#JeRC ####Java Runtime Compiler
Creating new code at runtime is a powerful feature. Projects like ASM and bcel have been giving us generated bytecode for a long time. But bytecode generation is difficult to get right and tedious to debug. Java now exposes the Java compiler at runtime, but not in a way that is convenient for us to use. What we really want is to compile Java source and have it accessible through a ClassLoader. The JeRC gives us exactly that.
###Usage
There are two main ways to use the JeRC. If you have a set of files generated in the file system, then you can pass the path. For example if you've generated a file for class "SomeClass" in the "org.example" package at "scripts/generated/org/example/SomeClass," you could compile and load it with the following:
RuntimeClassLoader jerc = new RuntimeClassLoader();
jerc.compile(Paths.get("scripts/generated"));
Class<?> type = jerc.loadClass("org.example.SomeClass");
Otherwise, if you're generating classes in a string, then you have to pass in a name for them as well.
String code = "package org.example;\n"+
"public class SomeClass implements Callable<String> {\n"+
" public String call() {\n"+
" return \"Hello, world!";\n"+
" }\n"+
"}";
RuntimeClassLoader jerc = new RuntimeClassLoader();
jerc.compile("org.example.SomeClass", code);
Class<?> type = jerc.loadClass("org.example.SomeClass");
Callable<String> call = (Callable<String>)type.newInstance();
Of course you can't use "SomeClass" explicitly in your code, as it doesn't exist at build-time.
If you want to build up classes over time and compile them all at once, the RuntimeCompiler abstraction might be worth looking at, but most use cases only need the RuntimeClassLoader.
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