@Autowired與@Resource相同點
兩者都可以寫在字段和setter方法上。兩者如果都寫在字段上，那么就不需要再寫setter方法。
@Autowired與@Resource不同點
1.@Autowired(org.springframework.beans.factory.annotation.Autowired)屬於Spring的注解，@Resource(javax.annotation.Resource)屬於J2EE的注解。
2.@Autowired是通過byType注入的；@Resource是通過byName注入的；
@Resource有2個重要的屬性分別是name和type,Spring將@Resource注解的name屬性解析為bean的名字,而type則解析為bean的類型。所以使用name屬性，則使用byName的自動注入策略，而使用byType屬性時則使用byType自動注入策略。如果沒用指定name或者type則默認通過byName自動注入策略。
注：最好是將@Resource放在setter方法上，因為這樣更符合面向對象的思想，通過set、get去操作屬性，而不是直接去操作屬性。
@Resource裝配順序
①如果同時指定了name和type，則從Spring上下文中找到唯一匹配的bean進行裝配，找不到則拋出異常。
②如果指定了name，則從上下文中查找名稱（id）匹配的bean進行裝配，找不到則拋出異常。
③如果指定了type，則從上下文中找到類似匹配的唯一bean進行裝配，找不到或是找到多個，都會拋出異常。
④如果既沒有指定name，又沒有指定type，則自動按照byName方式進行裝配；如果沒有匹配，則回退為一個原始類型進行匹配，如果匹配則自動裝配。
@Resource的作用相當於@Autowired，只不過@Autowired按照byType自動注入。
代碼演示：
定義一個 接口 OrderMapper，二個實現類 OrderService01、OrderService02。一個 PayService 調用 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 {
/**
* 新增訂單方法
*/
void add();
}
OrderServiceImpl01
package com.example.service.impl;
import com.example.service.OrderMapper;
import org.springframework.stereotype.Component;
/**
* @author mingtian
* @version V1.0
* @Description 訂單接口實現類
* @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 訂單接口實現類
* @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();
}
}
配置類
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") //開啟掃包范圍
* @date 2019/12/9 11:17
*/
@Configuration
@ComponentScan("com.example")
public class MyConfig {
}
測試類
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 測試類
* @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);
}
}
現在啟動報錯，錯誤信息如下：
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
由上面報錯的錯誤信息可知，通過 @Autowired 注解注入的 orderMapper 找到了二個實現類導致的錯誤。
解決辦法：
方法1 使用 @Autowired + @Qualifier(value="orderServiceImpl01") 顯示的指定一個實現類
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();
}
}
由上面的二種解決方法可知：
@Autowired + @Qualifier(value="orderServiceImpl01") 等同於 @Resource(name="orderServiceImpl01")
方法3 使用 @Primary 注解 指定默認加載的類，這樣的話 直接在PayService 中 直接使用 @Autowired 一個注解即可，默認啟動就會加載 OrderServiceImpl01 這個類
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 訂單接口實現類
* @date 2019/12/9 16:55
*/
@Primary
@Component
public class OrderServiceImpl01 implements OrderMapper {
public void add() {
System.out.println("OrderService01");
}
}
@Primary 這個注解 在 SpringBoot 多數據源的時候經常使用 ，用來設置加載默認的數據源(優先級)。
注意：使用 @Component 注解的時候，記得開啟掃包的范圍(使用 @ComponentScan("com.example")指定掃包范圍)，不然啟動會報錯的。
OrderMapper，二個實現類 OrderService01、OrderService02、