Springboot uses-static class to read configuration files

1 Two ways for springboot to read configuration files

属性上使用：@Value("${xxxx}")
类上使用：@ConfigurationProperties(prefix = "xxx")

2 static class read configuration file

Ideas

1 工具类增加静态属性的初始化方法init
2 创建bean对象
    - 通过@ConfigurationProperties读取配置文件
    - 通过component将bean对象注入到容器中
3 创建代理类
    - 通过component读取容器中bean对象的属性
    - 在构造方法中调用工具类静态属性的初始化方法init，从而初始化工具类的静态属性

• 1 Create a maven project GetProperties
• 2 Modify pom.xml to introduce parent/web/test dependency

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.0.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
    </dependencies>

• 3 Add the configuration file /resources/application.properties, the content is

study.theme=getProperties
study.result=true

• 4 Add startup class cn.ithzp.properties.PropertiesApplication

package cn.ithzp.properties;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class PropertiesApplication {
    public static void main(String[] args) {
        SpringApplication.run(PropertiesApplication.class);
    }
}

• 5 Core trilogy, tool class adds static variable initialization method init

package cn.ithzp.properties.util;

import cn.ithzp.properties.entity.StudyEntity;

public class StudyUtil {
    private static String theme;
    private static String result;
    public static void initStaticProperties(StudyEntity studyEntity){
        theme = studyEntity.getTheme();
        result = studyEntity.getResult();
    }
    
    public static String getStaticProperties() {
        return theme + ":" + result;
    }
}

• 6 Core trilogy, specific bean objects read configuration files

package cn.ithzp.properties.entity;

import lombok.Data;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.stereotype.Component;

@Data
@Component
@ConfigurationProperties(prefix = "study")
public class StudyEntity {
    private String theme;
    private String result;
}

• 7 The core trilogy, the initialization method of static properties of the tool class is called in the proxy class construction method

package cn.ithzp.properties.Proxy;

import cn.ithzp.properties.entity.StudyEntity;
import cn.ithzp.properties.util.StudyUtil;
import org.springframework.stereotype.Component;

@Component
public class StudyProxy {
    public StudyProxy(StudyEntity studyEntity) {
        StudyUtil.initStaticProperties(studyEntity);
    }
}

• 8 Add test category, test verification

package cn.ithzp.properties;

import cn.ithzp.properties.entity.StudyEntity;
import cn.ithzp.properties.util.StudyUtil;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@SpringBootTest(classes = {PropertiesApplication.class})
@RunWith(SpringRunner.class)
public class TestApplication {
    @Autowired
    private StudyEntity studyEntity;

    @Test
    public void test() {
        System.out.println(studyEntity);
        System.out.println(StudyUtil.getStaticProperties());
    }
}