Java™ Application Development on Linux - Dator

216Chapter 9Ant: An Introduction9.2THE NEED FOR A DIFFERENT BUILD TOOLJames Duncan Davidson had a problem. Perhaps you’ve had this problem, too.It has to do with the building of software—compiling, copying, and otherwisemodifying files to get all the pieces in all the right places for running a collectionof programs.There are a number of ways to automate the building of software. You canscript the compilation using shell scripts or batch jobs. That works fine, butthere are two problems with that solution. First, scripts are generally notportable across very different operating systems. That’s a serious problem for alanguage like Java, which is intended to be portable across operating systems.Second, it is difficult if not impossible, using scripting languages, to preventwasted compiles; the checking and comparing of date stamps on source andobject files makes scripts large and difficult to maintain.Very well, we hear you say. There’s make. The make program has beenaround for a long time. It is available on many operating systems. It handlesthe conditional compilation of files very well. It has been around for centuries(it seems). It is well known and widely used. All of this is true, but even thisvenerable tool falls a bit short in the Java world. First of all, although makefilesare generally far more portable than other scripts, there are still considerablevariations in details, and make does nothing to mask the differences in file,path, and disk designations that exist across operating systems. Moreover, bothmake and scripts suffer from a more basic problem. Although Java programscan execute reasonably quickly, the overhead of starting a JVM and tearing itdown again is considerable. Since javac is written in Java, each time it is invokedto compile a source file (one file at a time is the make way) this setupand teardown time cost is paid.But, we once more hear you protest, you can just use javac on the entireproject! Doesn’t it build everything that needs to be built? In the simplest case,yes, it does. But as soon as you share code between projects, or use RMI whichrequires execution of the rmic compiler, or use EJBs, or link in native methods,then javac’s dependency resolution just will not work.Luckily, James Duncan Davidson had this problem. And luckily it reallybothered him. And even more luckily for us all, he decided to share his solution.