Apache Common CLI - handling arguments in java

In this blog we will see how we can use Apache Common CLI (open source) to easily read the arguments passed to the Java program easily.

Use Case

• In Enterprise when building java that takes arguments and perform some business logic. We can use the Apache common CLI to minimize lots of manual codes.

• I have used shell script to pass the argument to the java main class which is executes on schedule set in the crontab on Linux VM.

  • For demonstration purpose we use the Linux command that list the flies from the current directory ls -lrt on the below java program, -lrt is know as options or switch.

  • Here we will use similar options, in the java program. We will pass the input as java program arguments.

Add the Apache Common CLI dependencies

<dependency>
    <groupId>commons-cli</groupId>
    <artifactId>commons-cli</artifactId>
    <version>1.5.0</version>
</dependency>

Java program that uses the CLI library methods

• Lets create a simple class using the CLI libraries.
  • The Options object is used to define the requires arguments, which can be easily understood from the below code.
  • We will also be using HelpFormatter to display the added options and its description as help command.

package com.demo.cli;

import org.apache.commons.cli.CommandLine;
import org.apache.commons.cli.CommandLineParser;
import org.apache.commons.cli.DefaultParser;
import org.apache.commons.cli.HelpFormatter;
import org.apache.commons.cli.Option;
import org.apache.commons.cli.Options;
import org.apache.commons.cli.ParseException;

public class SimpleMain {

    private static String input;
    private static boolean l;
    private static boolean r;
    private static boolean t;

    public static void main(String[] args) {
        CommandLineParser parser = new DefaultParser();

        // create the Options
        Options options = new Options();
        options.addOption("i","input",true,"pass input value to argument");
        options.addOption("l","list",false,"use long list formatting");
        options.addOption("r","reverse",false,"reverse order while sorting");
        options.addOption("t",false,"Sort by modification time");
        options.addOption("h","help",false,"help for option");
        // Alternate way to create the options using the builder pattern
        options.addOption(Option.builder("s").longOpt("size")
                                        .desc("print allocated size of each file")
                                        .hasArg(false)
                                        .build());
        options.addOption(Option.builder("S").longOpt("sort")
                .desc("sort by file size")
                .hasArg(false)
                .build());

        // if we need to test some of the arguments from the java class we can pass
        // String[] cmdArgs = new String[]{ "--input=10" };

        // used to print the help using the CLI jar
        HelpFormatter formatter = new HelpFormatter();

        try {
            // parse the command line arguments
            // passing the java arguments directly
            CommandLine line = parser.parse(options, args);

            // validate that input is set
            if(line.hasOption("i") || line.hasOption("input")) {
                System.out.println("printing input :- "+line.getOptionValue("input"));

                //Fetch the value from the arguments
                input = line.getOptionValue("input");
            }
            if(line.hasOption("h") || line.hasOption("help")) {
                formatter.printHelp("help", options);
            }

            if(line.hasOption("l") || line.hasOption("list")) {
                l=true;
            }
            if(line.hasOption("r") || line.hasOption("reverse")) {
                r=true;
            }
            if(line.hasOption("t")) {
                t=true;
            }
            // using the passed value to print the value, we can use this to perform business logic
            if(r) {System.out.println("reverse passed");}
            if(l) {System.out.println("list passed");}
            if(t) {System.out.println("time passed");}
        }
        catch (ParseException exp) {
            System.out.println("Unexpected exception:" + exp.getMessage());
        }
    }

Output of the program for different program argument

• using --help or -h as arguments to the java main class will print output as below

 $ java SimpleMain --help
usage: help
 -h,--help          help for option
 -i,--input <arg>   pass input value to argument
 -l,--list          use long list formatting
 -r,--reverse       reverse order while sorting
 -s,--size          print allocated size of each file
 -S,--sort          sort by file size
 -t                 Sort by modification time

• Using -i or --input along with -lrt will display the output like below

  $ java SimpleMain -i=10000 -lrt
  1000
  reverse passed
  list passed
  time passed