Spring学习--通过注解配置 Bean (一)

在 classpath 中扫描组件：

组件扫描(component scanning)： Spring 能够从 classpath 下自动扫描 , 侦测和实例化具有特定注解的组件。

特定组件包括：

@Component：基本注解 , 标识了一个受 Spring 管理的组件。
@Repository：标识持久层组件。
@Service：标识服务层(业务层)组件。
@Controller：标识表现层组件。

对于扫描到的组件 , Spring 有默认的命名策略：使用非限定类名 , 第一个字母小写。也可以通过 value 属性值标识组件的名称。

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <beans xmlns="http://www.springframework.org/schema/beans"
 3        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 4        xmlns:context="http://www.springframework.org/schema/context"
 5        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
 6        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
 7 
 8     <!-- 指定 Spring IOC 容器扫描的包-->
 9     <context:component-scan base-package="com.itdjx.spring.annotation">
10 
11     </context:component-scan>
12 
13 </beans>

注意：一定要添加 context 命名空间。

 1 package com.itdjx.spring.annotation;
 2 
 3 import org.springframework.stereotype.Component;
 4 
 5 /**
 6  * @author Wáng Chéng Dá
 7  * @create 2017-03-03 8:44
 8  */
 9 @Component
10 public class TestObject {
11 }

 1 package com.itdjx.spring.annotation.controller;
 2 
 3 import org.springframework.stereotype.Controller;
 4 
 5 /**
 6  * @author Wáng Chéng Dá
 7  * @create 2017-03-03 9:28
 8  */
 9 @Controller
10 public class UserController {
11 
12     public void execute() {
13         System.out.println("I am UserController's execute method...");
14     }
15 }

 1 package com.itdjx.spring.annotation.service;
 2 
 3 import org.springframework.stereotype.Service;
 4 
 5 /**
 6  * @author Wáng Chéng Dá
 7  * @create 2017-03-03 9:26
 8  */
 9 @Service
10 public class UserService {
11 
12     public void add() {
13         System.out.println("I am UserService's add method...");
14     }
15 }

 1 package com.itdjx.spring.annotation.repository;
 2 
 3 import org.springframework.stereotype.Repository;
 4 
 5 /**
 6  * @author Wáng Chéng Dá
 7  * @create 2017-03-03 9:24
 8  */
 9 @Repository("userRepository")
10 public class UserRepositoryImpl implements UserRepository {
11 
12     @Override
13     public void sava() {
14         System.out.println("I am UserRepositoryImpl's sava method...");
15     }
16 }

 1 package com.itdjx.spring.annotation.repository;
 2 
 3 /**
 4  * @author Wáng Chéng Dá
 5  * @create 2017-03-03 9:23
 6  */
 7 public interface UserRepository {
 8 
 9     void sava();
10 
11 }

 1 package com.itdjx.spring.annotation;
 2 
 3 import com.itdjx.spring.annotation.controller.UserController;
 4 import com.itdjx.spring.annotation.repository.UserRepository;
 5 import com.itdjx.spring.annotation.service.UserService;
 6 import org.springframework.context.ApplicationContext;
 7 import org.springframework.context.support.ClassPathXmlApplicationContext;
 8 
 9 /**
10  * @author Wáng Chéng Dá
11  * @create 2017-03-03 9:34
12  */
13 public class Main {
14 
15     public static void main(String[] args) {
16         ApplicationContext cxt = new ClassPathXmlApplicationContext("beans-annotation.xml");
17         TestObject testObject = (TestObject) cxt.getBean("testObject");
18         System.out.println(testObject);
19 
20         UserController userController = (UserController) cxt.getBean("userController");
21         System.out.println(userController);
22 
23         UserService userService = (UserService) cxt.getBean("userService");
24         System.out.println(userService);
25 
26         UserRepository userRepository = (UserRepository) cxt.getBean("userRepository");
27         System.out.println(userRepository);
28 
29     }
30 }

控制台输出：

com.itdjx.spring.annotation.TestObject@27ba32
com.itdjx.spring.annotation.controller.UserController@f82753
com.itdjx.spring.annotation.service.UserService@10fe47a
com.itdjx.spring.annotation.repository.UserRepositoryImpl@2b0582

注意：Spring 默认的命名策略：使用非限定类名 , 第一个字母小写。也可以通过 value 属性值标识组件的名称。

若不修改 @Repository("userRepository") 默认的 value 值 , bean 的 id 值是 userRepositoryImpl , UserRepository userRepository = (UserRepository) cxt.getBean("userRepository"); 会抛出找不到 userRepository 这个 bean 节点。

异常：

Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'userRepository' available
at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanDefinition(DefaultListableBeanFactory.java:687)
at org.springframework.beans.factory.support.AbstractBeanFactory.getMergedLocalBeanDefinition(AbstractBeanFactory.java:1207)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:284)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1081)
at com.itdjx.spring.annotation.Main.main(Main.java:26)