SpringBoot stepped in when using @Value read configuration files pit

Disclaimer: This article is a blogger original article, shall not be reproduced without the bloggers allowed. https://blog.csdn.net/Mr__Viking/article/details/84558251

Recently doing some projects with spingboot, today java Bean wanted to initialize the variables to value through a configuration file variable in the time to build the project, springboot is developed based annotation Well, it took a @Value comment to inject the configuration file variable. But in this place I trod several pits, so record it, so as not to make the same mistake the next time.

1. @ Value Notes can not be injected into the static keyword modified variables above

Originally, I wanted to write a static property as a property profile, external call to the convenience, but @Value comment does not support this operation ~, online search a bit, saying that @Value comment can not be used in static variables above, I also verified behind, indeed can not be injected into a static field to the top.

2. When calling a class member properties in the no-argument constructor @Value did not work

code show as below:

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;



/**
 * Created by viking on 2018/11/26
 * 自定义配置类
 */
@Component
public class MyConfiguration {

    @Value("${config.file}")
    private String fileName;

    public MyConfiguration(){
        System.out.println("读取到的配置文件名称:"+fileName);
    }
}

application.properties configuration variables:

config.file=MyConfiguration.properties

Then look at the results when the debug:

Direct is a null value, in accordance with the initialization sequence java class, the member variable initialization is certainly in preference to the constructor, @ Value annotation does not play any role, because @Value annotations are only acting after the constructor to initialize. So call the variables in the constructor and when no value.

3. Open the right way: in the class constructor after the initialization is complete to call

When spring is here, I used @PostContruct annotation, this annotation is applied to the method, indicating that the method will be executed after the constructor method execution is completed.

Let's look at operating results:

Now there is worth it.

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