spring —— IoC容器（二）

二、基于注解管理 bean

（一）Autowired 自动装配

（1）属性上自动装配

java 复制代码

package com.fourth.anno;

import org.springframework.stereotype.Component;

@Component
public class Dao {
    public void runDao(){
        System.out.println("hello world");
    }
}

java 复制代码

package com.fourth.anno;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class Service {
    @Autowired
    private Dao dao;
    public void runService(){
        dao.runDao();
    }
}

java 复制代码

package com.fourth.anno;

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

public class Test {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("bean-anno.xml");
        Service service = context.getBean(Service.class);
        service.runService();
    }
}

XML 复制代码

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

    <context:component-scan base-package="com.fourth.anno"></context:component-scan>
</beans>

（2）set 方法上自动装配

java 复制代码

package com.fourth.anno;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class Service {    
    private Dao dao;

    @Autowired
    public void setDao(Dao dao){
        this.dao=dao;
    }

    public void runService(){
        dao.runDao();
    }
}

（3）构造方法上自动装配

java 复制代码

package com.fourth.anno;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class Service {

    private Dao dao;
    @Autowired
    public Service(Dao dao) {
        this.dao = dao;
    }

    public void runService(){
        dao.runDao();
    }
}

（4）构造方法的形参上自动装配

java 复制代码

package com.fourth.anno;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class Service {

    private Dao dao;

    public Service(@Autowired Dao dao) {
        this.dao = dao;
    }

    public void runService(){
        dao.runDao();
    }
}

（二）Resource 自动装配

（1）属性上自动装配

java 复制代码

package com.fourth.anno;

import jakarta.annotation.Resource;
import org.springframework.stereotype.Component;

@Component
public class Service {
    @Resource
    private Dao dao;

    public void runService(){
        dao.runDao();
    }
}

（2）set 方法上自动装配

java 复制代码

package com.fourth.anno;

import jakarta.annotation.Resource;
import org.springframework.stereotype.Component;

@Component
public class Service {

    private Dao dao;
    @Resource
    public void setDao(Dao dao) {
        this.dao = dao;
    }

    public void runService(){
        dao.runDao();
    }
}

Autowired 与 Resource 比较：

Autowired 可以应用在属性、set 方法、构造方法、构造方法的形参上；其默认通过类型进行装配。

Resource 可以应用在属性、set 方法上；其默认通过名称进行装配。

Autowired 基于 spring 框架；Resource 基于 java 扩展包，如果 JDK 版本高于11或低于8，应引入以下依赖：

复制代码

<dependency>
    <groupId>jakarta.annotation</groupId>
    <artifactId>jakarta.annotation-api</artifactId>
    <version>2.1.1</version>
</dependency>

（三）全注解开发

全注解开发，即使用配置类代替 xml 配置文件：

java 复制代码

package com.fourth.anno;

import org.springframework.stereotype.Component;

@Component
public class Dao {
    public void runDao(){
        System.out.println("hello world");
    }
}

java 复制代码

package com.fourth.anno;

import jakarta.annotation.Resource;
import org.springframework.stereotype.Component;

@Component
public class Service {

    private Dao dao;
    @Resource
    public void setDao(Dao dao) {
        this.dao = dao;
    }

    public void runService(){
        dao.runDao();
    }
}

java 复制代码

package com.fourth.anno;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan(value = "com.fourth.anno")
public class SpringConfig {
}

java 复制代码

package com.fourth.anno;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class Test {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(SpringConfig.class);
        Service service = context.getBean(Service.class);
        service.runService();
    }
}