On the Execution Sequence of @ Value and @ Bean
- 2021-09-16 07:03:12
- OfStack
Problem description
Using @ Autowired to process multiple bean of the same type, there is a problem with the execution order of @ Value and @ Bean.
First, use scan package + annotation to register different bean of User type, which are user and user1 respectively. The registration method is as follows
package com.fanyinhang.bean;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
/**
* @author fanyinhang
* @version 1.0
* @create 2019/10/8-19:11
*/
@NoArgsConstructor
@Data
@AllArgsConstructor
@Component
public class User {
private Integer id;
private String name;
}
In this way, bean named user of User type is obtained
package com.fanyinhang.config;
import com.fanyinhang.bean.User;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan(value={"com.fanyinhang.dao"})
public class AnnotationConfig {
@Bean()
public User user1(){
return new User(2," Li 4");
}
}
The UserDao configuration is as follows:
package com.fanyinhang.dao;
import com.fanyinhang.bean.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;
/**
* @author fanyinhang
* @version 1.0
* @create 2019/10/8-19:17
*/
@Repository
public class UserDao {
@Autowired()
private User user1;
@Override
public String toString() {
return "UserDao{" +
"user1=" + user1 +
'}';
}
}
import com.fanyinhang.config.AnnotationConfig;
import com.fanyinhang.dao.UserDao;
import org.junit.Test;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
/**
* @author fanyinhang
* @version 1.0
* @create 2019/10/8-19:18
*/
public class Test3 {
@Test
public void testAutowired(){
AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AnnotationConfig.class);
UserDao userDao = context.getBean(UserDao.class);
System.out.println(userDao);
}
}
The output is as follows:
UserDao {user1=User (id=2, name=Li 4)}
No problem without @ Value annotation, but after @ Value is added,
package com.fanyinhang.bean;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
/**
* @author fanyinhang
* @version 1.0
* @create 2019/10/8-19:11
*/
@NoArgsConstructor
@Data
@AllArgsConstructor
@Component
public class User {
@Value("1")
private Integer id;
@Value(" Zhang 3")
private String name;
}
After running the testWired method again,
The result output is as follows:
UserDao {user1=User (id=1, name=Zhang 3)}
Why is this happening?
At first, I couldn't figure it out. Most of the information on the Internet said that @ Bean and @ Value had the order of execution.
To verify this statement, do a comparative test
One @ Value ("Zhang 3") has been removed
package com.fanyinhang.bean;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
/**
* @author fanyinhang
* @version 1.0
* @create 2019/10/8-19:11
*/
@NoArgsConstructor
@Data
@AllArgsConstructor
@Component
public class User {
@Value("1")
private Integer id;
//@Value(" Zhang 3")
private String name;
}
The result output is as follows:
UserDao {user1=User (id=1, name=Li 4)}
Causes of the problem
When @ Value and @ Bean are under different files, @ Bean executes before @ Value. This will invalidate the value injected by @ Bean.
Solution
When @ Value and @ Bean are under different files, @ Value executes before @ Bean, so I made the following settings
Remove the @ Value annotation under User. java and place the @ Value annotation under the @ bean same file
package com.fanyinhang.bean;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.stereotype.Component;
/**
* @author fanyinhang
* @version 1.0
* @create 2019/10/8-19:11
*/
@NoArgsConstructor
@Data
@AllArgsConstructor
@Component
public class User {
private Integer id;
private String name;
}
package com.fanyinhang.config;
import com.fanyinhang.bean.User;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan(value={"com.fanyinhang.dao"})
public class AnnotationConfig {
@Bean()
public User user1(@Value("1") Integer id,@Value(" Zhang 3") String name){
return new User(2," Li 4");
}
}
At this time, run the test mode again, and the output result is as follows:
UserDao {user1=User (id=2, name=Li 4)}