Syntax error when adding Runnable in static initializer with javassist - javassist

Question

I want to use javassist (version 3.19-GA) to generate bytecode of a static initializer of a class that starts a thread. For some reason I cannot understand javassist expects a ";" somewhere even though I believe the code I provide is syntactically correct. Does someone see more than I do? Here is the code. What is the problem?
ClassPool pool = ClassPool.getDefault();
final CtClass clazz = pool.get(somename);
clazz.makeClassInitializer().insertAfter(
"try{Runnable r=new Runnable () {public void run () { System.out.println (\"hello!!!!\"); }}; " +
"new Thread(r).start(); } catch(Exception e){}");
I'm getting the following exception:
javassist.CannotCompileException: [source error] ; is missing
at javassist.CtBehavior.insertAfter(CtBehavior.java:877)
at javassist.CtBehavior.insertAfter(CtBehavior.java:792)
at my.code(myclass.java:111)
Thanks for any hint.

Answer 1

Most probably javassist compiler does not support anonymous inner classes like new Runnable () {...}
You have to create new class, inherit it from Runnable, implement method run and create object of this class in your constructor.
package hello;
import javassist.*;
class Test{
}
class Main {
public static void main(String[] args) throws Exception {
ClassPool pool = ClassPool.getDefault();
final CtClass clazz = pool.get(Test.class.getCanonicalName());
CtClass runnable = pool.makeClass("my.custom.RunnableImpl");
runnable.addInterface(pool.get("java.lang.Runnable"));
CtMethod method = CtNewMethod.make("public void run() { System.out.println(\"hello!!!!\"); }", runnable);
runnable.addMethod(method);
// load class
runnable.toClass();
clazz.setName("newTest");
CtConstructor ctConstructor = clazz.makeClassInitializer();
ctConstructor.insertAfter("try{ new Thread( new my.custom.RunnableImpl() ).start(); } catch(Exception e){}");
Class aClass = clazz.toClass();
// call initializer
Class.forName(aClass.getCanonicalName());
Thread.sleep(1000);
}
}

Answer 2

From the official documentation of void insertAfter(String src):
Parameters:
src - the source code representing the inserted bytecode. It must be a
single statement or block.
In your src String parameter, you don't provide a single statement or a block.
A block is "{}".
Try insertBefore(String src) method with global enclosing "{}":
ClassPool pool = ClassPool.getDefault();
final CtClass clazz = pool.get(somename);
clazz.makeClassInitializer().insertBefore(
"{try{Runnable r = new Runnable () {public void run () { System.out.println (\"hello!!!!\"); }}; " +
"new Thread(r).start(); } catch(Exception e){}}");