Example for the presentation about JVM TI

patcher.cpp

#include <jvmti.h>
#include <stdio.h>

static jvmtiIterationControl JNICALL
heap_callback(jlong class_tag, jlong size, jlong* tag_ptr, void* user_data) {
    *tag_ptr = 1;
    return JVMTI_ITERATION_CONTINUE;
}

JNIEXPORT jint JNICALL Agent_OnAttach(JavaVM* vm, char* options, void* reserved) {
    jvmtiEnv* jvmti;
    vm->GetEnv((void**) &jvmti, JVMTI_VERSION_1_0);

    jvmtiCapabilities capabilities = {0};
    capabilities.can_tag_objects = 1;
    jvmti->AddCapabilities(&capabilities);

    JNIEnv* env;
    vm->GetEnv((void**) &env, JNI_VERSION_1_6);

    jclass AbstractButton = env->FindClass("javax/swing/AbstractButton");
    if (AbstractButton != NULL) {
        jclass Color = env->FindClass("java/awt/Color");
        jmethodID Color_init = env->GetMethodID(Color, "<init>", "(III)V");
        jobject red = options != NULL && options[0] == 'r'
            ? env->NewObject(Color, Color_init, 242, 242, 242)
            : env->NewObject(Color, Color_init, 255, 0, 0);

        jclass JComponent = env->FindClass("javax/swing/JComponent");
        jmethodID setBackground = env->GetMethodID(JComponent, "setBackground", "(Ljava/awt/Color;)V");

        jvmti->IterateOverInstancesOfClass(AbstractButton, JVMTI_HEAP_OBJECT_EITHER, heap_callback, NULL);

        jlong tag = 1;
        jint count = 0;
        jobject* objects = NULL;
        jvmti->GetObjectsWithTags(1, &tag, &count, &objects, NULL);

        for (int i = 0; i < count; i++) {
            env->CallVoidMethod(objects[i], setBackground, red);
        }

        jvmti->Deallocate((unsigned char*) objects);
    }

    jvmti->DisposeEnvironment();
    return 0;
}

This helped a lot