@Autowired与@Resource的区别
@Autowired与@Resource相同点
两者都可以写在字段和setter方法上。两者如果都写在字段上，那么就不需要再写setter方法。
@Autowired与@Resource不同点
1.@Autowired(org.springframework.beans.factory.annotation.Autowired)属于Spring的注解，@Resource(javax.annotation.Resource)属于J2EE的注解。
2.@Autowired是通过byType注入的；@Resource是通过byName注入的；
@Resource有2个重要的属性分别是name和type,Spring将@Resource注解的name属性解析为bean的名字,而type则解析为bean的类型。所以使用name属性，则使用byName的自动注入策略，而使用byType属性时则使用byType自动注入策略。如果没用指定name或者type则默认通过byName自动注入策略。
注：最好是将@Resource放在setter方法上，因为这样更符合面向对象的思想，通过set、get去操作属性，而不是直接去操作属性。
@Resource装配顺序
①如果同时指定了name和type，则从Spring上下文中找到唯一匹配的bean进行装配，找不到则抛出异常。
②如果指定了name，则从上下文中查找名称（id）匹配的bean进行装配，找不到则抛出异常。
③如果指定了type，则从上下文中找到类似匹配的唯一bean进行装配，找不到或是找到多个，都会抛出异常。
④如果既没有指定name，又没有指定type，则自动按照byName方式进行装配；如果没有匹配，则回退为一个原始类型进行匹配，如果匹配则自动装配。
@Resource的作用相当于@Autowired，只不过@Autowired按照byType自动注入。
代码演示：
定义一个 接口 OrderMapper，二个实现类 OrderService01、OrderService02。一个 PayService 调用 orderMapper 接口中的方法。
orderMapper
package com.example.service;
/**
* @author mingtian
* @version V1.0
* @Description
* @date 2019/12/9 16:57
*/
public interface OrderMapper {
/**
* 新增订单方法
*/
void add();
}
OrderServiceImpl01
package com.example.service.impl;
import com.example.service.OrderMapper;
import org.springframework.stereotype.Component;
/**
* @author mingtian
* @version V1.0
* @Description 订单接口实现类
* @date 2019/12/9 16:55
*/
@Component
public class OrderServiceImpl01 implements OrderMapper {
public void add() {
System.out.println("OrderService01");
}
}
OrderServiceImpl02
package com.example.service.impl;
import com.example.service.OrderMapper;
import org.springframework.stereotype.Component;
/**
* @author mingtian
* @version V1.0
* @Description 订单接口实现类
* @date 2019/12/9 16:55
*/
@Component
public class OrderServiceImpl02 implements OrderMapper {
public void add() {
System.out.println("OrderService02");
}
}
PayService 使用 @Auwowried
package com.example.service.impl;
import com.example.service.OrderMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;
import javax.annotation.Resource;
/**
* @author mingtian
* @version V1.0
* @Description PayService
* @date 2019/12/9 16:54
*/
@Component
public class PayService {
@Autowired
private OrderMapper orderMapper;
public void add() {
orderMapper.add();
}
}
配置类
package com.example.config;
import com.example.entity.Order;
import com.example.entity.Win10;
import org.springframework.context.annotation.*;
/**
* @author mingtian
* @version V1.0
* @Description
* @ComponentScan("com.example.entity") //开启扫包范围
* @date 2019/12/9 11:17
*/
@Configuration
@ComponentScan("com.example")
public class MyConfig {
}
测试类
package com.example.test;
import com.example.config.MyConfig;
import com.example.entity.FactoryBeanEntity;
import com.example.service.impl.PayService;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
/**
* @author mingtian
* @version V1.0
* @Description 测试类
* @date 2019/12/9 11:00
*/
public class Test005 {
public static AnnotationConfigApplicationContext context;
public static void main(String[] args) {
context = new AnnotationConfigApplicationContext(MyConfig.class);
PayService payService = (PayService) context.getBean("payService");
payService.add();
System.out.println("bean:" + payService);
}
}
现在启动报错，错误信息如下：
十二月 09, 2019 5:23:50 下午 org.springframework.context.support.AbstractApplicationContext refresh
警告: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'payService': Unsatisfied dependency expressed through field 'orderMapper'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.example.service.OrderMapper' available: expected single matching bean but found 2: orderServiceImpl01,orderServiceImpl02
Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'payService': Unsatisfied dependency expressed through field 'orderMapper'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.example.service.OrderMapper' available: expected single matching bean but found 2: orderServiceImpl01,orderServiceImpl02
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:643)
at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:116)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:399)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1422)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:594)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:517)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:323)
at org.springframework.beans.factory.support.AbstractBeanFactory$$Lambda$31/221036634.getObject(Unknown Source)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:321)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:879)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:878)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550)
at org.springframework.context.annotation.AnnotationConfigApplicationContext.<init>(AnnotationConfigApplicationContext.java:89)
at com.example.test.Test005.main(Test005.java:19)
Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.example.service.OrderMapper' available: expected single matching bean but found 2: orderServiceImpl01,orderServiceImpl02
at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:220)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1265)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1207)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:640)
... 15 more
由上面报错的错误信息可知，通过 @Autowired 注解注入的 orderMapper 找到了二个实现类导致的错误。
解决办法：
方法1 使用 @Autowired + @Qualifier(value="orderServiceImpl01") 显示的指定一个实现类
package com.example.service.impl;
import com.example.service.OrderMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;
import javax.annotation.Resource;
/**
* @author mingtian
* @version V1.0
* @Description PayService
* @date 2019/12/9 16:54
*/
@Component
public class PayService {
@Autowired
@Qualifier(value = "orderServiceImpl01")
private OrderMapper orderMapper;
public void add() {
orderMapper.add();
}
}
方法2 使用@Resource(name="orderServiceImpl01")
package com.example.service.impl;
import com.example.service.OrderMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;
import javax.annotation.Resource;
/**
* @author mingtian
* @version V1.0
* @Description PayService
* @date 2019/12/9 16:54
*/
@Component
public class PayService {
@Resource(name = "orderServiceImpl01")
private OrderMapper orderMapper;
public void add() {
orderMapper.add();
}
}
由上面的二种解决方法可知：
@Autowired + @Qualifier(value="orderServiceImpl01") 等同于 @Resource(name="orderServiceImpl01")
方法3 使用 @Primary 注解 指定默认加载的类，这样的话 直接在PayService 中 直接使用 @Autowired 一个注解即可，默认启动就会加载 OrderServiceImpl01 这个类
package com.example.service.impl;
import com.example.service.OrderMapper;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;
/**
* @author mingtian
* @version V1.0
* @Description 订单接口实现类
* @date 2019/12/9 16:55
*/
@Primary
@Component
public class OrderServiceImpl01 implements OrderMapper {
public void add() {
System.out.println("OrderService01");
}
}
@Primary 这个注解 在 SpringBoot 多数据源的时候经常使用 ，用来设置加载默认的数据源(优先级)。
注意：使用 @Component 注解的时候，记得开启扫包的范围(使用 @ComponentScan("com.example")指定扫包范围)，不然启动会报错的。
OrderMapper，二个实现类 OrderService01、OrderService02、
