Classpath resource not found when running as jar

Question

resource.getFile() expects the resource itself to be available on the file system, i.e. it can't be nested inside a jar file. This is why it works when you run your application in STS but doesn't work once you've built your application and run it from the executable jar. Rather than using getFile() to access the resource's contents, I'd recommend using getInputStream() instead. That'll allow you to read the resource's content regardless of where it's located.

If you're using Spring framework then reading ClassPathResource into a String is pretty simple using Spring framework's FileCopyUtils:

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);
}

If you want to use a file:

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);
}

when spring boot project running as a jar and need read some file in classpath, I implement it by below code

Resource resource = new ClassPathResource("data.sql");
BufferedReader reader = new BufferedReader(new InputStreamReader(resource.getInputStream()));
reader.lines().forEach(System.out::println);