Spring第三篇【依赖注入】

依赖注入（dependency injection）:是Spring框架核心ioc（inversion of control）的具体实现

注入bean

通过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>

备注：

1. name="userDao"中的userDao是根据setUserDao的UserDao（首字母变小写）来的

通过p命名空间的方式

p命名空间注入的本质就是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>

备注：

1. userDao-ref中的userDao是根据setUserDao的UserDao（首字母变小写）来的

通过构造器的方式

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>

备注：

1. name="userDao"中的userDao是根据public UserServiceImpl(UserDao userDao)（构造器参数名）来的

注入普通数据类型，数组，集合等

<?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="userServiceImpl" class="com.example.demo.service.impl.UserServiceImpl">
        <constructor-arg name="userDao" ref="userDao"/>
        <property name="name" value="张三"/>
        <property name="list">
            <list>
                <value>someone</value>
                <value>like</value>
                <value>you</value>
            </list>
        </property>
        <property name="arr">
            <list>
                <value>a</value>
                <value>b</value>
                <value>c</value>
            </list>
        </property>
        <property name="set">
            <set>
                <value>i</value>
                <value>o</value>
                <value>c</value>
            </set>
        </property>
        <property name="map">
            <map>
                <entry key="a" value-ref="user1"/>
                <entry key="b" value-ref="user2"/>
            </map>
        </property>
        <property name="properties">
            <props>
                <prop key="A">123
                </prop>
                <prop key="B">456
                </prop>
            </props>
        </property>
    </bean>

    <bean id="user1" class="com.example.demo.domain.User">
        <property name="age" value="18"/>
        <property name="sex" value="男"/>
    </bean>

    <bean id="user2" class="com.example.demo.domain.User">
        <property name="age" value="20"/>
        <property name="sex" value="女"/>
    </bean>
</beans>