SpringBoot部署jar加载不到资源文件

jar部署的SpringBoot项目，加载项目资源文件时，异常信息提示，文件路径包含jar包，导致文件找不到
*.jar!/templates/img/logo.png

1、功能需求描述

发送邮件时，邮件内容模板中包含图片文件，图片文件加载问题

-- 图片文件路径说明
resources 
-templates
--img
---logo.png

2、问题描述

1. 在IDEA开发环境测试时，使用以下代码加载resources目录下的logo.png图片文件没有任何问题

        Map<String, FileSystemResource> filesMap = new HashMap(1);
        try {
            // 正文模板中的图片
            Resource imgResource = new ClassPathResource("templates" + File.separator + "img" + File.separator + "logo.png");
            FileSystemResource imgFile = new FileSystemResource(imgResource.getFile());
            filesMap.put("logo", imgFile);
        } catch (IOException e) {
            log.error("[MuscleapeError] the image in email template load fail");
            e.printStackTrace();
        }

2. 服务器使用的DOCKER部署生成的jar文件，运行时出现报错信息：

java.io.FileNotFoundException: class path resource [templates/img/logo.png] cannot be resolved to absolute file path because it does not reside in the file system: jar:file:/usr/local/tomcat/webapps/ROOT/WEB-INF/lib/engine-core-bll-manager-1.0.jar!/templates/img/logo.png

3、解决办法

参考：https://stackoverflow.com/questions/25869428/classpath-resource-not-found-when-running-as-jar
参考：https://www.oschina.net/question/2272552_2269641

// 第一种实现方式
String data = "";
ClassPathResource cpr = new ClassPathResource("static/file.txt");
try {
    byte[] bdata = FileCopyUtils.copyToByteArray(cpr.getInputStream());
    data = new String(bdata, StandardCharsets.UTF_8);
} catch (IOException e) {
    LOG.warn("IOException", e);
}
// =========================================================================
// 第二种实现方式
ClassPathResource classPathResource = new ClassPathResource("static/something.txt");

InputStream inputStream = classPathResource.getInputStream();
File somethingFile = File.createTempFile("test", ".txt");
try {
    FileUtils.copyInputStreamToFile(inputStream, somethingFile);
} finally {
    IOUtils.closeQuietly(inputStream);
}
// =========================================================================
// 第三种实现方式
       Resource[] resources;

        try {
            resources = ResourcePatternUtils.getResourcePatternResolver(resourceLoader).getResources("classpath:" + location + "/*.json");
            for (int i = 0; i < resources.length; i++) {
                try {
                InputStream is = resources[i].getInputStream();
                byte[] encoded = IOUtils.toByteArray(is);
                String content = new String(encoded, Charset.forName("UTF-8"));
                }
            }
        } catch (IOException e) {
            throw new UncheckedIOException(e);
        }

根据以上第二种实现方法，改造问题代码为：

        Map<String, FileSystemResource> filesMap = new HashMap(1);
        ClassPathResource imgResource = new ClassPathResource("templates" + File.separator + "img" + File.separator + "logo.png");
        try (InputStream inputStream = imgResource.getInputStream()) {
            // 正文模板中的图片
            File imageFile = File.createTempFile("logo", ".png");
            FileUtils.copyInputStreamToFile(inputStream, imageFile);
            FileSystemResource imgFile = new FileSystemResource(imageFile);

            filesMap.put("logo", imgFile);
        } catch (IOException e) {
            log.error("[MuscleapeError] the image in email template load fail");
            e.printStackTrace();
        }