How to parse command line arguments in Java

If you are using Eclipse, you might want to add your arguments. To specify them, go to: Run → Run Configurations ... → Arguments

args4j ¶

args4j is a small Java class library that makes it easy to parse command line options/arguments in your CUI application.

Source: args4j.kohsuke.org

Lets see how easy it really is.

Requirements ¶

First, you have to get the package. It is not in my Ubuntu-Version, but Ubuntu Quantal will have args4j. The package is called libargs4j-java.

If you can't install it this way, you have to download args4j. Currently, it is args4j-2.0.21.jar.

You can add this as an external jar to Eclipse:

Right-click on your project.
Select "Properties"
Type "java build path" in the input field at the upper left corner of the window.

Now it should look like this:

Project properties in Eclipse - Libraries

Now you have to click on "Add External Jar" and add the args4j.jar file.

Source Example ¶

As always in Java, you add another class for parsing your command line values. I've called it CommandLineValues.java and it does only check for the command line argument -i FILE or --input FILE.

import java.io.File;

import org.kohsuke.args4j.CmdLineException;
import org.kohsuke.args4j.CmdLineParser;
import org.kohsuke.args4j.Option;

/**
 * This class handles the programs arguments.
 */
public class CommandLineValues {
    @Option(name = "-i", aliases = { "--input" }, required = true,
            usage = "input file with two matrices")
    private File source;

    private boolean errorFree = false;

    public CommandLineValues(String... args) {
        CmdLineParser parser = new CmdLineParser(this);
        parser.setUsageWidth(80);
        try {
            parser.parseArgument(args);

            if (!getSource().isFile()) {
                throw new CmdLineException(parser,
                        "--input is no valid input file.");
            }

            errorFree = true;
        } catch (CmdLineException e) {
            System.err.println(e.getMessage());
            parser.printUsage(System.err);
        }
    }

    /**
     * Returns whether the parameters could be parsed without an
     * error.
     *
     * @return true if no error occurred.
     */
    public boolean isErrorFree() {
        return errorFree;
    }

    /**
     * Returns the source file.
     *
     * @return The source file.
     */
    public File getSource() {
        return source;
    }
}

Here is some part of the main file:

public static void main(String[] args) {
    CommandLineValues values = new CommandLineValues(args);
    CmdLineParser parser = new CmdLineParser(values);

    try {
        parser.parseArgument(args);
    } catch (CmdLineException e) {
        System.exit(1);
    }

    // Now you can use the command line values
    List<ArrayList<ArrayList<Integer>>> matrices =
        read(values.getSource());
    ArrayList<ArrayList<Integer>> A = matrices.get(0);
    ArrayList<ArrayList<Integer>> B = matrices.get(1);
    int[][] C = ijkAlgorithm(A, B);
    printMatrix(C);
}

Usage Examples ¶

If you do not specify the required parameters, you get a quite good error message:

moose@pc07:~/Desktop$ java -jar matrix-multiplication.jar
Option "-i (--input)" is required
 -i (--input) FILE : input file with two matrices

Help is not automatically generated:

moose@pc07:~/Desktop$ java -jar matrix-multiplication.jar --help
"--help" is not a valid option
 -i (--input) FILE : input file with two matrices

If you want to have default parameters, you simply assign the values to the attributes:

@Option(name = "-l", aliases = { "--leafsize" }, required = false,
        usage = "input file with two matrices")
private int leafsize = 32;

Note: How can I prevent Eclipse from adding the 'final' for certain lines of Java code?

Commons CLI ¶

Installation ¶

As for args4j, they offer a jar file which is in commons-cli-1.2-bin.tar.gz on the download-page.

If you just want to test if you have the required packages, copy this piece of code to Eclipse:

public class CommandLineValues {
    CommandLineParser parser = new BasicParser();
}

If you get the following error, you don't have the required org.apache.commons.cli:

Java error mentioned by Eclipse: Missing org.apache.commons.cli

Usage examples ¶

I have not found a single, complete and working usage example.

How to parse command line arguments in Java

args4j ¶

Requirements ¶

Source Example ¶

Usage Examples ¶

Commons CLI ¶

Installation ¶

Usage examples ¶

See also ¶

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