每天一个SpringBoot注解之@Configuration

先按照简单代码示例注解的作用，最后再做一个总结。
　　从Spring3.0，@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AnnotationConfigApplicationContext或AnnotationConfigWebApplicationContext类进行扫描，并用于构建bean定义，初始化Spring容器。
1.先看看最简单的应用，我们创建一个类，加上Configuration注解

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

然后启动主程序，让我们看看输出，很明显，只要加上了这个注解，就可以启动spring容器

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::                (v2.4.1)

2021-01-12 20:13:46.018  INFO 35216 --- [           main] com.example.demo.DemoApplication         : Starting DemoApplication using Java 1.8.0_211 on DESKTOP-AD5JM34 with PID 35216 (D:\Idea\workspace\demo\target\classes started by dell in D:\Idea\workspace\demo)
2021-01-12 20:13:46.022  INFO 35216 --- [           main] com.example.demo.DemoApplication         : No active profile set, falling back to default profiles: default
2021-01-12 20:13:46.801  INFO 35216 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2021-01-12 20:13:46.809  INFO 35216 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2021-01-12 20:13:46.809  INFO 35216 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.41]
2021-01-12 20:13:46.876  INFO 35216 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2021-01-12 20:13:46.876  INFO 35216 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 808 ms
TestConfiguration容器启动初始化。。。

2.我们再结合@Bean注解来加载对象，新建一个TestBean对象

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。。。");
    }
}

这次我们直接在刚刚的类里面用main方法来测试，而不是项目的启动类

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

    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(ConfigurationTest.class);
        TestBean testBean = context.getBean(TestBean.class);
        testBean.sayHello();
    }

    @Bean
    @Scope("prototype")
    public TestBean testBean() {
        return new TestBean();
    }
}

当启动main方法后，我们来看看输出
很明显，对象创建好了，而且sayHello方法也能正常调用

20:18:20.699 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'configurationTest'
TestConfiguration容器启动初始化。。。
20:18:20.704 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'testBean2'
TestBean sayHello...

当然@Bean还可以加其他参数
我们可以加上name(不指定就是方法名同名)，destroyMethod ，initMethod 方法，指定为我们刚刚创建的对象中TestBean 中的方法

    @Bean(name = "TestBean",destroyMethod = "cleanUp",initMethod = "start")
    @Scope("prototype")
    public TestBean testBean() {
        return new TestBean();
    }

让我们再看看输出

20:21:07.822 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'configurationTest'
TestConfiguration容器启动初始化。。。
TestBean 初始化。。。
TestBean sayHello..

@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
3.我们可以用@Configuration配合@Component注册一个Bean
我们为对象加上@Component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。。。");
    }
}

然后再@Configuration注解的类中加上@ComponentScan

@Configuration
@ComponentScan(basePackages = "com.example.demo.configuration")
public class ConfigurationTest {
    public ConfigurationTest() {
        System.out.println("TestConfiguration容器启动初始化。。。");
    }

    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(ConfigurationTest.class);
        TestBean testBean = context.getBean(TestBean.class);
        testBean.sayHello();
    }

//    @Bean(name = "TestBean",destroyMethod = "cleanUp",initMethod = "start")
//    @Scope("prototype")
//    public TestBean testBean() {
//        return new TestBean();
//    }
}

看看输出，仍然没有问题

20:24:41.892 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'configurationTest'
TestConfiguration容器启动初始化。。。
20:24:41.902 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'testBean'
TestBean sayHello...

最后总结一下，相比于SSM的xml

 @Configuation等价于<Beans></Beans>

 @Bean等价于<Bean></Bean>

 @ComponentScan等价于<context:component-scan base-package="com.dxz.demo"/>

本文地址：https://blog.csdn.net/StreamlineWq/article/details/112546214