Spring自动装配

实体类：

package com.bxw.po;

public class User {
    private String username;    //账号
    private String password;    //密码
    public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    
    
}

Dao：

package com.bxw.dao;

import com.bxw.po.User;

public interface UserDao {
    public void save(User u);    
}

DaoImpl:

package com.bxw.dao.impl;

import com.bxw.dao.UserDao;
import com.bxw.po.User;

public class UserDaoImpl implements UserDao {
    public void save(User u){
        System.out.println("user saved");
    }
}

UserService:

package com.bxw.service;

import com.bxw.dao.UserDao;
import com.bxw.dao.impl.UserDaoImpl;
import com.bxw.po.User;

public class UserService {
    private UserDao userDao = new UserDaoImpl();

    public UserDao getUserDao() {
        return userDao;
    }

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }

    
    public void add(User u){
        this.userDao.save(u);
    }
    
}

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:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd">
    
    <bean id="userDao" class="com.bxw.dao.impl.UserDaoImpl" />
    <bean id="userService" class="com.bxw.service.UserService" autowire="byName" />

</beans>

UserServiceTest.java:

package com.bxw.test;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.bxw.po.User;
import com.bxw.service.UserService;

public class UserServiceTest {

    @Test
    public void testAdd() throws Exception{
//        BeanFactory ac = new ClassPathXMLApplicationContext();    //初始化所有bean
//        UserService service = (UserService) ac.getBean("userService");    //拿到id为userService，依赖注入userDao
        ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
        UserService service = (UserService) ac.getBean("userService");
        User u = new User();
        service.add(u);
    }
}

autowire常见取值有byname,bytype(其余取值不常用)。如果取值为byName,则UserService会去找名为UserDao的bean;如果取值为byType,则UserService则会去找与UserDao类型相同的bean。如果取值为defaule，则效果与在beans中指定default-autowire指定的属性相同。

===============华丽的分界线==================

<?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:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.1.xsd">
    
    <bean id="userDao" class="com.bxw.dao.impl.UserDaoImpl" />
    <bean id="userService" class="com.bxw.service.UserService" autowire="byName" lazy-init="true" scope="singleton" init-method="init" destroy-method="destroy"/>

</beans>

lazy-init=true,则说明该bean在getBean时才初始化，如果在<beans>标签中指定default-lazy-init=ture则该beans中的所有bean都按照这种方式加载。反之在ClassPathXmlApplicationContext被new出来时加载。

scope=singleton，则说明该bean采用单例模式，即自始至终该bean只有一个，若scope=prototype，则该bean每次get时都有一个新的对象（其余不常用）。

init-method:该bean初始化时调用的方法。

destroy-method：destroy时调用的方法。