JavaConfig 使用Java代码进行显示配置

从Spring 3起，JavaConfig功能已经包含在Spring核心模块，它允许开发者将bean定义和在Spring配置XML文件到Java类中。

需要先加载spring-context 包

   <!-- https://mvnrepository.com/artifact/org.springframework/spring-context -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>4.3.6.RELEASE</version>
    </dependency>

代码：

package com.company;

/**
 * Created by Administrator on 2017/2/22 0022.
 */
public interface ISay {
    void say(String msg);
}

package com.company;

/**
 * Created by Administrator on 2017/2/22 0022.
 */
public class SayImpl implements com.company.ISay {
    public void say(String msg){
        System.out.println("Person Say:"+msg);
    }
}

使用 @Configuration 注释告诉 Spring，这是核心的 Spring 配置文件，并通过 @Bean 定义 bean。

package com.company;

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

/**
 * Created by Administrator on 2017/2/22 0022.
 */
@Configuration
public class JavaConfig {
    @Bean(name="GetSay")
    public com.company.ISay GetSay(){
        return new com.company.SayImpl();
    }
}

package com.company;

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

public class Main {
    public static void main(String[] args)   {
        ApplicationContext context =new AnnotationConfigApplicationContext(com.company.JavaConfig.class);
        com.company.ISay obj=(com.company.ISay) context.getBean("GetSay");
        obj.say("hongdada");
    }
}

log4j:WARN No appenders could be found for logger (org.springframework.core.env.StandardEnvironment).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Person Say:hongdada

多个Bean

package com.company;

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

interface ISay {
    String Country="China";
    void say(String msg);
}

class SayImpl implements com.company.ISay {
    public void say(String msg){
        System.out.println("Person Say:"+msg);
    }
}

class SayImpl2 implements com.company.ISay {
    public void say(String msg){
        System.out.println(com.company.ISay.Country+" Person2  Say:"+msg);
    }
}

@Configuration
class JavaConfig {
    @Bean(name="GetSay")
    public com.company.ISay GetSay(){
        return new com.company.SayImpl();
    }

    @Bean(name="GetSay2")
    public com.company.ISay GetSayTwo(){
        return new com.company.SayImpl2();
    }
}

public class Main {
    public static void main(String[] args)   {
        ApplicationContext context =new AnnotationConfigApplicationContext(com.company.JavaConfig.class);
        com.company.ISay obj=(com.company.ISay) context.getBean("GetSay");
        obj.say("hongdada");

        com.company.ISay obj2=(com.company.ISay) context.getBean("GetSay2");
        obj2.say("hongdada");
    }
}

Person Say:hongdada
China Person2  Say:hongdada

另外一种获取Bean的方式：

package com.company;

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

interface ISay {
    String Country="China";
    void say(String msg);
}

class SayImpl implements com.company.ISay {
    public void say(String msg){
        System.out.println("Person Say:"+msg);
    }
}

class SayImpl2 implements com.company.ISay {
    public void say(String msg){
        System.out.println(com.company.ISay.Country+" Person2  Say:"+msg);
    }
}

@Configuration
class JavaConfig {
    @Bean(name="GetSay")
    public com.company.ISay GetSay(){
        return new com.company.SayImpl();
    }

//    @Bean(name="GetSay2")
//    public com.company.ISay GetSayTwo(){
//        return new com.company.SayImpl2();
//    }
}

public class Main {
    public static void main(String[] args)   {
//        ApplicationContext context =new AnnotationConfigApplicationContext(com.company.JavaConfig.class);
//        com.company.ISay obj=(com.company.ISay) context.getBean("GetSay");
//        obj.say("hongdada");
//
//        com.company.ISay obj2=(com.company.ISay) context.getBean("GetSay2");
//        obj2.say("hongdada");
        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
        ctx.register(JavaConfig.class);
        ctx.refresh();
        ISay obj=ctx.getBean(ISay.class);
        obj.say("hongdada");
    }
}

Person Say:hongdada

可以发现，这里面直接根据ISay.class来获取对应的Bean，那么JavaConfig里面必须只有一个返回值是ISay的Bean,不然就会报错。

Exception in thread "main" org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.company.ISay' available: expected single matching bean but found 2: GetSay,GetSay2
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveNamedBean(DefaultListableBeanFactory.java:1041)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:345)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:340)
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1093)
    at com.company.Main.main(Main.java:49)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

========================

@ImportClass

http://www.manongjc.com/article/1603.html

http://www.cnblogs.com/strivelearn/p/6096128.html

http://www.kancloud.cn/evankaka/springlearning/119666