ANTLR - Semantic Predicates

Parsing simple grammar with antlr is simple. All you have to do is to use regular expressions to describe your language and let antlr generate lexer and parser. Parsing big or complicated languages occasionally require more, because describing them in regular expressions only can be hard or even impossible.

Semantic predicates are java (or C++, or JavaScript, or ...) conditions written inside the grammar. Antlr uses them either to choose between multiple alternatives or as additional assertions to be checked. They can be placed inside both lexer and parser, but this post focus only on their usage within the parser. They add a lot of power to antlr.

Project Report - Less4j

Few months ago I decided to create java port of less.js. Less is an extension of CSS - it adds constants, mixins, ruleset nesting, namespaces and so on. Both reasons why I picked up less and short less introduction are written in introduction into less.

This report starts with current project status and its possible future directions. Second part recaps development and my experiences with used tools. Finally, the last part sums up why did I started with the project in the first place and whether it was worth it.

Travis-CI - Continuous Integration Server

Travis-CI is hosted continuous integration server for Github projects. The continuous integration part is fairly standard: it runs unit tests and report results after each project change.

The hosting part is unusual: the service runs tests on their own infrastructure and provides access to test results. The user does not need his own hardware nor to install and run the server. All that is part of the service.

Any public repository hosted on Github can use Travis-CI for free. Private repositories have to pay and the Travis Pro version they get is a bit different from the regular one.

This post is mainly about the free version. First chapter describes what Travis-CI does. Second part contains few things about Travis-CI server, infrastructure and organization behind it. Mini review with our experiences is located in the last chapter.

Tackling Comments in ANTLR Compiler

Most compilers treat comments as just another meaningless whitespaces. They identify them in the source code and then throw them away. On the other hand, things are a bit harder if you need to know comments content and their position.

Such requirement is not too common and official ANTLR documentation does not says much about how to do it. The compiler we have been working on needed to preserve comments, so we had to come up with our own solution. This post documents it.

First chapter introduces our compiler. It describes what it does, where it is located and how it is written. Second chapter explains our comment preserving requirements. The rest of the post describes datastructures and algorithms used in our solution.

Wro4j, Page Load Optimization and Less.js

Wro4j is primary a JavaScript and CSS merge and minimization library. Its original purpose was to speed up the page load. However, its final design made it easy to add integration with LESS, CoffeScript and few other technologies.

Less was introduced in previous article. In short, it is CSS with object oriented inheritance, variables and few other additional features. It is compiled into regular style sheets and served to the browser. Less was written in JavaScript and usually runs in the browser. If you want to run it on the server side, you have to use wro4j or some other integration library.

The post is mostly wro4j tutorial with focus on Less integration. It explains how wro4j works and how to configure it. There is very little about Less and almost everything is about wro4j.

Inheritance and Variables in CSS with Less

I always missed object oriented inheritance and variables in CSS. Style sheets could be much more readable and maintainable, if they would have ability to say:

• I want this selector color to be just like that one.
• I want this class to be just like that one, with one simple change.

As multiple projects run into CSS explosion and maintenance problems problems, it was only question of time until someone comes with another solution. The original solution came from the Ruby world and is quite simple and elegant:

• extend CSS with needed features,
• compile extended CSS into regular CSS,
• serve the result to the browser.

The browser does not have to deal with a new syntax. It was given standard CSS file and will process it as usually. On the other hand, the programmer had variables, inheritance and few other features available.

Stanford Free Crypto Class - Review

The free online cryptography course I attended this April was taught by Stanford professor Dan Boneh. Its infrastructure and organization are provided by coursera company.

The course was everything I expect from an university course. It explains both the theory and its practical consequences. It shows how ciphers work, how to use them, what are their limitations and why they have been designed the way they have been designed.

Secure Encryption in Java

Last time I wrote about cryptography, I outlined Apache Shiro crypto API and shown how to use its two symmetric ciphers. I also wrote that "You do not need more to encrypt and decrypt sensitive data in your applications."

I learned more about cryptography and found out that you need to know more. What I wrote is true to some extend, but unless you are careful your sensitive data may not be secure against all attackers.

Out of the box Shiro provides Blowfish-CBC and AES-CBC encryption methods and I recommended to use them. Both have been designed to protect against passive eavesdropping attacker and are good at it. Unfortunately, real attackers are more sophisticated and may break the system based on them.

Writing Eclipse Plugins Tutorial - Part 1

Eclipse is one of three most popular java development IDEs. One reason for its success is its extensibility. Writing eclipse plugins can be very fast and easy for anyone who knows what to do and already done it.

Unfortunately, doing something in Eclipse for the first time can be very time consuming and frustrating. Eclipse framework is huge, powerful and sometimes complicated. It may be difficult to figure out which features are available and how to use them.

This tutorial explains basics of all eclipse features needed to automate a simple java refactoring task. It shows how to add new items into the menu and how to analyze, modify and format java source code. It also shows how to use dialogs to communicate with users.

JPA Tutorial

Java persistent API is a specification and set of interfaces that helps with persistence of java objects into the database. It has been created after success of object relational mapping frameworks - the most popular is Hibernate.

JPA defines standard basic set of features that every object relational mapping framework should have. Almost all current O/R frameworks implement JPA specification. Of course, most of them have additional features to set them apart.

Saving/loading data with JPA is easier, faster and less error prone than writing SQL and mapping query results to objects. However, JPA does not free you from relational database understanding. And while you do not have to write SQL anymore, you have to learn JPQL which is very similar.

Running JNDI and JPA Without J2EE Container

We wanted to test some JPA code with as simple setup as possible. The plan was to use only Java and Maven, without an application server or other J2EE container.

Our JPA configuration needs two things to run successfully:

• database to store data,
• JNDI to access the database.

This post has two parts. First part shows how to use standalone JNDI and an embedded in-memory database in test. Remaining chapters explain how the solution works.

JavaScript Testing with JSTestDriver

Js-test-driver is an open source JavaScript unit tests runner written in Java. The project was started at Google and is under active development. It is available under Apache License 2.0 license.

Js-test-driver is able to run from command line and reports results to the standard output. As a result, it is possible to fully automate JavaScript tests and run them on a continuous integration server.

Additionally, js-test-driver comes with IntelliJ IDEA plugin and Eclipse plugin. Of course, Eclipse plugin is compatible with Aptana Studio. If you use one of these IDEs, you can run tests directly from IDE and see progress and results in a view. It is very similar to java jUnit plugin.