Asked  7 Months ago    Answers:  5   Viewed   42 times

I am looking for a way to get a list of all resource names from a given classpath directory, something like a method List<String> getResourceNames (String directoryName).

For example, given a classpath directory x/y/z containing files a.html, b.html, c.html and a subdirectory d, getResourceNames("x/y/z") should return a List<String> containing the following strings:['a.html', 'b.html', 'c.html', 'd'].

It should work both for resources in filesystem and jars.

I know that I can write a quick snippet with Files, JarFiles and URLs, but I do not want to reinvent the wheel. My question is, given existing publicly available libraries, what is the quickest way to implement getResourceNames? Spring and Apache Commons stacks are both feasible.



Custom Scanner

Implement your own scanner. For example:

(limitations of this solution are mentioned in the comments)

private List<String> getResourceFiles(String path) throws IOException {
    List<String> filenames = new ArrayList<>();

    try (
            InputStream in = getResourceAsStream(path);
            BufferedReader br = new BufferedReader(new InputStreamReader(in))) {
        String resource;

        while ((resource = br.readLine()) != null) {

    return filenames;

private InputStream getResourceAsStream(String resource) {
    final InputStream in
            = getContextClassLoader().getResourceAsStream(resource);

    return in == null ? getClass().getResourceAsStream(resource) : in;

private ClassLoader getContextClassLoader() {
    return Thread.currentThread().getContextClassLoader();

Spring Framework

Use PathMatchingResourcePatternResolver from Spring Framework.

Ronmamo Reflections

The other techniques might be slow at runtime for huge CLASSPATH values. A faster solution is to use ronmamo's Reflections API, which precompiles the search at compile time.

Tuesday, June 1, 2021
answered 7 Months ago

Assuming every dict has a value key, you can write (assuming your list is named l)

[d['value'] for d in l]

If value might be missing, you can use

[d['value'] for d in l if 'value' in d]
Tuesday, June 1, 2021
answered 7 Months ago

Using a simple list comprehension (if you're sure every dictionary has the key):

In [10]: [d['key'] for d in l]
Out[10]: [1, 2, 3]

Otherwise you'll need to check for existence first:

In [11]: [d['key'] for d in l if 'key' in d]
Out[11]: [1, 2, 3]
Tuesday, June 15, 2021
answered 6 Months ago

Probably because of this bug or any of the many similar bugs in the Java bug database:

The reason is that "!/" in a jar URL is interpreted as the separator between the JAR file name and the path within the JAR itself. If a directory name ends with !, the "!/" character sequence at the end of the directory is incorrectly interpreted. In your case, you are actually trying to access a resource with the following URL:


The bug has been open for almost 12 years and is not likely to be fixed. Actually I don't know how it can be fixed without breaking other things. The problem is the design decision to use ! as a character with a special meaning (separator) in the URL scheme for JAR files:

jar:<URL for JAR file>!/<path within the JAR file>

Since the exclamation mark is an allowed character in URLs, it may occur both in the URL to the JAR file itself, as well as in the path within the JAR file, making it impossible in some cases to find the actual "!/" separator.

Friday, July 30, 2021
answered 4 Months ago

My guess is that the absolute path issue is because of the outputDirectory in the target of your maven POM . In my project the outputDirectory war/WEB-INF/classes and the it is from here the classes get executed . If I change it to some junk value , the class no longer gets executed .

So I believe the absolute path has to do something with the location of your .class files . Hope this helps .

Tuesday, August 10, 2021
answered 4 Months ago
Only authorized users can answer the question. Please sign in first, or register a free account.
Not the answer you're looking for? Browse other questions tagged :