Facing FileNotFoundException while accessing JSON File in classpath using java in docker containers(SprintBootApplication)

Question

I'm Facing a FileNotFoundException while loading a JSON file which is in class path of Java jar using docker containers, it is a Spring-Boot application. This JSON file is available in resource folder . I'm Able to see the JSON file in docker under ./target/classes/ path.

Resource resource = resourceLoader.getResource("classpath:folderNm/file.json");
HashMap<String, String> headerMapping = (HashMap<String, String>) parser.parse(new FileReader(resource.getFile().getAbsolutePath()));

But I get this exception:

java.io.FileNotFoundException: class path resource [folderNm/file.json] cannot be resolved to absolute file path because it does not reside in the file system: jar:file:/app.jar!/folderNm/file.json

I tried

-> resource.getFile().getPath(); -> resource.getFile().getCanonicalPath(); -> "./target/classes/folderName/fileName" (hardcoded FilePath location) -> "/app.jar!/folderNm/file.json" (hardcoded FilePath location)

InputStream inputStream = getClass().getResourceAsStream("xyz.json");
BufferedReader br = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"));
            StringBuilder responseStrBuilder = new StringBuilder();
            String inputStr;
            while ((inputStr = br.readLine()) != null)
                responseStrBuilder.append(inputStr);

none of the way above are running. Kindly Suggest a way to resolve this issue.

Answer 1

Assuming that in the maven structure (you are using maven, right?) your file is located at src/main/resources/folderName/file.json, the path you pass to getResourceAsStream should be /folderName/file.json

Actually everything is explained in javadocs:

Before delegation, an absolute resource name is constructed from the given resource name using this algorithm:

• If the name begins with a '/' ('\u002f'), then the absolute name of the resource is the portion of the name following the '/'.
• Otherwise, the absolute name is of the following form: modified_package_name/name

Where the modified_package_name is the package name of this object with '/' substituted for '.' ('\u002e').

Basically if you skip the '/' in front, it looks for the folderName inside the package of your class. Following code works fine for me:

    InputStream inputStream = StackTest.class.getResourceAsStream("/folderName/file.json");
    BufferedReader br = new BufferedReader(new InputStreamReader(inputStream, "UTF-8"));
    StringBuilder responseStrBuilder = new StringBuilder();
    String inputStr;
    while ((inputStr = br.readLine()) != null)
        responseStrBuilder.append(inputStr);
    System.out.println(responseStrBuilder.toString());

assuming I have my file.json in src/main/resources/folderName. I don't think it has anything to do with docker. Btw, I think you could make use of Apache Commons IOUtils.toString that helps turning InputStream into a String.