什么是错的这个调用Java方法？ [英] what is wrong with this call to the java method?
问题描述
我试图调用从code Java方法。 C $ C $ç听为退出，移，控制键preSS，那么它调用Java方法告诉这关键是pressed。以下是在这方面发挥作用的片段。
I am trying to call a Java method from the code. C code listens to either Escape, Shift, Ctrl key press, then it calls the Java method telling which key was pressed. Following are the snippets that play a role in this.
的ç段：的
mid = (*env)->GetMethodID(env,cls,"callBack","(Ljava/lang/String;)V");
Env = env;
if(called)
switch(param) {
case VK_CONTROL:
printf("Control pressed !\n");
(*Env)->CallVoidMethodA(Env,Obj,mid,"11"); // calling the java method
break;
case VK_SHIFT:
printf("Shift pressed !\n");
(*Env)->CallVoidMethodA(Env,Obj,mid,"10"); // calling the java method
break;
case VK_ESCAPE:
printf("Escape pressed !\n");
(*Env)->CallVoidMethodA(Env,Obj,mid,"1B"); // calling the java method
break;
default:
printf("The default case\n");
break;
}
的 Java代码：的
public void callBack(String key) {
String x = KeyEvent.getKeyText(Integer.parseInt(key, 16));
System.out.println(x);
}
当我运行PSS的退出键，程序和$ P $我得到这个在控制台上：
When I run the program and press the Escape key I get this on the console:
Escape pressed !
#
# A fatal error has been detected by the Java Runtime Environment:
#
# EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x5c8b809a, pid=7588, tid=8088
#
# JRE version: 7.0
# Java VM: Java HotSpot(TM) Client VM (20.0-b01 mixed mode, sharing windows-x86 )
# Problematic frame:
# V [jvm.dll+0x19809a]
#
# An error report file with more information is saved as:
# W:\UnderTest\NetbeansCurrent\KeyLoggerTester\build\classes\hs_err_pid7588.log
#
# If you would like to submit a bug report, please visit:
# http://java.sun.com/webapps/bugreport/crash.jsp
#
我知道我调用Java函数走错路了，但我不知道我错了。从输出，它满足的时候我preSS的情况下，逃生键，然后发生意外错误。
I know I am calling the Java function the wrong way, but I don't know where I am wrong. As from the output, it satisfies the case when I press the Escape key and then an unexpected error occurs.
编辑：
以 mavroprovato 的答案后，我仍然得到同样的错误。
After the answer by mavroprovato I still get the same errors.
我编辑的是这样的：
(*Env)->CallVoidMethodA(Env,Obj,mid,(*Env)->NewStringUTF(Env,"1B"));
编辑：
推荐答案
JVM的崩溃，因为的JNIEnv 时使用不是有效的。没有与code以及其他的问题。
The JVM is crashing because the JNIEnv that is used is not a valid one. There are other issues with the code as well.
借助孙JNI文档是关于提供非常好的信息线程。
The Sun JNI documentation is providing very good information regarding threads.
下面谈到某些部分是显而易见的：
Here comes some parts that are obvious:
创建您的code一 JNI_OnLoad 功能。加载库时它会被调用。然后缓存的JavaVM 指针，因为这是跨线程有效。另一种方法是调用（* ENV） - GT; GetJavaVM 在 initializeJNIVars 的功能，但我preFER的第一个。
Create a JNI_OnLoad function in your code. It will be called when the library is loaded. Then cache the JavaVM pointer because that is valid across threads. An alternative is to call (*env)->GetJavaVM in the initializeJNIVars function but I prefer the first one.
在你的 initializeJNIVars 您可以通过调用保存 OBJ 引用的OBJ =（* ENV） - 方式＆gt; NewGlobalRef（OBJ）
In your initializeJNIVars you can save the obj reference by calling Obj = (*env)->NewGlobalRef(obj).
在 LowLevelKeyboardProc 你必须获得 ENV 指针：
AttachCurrentThread（JavaVM的* JVM，JNIEnv的＆安培; ENV，NULL）;
修改
OK，这里有code，你应该添加得到它的工作，我已经尝试过了自己和它的作品。 NB ：我还没有分析了一下你的code究竟是干什么，所以我只是做了一些修正，以得到它的工作。
OK, here are the code that you should add to get it working, I have tried it myself and it works. NB: I have not analyzed what your code is actually doing so I just did some fixes to get it working.
添加其他的全局变量之间的这些变量：
Add these variables among your other global variables:
static JavaVM *javaVM = NULL;
static jmethodID callbackMethod = NULL;
static jobject callbackObject = NULL;
您可以删除 CLS ，中期，信封和的OBJ 变量，并用我的吧。
You can remove your cls, mid, Env and Obj variables and use mine instead.
创建JNI_OnLoad方法，您缓存的JavaVM指针：
Create the JNI_OnLoad method where you cache the JavaVM pointer:
JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *jvm, void *reserved) {
JNIEnv *env = 0;
if ((*jvm)->GetEnv(jvm, (void**)&env, JNI_VERSION_1_4)) {
return JNI_ERR;
}
javaVM = jvm;
return JNI_VERSION_1_4;
}
改变你的 initializeJNIVars 来如下所示：
void Java_keylogger_TestKeys_initializeJNIVars(JNIEnv *env, jobject obj) {
jclass cls = (*env)->GetObjectClass(env,obj);
callbackMethod = (*env)->GetMethodID(env, cls, "callBack", "(Ljava/lang/String;)V");
callbackObject = (*env)->NewGlobalRef(env, obj);
if(cls == NULL || callbackMethod == NULL) {
printf("One of them is null \n");
}
called = TRUE;
}
终于在你的 LowLoevelKeyboardProc code，你将不得不添加以下内容：
And finally in your LowLoevelKeyboardProc code you will have to add the following:
...
WPARAM param = kbhook->vkCode;
JNIEnv *env;
jint rs = (*javaVM)->AttachCurrentThread(javaVM, (void**)&env, NULL);
if (rs != JNI_OK) {
return NULL; // Or something appropriate...
}
...
case VK_ESCAPE:
printf("Escape pressed !\n");
jstring message = (*env)->NewStringUTF(env, "1B");
(*env)->CallVoidMethod(env, callbackObject, callbackMethod, message);
break;
...
在你的 unregisterWinHook 你应该删除全局引用，以便对象可以GC'd。
In your unregisterWinHook you should delete the global reference so that objects can be GC'd.
...
(*env)->DeleteGlobalRef(env, callbackObject);
这就是它。
这篇关于什么是错的这个调用Java方法？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
