Java Joyless

27 January 2021

Mr Haki has a Java Joy article about transforming a stream of strings into a map using functional Java. I’m having a bit of trouble embracing it enthusiastically, since each example is 81 lines of Java code and a pointy pile of type declarations!

I dashed out the same functionality in 4 lines of Clojure, and I can understand it a whole lot easier. I’m not even sure this is the fewest forms, but it’s still nicer.

    ["language" "clojure" "username" "john"]
    (partition 2)
    (reduce (fn [m [k v]] (assoc m k v)) {}))
  ;; => {"language" "clojure", "username" "john"}

Update 2021-04-14: It can be done in one line of Clojure.

  (apply hash-map ["language" "clojure" "username" "john"])
  ;; => {"language" "clojure", "username" "john"}

Written with Clojure 1.10.2.

Missing Classes in IDEA

25 November 2019

I use InteliJ IDEA for work when working on Java code. When the IDE doesn’t work, though, it’s incredibly distracting.

I had a problem where IDEA would not find a few auxiliary classes in my application. It would highlight them as errors in imports, and the search would find the source file, but technically not the class definition. I’d poke at the problem over a couple weeks, but I’d otherwise ignore it most the time until it seemed to be losing more and more of my classes, some of which I was actively modifying.

Re-importing the project’s Maven build didn’t fix it; re-cloning a brand new project didn’t fix it; and re-installing IDEA didn’t even work. Finally, I found IDEA’s config directories, and wiped those out to start over, and that cleared up the problem: I was able to find all my classes again.

Quick and Easy Groovy for the Web

22 June 2011

Groovy can be used pretty easily to spin up some simple web pages in almost the same way one would hack out some PHP or JSP without going to the trouble to do an all-out Grails project.

The Groovy Servlet allows you to pack up the groovy-all-*.jar, a simple web.xml, and whatever *.groovy scripts you want and deploy it right into Tomcat as a plain WAR file. The Groovy Servlet page

Here's a bit of a script I put together to jump start a simple Groovlet project by packaging a WAR file from a directory of scripts. This isn't Groovy Servlet code itself, but just a command-line tool. (The Groovy Servlet page linked previously has examples for writing your own servlets.) This script will copy in the Groovy JAR and generate the basic web.xml to wire up the GroovyServlet to dynamically execute your scripts. I also have a downloadable copy of package_groovlet.groovy.

#!/usr/bin/env groovy

if (args.size() < 1) {
    print """\
        |Usage: package_groovlet.groovy <war-name>
        |Package the current directory into a Groovy Servlet war.

def war = args[0]
def embed = "${System.getenv()['GROOVY_HOME']}/embeddable"

def ant = new AntBuilder()

ant.sequential {
    delete(dir: 'build')
    mkdir(dir: 'build/WEB-INF/lib')
    copy(toDir: 'build/WEB-INF/lib') {
        fileset(dir: embed) {
            include(name: 'groovy-all-*.jar')
    copy(toDir: 'build') {
        fileset(dir: '.') {
            exclude(name: 'build/**')

new FileOutputStream('build/WEB-INF/web.xml').withWriter { webxml ->
    webxml.print """\
        <!DOCTYPE web-app PUBLIC
          "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
          "" >

ant.jar(destfile: "build/${war}", basedir: 'build')
println "Created build/${war}"

A Groovy First Monday

22 September 2010

The new K-Prep website is implemented in Grails now, so I was looking for a Groovy way to let the computer do the heavy lifting of figuring out dates for each week (starting with the first Monday) of the school year and matching them to a list of themes.

I got the algorithm working in about 8 lines of Groovy code, and then generalized it a bit more for you here to allow you to ask for any day of any week of any month. e.g. 3rd Wednesday in December.

To get the date for the 3rd Wednesday in December, my call looks like this:

dayByWeek(2010, DECEMBER, 2, WEDNESDAY, 0)

And the implementation looks like this:

import static java.util.Calendar.*

def dayByWeek = { year, month, week, day, shift ->
    def c = Calendar.instance
    c.minimalDaysInFirstWeek = c.firstDayOfWeek + 7 - day
    c[YEAR] = year
    c[MONTH] = month
    c[WEEK_OF_MONTH] = week + 1 + (shift?:0)
    c[DAY_OF_WEEK] = day

The shift parameter allows me to optionally start a theme on the previous week in cases where that day is the end of the previous month. The static import allows me to conveniently refer to the Calendar constants without qualifying them, and finally, setting the minimalDaysInFirstWeek allows days early or late in the week to still be found when the Calendar would have otherwise preferred a longer week to start searching.

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