通过之前的学习,我们也能够实现基本的 Spring 读取和存储对象操作,感觉有点麻烦,接下来, 更简单的存储和读取对象的核心就是使用注解
1 存储 Bean 对象
1.1 配置扫描路径(重要)
先把依赖文件导入pom.xml:
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>5.2.3.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
<version>5.2.3.RELEASE</version>
</dependency>
</dependencies>
接下来写入配置文件,名字最好起的有意义
把这串类容粘贴进去:
<?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">
<!-- 配置 Spring 扫描的根路径（此根路径下的所有 Spring 存对象的注解才能生效） -->
<content:component-scan base-package="beans"></content:component-scan>
</beans>
1.2 添加注解存储 Bean 对象
有两种注解类型可以实现:
1.2.1 类注解
① @Controller(控制器存储)
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
public void sayHi(String name){
System.out.println("hello: "+name);
}
}
后面解释原因.
② @Service(服务存储)
import org.springframework.stereotype.Service;
@Service
public class UserService {
public void sayHi(String name){
System.out.println("hello: "+name);
}
}
③ @Repository(仓库存储)
import org.springframework.stereotype.Repository;
@Repository
public class UserRepository {
public void sayHi(String name){
System.out.println("hello: "+name);
}
}
④ Configuration(配置存储)
import org.springframework.context.annotation.Configuration;
@Configuration
public class UserConfiguration {
public void sayHi(String name){
System.out.println("hello: "+name);
}
}
⑤ Component(组件存储)
import org.springframework.stereotype.Component;
@Component
public class UserComponent {
public void sayHi(String name){
System.out.println("hello: "+name);
}
}
测试读取 bean 的代码
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");
//Controller
UserController userController = context.getBean("userController",UserController.class);
userController.sayHi("Controller");
//Service
UserService userService = context.getBean("userService",UserService.class);
userService.sayHi("Service");
//Repository
UserRepository userRepository = context.getBean("userRepository",UserRepository.class);
userRepository.sayHi("Repository");
//Configuration
UserConfiguration userConfiguration = context.getBean("userConfiguration",UserConfiguration.class);
userConfiguration.sayHi("Configuration");
//Component
UserComponent userComponent = context.getBean("userComponent",UserComponent.class);
userComponent.sayHi("Component");
}
}
注意事项
为什么需要这么多类注解?
让代码的可读性更高,能够让程序员能够直观的判断当前类的用途
程序的⼯程分层，调⽤流程如下：
类注解之间的关系
查看 @Controller/@Service/@Repository/@Configuration等注解的源码发现:
这几个注解都有一个注解@Component,说明了它们本身就是属于@Component的"子类"
1.2.2 @Bean(方法注解)
类注解是添加到某个类上的，⽽⽅法注解是放到某个⽅法上的，如以下代码的实现:
先创建一个User类:
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;
}
}
在创一个UserBean:
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;
@Component
public class UserBean {
@Bean
public User user(){
User user = new User();
user.setId(1);
user.setName("张三");
return user;
}
}
测试读取的内容:
import beans.User;
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");
User user = context.getBean("user",User.class);
System.out.println(user.toString());
}
}
如果不加类注解:
方法重命名
可以通过设置 name 属性给 Bean 对象进⾏重命名操作，如下代码所示:
他也可以重命名多个:
2. 获取 Bean 对象(对象装配)
获取 bean 对象也叫做对象装配，是把对象取出来放到某个类中，有时候也叫对象注⼊
对象注入(对象装配)[从容器中将对象读取出来]三种方式:
- 属性注入(字段注入)
- 构造方法注入
- Setter注入
2.1 属性注入
属性注入使用 @Autowired 实现的,我们来将 Service 类注入到 Controller 类中:
Service:
import org.springframework.stereotype.Service;
@Service
public class UserService {
public void sayHi(){
System.out.println("hello,Service!");
}
}
Controller:
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
@Autowired
private UserService userService;
public void sayHi(){
userService.sayHi();
}
}
App启动:
import beans.UserController;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class App2 {
public static void main(String[] args) {
ApplicationContext context =
new ClassPathXmlApplicationContext("spring-config.xml");
UserController userController = context.getBean(UserController.class);
userController.sayHi();
}
}
2.2 构造方法注入
构造⽅法注⼊是在类的构造⽅法中实现注⼊
2.3 Setter注入
Setter 注⼊和属性的 Setter ⽅法实现类似，只不过在设置 set ⽅法的时候需要加上 @Autowired 注解
三种注入优缺点分析
2.4 @Resource: 另一种注入关键字
在进⾏类注⼊时，除了可以使⽤ @Autowired 关键字之外，我们还可以使⽤ @Resource 进⾏注⼊,注意一点的是,@Resource 无法进行构造方法注入
属性注入:
Setter注入:
构造方法注入就不行:
@Autowired 和 @Resource 的区别
同一个类型多个 @Bean 报错
报错的原因就是非唯一的 Bean 对象
解决办法: