Question

可能重复：
what is wrong with this call to the java method?

每当按下转义键时，以下C片段都会调用java函数。 C片段的第一个块在不同的线程上执行，第二个块在不同的线程上执行。当我按下转义键时，显示消息escape key pressed，然后jvm崩溃。为什么java函数没有得到叫？

C代码：

    if(called) {// starts on a different thread
    switch(param) {
        case VK_CONTROL:
            printf("Control pressed !\n");
            //(*Env)->CallVoidMethodA(Env,Obj,mid,"11");
            break;
        case VK_SHIFT:
            printf("Shift pressed !\n");
            //(*Env)->CallVoidMethodA(Env,Obj,mid,"10");
            break;
        case VK_ESCAPE:
            printf("Escape pressed !\n");
            JavaVM *jvm;
            JNIEnv *env;
            jmethodID mid;
            env = (*jvm)->AttachCurrentThread(jvm,&env,NULL);
            jclass cls = (*env)->GetObjectClass(env,Obj);
            mid = (*env)->GetMethodID(env,cls,"callBack","(Ljava/lang/String;)V");
            (*env)->CallVoidMethodA(env,Obj,mid,(*env)->NewStringUTF(env,"1B")); // Calling the java function
            break;
        default:
            printf("The default case\n");
            break;
    }}

    void Java_keylogger_TestKeys_initializeJNIVars
     (JNIEnv *env, jobject obj) { // starts on a different thread

      Obj = (*env)->NewGlobalRef(env,obj);
      if(Obj == NULL) {
        printf("Obj is Null\n");
      }
      called = TRUE;
   }

Java代码段：

    public void callBack(String key) {
      String x = KeyEvent.getKeyText(Integer.parseInt(key, 16));
      System.out.println(x);
    }

I have uploaded the complete code with the output here.

Answer 1

您需要初始化jvm变量。您可以使用JNI_CreateJavaVM()方法执行此操作。有关详细信息，请参阅此处：http://docs.oracle.com/javase/1.4.2/docs/guide/jni/spec/invocation.html

我一按下逃跑，jvm就崩溃了

1 个答案: