2.3 自动装配 - Spring自动装配 - 《Java企业级框架》

1. 环境搭建
2. xml配置实现自动装配
- 2.1 byName
- 2.2 byType
3. 注解实现自动装配

具体的可以查看官方文档

Spring中bean有三种装配机制，分别是：

在xml中显式配置
在java中显式配置
隐式的bean发现机制和自动装配

本文主要讲第三种：自动化装配bean

Spring的自动装配需要从两个角度来实现，或者说是两个操作：

组件扫描(component scanning)：spring会自动发现应用上下文中所创建的bean
自动装配(autowiring)：spring自动满足bean之间的依赖，也就是我们说的IoC/DI

1. 环境搭建

public class Cat {
    public void shout() {
        System.out.println("miao~");
    }
}

public class Dog {
    public void shout() {
        System.out.println("wang~");
    }
}

public class Student {
    private Cat cat;
    private Dog dog;
    private String name;
    public void setCat(Cat cat) {
        this.cat = cat;
    }
    public void setDog(Dog dog) {
        this.dog = dog;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Cat getCat() {
        return cat;
    }
    public Dog getDog() {
        return dog;
    }
    public String getName() {
        return name;
    }
}

2. xml配置实现自动装配

2.1 byName

<?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="cat" class="com.comprehensive.pojo.Cat"/>
    <bean id="dog" class="com.comprehensive.pojo.Dog"/>
    <bean id="stu1" class="com.comprehensive.pojo.Student" autowire="byName">
        <property name="name" value="comprehensive"/>
    </bean>
</beans>

//测试类
public class Test_byName {
    @Test
    public void test1() {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        Student stu1 = context.getBean("stu1", Student.class);
        stu1.getCat().shout();
        stu1.getDog().shout();
    }
}

将 cat 的bean id修改下（如下所示），继续测试

<?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">

        <!-- 注意此处，id修改 -->
    <bean id="cat123" class="com.comprehensive.pojo.Cat"/>
    <bean id="dog" class="com.comprehensive.pojo.Dog"/>

    <bean id="stu1" class="com.comprehensive.pojo.Student" autowire="byName">
        <property name="name" value="comprehensive"/>
    </bean>

</beans>

2.2 byType

<?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="cat123" class="com.comprehensive.pojo.Cat"/>
    <bean id="dog_wang" class="com.comprehensive.pojo.Dog"/>

    <bean id="stu2" class="com.comprehensive.pojo.Student" autowire="byType">
        <property name="name" value="comprehensive"/>
    </bean>

</beans>

//测试类
public class Test_byType {
    @Test
    public void test2() {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans2.xml");
        Student stu2 = context.getBean("stu2", Student.class);
        stu2.getCat().shout();
        stu2.getDog().shout();
    }
}

如果xml这里再注册一个cat 的bean对象（如下所示），继续测试

<?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="cat123" class="com.comprehensive.pojo.Cat"/>
    <bean id="cat12" class="com.comprehensive.pojo.Cat"/>
    <bean id="dog_wang" class="com.comprehensive.pojo.Dog"/>

    <bean id="stu2" class="com.comprehensive.pojo.Student" autowire="byType">
        <property name="name" value="comprehensive"/>
    </bean>

</beans>

3. 注解实现自动装配

3.1 准备工作

在spring配置文件中引入context文件头 ```xml xmlns:context=”http://www.springframework.org/schema/context“

http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd


- 开启属性注解支持！
```xml
<context:annotation-config/>

@Autowired

@Autowired是按类型自动装配的，不支持id匹配。
需要导入 spring-aop的包！ ```xml <?xml version=”1.0” encoding=”UTF-8”?>

```java
public class Student {
    @Autowired
    private Cat cat;
    @Autowired
    private Dog dog;
    private String name;

    public void setCat(Cat cat) {
        this.cat = cat;
    }

    public void setDog(Dog dog) {
        this.dog = dog;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Cat getCat() {
        return cat;
    }

    public Dog getDog() {
        return dog;
    }

    public String getName() {
        return name;
    }
}

//测试类
public class Test_Autowired {
    @Test
    public void test3() {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans_Autowired.xml");
        Student stu3 = context.getBean("stu3", Student.class);
        stu3.getCat().shout();
        stu3.getDog().shout();
    }
}

@Autowired(required=false) 说明：false，对象可以为null；true，对象必须存对象，不能为null

@Qualifier

@Autowired是根据类型自动装配的，加上@Qualifier则可以根据byName的方式自动装配
@Qualifier不能单独使用 ```xml <?xml version=”1.0” encoding=”UTF-8”?>

```java
public class Student {
    @Autowired
    @Qualifier("cat2")
    private Cat cat;
    @Autowired
    @Qualifier("dog1")
    private Dog dog;
    private String name;

    public void setCat(Cat cat) {
        this.cat = cat;
    }

    public void setDog(Dog dog) {
        this.dog = dog;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Cat getCat() {
        return cat;
    }

    public Dog getDog() {
        return dog;
    }

    public String getName() {
        return name;
    }
}

//测试类
public class Test_Qualifier {
    @Test
    public void test4() {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans_Qualifier.xml");
        Student stu4 = context.getBean("stu4", Student.class);
        stu4.getCat().shout();
        stu4.getDog().shout();
    }
}

@Resource

@Resource如有指定的name属性，先按该属性进行byName方式查找装配
其次再进行默认的byName方式进行装配
如果以上都不成功，则按byType的方式自动装配
都不成功，则报异常 ```xml <?xml version=”1.0” encoding=”UTF-8”?>

**注意**：这里使用的@Resource注解来自于`javax.annotation`包，javax为Java扩展包，我这里使用的JDK版本为14，没有自带javax拓展包。解决方法：在maven项目的配置文件中导入依赖即可（亲测有效）
```xml
<dependencies>
  <dependency>
    <groupId>javax.annotation</groupId>
    <artifactId>javax.annotation-api</artifactId>
    <version>1.3.1</version>
  </dependency>
</dependencies>

public class Student {
    @Resource(name = "cat2")
    private Cat cat;
    @Resource
    private Dog dog;
    private String name;

    public void setCat(Cat cat) {
        this.cat = cat;
    }

    public void setDog(Dog dog) {
        this.dog = dog;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Cat getCat() {
        return cat;
    }

    public Dog getDog() {
        return dog;
    }

    public String getName() {
        return name;
    }
}

//测试类
public class Test_Resource {
    @Test
    public void test5() {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans_Resource.xml");
        Student stu5 = context.getBean("stu5", Student.class);
        stu5.getCat().shout();
        stu5.getDog().shout();
    }
}