Spring 基于 Java 的配置

带有 @Configuration 的注解类表示这个类可以使用 Spring IoC 容器作为 bean 定义的来源。
@Bean 注解告诉 Spring，一个带有 @Bean 的注解方法将返回一个对象，该对象应该被注册为在 Spring 应用程序上下文中的 bean
案例代码：
HelloWorld.java

package com.baklib.hello;
public class HelloWorld {
    private String message;
    public void getMessage() {
        System.out.println("Your Message : "+message);
    }
    public void setMessage(String message) {
        this.message = message;
    }
}

HelloWorldConfig.java

package com.baklib.hello;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class HelloWorldConfig {
    @Bean
    public HelloWorld helloWorld(){
        return new HelloWorld();
    }
}

MainApp.java

package com.baklib.hello;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class MainApp {
    public static void main(String[] args) {
        ApplicationContext ctx = new AnnotationConfigApplicationContext(HelloWorldConfig.class);
        HelloWorld helloWorld = ctx.getBean(HelloWorld.class);
        helloWorld.setMessage("Hello World!");
        helloWorld.getMessage();
    }
}

编写完以上代码，就可以运行这个程序，运行结束后，可以在控制台看到下面的信息

Your Message : Hello World!

注入 Bean 的依赖
案例代码：
SpellChecker.java

package com.baklib.hellobean;
public class SpellChecker {
    public SpellChecker() {
        System.out.println("Inside SpellChecker constructor.");
    }
    public void checkSpelling() {
        System.out.println("Inside checkSpelling.");
    }
}

TextEditor.java

package com.baklib.hellobean;
public class TextEditor {
    private SpellChecker spellChecker;
    public TextEditor(SpellChecker spellChecker) {
        System.out.println("Inside TextEditor constructor.");
        this.spellChecker = spellChecker;
    }
    public void spellCheck(){
        spellChecker.checkSpelling();
    }
}

TextEditorConfig.java

package com.baklib.hellobean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class TextEditorConfig {
    @Bean
    public TextEditor textEditor() {
        return new TextEditor(spellChecker());
    }
    @Bean
    public SpellChecker spellChecker(){
        return new SpellChecker();
    }
}

MainApp.java

package com.baklib.hellobean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class MainApp {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(TextEditorConfig.class);
        TextEditor te = context.getBean(TextEditor.class);
        te.spellCheck();
    }
}

编写完以上代码，就可以运行这个程序，运行结束后，可以在控制台看到下面的信息

Inside SpellChecker constructor.
Inside TextEditor constructor.
Inside checkSpelling.

@import 注解允许从另一个配置类中加载 @Bean 定义
案例代码：
新建 A.java 和 B.java
ConfigA.java

package com.baklib.helloImport;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class ConfigA {
    @Bean
    public A a() {
        return new A();
    }
}

ConfigB.java

package com.baklib.helloImport;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
@Configuration
@Import(ConfigA.class)
public class ConfigB {
    @Bean
    public B b(){
        return new B();
    }
}

MainApp.java

package com.baklib.helloImport;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class MainApp {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(ConfigB.class);
        A a = context.getBean(A.class);
        B b = context.getBean(B.class);
    }
}

@Bean(initMethod = “init”, destroyMethod = “cleanup” ) 指定任意的初始化和销毁的回调方法
@Scope 注解指定 Bean 的范围