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Spring4.0: @Configuration

Gaaidou 2022-08-30 阅读 41


前言:
今天详细学习了一下@Configuration的使用,在此做个记录吧。

1. 介绍

@Configuration 用于定义配置类,可替换XML配置文件,被注解的类内部包含有一个或多个被@Bean注解的方法,这些方法将会被AnnotationConfigApplicationContextAnnotationConfigWebApplicationContext类进行扫描,并用于构建bean定义,初始化Spring容器。

备注:@Configuration注解配置有如下要求

  • @Configuration 不可以是final类型
  • @Configuration 不可以是匿名内部类
  • 嵌套的configuration必须是静态类

2.使用方法

1.@Configuration配置Spring

@Configuration 标注在类上,相当于把类作为spring的xml配置文件中的,作用为:配置Spring容器(上下文)
例子:

import org.springframework.context.annotation.Configuration;

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

测试:

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

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");
}
}

2. @Configuration启动容器和@Bean注册

@Bean 标注在方法上(返回某个实例的方法),等价于spring的xml配置文件中,作用为bean对象;

bean类如下:

public class TestBean {

private String username;
private String url;
private String password;

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。。。");
}
}

配置类:

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;

@Configuration
public class TestConfiguration {
public TestConfiguration() {
System.out.println("TestConfiguration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="testBean",initMethod="start",destroyMethod="cleanUp")
@Bean
@Scope("prototype") //配置声明周期类型为prototype
public TestBean testBean() {
return new TestBean();
}
}

主测试类:

package com.dxz.demo.configuration;

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

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");

//获取bean
TestBean tb = (TestBean) context.getBean("testBean");
tb.sayHello();
}
}

备注:

  • @Bean注解在返回实例的方法上,如果未通过@Bean指定bean的名称,则默认与标注的方法名相同。
  • @Bean注解默认作用域为单例singleton作用域,可通过@Scope(“prototype”)设置为原型作用域
  • @Bean的作用是注册Bean对象,那么完全可以使用@Component、@Controller、@Service、@Repository等注解注册bean,当然需要配置@ComponentScan注解进行自动扫描。

@Configuration启动容器@Component注册Bean

Bean类:

import org.springframework.stereotype.Component;

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

private String username;
private String url;
private String password;

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。。。");
}
}

配置类:

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

@Configuration
//添加自动扫描注解,basePackages为TestBean包路径
@ComponentScan(basePackages = "com.dxz.demo.configuration")
public class TestConfiguration {
public TestConfiguration() {
System.out.println("TestConfiguration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();
}*/
}

测试方法:

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

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");

//获取bean
TestBean tb = (TestBean) context.getBean("testBean");
tb.sayHello();
}
}

3 AnnotationConfigApplicationContext注册AppContext

有两种方法注册AppContext:

  • 配置类的注册方式是将其传递给AnnotationConfigApplicationContext构造函数

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);

//获取bean
TestBean tb = (TestBean) context.getBean("testBean");
tb.sayHello();
}

  • AnnotationConfigApplicationContext 的register 方法传入配置类来注册配置类

public static void main(String[] args) {
ApplicationContext ctx = new AnnotationConfigApplicationContext();
ctx.register(AppContext.class)
}

总结

  • @Configuration等价于
  • @Bean等价于
  • @ComponentScan等价于<context:component-scan base-package=“com.dxz.demo”/>


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