Android JNI 使用的数据结构JNINativeMethod详解

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最近在做关于Android语音识别的东东。研究Recognizer源码的时候碰到个关于JNINativeMethod的结构体,不解,Google之在网上找到了片文章,见文后。结构体代码如下:

/* * Table of methods associated with a single class. */static JNINativeMethod gMethods[] = {    /* name, signature, funcPtr */    // PMem    {"PMemInit",                           "()V",                     (void*)Java_android_speech_srec_Recognizer_PMemInit},    {"PMemShutdown",                       "()V",                     (void*)Java_android_speech_srec_Recognizer_PMemShutdown},    // SR_Session    {"SR_SessionCreate",                   "(Ljava/lang/String;)V",   (void*)Java_android_speech_srec_Recognizer_SR_1SessionCreate},    {"SR_SessionDestroy",                  "()V",                     (void*)Java_android_speech_srec_Recognizer_SR_1SessionDestroy},    // SR_Recognizer    {"SR_RecognizerStart",                 "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerStart},    {"SR_RecognizerStop",                  "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerStop},    {"SR_RecognizerCreate",                "()I",                     (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerCreate},    {"SR_RecognizerDestroy",               "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerDestroy},    {"SR_RecognizerSetup",                 "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerSetup},    {"SR_RecognizerUnsetup",               "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerUnsetup},    {"SR_RecognizerIsSetup",               "(I)Z",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerIsSetup},    {"SR_RecognizerGetParameter",          "(ILjava/lang/String;)Ljava/lang/String;", (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerGetParameter},    {"SR_RecognizerGetSize_tParameter",    "(ILjava/lang/String;)I",  (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerGetSize_1tParameter},    {"SR_RecognizerGetBoolParameter",      "(ILjava/lang/String;)Z",  (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerGetBoolParameter},    {"SR_RecognizerSetParameter",          "(ILjava/lang/String;Ljava/lang/String;)V", (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerSetParameter},    {"SR_RecognizerSetSize_tParameter",    "(ILjava/lang/String;I)V", (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerSetSize_1tParameter},    {"SR_RecognizerSetBoolParameter",      "(ILjava/lang/String;Z)V", (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerSetBoolParameter},    {"SR_RecognizerSetupRule",             "(IILjava/lang/String;)V", (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerSetupRule},    {"SR_RecognizerHasSetupRules",         "(I)Z",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerHasSetupRules},    {"SR_RecognizerActivateRule",          "(IILjava/lang/String;I)V", (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerActivateRule},    {"SR_RecognizerDeactivateRule",        "(IILjava/lang/String;)V", (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerDeactivateRule},    {"SR_RecognizerDeactivateAllRules",    "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerDeactivateAllRules},    {"SR_RecognizerIsActiveRule",          "(IILjava/lang/String;)Z", (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerIsActiveRule},    {"SR_RecognizerCheckGrammarConsistency", "(II)Z",                 (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerCheckGrammarConsistency},    {"SR_RecognizerPutAudio",              "(I[BIIZ)I",               (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerPutAudio},    {"SR_RecognizerAdvance",               "(I)I",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerAdvance},    {"SR_RecognizerIsSignalClipping",      "(I)Z",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerIsSignalClipping},    {"SR_RecognizerIsSignalDCOffset",      "(I)Z",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerIsSignalDCOffset},    {"SR_RecognizerIsSignalNoisy",         "(I)Z",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerIsSignalNoisy},    {"SR_RecognizerIsSignalTooQuiet",      "(I)Z",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerIsSignalTooQuiet},    {"SR_RecognizerIsSignalTooFewSamples", "(I)Z",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerIsSignalTooFewSamples},    {"SR_RecognizerIsSignalTooManySamples", "(I)Z",                   (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerIsSignalTooManySamples},    // SR_AcousticState    {"SR_AcousticStateReset",               "(I)V",                   (void*)Java_android_speech_srec_Recognizer_SR_1AcousticStateReset},    {"SR_AcousticStateSet",                 "(ILjava/lang/String;)V", (void*)Java_android_speech_srec_Recognizer_SR_1AcousticStateSet},    {"SR_AcousticStateGet",                 "(I)Ljava/lang/String;",  (void*)Java_android_speech_srec_Recognizer_SR_1AcousticStateGet},    // SR_Grammar    {"SR_GrammarCompile",                  "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1GrammarCompile},    {"SR_GrammarAddWordToSlot",            "(ILjava/lang/String;Ljava/lang/String;Ljava/lang/String;ILjava/lang/String;)V", (void*)Java_android_speech_srec_Recognizer_SR_1GrammarAddWordToSlot},    {"SR_GrammarResetAllSlots",            "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1GrammarResetAllSlots},    {"SR_GrammarSetupVocabulary",          "(II)V",                   (void*)Java_android_speech_srec_Recognizer_SR_1GrammarSetupVocabulary},    {"SR_GrammarSetupRecognizer",          "(II)V",                   (void*)Java_android_speech_srec_Recognizer_SR_1GrammarSetupRecognizer},    {"SR_GrammarUnsetupRecognizer",        "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1GrammarUnsetupRecognizer},    {"SR_GrammarCreate",                   "()I",                     (void*)Java_android_speech_srec_Recognizer_SR_1GrammarCreate},    {"SR_GrammarDestroy",                  "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1GrammarDestroy},    {"SR_GrammarLoad",                     "(Ljava/lang/String;)I",   (void*)Java_android_speech_srec_Recognizer_SR_1GrammarLoad},    {"SR_GrammarSave",                     "(ILjava/lang/String;)V",  (void*)Java_android_speech_srec_Recognizer_SR_1GrammarSave},    {"SR_GrammarAllowOnly",                "(ILjava/lang/String;)V",  (void*)Java_android_speech_srec_Recognizer_SR_1GrammarAllowOnly},    {"SR_GrammarAllowAll",                 "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1GrammarAllowAll},    // SR_Vocabulary    {"SR_VocabularyLoad",                  "()I",                     (void*)Java_android_speech_srec_Recognizer_SR_1VocabularyLoad},    {"SR_VocabularyDestroy",               "(I)V",                    (void*)Java_android_speech_srec_Recognizer_SR_1VocabularyDestroy},    {"SR_VocabularyGetPronunciation",      "(ILjava/lang/String;)Ljava/lang/String;",  (void*)Java_android_speech_srec_Recognizer_SR_1VocabularyGetPronunciation},    // SR_RecognizerResult    {"SR_RecognizerResultGetWaveform",     "(I)[B",                   (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerResultGetWaveform},    {"SR_RecognizerResultGetSize",         "(I)I",                    (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerResultGetSize},    {"SR_RecognizerResultGetKeyCount",     "(II)I",                   (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerResultGetKeyCount},    {"SR_RecognizerResultGetKeyList",      "(II)[Ljava/lang/String;", (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerResultGetKeyList},    {"SR_RecognizerResultGetValue",        "(IILjava/lang/String;)Ljava/lang/String;", (void*)Java_android_speech_srec_Recognizer_SR_1RecognizerResultGetValue},};

Andoird 中使用了一种不同传统Java JNI的方式来定义其native的函数。其中很重要的区别是Andorid使用了一种Java 和 C 函数的映射表数组,并在其中描述了函数的参数和返回值。这个数组的类型是JNINativeMethod,定义如下:

typedef struct {const char* name;const char* signature;void* fnPtr;} JNINativeMethod;

第一个变量name是Java中函数的名字。

第二个变量signature,用字符串是描述了函数的参数和返回值

第三个变量fnPtr是函数指针,指向C函数。

其中比较难以理解的是第二个参数,例如

"()V"

"(II)V"

"(Ljava/lang/String;Ljava/lang/String;)V"

实际上这些字符是与函数的参数类型一一对应的。

"()" 中的字符表示参数,后面的则代表返回值。例如"()V" 就表示void Func();

"(II)V" 表示 void Func(int, int);

具体的每一个字符的对应关系如下

字符 Java类型 C类型

V      void            void
Z       jboolean     boolean
I        jint              int
J       jlong            long
D      jdouble       double
F      jfloat            float
B      jbyte            byte
C      jchar           char
S      jshort          short

数组则以"["开始,用两个字符表示

[I       jintArray      int[]
[F     jfloatArray    float[]
[B     jbyteArray    byte[]
[C    jcharArray    char[]
[S    jshortArray   short[]
[D    jdoubleArray double[]
[J     jlongArray     long[]
[Z    jbooleanArray boolean[]

上面的都是基本类型。如果Java函数的参数是class,则以"L"开头,以";"结尾中间是用"/" 隔开的包及类名。而其对应的C函数名的参数则为jobject. 一个例外是String类,其对应的类为jstring

Ljava/lang/String; String jstring
Ljava/net/Socket; Socket jobject

如果JAVA函数位于一个嵌入类,则用$作为类名间的分隔符。

例如 "(Ljava/lang/String;Landroid/os/FileUtils$FileStatus;)Z"

文章出处:http://hi.baidu.com/leicejbgnndjrze/item/b87a4895e06a6c1c924f41f4

另供参考:http://blog.csdn.net/bigapple88/article/details/6756204


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