【Spring】注解器

applicationContext.xml

<?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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
      http://www.springframework.org/schema/beans/spring-beans.xsd
      http://www.springframework.org/schema/context
  http://www.springframework.org/schema/context/spring-context.xsd">
    <!-- 使用context命名空间，开启注解处理器 -->
    <context:component-scan base-package="com.xiaobiti"/>
</beans>

实体：

User.java

package com.xiaobiti.entity;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

@Component("user")
@Scope("singleton")//bean作用域单例模式
public class User {
    @Value("1")
    private int id;//实例化给id赋值为1
    @Value("张三")
    private String name;//实例化给name赋值为张三
    @Value("123")
    private String password;//实例化给password赋值为123

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    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;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", password='" + password + '\'' +
                '}';
    }
}

数据访问层：

UserDaoImpl.java

package com.xiaobiti.dao.impl;

import com.xiaobiti.dao.UserDao;
import com.xiaobiti.entity.User;
import org.springframework.stereotype.Repository;

import javax.annotation.Resource;

@Repository("userDao")
public class UserDaoImpl implements UserDao {
    @Resource(name = "user")
    private User user;
    @Override
    public boolean login(String username, String password) {
        if (username.equals("admin") && password.equals("1234")){
            return true;
        }
        return false;
    }

    @Override
    public void save() {
        System.out.println("执行dao中的方法");
        System.out.println(user);
    }
}

UserDao.java

package com.xiaobiti.dao;

public interface UserDao {
    public boolean login(String username,String password);
    public void save();
}

业务逻辑层：

UserServiceImpl.java

package com.xiaobiti.service.impl;

import com.xiaobiti.dao.UserDao;
import com.xiaobiti.service.UserService;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;

@Service("userService")
public class UserServiceImpl implements UserService {
    @Resource(name = "userDao")
    private UserDao userDao;
    //setter方式注入
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }
    @Override
    public boolean login(String username, String password) {
        return userDao.login(username,password);
    }
    @Override
    public void save(){
        userDao.save();
        System.out.println("执行service中的方法");
    }
}

UserService.java

package com.xiaobiti.service;

public interface UserService {
    public boolean login(String username,String password);
    public void save();
}

控制层：

UserController.java

package com.xiaobiti.controller;

import com.xiaobiti.service.UserService;
import org.springframework.stereotype.Controller;

import javax.annotation.Resource;

@Controller("userController")
public class UserController {
    @Resource(name = "userService")
    private UserService userService;
    public void setUserService(UserService userService) {this.userService = userService;}
    public void save(){
        userService.save();
        System.out.println("执行了controller中的方法");
    }
}

运行测试代码：

public static void main(String[] args) {
        //加载核心配置文件
        ApplicationContext  applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        UserController userController = (UserController) applicationContext.getBean("userController");
        userController.save();
    }

运行结果：

@Component  用于指定普通bean，可以用于任何层次

@Repository  用于指定数据访问组件bean，用于数据访问层，功能上等同@Component

@Service　　用于指定业务逻辑组件bean，用于业务逻辑层，功能上等同@Component

@Controller　用于指定类控制器组件bean，用于控制层，功能上等同@Component

@Resource　用于实现依赖注入

@Resource注解和jdk的版本兼容问题导致空指针异常：

　　解决方法：@Resource注解和jdk的版本兼容问题_@resource null_lane_zhou的博客-CSDN博客