Coding a parser for a domain specific language in Java

We want to design a simple domain specific language for wri开发者_Go百科ting test scripts to automatically test a XML-based interface of one of our applications. A sample test would be:

• Get an input XML file from network shared folder or subversion repository
• Import the XML file using the interface
• Check if the import result message was successfull
• Export the XML corresponding to the object that was just imported using the interface and check if it correct.

If the domain specific language can be declarative and its statements look as close as my sentences in the sample above as possible, it will be awesome because people won't necessarily have to be programmers to understand/write/maintain the tests. Something like:

newObject = GET FILE "http://svn/repos/template1.xml"
reponseMessage = IMPORT newObject
newObjectID = GET PROPERTY '/object/id/' FROM responseMessage
(..)

But then I'm not sure how to implement a simple parser for that languange in Java. Back in school, 10 years ago, I coded a language parser using Lex and Yacc for the C language. Maybe an approach would be to use some equivalent for Java?

Or, I could give up the idea of having a declarative language and choose an XML-based language instead, which would possibly be easier to create a parser for? What approach would you recommend?

You could try JavaCC or Antlr for creating a parser for your domain specific language. If the editors of that file are not programmers, I would prefer this approach over XML.

Take a look at Xtext - it will take a grammar definition and generate a parser as well as a fully-featured eclipse editor pluging with syntax highlighting and -checking.

ANTLR should suffice

ANTLR, ANother Tool for Language Recognition, is a language tool that provides a framework for constructing recognizers, interpreters, compilers, and translators from grammatical descriptions containing actions in a variety of target languages. ANTLR provides excellent support for tree construction, tree walking, translation, error recovery, and error reporting.

Look at Antlr library. You'll have to use EBNF grammatic to describe your language and then use Antlr to make java classes from your grammatic.

Have a look at how Cucumber defines its test cases:

http://cukes.info/ - can run in JRuby.

Or, I could give up the idea of having a declarative language and choose an XML-based language instead, which would possibly be easier to create a parser for? What approach would you recommend?

1. This could be easily done using XML to describe your test scenarios.

   < GETFILE object="newObject" file="http://svn/repos/template1.xml"/ >

2. Since your example of syntax is quite simple, it should also be possible to simply use StringTokenizer to tokenize and parse these kind of scripts.

If you want to introduce more complex expressions or control structures you probably better choose ANTLR

I realize this thread is 3 years old but still feel prompted to offer my take on it. The questioner asked if Java could be used for a DSL to look as closely as possible like

Get an input XML file from network shared folder or subversion repository
Import the XML file using the interface
Check if the import result message was successfull
Export the XML corresponding to the object that was just imported
   using the interface and check if it correct.

The answer is yes it can be done, and has been done for similar needs. Many years ago I built a Java DSL framework that - with simple customization - could allow the following syntax to be used for compilable, runnable code:

file InputFile
message Message

get InputFile from http://<....>
import Message from InputFile
if validate Message export Message
else
begin
   ! Signal an error
end

In the above, the keywords file, message, get, import, validate and export are all custom keywords, each one requiring two simple classes of less than a page of code to implement their compiler and runtime functions. As each piece of functionality is completed it is dropped into the framework, where it is immediately available to do its job.

Note that this is just one possible form; the exact syntax can be freely chosen by the implementor. The system is effectively a DIY high-level assembly language, using pre-written Java classes to perform all the functional blocks, both for compiling and for the runtime. The framework defines where these bits of functionality have to be placed, and provides the necessary abstract classes and interfaces to be implemented.

The system meets the primary need of clarity, where non-programmers can easily see what's happening. Changes can be made quickly and run immediately as compilation is almost instantaneous.

Complete (open) source code is available on request. There's a generic Java version and also one for Android.