Apache CLI, Executable jar, classLoader().getResource()

Question

My goal is to use Apache CLI with an executable jar file to read in a text file, perform string manipulations, and then write to a CSV. You would execute the tool in the terminal like this:

$ java -jar my-tool-with-dependencies.jar -i input.txt -o output.csv

I've written tests for this functionality and those tests are passing. The test input text file is located in src/test/resources/. The following test is passing:

@Test
public void testWordockerWriteCsvFileContents() {
// Make sure the csv file contains contents
Wordocker w = new Wordocker();
String intext = "/textformat/example_format.txt";
String outcsv = "/tmp/foo.csv";
w.writeCsvFile(intext, outcsv);
try {
Reader in = new FileReader(outcsv);
Iterable<CSVRecord> records = CSVFormat.DEFAULT.parse(in);
for (CSVRecord record : records) {
 assertTrue(record.toString().length() > 0);
}
} catch(FileNotFoundException e){
 assertTrue(false);
} catch(IOException e) {
 assertTrue(false);
}
File file = new File(outcsv);
if (file.exists()) {
 file.delete();
}
}

We I compile my jar files with dependencies using mvn clean compile assembly:single then I raise the following FileNotFoundException:

 // Get file from resources folder
 URL resourceURL = ParseDoc.class.getClassLoader().getResource(fileName);
 if (resourceURL == null) {
 throw new FileNotFoundException(fileName + " not found");
 }
 file = new File(resourceURL.getFile());

This leads me to believe that there is an issue with where ParseDoc.class.getClassLoader().getResource(fileName); is looking for the file. I'm aware of related questions which have been asked. Related questions are the following:

• Strange behavior of Class.getResource() and ClassLoader.getResource() in executable jar
• What is the difference between Class.getResource() and ClassLoader.getResource()?
• MyClass.class.getClassLoader().getResource("").getPath() throws NullPointerException
• this.getClass().getClassLoader().getResource("...") and NullPointerException
• getResourceAsStream returns null

None of these questions appear to ask about how to use an executable jar with Apache CLI. I think the basic issue is that the filepath given by my command line argument cannot be found by URL resourceURL = ParseDoc.class.getClassLoader().getResource(fileName);.

Please let me know what you think. Thank you for your time.

• centic: Why are you not using FileReader as in your tests? GetResource only finds files that are packaged within the jar-file, is this what you are trying to do?
• Tyler: definitely not, it sounds like FileReader would be the thing to do.

Answer 1

I'm posting this as answer as well after discussion via comments:

Classloader.getResource() is only fetching files that are packaged as part of the Jar-file or located in the classpath-folders.

For reading a normal file you would use something like your first example, i.e. FileReader or FileInputStream or simply pass a java.io.File depending on what the library that you are trying to use supports.