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import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.invoke.CallSite;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import org.objectweb.asm.*;
public class Generator implements Opcodes {
private String generatedRunnerTypename,linkClassName,dynMethodName,dynMethodDescriptor;
private byte[] bytes;
/**
* Main entry point generates a default thing, in this case a class called 'Invoker' that will use the bootstrap method on Code1 to run 'foo()'
* @param args
* @throws Throwable
*/
public static void main(String[] args) throws Throwable {
Generator g = new Generator("Invoker","Code1","foo","()V");
g.dump();
}
public byte[] getBytes() {
return bytes;
}
public Generator(String generatedRunnerTypename, String linkClassName, String dynMethodName, String dynMethodDescriptor) {
this.generatedRunnerTypename = generatedRunnerTypename;
this.linkClassName = linkClassName;
this.dynMethodName = dynMethodName;
this.dynMethodDescriptor = dynMethodDescriptor;
this.bytes = generateClass();
}
public void dump() {
try {
FileOutputStream fos
= new FileOutputStream(new File(generatedRunnerTypename+".class"));
fos.write(bytes);
fos.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public byte[] generateClass() {
ClassWriter cw = new ClassWriter(0);
cw.visit(V1_7, ACC_PUBLIC + ACC_SUPER, generatedRunnerTypename, null, "java/lang/Object", null);
createConstructor(cw);
createMain(cw);
cw.visitEnd();
return cw.toByteArray();
}
private void createMain(ClassWriter cw) {
MethodVisitor mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC, "main", "([Ljava/lang/String;)V", null, null);
mv.visitCode();
MethodType mt = MethodType.methodType(CallSite.class, MethodHandles.Lookup.class, String.class,
MethodType.class);
Handle bootstrap = new Handle(Opcodes.H_INVOKESTATIC, this.linkClassName, "bootstrap",
mt.toMethodDescriptorString());
int maxStackSize = 0;//addMethodParameters(mv);
mv.visitInvokeDynamicInsn(dynMethodName, dynMethodDescriptor, bootstrap);
mv.visitInsn(RETURN);
mv.visitMaxs(maxStackSize, 1);
mv.visitEnd();
}
// public byte[] dump(String dynamicInvokerClassName, String dynamicLinkageClassName, String bootstrapMethodName, String targetMethodDescriptor)
// throws Exception {
// ClassWriter cw = new ClassWriter(0);
// cw.visit(V1_7, ACC_PUBLIC + ACC_SUPER, dynamicInvokerClassName, null, "java/lang/Object", null);
// createConstructor(cw);
// createMain(dynamicLinkageClassName, bootstrapMethodName, targetMethodDescriptor, cw);
// cw.visitEnd();
// return cw.toByteArray();
// }
// protected int addMethodParameters(MethodVisitor mv) {
// return 0;
// }
private void createConstructor(ClassWriter cw) {
MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
mv.visitCode();
mv.visitVarInsn(ALOAD, 0);
mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V");
mv.visitInsn(RETURN);
mv.visitMaxs(1, 1);
mv.visitEnd();
}
}
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