Refactoring and Rewritting Git History

This blog is about refactoring the codes of Blink and usage of some Git commands which helps to manipulate already committed codes, more specifically git rebase and git commit --amend.

Refactoring

My goal is to refactor the codes so that it becomes more maintainable. Currently, the code base of Blink is organized into following modules-

• App.java : Entry point of the application
• Environment.java: Responsible for maintaining environmental variables
• CliParser.java: Responsible for constructing command line argument and parsing arguments
• FileParser.java: Responsible for parsing files
• Checker.java: Responsible for checking URLs
• Writer.java: Provides functionality to write to file
• HttpStatusToText.java: Maps HTTP status code to descriptive text e.g. 200 maps to GOOD.
• PrintColor.java: Stores color configuration and attach colors to HTTP codes e.g. 200 has color green.
• UrlStatus.java: Stores information about an URL.
• UrlPrinter.java: Stores configuration for printing an URL to screen.

Each of the classes has a specific responsibility and the classes are small. However, I noticed there is a bug in the extractAllVariables() function.

// extracts all variables
  public static void extractAllVariables() {
    cliColor = Integer.parseInt(System.getenv("CLICOLOR"))==1?true:false;
  }

There can be NullPointerException if the CLICOLOR environmental variable is not set. So, I added a null pointer check.

Loose coupling of CliParser

I implemented CliParser using Apache Commons CLI. My App class was interacting directly with the implementation. I think this is bad. For any reason, if I need to change the implementation of my cli parser, I also need to make change to my App class. My App should rather interact with an interface so that it doesn’t need to know anything about the implementation of cli parser. For this, I created an interface CliParser which provides some methods that will be used by the application.

  public interface CliParser {
      void registerCliOption(CliOption option);
      void defineCliOptionWithArgument(CliOption option);
      void defineCliGroupOption(CliOption... options);
      void parse(String[] args);
      boolean isCliOptionSet(CliOption option);
      String getCliOptionArgValue(CliOption option);
      void printHelp();
  }

I created CliParserImpl class which implements the interface using the Apache Commons CLI. Now, if I need to change my implementation for example if I want use different library, I can easily do that. The implementation must implement the interface and my application is interacting with the interface. This is more maintainable.

Removing dead code

In some of my classes, there were some unused codes. I removed those to clean things up.

Working with Git History

All my refactoring work was done in a feature branch called refactoring. I made total 3 commits. But at the end all those commits were for the same purpose- to refactor codes. So, instead of having 3 different commits, I have put them together in a single commit. This keeps git history nice and clean. To combine multiple commits into one, we can use git rebase --interactive command. After combining my commits looks like below-

The commit shows all three commit messages from three commits. We can further clean it up by just putting one commit message in stead of three. git commit --amend is the command for this. This lets us edit the commit message. After modification my commit looks like below-

Next, I merged the refactoring branch to the master branch and pushed it to the remote server.