Is it possible to specify a custom classloader for javac (or some alternative java compiler)?
I'd love such a feat because it would allow me to compile classes that use classes that are only found by my special classloader.
For the curious ones: I'd write a classloder that connects to a database and creates classes based on the tables it finds.
When you run javac you can specify the classloader like so:
javac -J-Djava.system.class.loader=org.awesome.classloader sourcefile.java
It may be possible to initialize a custom classloader and then use it while calling the new Java 6 Compiler API in javax.tools.
The only two ways I know of plugging directly into javac (as run on the command line) are via the annotation processor or via a compiler-specific hack.
Just to expand on Michael's answer, if you cannot use Java6, look at the sun. packages--they have always been available to java apps and have always had a compiler in there, it's just not standard Java so you don't hear about it much and the API is subject to change (like moving it to the javax.tools package!)
Take a look at ClassLoader.defineClass. I used it myself for loading plugins into a program I created, in which I loaded a file's bytes into a new class.
If the classes all conform to the same Interface you could just provide that at compile time..
If not then I don't see what you are gaining by not outputing .java files based on the DB and compiling that.
来源：https://stackoverflow.com/questions/945971/use-a-custom-classloader-at-compile-time