java - Spring 是从众多接口(interface)实现中单独挑选出一个接口(interface)实现吗？

Question

下面的 friend 是我的代码，我正在尝试使用 Spring 运行依赖注入(inject)

我有一个接口(interface)，该接口(interface)的两个类实现。

一个 bean.xml 和一个 main 方法类。

接口(interface)IWriter.java

package DI;
    public interface IWriter {
    public void writer(String s);
}  

类Writer.java

     package DI;

     import org.springframework.stereotype.Service;

     @Service
     public class Writer implements IWriter {
        public void writer (String s){
            System.out.println(s);
        }
     } 

NiceWriter.java 类

package DI;

import org.springframework.stereotype.Service;

@Service
public class NiceWriter implements IWriter {
    public void writer (String s){
        System.out.println("The string is " + s);
    }
} 

另一个类

package DI;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;

@Service
public class MySpringBeanWithDependency {

    @Autowired
    private IWriter writer;

    public void run() {
        String s = "This is my test";
        writer.writer(s);
    }
}

主.java

package DI;

import org.springframework.beans.factory.BeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import DI.MySpringBeanWithDependency;

public class Main {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");
        BeanFactory factory = context;
        MySpringBeanWithDependency test = (MySpringBeanWithDependency) factory.getBean("mySpringBeanWithDependency");
        test.run();
    }
}

bean.xml

          <?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:aop="http://www.springframework.org/schema/aop"
           xmlns:context="http://www.springframework.org/schema/context"
          xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
       http://www.springframework.org/schema/aop
       http://www.springframework.org/schema/aop/spring-aop-2.5.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context-2.5.xsd">

       <context:component-scan base-package="DI" />

       </beans> 

当我运行代码时，Spring 容器给出了 Writer.java 类方法的输出。我没有在任何地方指定选择哪个实现。 Spring 是如何接手 Writer.java 的实现的？？

Answer 1

如下更改您的代码。

类Writer.java

  package DI;

     import org.springframework.stereotype.Service;

     @Service("writer")
     public class Writer implements IWriter {
     public void writer (String s){
      System.out.println(s);
     }
    } 

NiceWriter.java 类

    package DI;

    import org.springframework.stereotype.Service;

   @Service("niceWriter")
   public class NiceWriter implements IWriter {
   public void writer (String s){
    System.out.println("The string is " + s);
   }
  } 

另一个类

     package DI;

      import org.springframework.beans.factory.annotation.Autowired;
      import org.springframework.beans.factory.annotation.Qualifier;
      import org.springframework.stereotype.Service;

      @Service
      public class MySpringBeanWithDependency {

     @Autowired
     @Qualifier("writer")//if you need to autowire Writer service   
     private IWriter writer;

     @Autowired
    @Qualifier("niceWriter")//if you need to autowire NiceWriter service
    private IWriter niceWriter


       public void run() {
       String s = "This is my test";
        writer.writer(s);
      }
    }