如何在使用JNI时获取C ++中的Java异常的描述? [英] How to obtain a description of a Java exception in C++ when using JNI?
问题描述
我想确定在使用JNI从C ++代码调用该函数时,Java函数抛出了什么异常。我有以下代码捕获Java异常:
JNIEnv * pEnv; //假设这个正确初始化
jclass javaClass; // ditto
jmethodID javaFunction; // ditto
pEnv-> CallStaticVoidMethod(javaClass,javaFunction);
jthrowable exc
if(exc = pEnv-> ExceptionOccurred())
{
pEnv-> ExceptionClear();
}
我不知道如何获取关于此C ++中的Java异常的描述性信息码。
我已经省略了调用 ExceptionCheck()
每个JNI调用查看是否有失败的尝试,以找到简洁的方法:你应该实施时添加这些
首先,存储异常,然后获得必要的Java方法获取有关 Throwable
的信息:
//获取异常并清除as no
//当存在异常时可以调用JNI。
jthrowable exception = pEnv-> ExceptionOccurred();
pEnv-> ExceptionClear();
jclass throwable_class = pEnv-> FindClass(java / lang / Throwable);
jmethodID mid_throwable_getCause =
pEnv-> GetMethodID(throwable_class,
getCause,
()Ljava / lang / Throwable;);
jmethodID mid_throwable_getStackTrace =
pEnv-> GetMethodID(throwable_class,
getStackTrace,
()[Ljava / lang / StackTraceElement;);
jmethodID mid_throwable_toString =
pEnv-> GetMethodID(throwable_class,
toString,
()Ljava / lang / String;);
jclass frame_class = pEnv-> FindClass(java / lang / StackTraceElement);
jmethodID mid_frame_toString =
pEnv-> GetMethodID(frame_class,
toString,
()Ljava / lang / String;);
其次,递归构造错误消息(您可能需要修改此):
std :: string error_msg; //可以使用ostringstream代替。
_append_exception_trace_messages(* pEnv,
ERROR_MSG,
例外,
mid_throwable_getCause,
mid_throwable_getStackTrace,
mid_throwable_toString,
mid_frame_toString);
无效_append_exception_trace_messages(
JNIEnv的&放大器; a_jni_env,
的std :: string的&放大器; a_error_msg,
jthrowable a_exception,
jmethodID a_mid_throwable_getCause,
jmethodID a_mid_throwable_getStackTrace ,
jmethodID a_mid_throwable_toString,
jmethodID a_mid_frame_toString)
{
//获取StackTraceElements的数组。
jobjectArray帧=
(jobjectArray)a_jni_env.CallObjectMethod(
a_exception,
a_mid_throwable_getStackTrace);
jsize frames_length = a_jni_env.GetArrayLength(frames);
//在下降
//之前添加Throwable.toString()堆栈跟踪消息。
如果(!0 =帧)
{
的jstring msg_obj =
(的jstring)a_jni_env.CallObjectMethod(a_exception,
a_mid_throwable_toString);
const char * msg_str = a_jni_env.GetStringUTFChars(msg_obj,0);
//如果这不是跟踪的顶部,那么
//这是一个原因。
if(!a_error_msg.empty())
{
a_error_msg + =\\\
Caused by:;
a_error_msg + = msg_str;
}
else
{
a_error_msg = msg_str;
}
a_jni_env.ReleaseStringUTFChars(msg_obj,msg_str);
a_jni_env.DeleteLocalRef(msg_obj);
}
//如果有任何附加栈跟踪消息。
if(frames_length> 0)
{
jsize i = 0;
for(i = 0; i {
//获取从'toString()'返回的字符串
//下一帧的方法并将其附加到
//错误消息。
jobject frame = a_jni_env.GetObjectArrayElement(frames,i);
jstring msg_obj =
(jstring)a_jni_env.CallObjectMethod(frame,
a_mid_frame_toString);
const char * msg_str = a_jni_env.GetStringUTFChars(msg_obj,0);
a_error_msg + =\\\
;
a_error_msg + = msg_str;
a_jni_env.ReleaseStringUTFChars(msg_obj,msg_str);
a_jni_env.DeleteLocalRef(msg_obj);
a_jni_env.DeleteLocalRef(frame);
}
}
//如果'a_exception'有原因,则从原因追加
//堆栈跟踪消息。
如果(!0 =帧)
{
jthrowable原因=
(jthrowable)a_jni_env.CallObjectMethod(
a_exception,
a_mid_throwable_getCause);
如果(0!=原因)
{
_append_exception_trace_messages(a_jni_env,
a_error_msg,
的原因,
a_mid_throwable_getCause,
a_mid_throwable_getStackTrace,
a_mid_throwable_toString,
a_mid_frame_toString);
}
}
}
写了几年前(修改为消除锅炉板 ExceptionCheck()
s),但我没有编译我已经发布,但一般的方法是希望明确。 >
I would like to determine what exception has been thrown by a Java function when calling that function from C++ code using JNI. I have the following code that catches the Java exception:
JNIEnv * pEnv; // assume this is properly initialized
jclass javaClass; // ditto
jmethodID javaFunction; // ditto
pEnv->CallStaticVoidMethod(javaClass, javaFunction);
jthrowable exc;
if(exc = pEnv->ExceptionOccurred())
{
pEnv->ExceptionClear();
}
I do not know how to obtain descriptive information about the Java exception within this C++ code. Can somebody help?
I have omitted calling ExceptionCheck()
after each JNI call and checking for any failed attempts to locate methods for brevity: you should add these when implementing.
First, store the exception and then acquire the Java methods necessary for obtaining information about the Throwable
:
// Get the exception and clear as no
// JNI calls can be made while an exception exists.
jthrowable exception = pEnv->ExceptionOccurred();
pEnv->ExceptionClear();
jclass throwable_class = pEnv->FindClass("java/lang/Throwable");
jmethodID mid_throwable_getCause =
pEnv->GetMethodID(throwable_class,
"getCause",
"()Ljava/lang/Throwable;");
jmethodID mid_throwable_getStackTrace =
pEnv->GetMethodID(throwable_class,
"getStackTrace",
"()[Ljava/lang/StackTraceElement;");
jmethodID mid_throwable_toString =
pEnv->GetMethodID(throwable_class,
"toString",
"()Ljava/lang/String;");
jclass frame_class = pEnv->FindClass("java/lang/StackTraceElement");
jmethodID mid_frame_toString =
pEnv->GetMethodID(frame_class,
"toString",
"()Ljava/lang/String;");
Second, recursively construct the error message (you may want to modify this):
std::string error_msg; // Could use ostringstream instead.
_append_exception_trace_messages(*pEnv,
error_msg,
exception,
mid_throwable_getCause,
mid_throwable_getStackTrace,
mid_throwable_toString,
mid_frame_toString);
void _append_exception_trace_messages(
JNIEnv& a_jni_env,
std::string& a_error_msg,
jthrowable a_exception,
jmethodID a_mid_throwable_getCause,
jmethodID a_mid_throwable_getStackTrace,
jmethodID a_mid_throwable_toString,
jmethodID a_mid_frame_toString)
{
// Get the array of StackTraceElements.
jobjectArray frames =
(jobjectArray) a_jni_env.CallObjectMethod(
a_exception,
a_mid_throwable_getStackTrace);
jsize frames_length = a_jni_env.GetArrayLength(frames);
// Add Throwable.toString() before descending
// stack trace messages.
if (0 != frames)
{
jstring msg_obj =
(jstring) a_jni_env.CallObjectMethod(a_exception,
a_mid_throwable_toString);
const char* msg_str = a_jni_env.GetStringUTFChars(msg_obj, 0);
// If this is not the top-of-the-trace then
// this is a cause.
if (!a_error_msg.empty())
{
a_error_msg += "\nCaused by: ";
a_error_msg += msg_str;
}
else
{
a_error_msg = msg_str;
}
a_jni_env.ReleaseStringUTFChars(msg_obj, msg_str);
a_jni_env.DeleteLocalRef(msg_obj);
}
// Append stack trace messages if there are any.
if (frames_length > 0)
{
jsize i = 0;
for (i = 0; i < frames_length; i++)
{
// Get the string returned from the 'toString()'
// method of the next frame and append it to
// the error message.
jobject frame = a_jni_env.GetObjectArrayElement(frames, i);
jstring msg_obj =
(jstring) a_jni_env.CallObjectMethod(frame,
a_mid_frame_toString);
const char* msg_str = a_jni_env.GetStringUTFChars(msg_obj, 0);
a_error_msg += "\n ";
a_error_msg += msg_str;
a_jni_env.ReleaseStringUTFChars(msg_obj, msg_str);
a_jni_env.DeleteLocalRef(msg_obj);
a_jni_env.DeleteLocalRef(frame);
}
}
// If 'a_exception' has a cause then append the
// stack trace messages from the cause.
if (0 != frames)
{
jthrowable cause =
(jthrowable) a_jni_env.CallObjectMethod(
a_exception,
a_mid_throwable_getCause);
if (0 != cause)
{
_append_exception_trace_messages(a_jni_env,
a_error_msg,
cause,
a_mid_throwable_getCause,
a_mid_throwable_getStackTrace,
a_mid_throwable_toString,
a_mid_frame_toString);
}
}
}
I copied this from code I wrote a few years ago (modified to eliminate boiler plate ExceptionCheck()
s), but I did not compile what I have posted but the general approach is hopefully clear.
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