How do I get a Java resource as a File?

Question

I have to read a file containing a list of strings. I'm trying to follow the advice in this post. Both solutions require using FileUtils.readLines, but use a String, not a File as the parameter.

Set<String> lines = new HashSet<String>(FileUtils.readLines("foo.txt"));

I need a File.

This post would be my question, except the OP was dissuaded from using files entirely. I need a file if I want to use the Apache method, which is the my preferred solution to my initial problem.

My file is small (a hundred lines or so) and a singleton per program instance, so I do not need to worry about having another copy of the file in memory. Therefore I could use more basic methods to read the file, but so far it looks like FileUtils.readLines could be much cleaner. How do I go from resource to file.

Answer 1

Apache Commons-IO has an IOUtils class as well as a FileUtils, which includes a readLines method similar to the one in FileUtils.

So you can use getResourceAsStream or getSystemResourceAsStream and pass the result of that to IOUtils.readLines to get a List<String> of the contents of your file:

List<String> myLines = IOUtils.readLines(ClassLoader.getSystemResourceAsStream("my_data_file.txt"));

Answer 2

I am assuming the file you want to read is a true resource on your classpath, and not simply some arbitrary file you could just access via new File("path_to_file");.

Try the following using ClassLoader, where resource is a String representation of the path to your resource file in your class path.

Valid String values for resource can include:

• "foo.txt"
• "com/company/bar.txt"
• "com\\company\\bar.txt"
• "\\com\\company\\bar.txt"

and path is not limited to com.company

Relevant code to get a File not in a JAR:

File file = null;

try {

    URL url = null;
    ClassLoader classLoader = {YourClass}.class.getClassLoader(); 

    if (classLoader != null) {

        url = classLoader.getResource(resource);
    }

    if (url == null) {

        url = ClassLoader.getSystemResource(resource);
    }

    if (url != null) {

        try {

            file = new File(url.toURI());

        } catch (URISyntaxException e) {

            file = new File(url.getPath());
        }
    }

} catch (Exception ex) { /* handle it */ }

// file may be null

Alternately, if your resource is in a JAR, you will have to use Class.getResourceAsStream(resource); and cycle through the file using a BufferedReader to simulate the call to readLines().