Question

I am trying to read a text file which is set in CLASSPATH system variable. Not a user variable.

I am trying to get input stream to the file as below:

Place the directory of file (D:\myDir) in CLASSPATH and try below:

InputStream in = this.getClass().getClassLoader().getResourceAsStream("SomeTextFile.txt");
InputStream in = this.getClass().getClassLoader().getResourceAsStream("/SomeTextFile.txt");
InputStream in = this.getClass().getClassLoader().getResourceAsStream("//SomeTextFile.txt");

Place full path of file (D:\myDir\SomeTextFile.txt) in CLASSPATH and try the same above 3 lines of code.

But unfortunately NONE of them are working and I am always getting null into my InputStream in.

Answer 1

With the directory on the classpath, from a class loaded by the same classloader, you should be able to use either of:

// From ClassLoader, all paths are "absolute" already - there's no context
// from which they could be relative. Therefore you don't need a leading slash.
InputStream in = this.getClass().getClassLoader()
                                .getResourceAsStream("SomeTextFile.txt");
// From Class, the path is relative to the package of the class unless
// you include a leading slash, so if you don't want to use the current
// package, include a slash like this:
InputStream in = this.getClass().getResourceAsStream("/SomeTextFile.txt");

If those aren’t working, that suggests something else is wrong.

So for example, take this code:

package dummy;

import java.io.*;

public class Test
{
    public static void main(String[] args)
    {
        InputStream stream = Test.class.getResourceAsStream("/SomeTextFile.txt");
        System.out.println(stream != null);
        stream = Test.class.getClassLoader().getResourceAsStream("SomeTextFile.txt");
        System.out.println(stream != null);
    }
}

And this directory structure:

code
    dummy
          Test.class
txt
    SomeTextFile.txt

And then (using the Unix path separator as I’m on a Linux box):

java -classpath code:txt dummy.Test

Results:

true
true