Spring中@Resource與@Autowired

問題

　　這其實就是@Autoware與@Resource沒有正確的使用，這個錯誤是因為wmPoiOplogService這個變量裝配方式是@Resource，按照@Resource的按名字查找的方式，並沒有找到bean id為wmPoiOplogService的bean所以就報出這個錯誤。

舉個栗子🌰

　　

　　Bean.java

package service.test;


import java.util.List;

/**
 * Created by zhengbin on 16/8/28.
 */
public interface Bean {
    public String sayHello();
    
    public List<String> sayHellos();
}

　　BeanImpl.java

package service.test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import javax.annotation.Resource;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

/**
 * Created by zhengbin on 16/8/28.
 */
@Component("Bean")
public class BeanImpl implements Bean {
    @Resource
    private Hello hello2;
    
    @Autowired
    private Hello hello1;
    
    @Autowired
    private List<Hello> hellos;
    
    @Override
    public String sayHello() {
        return "say " + hello2.say();
    }
    
    @Override
    public List<String> sayHellos() {
        List<String> stringList = new ArrayList<String>();
        for (Hello hello : hellos) {
            stringList.add(hello.say());
        }
        return stringList;
    }
}

 

　　Hello.java

package service.test;

/**
 * Created by zhengbin on 16/8/28.
 */
public interface Hello {
    public String say();
}

　　HelloImpl.java

package service.test;

import org.springframework.stereotype.Component;

/**
 * Created by zhengbin on 16/8/28.
 */
@Component("hello1")
public class HelloImpl implements Hello {
    @Override
    public String say() {
        return "Hello1";
    }
}

　　HelloImple.java

package service.test;

import org.springframework.stereotype.Component;

/**
 * Created by zhengbin on 16/8/28.
 */
@Component("hello2")
public class HelloImple implements Hello {
    @Override
    public String say() {
        return "Hello2";
    }
}

　　BeanTest.java

package service.test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * Created by zhengbin on 16/8/28.
 */
public class BeanTest {
    
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext-test.xml");
        Bean bean = context.getBean("Bean", Bean.class);
        System.out.println(bean.sayHello());
        System.out.println(bean.sayHellos());
    }
    
}

　　改動BeanImpl.java

private Hello hello2;

　　改為：

private Hello hello1;

　　運行結果也由

say Hello2

　　變為：

say Hello1

　　這說明@Resource是按變量名去找相應的Bean

　　而當用第20行的@Autoware方式去執行sayHello()方法時，會報出這個錯誤：

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: 
Error creating bean with name 'Bean': Injection of resource dependencies failed; 
nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: 
No qualifying bean of type [service.test.Hello] is defined: expected single matching bean but found 2: hello1,hello2

　　‘bean of type’說明@Autoware匹配bean的方式是按類型，按類型查找Hello，查找出2個，也就是：‘expected single matching bean but found 2: hello1,hello2’

　　所以相應的第23行的hellos與第31行的sayHellos方法就說明了，當按@Autoware匹配切有該類型有多個時，可用List裝載

private List<Hello> hellos;

public List<String> sayHellos() {
　　List<String> stringList = new ArrayList<String>();
   　　for (Hello hello : hellos) {
      　　stringList.add(hello.say());
      }
   return stringList;
37 }

@Resource

　　@Resource要求提供一個Bean名稱的屬性(name)，如果屬性為空，則自動采用標注處的變量名或方法名作為Bean的名稱。

　　　　type屬性：

　　　　name屬性：

@Autoware

　　@Autoware默認按類型匹配注入Bean

　　　　required屬性：如果希望Spring即使找不到匹配的Bean完成注入也不要拋出異常，那么可以使用@Autoware(required=false)進行標注：

@Autowired(required = false)
private List<Hello> hellos;

　　@Qualifier：指定注入Bean的名稱

@Autowired
@Qualifier("hello1")
private Hello hello;

 　　這也就解決了容器中有一個以上匹配的Bean時，報錯：expected single matching bean but found 2: hello1,hello2

詳細文檔

　　3.11. 基於注解（Annotation-based）的配置