService里面
所在UserService里面UserDAO 对象还是没初始化，为null的，那么后面这样子调用userDAO.save(user);就会出错了

没依赖注入

#4

那应该怎么修改呢？

#5

引用 4 楼 zsm653983 的回复:

那应该怎么修改呢？

遇到同样问题了，请问怎么解决呀？？？？弄了一个晚上了，毫无头绪，急求解决方案