~lunasspecto on TTBP

16 august 2018

I thought I'd try something a little unusual for what I do here and share some code. This isn't great or useful code. It's actually beginner code, in a sense. I'm used to C, C++, Python, and Bash scripting, but I've known so many people who habitually write in Java and today I decided to have an earnest go at it. This little Java program is supposed to immitate the functionality of cat, a standard utility on Unix-like systems that simply outputs text either from the files named as command line arguments, or from the standard input. (If you need a reference for these terms, I recommend ~brennen's friendly guide on the subject.)

// I only use Apache Commons CLI here instead of args because I
// thought I was going to add a help option, but I haven't
// bothered yet
import org.apache.commons.cli.Options;
import org.apache.commons.cli.CommandLineParser;
import org.apache.commons.cli.DefaultParser;
import org.apache.commons.cli.CommandLine;
import org.apache.commons.cli.ParseException;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;

class CatApp {
  public static void processBuffer(BufferedReader in) {
    while (true) {
      try {
        String line = in.readLine();
        if (line == null){
          break;
        }
        System.out.println(line);
      } catch (java.io.IOException e) {
        break;
      }
    }
  }
  public static void main(String[] args) {
    // Parse command line arguments
    Options options = new Options();
    CommandLineParser parser = new DefaultParser();
    CommandLine cl;
    try {
      cl = parser.parse(options, args);
    } catch (ParseException e) {
      System.err.println(e.getMessage());
      return;
    }
    List<String> filenames = cl.getArgList();

    if (filenames.size() > 0) {
      // Attempt to read files to stdout if filenames were supplied
      // on the command line.
      List<FileReader> files = new ArrayList<FileReader>();
      // Iterate over filenames, trying to open a FileReader for each
      for(String filename : filenames){
        try {
          files.add(new FileReader(filename));
        } catch (FileNotFoundException e) {
          System.err.println("Invalid filename " + filename);
          return;
        }
      }
      for (FileReader file : files)
      {
        processBuffer(new BufferedReader(file));
      }
    } else {
      // If no filenames were supplied on the command line, read from
      // the standard input instead.
      processBuffer(new BufferedReader(new InputStreamReader(System.in)));
    }
  }
}

I don't know if I'm going to do more in Java anytime soon. My coworkers thought it was funny that I'd try it, as they have an aversion to using the language, probably because it doesn't fit so well into their workflows which center mostly on automation with Python and Ansible. Also, in the end, because I invoked a third-party library, the .class file I compile from this can only be run in the Java VM if I specify the location of the Apache Commons CLI classes, and most of the solutions for packaging the app in such a way that an end-user can run it without doing this are a little more involved than, say, just distributing a Python app with import statements in it.

Attending my first professional conference tomorrow. This will require actually going into the city, which I rarely do. But I'm just there as a student/intern attendee, so I guess I can relax and try to enjoy myself.

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~lunasspecto@TTBP

16 august 2018