@Configuration annotation, @Bean annotation

1. @Configuration is marked on a class, which is equivalent to using the class as spring's xml configuration file. The <beans>function is to configure the spring container (application context)

package com.test.spring.support.configuration;

@Configuration
public class TestConfiguration {
    public TestConfiguration(){
        System.out.println("spring容器启动初始化。。。");
    }
}

is equivalent to:

<?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:context="http://www.springframework.org/schema/context" xmlns:jdbc="http://www.springframework.org/schema/jdbc"  
    xmlns:jee="http://www.springframework.org/schema/jee" xmlns:tx="http://www.springframework.org/schema/tx"
    xmlns:util="http://www.springframework.org/schema/util" xmlns:task="http://www.springframework.org/schema/task" xsi:schemaLocation="
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd
        http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-4.0.xsd
        http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-4.0.xsd
        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd
        http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.0.xsd
        http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-4.0.xsd" default-lazy-init="false">


</beans>

Main method to test:

package com.test.spring.support.configuration;

public class TestMain {
    public static void main(String[] args) {

        //@Configuration注解的spring容器加载方式，用AnnotationConfigApplicationContext替换ClassPathXmlApplicationContext
        ApplicationContext context = new AnnotationConfigApplicationContext(TestConfiguration.class);

        //如果加载spring-context.xml文件：
        //ApplicationContext context = new ClassPathXmlApplicationContext("spring-context.xml");
    }
}

As can be seen from the results of running the main method, the spring container has been started:

八月 11, 2016 12:04:11 下午 org.springframework.context.annotation.AnnotationConfigApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@203e25d3: startup date [Thu Aug 11 12:04:11 CST 2016]; root of context hierarchy
spring容器启动初始化。。。

2. @Bean is marked on the method (the method that returns an instance), which is equivalent to that in spring's xml configuration file. The <bean>function is to register the bean object

bean class:

package com.test.spring.support.configuration;

public class TestBean {

    public void sayHello(){
        System.out.println("TestBean sayHello...");
    }

    public String toString(){
        return "username:"+this.username+",url:"+this.url+",password:"+this.password;
    }

    public void start(){
        System.out.println("TestBean 初始化。。。");
    }

    public void cleanUp(){
        System.out.println("TestBean 销毁。。。");
    }
}

Configuration class:

package com.test.spring.support.configuration;

@Configuration
public class TestConfiguration {
        public TestConfiguration(){
            System.out.println("spring容器启动初始化。。。");
        }

    //@Bean注解注册bean,同时可以指定初始化和销毁方法
    //@Bean(name="testNean",initMethod="start",destroyMethod="cleanUp")
    @Bean
    @Scope("prototype")
    public TestBean testBean() {
        return new TestBean();
    }
}

Main method test class:

package com.test.spring.support.configuration;

public class TestMain {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(TestConfiguration.class);
        //获取bean
        TestBean tb = context.getBean("testBean");
        tb.sayHello();
    }
}

Note: 
(1), @Bean annotation on the method of returning an instance, if the name of the bean is not specified through @Bean, the default is the same as the method name of the annotation; 

(2), the default scope of the @Bean annotation is the singleton function domain, which can be set to the prototype scope through @Scope("prototype"); 

(3) Since the role of @Bean is to register bean objects, you can use @Component, @Controller, @Service, @Ripository and other annotations to register beans , of course, you need to configure the @ComponentScan annotation for automatic scanning.

bean class:

package com.test.spring.support.configuration;

//添加注册bean的注解
@Component
public class TestBean {

    public void sayHello(){
        System.out.println("TestBean sayHello...");
    }

    public String toString(){
        return "username:"+this.username+",url:"+this.url+",password:"+this.password;
    }
}

Configuration class:

@Configuration

//添加自动扫描注解，basePackages为TestBean包路径
@ComponentScan(basePackages = "com.test.spring.support.configuration")
public class TestConfiguration {
    public TestConfiguration(){
        System.out.println("spring容器启动初始化。。。");
    }

    //取消@Bean注解注册bean的方式
    //@Bean
    //@Scope("prototype")
    //public TestBean testBean() {
    //  return new TestBean();
    //}
}

The main method test gets the bean object:

public class TestMain {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(TestConfiguration.class);
        //获取bean
        TestBean tb = context.getBean("testBean");
        tb.sayHello();
    }
}

The sayHello() method is called normally.

Original link: https://blog.csdn.net/javaloveiphone/article/details/52182899