How to specify the value of the configuration properties file in Springboot

test.number=123456789

package com.test.webflux.util; 
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.util.StringUtils; 
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Properties;
 
/**
 * 配置文件读取
 *
 * @Author: JCccc
 * @Des: ElegantDay
 */
public class PropertiesUtil { 
    private static Logger log = LoggerFactory.getLogger(PropertiesUtil.class);
    private static Properties props;
//项目根目录文件夹内读取
        // static {
        //     if (props == null) {
        //         props = new Properties();
        //         try {
        //             props.load(new FileInputStream("/testDemo/config/test_config.properties"));
        //         } catch (IOException e) {
        //             log.error("配置文件读取异常", e);
        //         }
        //     }
        // }
 
//resource文件夹内读取
       static {
           String fileName = "test_config.properties";
           props = new Properties();
           try {
               props.load(new InputStreamReader(PropertiesUtil.class.getClassLoader().getResourceAsStream(fileName), "UTF-8"));
           } catch (IOException e) {
               log.error("配置文件读取异常", e);
           }
       }
    /**
     * 根据配置文件中的key获取value
     * @param key
     * @return
     */
    public static String getProperty(String key) {
        String value = props.getProperty(key.trim());
        if (StringUtils.isEmpty(value)) {
            return null;
        }
        return value.trim();
    }
    /**
     * 根据配置文件中的key获取value (当获取不到值赋予默认值)
     * @param key
     * @param defaultValue
     * @return
     */
    public static String getProperty(String key, String defaultValue) {
        String value = props.getProperty(key.trim());
        if (StringUtils.isEmpty(value)) {
            value = defaultValue;
        }
        return value.trim();
    }
    public static void main(String[] args) {
        System.out.println("配置文件中有key&value："+PropertiesUtil.getProperty("test.number"));
        System.out.println("配置文件无有key&value，赋予默认值"+PropertiesUtil.getProperty("test.numberNone","默认值 JCccc"));
    }
}