目录
2. 存储 Bean 对象 ( 添加注解存储 Bean 对象)
面试题: @Autowired 和 @Resource 的区别
在上一篇中,可以看到,创建Spring需要三步,存 bean 需要三步, 取 bean 需要三步,感觉这个读取和存储对象的步骤并没有想象的那么 "简单" 啊
所以本篇将学习通过 "使用注解" 来更简单的存储和读取对象
前面在存储 Bean 时,需要在 spring-config 中添加一行 bean 注册内容,这个XML文件有一点不好的是调试,而且XML文件报错了是不影响项目运行的,即使报错了,也可能发现不了.
1. 先进行配置扫描路径
<?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:content="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
<content:component-scan base-package="com.bit.service"></content:component-scan>
</beans>在 spring 配置文件中设置 bean 的扫描根路径
2. 存储 Bean 对象 ( 添加注解存储 Bean 对象)
使用 5 大类注解实现,就不用在spring-config 中添加一行 bean 注册内容了
2.1 @Controller [控制器存储]
package com.beans;
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
public void sayHi() {
System.out.println("你好,UserController!");
}
}
import com.beans.UserController;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class app {
public static void main(String[] args) {
//1. 先得到上下文对象
ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
//2. 得到 bean
UserController controller = context.getBean("userController",UserController.class);
//3. 使用 bean
controller.sayHi();
}
}
2.2 @Service [服务存储]
import com.beans.UserController;
import com.beans.UserService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class app {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
UserService service = context.getBean("userService",UserService.class);
service.sayHi();
}
}
package com.beans;
import org.springframework.stereotype.Service;
@Service
public class UserService {
public void sayHi() {
System.out.println("你好,Service!");
}
}
2.3 @Repository [仓库存储]
import com.beans.UserRepository;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class app {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
UserRepository repository = context.getBean("userRepository",UserRepository.class);
repository.sayHi();
}
}
package com.beans;
import org.springframework.stereotype.Repository;
@Repository
public class UserRepository {
public void sayHi() {
System.out.println("你好,Repository!");
}
}
2.4 @Configuration [配置存储]
package com.beans;
import org.springframework.context.annotation.Configuration;
@Configuration
public class UserConfiguration {
public void sayHi() {
System.out.println("你好,Configuration!");
}
}
import com.beans.UserConfiguration;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class app {
public static void main(String[] args) {
//1. 先得到上下文对象
ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml"); UserConfiguration configuration = context.getBean("userConfiguration",UserConfiguration.class);
configuration.sayHi();
}
}
2.5 @Component [组件存储]
package com.beans;
import org.springframework.stereotype.Component;
@Component
public class UserComponent {
public void sayHi() {
System.out.println("你好,Component!");
}
}
import com.beans.*;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class app {
public static void main(String[] args) {
ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
UserComponent component = context.getBean("userComponent",UserComponent.class);
component.sayHi();
}
}
2.6 五大类注解的作用和关系
(1) 作用:
程序的最基础⼯程分层，调⽤流程如下
(2) 关系:
下面看一下源码
2.7 Bean的命名规则
在前按照规范"大驼峰"取类名,然后getBean按照规范"小驼峰"是可以运行成功的
而写如果写一个这样的类
但是如果,这样写就可以运行成功
那么 Bean 的命名规则到底应该是什么样的
2.8 使用方法注解 @Bean
package com.beans;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;
@Component
public class UserBeans {
@Bean //[只使用一个 @Bean 是无法将对象存储到容器中]
public User user1() {
User user = new User();
user.setId(1);
user.setName("张三");
return user;
}
}
import com.beans.*;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class app {
public static void main(String[] args) {
//1. 先得到上下文对象
ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
User user = context.getBean("user1",User.class);
// User user = context.getBean(User.class);
System.out.println(user);
}
}
package com.beans;
public class User {
private int id;
private String name;
@Override
public String toString() {
return "User{" +
"id=" + id +
", name='" + name + '\'' +
'}';
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
2.8.1 重命名 Bean
package com.beans;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;
@Component
public class UserBeans {
@Bean(name = "userinfo") //[只使用一个 @Bean 是无法将对象存储到容器中]
public User user1() {
User user = new User();
user.setId(1);
user.setName("张三");
return user;
}
}
3. 获取 Bean 对象 (对象装配)
3.1 属性注入
package com.beans;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController2 {
// 对象注入1: 属性注入
@Autowired
private UserService userService;
public void sayHi() {
userService.sayHi();
}
}
import com.beans.*;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class app {
public static void main(String[] args) {
//1. 先得到上下文对象
ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
UserController2 controller2 = context.getBean(UserController2.class);
controller2.sayHi();
}
}
3.2 构造方法注入
package com.beans;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController2 {
//使用构造方法实现 bean 注入(官方推荐写法)
private UserService userService;
@Autowired
public UserController2(UserService userService) {
// userService = new UserService(); //传统的写法
this.userService = userService;
}
public void saHi() {
userService.sayHi();
}
}
3.3 Setter注入
package com.beans;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController2 {
//3. 使用 Setter 注入
private UserService userService;
@Autowired
public void setUserService(UserService userService) {
this.userService = userService;
}
public void sayHi() {
userService.sayHi();
}
}
3.4 面试题: 三种注入优缺点分析
3.5 @Resource:另一种注入关键字
面试题: @Autowired 和 @Resource 的区别
3.6 @Bean 将一个类型的对象注入多次的问题:
解决方法
package com.beans;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
@Autowired //[属性注入/字段注入]
private User user2;
public void sayHi() {
System.out.println("User -> " + user2);
}
}
import com.beans.*;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class app {
public static void main(String[] args) {
//1. 先得到上下文对象
ApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");
UserController controller = context.getBean(UserController.class);
controller.sayHi();
}
}
package com.beans;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;
@Component
public class UserBeans {
@Bean(name = "userinfo") //[只使用一个 @Bean 是无法将对象存储到容器中]
public User user1() {
User user = new User();
user.setId(1);
user.setName("张三");
return user;
}
@Bean
public User user2() {
User user = new User();
user.setId(2);
user.setName("李四");
return user;
}
}
