1 Use annotations
After spring 4, if you want to use the annotation form, you must introduce the aop package
org.springframework:spring-aop:5.2.0.RELEASE
In the configuration file, you have to introduce a context constraint
<?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:context="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
http://www.springframework.org/schema/context/spring-context.xsd">
</beans>
Implementation of Bean
We used bean tags for bean injection before, but in actual development, we generally use annotations!
beans.xml
1 Configure annotations under which packages are scanned
<!-- 开启注解支持-->
<context:annotation-config/>
<!--指定扫描的包，这个包下的注解就会生效-->
<context:component-scan base-package="com.zs.pojo"/>
2 Write the class under the specified package and add the annotation
User.class
package com.zs.pojo;
import org.springframework.stereotype.Component;
@Component //组件
public class User {
public String name = "zs";
}
3 How to inject attributes
package com.zs.pojo;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
@Component //组件
public class User {
@Value("zs") // 简单属性注入
public String name;
}
4 Derivative Annotations
@Component Three Derivative Annotations
In order to better layer, Spring can use other three annotations, the functions are the same, which function is the same currently.
@Controller: web layer
@Service: service layer
@Repository: dao layer
Writing these annotations is equivalent to giving this class to Spring to manage and assemble!
5 Scope
@scope
singleton: By default, Spring will create this object in singleton mode. Close the factory and all objects will be destroyed.
Prototype: Multi-example mode. Close the factory, all objects will not be destroyed. The internal garbage collection mechanism will recycle
@Component //组件
@Scope("singleton")
public class User {
@Value("zs") // 简单属性注入
public String name;
}
6 Summary
Comparison of XML and annotations
1 XML can be used in any scenario, with clear structure and easy maintenance.
2 Annotations are not self-provided classes and cannot be used. Development is simple and convenient.
XML and annotation integration development: recommended best practices
1 xml management bean
2 annotations complete attribute injection
Enable annotation support
<context:annotation-config/>
2 Configure spring using java
It does not apply to spring xml configuration at all, it is all done by java.
1 Write an entity class
package com.zs.pojo;
import lombok.Data;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Repository;
@Data
@Repository //这个注解的意思，就是说明这个类被spring接管了，注册到容器中
public class User {
@Value("zs") //属性注入值
public String name;
}
2 Create a new config configuration package
package com.zs.config;
import com.zs.pojo.User;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
@Configuration // 这个也会被spring容器托管，注册到容器中 因为它本身是一个@Component
// @Configuration代表这是一个配置类 就和我们之前看的beans.xml
@Import(UserConfig1.class) // 导入另一个配置类UserConfig1
public class UserConfig {
// 注册一个bean 就相当于我们之前写的一个bean标签
// 这个方法的名字就相当于bean标签中的id属性
// 这个方法的返回值 就相当于bean标签中的class
@Bean
public User getUser() {
return new User(); //就是返回要注入到bean的对象
}
}
3 Test category
package com.zs.test;
import com.zs.config.UserConfig;
import com.zs.pojo.User;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test {
@org.junit.Test
public void test() {
// AnnotationConfigApplicationContext 来获取容器
ApplicationContext context = new AnnotationConfigApplicationContext(UserConfig.class);
User user = (User) context.getBean("getUser");
System.out.println(user.name);
}
}
In addition
