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import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.ConstantDynamic;
import org.objectweb.asm.Handle;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import java.io.FileOutputStream;
import java.io.IOException;
/**
* This class was created by ASM-ifying a class generated by Byte Buddy.
* Its purpose it to create a class <tt>CondyCallable</tt> making use of
* dynamic class-file constants, a Java 11 feature introduced by JEP 309.
*
* @see https://openjdk.java.net/jeps/309
*/
public class Generator implements Opcodes {
private static final String CLASS_FILE = "CondyCallable.class";
public static void main(String[] args) throws IOException {
try (FileOutputStream fos = new FileOutputStream(CLASS_FILE)) {
fos.write(getClassBytes());
}
System.out.println(CLASS_FILE + " generated successfully");
}
private static byte[] getClassBytes() {
ClassWriter classWriter = new ClassWriter(0);
classWriter.visit(V11, ACC_PUBLIC | ACC_SUPER, "CondyCallable", null, "java/lang/Object", new String[] { "java/util/concurrent/Callable" });
createDefaultConstructor(classWriter);
createMethod_call(classWriter);
classWriter.visitEnd();
return classWriter.toByteArray();
}
private static void createDefaultConstructor(ClassWriter classWriter) {
MethodVisitor methodVisitor = classWriter.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
methodVisitor.visitCode();
methodVisitor.visitVarInsn(ALOAD, 0);
methodVisitor.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
methodVisitor.visitInsn(RETURN);
methodVisitor.visitMaxs(1, 1);
methodVisitor.visitEnd();
}
private static void createMethod_call(ClassWriter classWriter) {
MethodVisitor methodVisitor = classWriter.visitMethod(ACC_PUBLIC, "call", "()Ljava/lang/Object;", null, new String[] { "java/lang/Exception" });
methodVisitor.visitCode();
methodVisitor.visitLdcInsn(
// Create constant-dynamic instruction
new ConstantDynamic(
// Dummy name
"_",
// Constant type
"LApplication;",
// Bootstrap method: ConstantBootstraps::invoke, dispatching to an existing method/constructor
new Handle(Opcodes.H_INVOKESTATIC, "java/lang/invoke/ConstantBootstraps", "invoke", "(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/Class;Ljava/lang/invoke/MethodHandle;[Ljava/lang/Object;)Ljava/lang/Object;", false),
// Bootstrap method arguments: here we simply dispatch to the constructor of class Application
new Handle(Opcodes.H_NEWINVOKESPECIAL, "Application", "<init>", "()V", false))
);
methodVisitor.visitInsn(ARETURN);
methodVisitor.visitMaxs(1, 1);
methodVisitor.visitEnd();
}
}
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