Java on ShrimpWorks

Use Java's built-in HTTP Server for Mocking

Fri, 06 Nov 2020 00:00:00 +0000

Frequently while implementing HTTP API or other HTTP clients, you want to be able to test your client implementation against an actual HTTP service, which helps validate that your headers are set correctly, body is serialised appropriately, and responses are parsed as expected.

This can be done through the use of various additional libraries and mocking frameworks, however I’d argue that for most use cases, something that can simply validate and respond to an HTTP request is more than enough.

Run Your Java Services with SystemD

Tue, 01 Sep 2020 00:00:00 +0000

There’s a strong tendency to want to run everything in Docker these days, especially if you’re trying to run something as an always-on service, since passing --restart=always to your run invocation or Docker Compose configuration ensures that running containers start back up after reboots or failures, and seems to involve a little less “black magic” than actually configuring software to run as services directly on a host.

The downside to this is the approach is that running a service in a container leads to significantly longer startup times, more memory and CPU overhead, lost logs, and in my opinion offer a false sense of security and isolation since most images are still configured to run as root, and more often than not large swathes of the host filesystem are mounted as volumes to achieve simple tasks.

There’s also a belief that your software will magically run anywhere - but if you’re writing Java (or any JVM language) code - that’s one of Java’s biggest selling points - it already has its own VM your code is running in, no most platforms!

Therefore, let’s see how easy it actually is to configure our software to run as a standard system service, providing us with the ability to run it as a separate restricted user, complete with standard logging configuration, and give us control over via standard service myservice start|status|restart|stop commands.

Simple Java Value Objects

Sun, 11 Aug 2019 00:00:00 +0000

It’s a really simple thing, but I’ve been using this simple “pattern” for defining simple value objects for years, and it has served me well.

While there’s nothing particularly special about this style, I still see a significant amount of Java code needlessly following the JavaBeans style, when using these objects as Beans in the strict sense is not actually desired, intended, or required, and simply makes code needlessly verbose and leaves objects implemented as Beans open to abuse due to leaving their internal state open for mutation.

Image Halftone Processor

Sun, 20 Mar 2016 00:00:00 +0000

More a curiosity than an actual useful project, I just had an Idea I wanted to try out, and this is the result.

This Java application (or library, if you want to include it in your own project) simply takes a source image, a couple of optional parameters, and outputs a new image with a halftone- like effect.

Briefly, works by stepping through the pixels of the source image at an interval defined by the dot size specified, samples the brightness of that pixel, and draws a circle onto the destination image, scaled according to the source pixel brightness.

Introduction to Ant Part 4: Unit Tests with JUnit

Fri, 18 Sep 2015 08:24:28 +0000

Now that we have dependency management with Ivy working along with everything else covered before, we’ve covered almost everything required to start building real projects with Ant.

Another thing any real project should have, is unit tests. Thankfully, using the scaffolding already put in place in earlier parts of this series, integrating a JUnit testing task into our existing build script is really straight-forward.

Introduction to Ant Part 3: Dependency Management with Ivy

Fri, 07 Aug 2015 10:20:45 +0000

So far, we’ve covered the basics of creating a re-distributable .jar package suitable for use as a library, and building a Jar file which can be run by a user or server process.

A major part of any non-trivial application these days is the inclusion and re-use of 3rd party libraries which implement functionality your applications require. When a project starts, it’s probably easy enough to manually drop the odd jar library into a lib directory and forget about it, but maintaining a large application which depends on many libraries, which in turn depend on additional libraries for their own functionality, it can quickly turn into a nightmare to manage.

To solve this problem, many dependency management tools have been introduced, most notably, Apache Maven. Maven however, is so much more than just a dependency management tool, and is actually intended to manage your entire project structure. I believe however, the combination of Ant and Ivy provides far more flexibility, extensibility and control over your build and dependency management processes.

So, let’s integrate Apache Ivy into our Ant script as we left it in part 2.

Introduction to Ant Part 2: Runnable Jar File

Sat, 11 Jul 2015 10:26:27 +0000

In part 1, we went over the basics of using Ant to create a redistributable .jar file, suitable for use as a library in other projects. A lot of the time however, you’re probably going to want to be building things which can actually be run as regular Java applications.

Once again, the code for this tutorial is available in GitHub. More usefully, you may want to see the diff between the part 1 script and the new one.

Here’s a quick explanation of what we’ve done to achieve an executable jar file:

Introduction to Ant Part 1: A Basic Build

Tue, 07 Jul 2015 21:01:04 +0000

Apache Ant is a general-purpose build tool, primarily used for the building of Java applications, but it is flexible enough to be used for various tasks.

In the Java world at least, Ant seems to be largely passed over for the immediate convenience and IDE support of Maven, however long term, I believe a good set of Ant scripts offer far more flexibility and room for tweaking your build processes. The downside is that there’s a lot of stuff you need to learn and figure out and build by hand.

In this series of tutorials, I’ll try to document the process of learning I’ve gone through building and maintaining Ant build files, from the most basic of “just compile my stuff” steps to automatic generation of JavaDoc output, dependency management using Ant’s companion, Ivy, unit testing using JUnit, and integrating with some additional tools I’ve been using, such as Checkstyle and FindBugs.

For part 1 of this tutorial, I’ve created a simple Hello World library. It doesn’t have a main executable itself, the goal of this is to produce a .jar file we can include in other projects, to start our Ant script off fairly simply.

The source for this project can be found in GitHub. Here’s the breakdown of everything going on in this project:

Simple HTTP Server in Java

Tue, 17 Dec 2013 21:28:42 +0000

Some thing I’ve been using for a while, and which recently became useful at work as well, is a simple HTTP service written in plain Java with existing JRE functionality, using an HttpServer.

Here’s a simple “main()” which sets up two basic “pages”, a root (/) and one which echoes your browser’s request headers (/headers/).

public class SimpleHTTPService {

 public static void main(String[] args) throws IOException {
 HttpServer server = HttpServerProvider.provider().createHttpServer(new InetSocketAddress(8080), 0);

 server.createContext("/", new HttpHandler() {
 @Override
 public void handle(HttpExchange he) throws IOException {
 byte[] output = "Hello world!".getBytes();
 he.sendResponseHeaders(200, output.length);
 he.getResponseBody().write(output);
 }
 });

 server.createContext("/headers", new HttpHandler() {
 @Override
 public void handle(HttpExchange he) throws IOException {
 StringBuilder result = new StringBuilder("Request Headers");
 for (Entry< String, List< String>> header : he.getRequestHeaders().entrySet()) {
 result.append(String.format("%s", header.getKey()));
 for (String val : header.getValue()) {
 result.append(String.format("%s", val));
 }
 result.append("");
 }

 byte[] output = result.toString().getBytes();
 he.sendResponseHeaders(200, output.length);
 he.getResponseBody().write(output);
 }
 });

 server.setExecutor(Executors.newCachedThreadPool());

 server.start();

 System.out.println("HTTP Listening on port " + server.getAddress().getPort());
 }
}

Running this as-is will allow you to load up the URLs http://localhost:8080/ and http://localhost:8080/headers/ and see some output generated by the two registered contexts.

HTTP Utility Class for Java

Mon, 22 Apr 2013 18:42:21 +0000

Here’s a small Java class I’ve been using in loads of applications and things for a few years (it’s evolved a little over the years).

It simply exposes a few very basic HTTP methods (for HEAD, GET and POST) which all just return strings containing the web server’s response. It’s seemed pretty useful and reliable in applications large and small, so maybe it’s of some use to someone else as well.