03_实现DI（注入依赖）

Bean包

AnimalDao.java

package com.cq.dao;
public class AnimalDao {
    public void add(){
        System.out.println("dao---------add----------");
    }
    public AnimalDao() {
        System.out.println("dao---------constructor---------");
    }
}

AnimalService.java

package com.cq.service;
import com.cq.dao.AnimalDao;
public class AnimalService {
    private AnimalDao animalDao; //不能new对象
    public AnimalService(AnimalDao animalDao) {
        this.animalDao = animalDao;
    }
    public AnimalService() {
    }
    public void add(){
        animalDao.add();
        System.out.println("service---------add----------");
    }
    public AnimalDao getAnimalDao() {
        return animalDao;
    }
    public void setAnimalDao(AnimalDao animalDao) {
        this.animalDao = animalDao;
    }
}

方法1: set方法注入

DI.xml

<bean id="animalDao" class="com.cq.dao.AnimalDao"></bean>
<bean id="animalService" class="com.cq.service.AnimalService">
    <!-- 使用set方法注入属性值 -->
    <property name="animalDao" ref="animalDao"></property>
</bean>

Test.java

@Test
    public void test02(){
        ApplicationContext ac = new ClassPathXmlApplicationContext("DI.xml");
        AnimalService animalService = (AnimalService) ac.getBean("animalService");
        animalService.add();
    }

方法2: 构造方法注入

DI.xml

<bean id="animalDao" class="com.cq.dao.AnimalDao"></bean>
<bean id="animalService2" class="com.cq.service.AnimalService">
    <!-- 使用构造方法注入属性值 -->
    <constructor-arg name="animalDao" ref="animalDao"></constructor-arg>
</bean>

Test.java

@Test
    public void test02(){
        ApplicationContext ac = new ClassPathXmlApplicationContext("DI.xml");
        AnimalService animalService2 = (AnimalService) ac.getBean("animalService2");
        animalService2.add();
    }

方法3: byName注入

DI.xml

<bean id="animalDao" class="com.cq.dao.AnimalDao"></bean>
<!-- 查询与属性名相同的容器中的对象，属性名相同 -->
<bean id="animalService3" class="com.cq.service.AnimalService" autowire="byName"> </bean>

Test.java

@Test
    public void test02(){
        ApplicationContext ac = new ClassPathXmlApplicationContext("DI.xml");
        AnimalService animalService3 = (AnimalService) ac.getBean("animalService3");
        animalService3.add();
    }

方法4: byType注入（对象唯一）

DI.xml

<bean id="animalDao" class="com.cq.dao.AnimalDao"></bean>
<!-- 查询与属性值相同类型的容器中的对象，但是要求类型相同的对象唯一，否则抛出异常，不知道用哪个匹配 -->
<!-- 弊端：Dao的对象只能有一个 -->
<bean id="animalService4" class="com.cq.service.AnimalService" autowire="byType"> </bean>

Test.java

@Test
    public void test02(){
        ApplicationContext ac = new ClassPathXmlApplicationContext("DI.xml");
        AnimalService animalService4 = (AnimalService) ac.getBean("animalService4");
        animalService4.add();
    }