依賴注入（dependency injection）:是Spring框架核心ioc（inversion of control）的具體實現

注入bean

通過set的方式

package com.example.demo.service.impl;

import com.example.demo.dao.UserDao;
import com.example.demo.service.UserService;

public class UserServiceImpl implements UserService {

    private UserDao userDao;

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

    @Override
    public void save() {
        userDao.save();
    }
}
 

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

<bean id="userDao" class="com.example.demo.dao.UserDao" />

<bean id="userServiceImpl" class="com.example.demo.service.impl.UserServiceImpl">
    <property name="userDao" ref="userDao"/>
</bean>
    
</beans>
 

備註：

1. name="userDao"中的userDao是根據setUserDao的UserDao（首字母變小寫）來的

通過p名稱空間的方式

p名稱空間注入的本質就是set注入

<?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.xsd">

<bean id="userDao" class="com.example.demo.dao.UserDao" />

<bean id="userServiceImpl" class="com.example.demo.service.impl.UserServiceImpl" p:userDao-ref="userDao"/>
 
</beans>
 

備註：

1. userDao-ref中的userDao是根據setUserDao的UserDao（首字母變小寫）來的

通過構造器的方式

package com.example.demo.service.impl;

import com.example.demo.dao.UserDao;
import com.example.demo.service.UserService;

public class UserServiceImpl implements UserService {

    private UserDao userDao;

    public UserServiceImpl(UserDao userDao) {
        this.userDao = userDao;
    }

    @Override
    public void save() {
        userDao.save();
    }
}

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

<bean id="userDao" class="com.example.demo.dao.UserDao" />

    <bean id="userServiceImpl" class="com.example.demo.service.impl.UserServiceImpl">
        <constructor-arg name="userDao" ref="userDao"/>
    </bean>

</beans>

備註：

1. name="userDao"中的userDao是根據public UserServiceImpl(UserDao userDao)（構造器引數名）來的

注入普通資料型別，集合等