<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="//maven.apache.org/POM/4.0.0" xmlns:xsi="//www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="//maven.apache.org/POM/4.0.0 //maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.5.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.sxy</groupId>
    <artifactId>properties-read-demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>properties-read-demo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <commons.io.version>2.5</commons.io.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>

        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>${commons.io.version}</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

this.custom.config.content = 這是我的自定義配置內容

package com.sxy.propertiesreaddemo.utils;

import lombok.extern.slf4j.Slf4j;
import org.apache.commons.io.IOUtils;
import org.springframework.core.io.DefaultResourceLoader;
import org.springframework.core.io.Resource;
import org.springframework.core.io.ResourceLoader;

import java.io.IOException;
import java.io.InputStream;
import java.util.NoSuchElementException;
import java.util.Properties;

/**
 * @Description 文件載入工具類.
 *                   可載入多個properties文件,
 *                   相同的屬性在最後載入的文件中的值將會覆蓋之前的值，但以System的Property優先.
 * @Author SuXingYong
 * @Date 2020/7/11 20:55
 **/
@Slf4j
public class PropertiesLoader {

    private static ResourceLoader resourceLoader = new DefaultResourceLoader();

    private final Properties properties;

    public PropertiesLoader(String... resourcesPaths) {
        properties = loadProperties(resourcesPaths);
    }

    /**
     * @Description  取出Property，但以System的Property優先,取不到返回空字元串.
     * @Author SuXingYong
     * @Date 2020/7/11 20:55
     * @Param [key]
     * @param key 配置文件的key
     * @Return java.lang.String
     **/
    private String getValue(String key) {
        String systemProperty = System.getProperty(key);
        if (systemProperty != null) {
            return systemProperty;
        }
        if (properties.containsKey(key)) {
            return properties.getProperty(key);
        }
        return "";
    }

    /**
     * @Description 取出String類型的Property，但以System的Property優先,如果都為Null則拋出異常.
     * @Author SuXingYong
     * @Date 2020/7/11 20:55
     * @Param [key]
     * @Return java.lang.String
     **/
    public String getProperty(String key) {
        String value = getValue(key);
        if (value == null) {
            throw new NoSuchElementException();
        }
        return value;
    }

    /**
     * @Description 載入多個文件, 文件路徑使用Spring Resource格式.
     * @Author SuXingYong
     * @Date 2020/7/11 20:55
     * @Param [resourcesPaths]
     * @Return java.util.Properties
     **/
    private Properties loadProperties(String... resourcesPaths) {
        Properties props = new Properties();

        for (String location : resourcesPaths) {
            log.debug("Loading properties file from:" + location);
            InputStream is = null;
            try {
                Resource resource = resourceLoader.getResource(location);
                is = resource.getInputStream();
                props.load(is);
            } catch (IOException ex) {
                log.info("Could not load properties from path:" + location + ", " + ex.getMessage());
            } finally {
                IOUtils.closeQuietly(is);
            }
        }
        return props;
    }
}