In my current project, I need to compile java code at runtime (in the background to process input from the user). This works fine with tools.jar in the classpath. However, not all users of my program have JDK installed on their system. Some of them only have JRE and in that case there is no java compiler available at runtime. I can solve that problem by including tools.jar from Sun as a part of my tool.
But tools.jar is very big (>12 MB). The problem is that I have to include the large jar file, although I am interested only in a small fraction of the functionality provided by this jar.
Is it possible to break up the tools.jar file so that I have a small subset of classes that are required for compiling java code only?
Is this illegal?
Thanks a lot.
The eclise compiler is only 1.6 MB and should work without eclipse. You can download it here. Also it looks like it implements the JavaCompiler api.
It is licensed under the eclipse public licence so including it in your own aplication should be no problem.
I don't think it would be possible to breakup tools.jar, And also it should not be legal to include tools.jar.
Check http://forums.sun.com/thread.jspa?threadID=5161541
You could look for some 3rd party Java Compiler and change your code to use same.
GCJ, a part of gcc which compiles C, Fortran, Pascal and other programming languages besides Java. It can also generate native code using the back-end of gcc. http://en.wikipedia.org/wiki/GNU_Compiler_for_Java
ECJ, the Eclipse Compiler for Java, is an open source incremental compiler used by the Eclipse JDT.
http://en.wikipedia.org/wiki/Jikes (This one doesn't support Java 6 and limited support for Java5)
But I don't know exact code for compiling using these.
Probably a better question is why?
If you need to do dynamic math calculations, then consider JEval. If you need people to write simple plugins, consider some of the dynamic languages like Javascript or Python that @Jay mentioned.
For anything else, you should require that your user download the JDK, since thats what writing Java requires. It would be hard to find a good reason why you would want to embed a compiler into your program
Instead of compiling code at runtime, I would rewrite the code in a scripting language and use the scripting framework. There's no need then for the jdk and there are no legal issues to get around. Then you also have many choices of languages to use such as Beanshell, JavaScript, or jython.
do you want something like java-scripting like BeanShell? It help run java code without compile them.
You may want to have a look at the Javassist library which contains a snippet compiler suitable for creating a method to do a calculation and then using that method.
Which one is most suitable depends on your actual needs - especially how frequently you need to do this.
来源：https://stackoverflow.com/questions/3537427/java-compiler-at-runtime