Gist for "Java Build Tools, JavaScript Package Managers and Task Runners (Part 3)" blog-post.

gulpfile.js

/* File: gulpfile.js */

//import our gulp packages
var gulp  = require('gulp'),
    gutil = require('gulp-util')
    minify = require('gulp-minify')
    del = require('del');

//create a 'default' task - to be executed when 'gulp' is run from terminal. The 'default' task depends on 'clean-prod' and 'minify-js' tasks; in that order.
gulp.task('default', ['minify-js']);

//this task is responsible for deleting all files and sub-folders under the folder "/prod"; essentially cleaning the parent folder before generating minified code from "/dev".
gulp.task('clean-prod', function(){
	//log a message using "gutil".
	gutil.log('Cleaning \'prod\' folder from previously generated files.')
	
	return del([
	     //here we use a globbing pattern to match everything inside the `prod` folder
	     'src/main/resources/prod/**/*',
    ]);
});

//this task is responsible for minifying all JS files under "/dev"; with the result output in the "/prod" folder.
gulp.task('minify-js', ['clean-prod'], function() {
  //log a message using "gutil".
  gutil.log('Minifying custom JS files.')
  
  //set every ".js" file under "/dev" as source.
  gulp.src('src/main/resources/dev/**/*.js')
    .pipe(minify({
        ext:{
        	//the original source is output with a trailing "-debug.js".
        	src:'-debug.js',
        	//the minified source is output with a trailing ".js"; after minification.
            	min:'.js'
        },
        //will not output the source in the destination directory.
        noSource: 'true',
        //ignore files with the following trails:
        ignoreFiles: ['.combo.js', '-min.js', '.min.js']
    }))
    //the destination for the above implementation is defined next:
    .pipe(gulp.dest('src/main/resources/prod'));
});