Android NDK开发之JNI基础知识

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android中级知识

JAVA层与JNI层数据类型的对应

下面是一个测试方法

public native void test(char c,short s,byte by,int i,long l,float f,double d,boolean b,String str,Object o,Test t,int[] arr);

jni层面生成的函数原型

JNIEXPORT void JNICALL
Java_com_kltz88_car_jnidemo_Test_test(JNIEnv *env, jobject instance, jbyte by, jchar c, jshort s, jint i,
                                      jlong l, jfloat f, jdouble d, jboolean b, jstring str_,
                                      jobject o, jobject t, jintArray arr);

我们会发现基本数据类型直接会有一种对应关系

其实只是使用了typedef重新定义了一下

typedef unsigned char   jboolean;       /* unsigned 8 bits */
typedef signed char     jbyte;          /* signed 8 bits */
typedef unsigned short  jchar;          /* unsigned 16 bits */
typedef short           jshort;         /* signed 16 bits */
typedef int             jint;           /* signed 32 bits */
typedef long long       jlong;          /* signed 64 bits */
typedef float           jfloat;         /* 32-bit IEEE 754 */
typedef double          jdouble;        /* 64-bit IEEE 754 */

进一步还会发现，引用类型也存在一定的对应关系

也是通过typedef重新定义了一下，都是一个指针

typedef void*           jobject;
typedef jobject         jclass;
typedef jobject         jstring;
typedef jobject         jarray;
typedef jarray          jobjectArray;
typedef jarray          jbooleanArray;
typedef jarray          jbyteArray;
typedef jarray          jcharArray;
typedef jarray          jshortArray;
typedef jarray          jintArray;
typedef jarray          jlongArray;
typedef jarray          jfloatArray;
typedef jarray          jdoubleArray;
typedef jobject         jthrowable;
typedef jobject         jweak;

方法签名

字段描述

值得注意的是
- 类是使用L全限定名;，比如String, 其签名为Ljava/lang/util/String;
- 数组是使用[类型签名，比如 [B

方法描述

JNI层暴露的方法

    jint        (*GetVersion)(JNIEnv *);

    jclass      (*DefineClass)(JNIEnv*, const char*, jobject, const jbyte*,
                        jsize);
    jclass      (*FindClass)(JNIEnv*, const char*);

    jmethodID   (*FromReflectedMethod)(JNIEnv*, jobject);
    jfieldID    (*FromReflectedField)(JNIEnv*, jobject);
    /* spec doesn't show jboolean parameter */
    jobject     (*ToReflectedMethod)(JNIEnv*, jclass, jmethodID, jboolean);

    jclass      (*GetSuperclass)(JNIEnv*, jclass);
    jboolean    (*IsAssignableFrom)(JNIEnv*, jclass, jclass);

    /* spec doesn't show jboolean parameter */
    jobject     (*ToReflectedField)(JNIEnv*, jclass, jfieldID, jboolean);

    jint        (*Throw)(JNIEnv*, jthrowable);
    jint        (*ThrowNew)(JNIEnv *, jclass, const char *);
    jthrowable  (*ExceptionOccurred)(JNIEnv*);
    void        (*ExceptionDescribe)(JNIEnv*);
    void        (*ExceptionClear)(JNIEnv*);
    void        (*FatalError)(JNIEnv*, const char*);

    jint        (*PushLocalFrame)(JNIEnv*, jint);
    jobject     (*PopLocalFrame)(JNIEnv*, jobject);

    jobject     (*NewGlobalRef)(JNIEnv*, jobject);
    void        (*DeleteGlobalRef)(JNIEnv*, jobject);
    void        (*DeleteLocalRef)(JNIEnv*, jobject);
    jboolean    (*IsSameObject)(JNIEnv*, jobject, jobject);

    jobject     (*NewLocalRef)(JNIEnv*, jobject);
    jint        (*EnsureLocalCapacity)(JNIEnv*, jint);

    jobject     (*AllocObject)(JNIEnv*, jclass);
    jobject     (*NewObject)(JNIEnv*, jclass, jmethodID, ...);
    jobject     (*NewObjectV)(JNIEnv*, jclass, jmethodID, va_list);
    jobject     (*NewObjectA)(JNIEnv*, jclass, jmethodID, jvalue*);

    jclass      (*GetObjectClass)(JNIEnv*, jobject);
    jboolean    (*IsInstanceOf)(JNIEnv*, jobject, jclass);
    jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);

    jobject     (*CallObjectMethod)(JNIEnv*, jobject, jmethodID, ...);
    jobject     (*CallObjectMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jobject     (*CallObjectMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jboolean    (*CallBooleanMethod)(JNIEnv*, jobject, jmethodID, ...);
    jboolean    (*CallBooleanMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jboolean    (*CallBooleanMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jbyte       (*CallByteMethod)(JNIEnv*, jobject, jmethodID, ...);
    jbyte       (*CallByteMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jbyte       (*CallByteMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jchar       (*CallCharMethod)(JNIEnv*, jobject, jmethodID, ...);
    jchar       (*CallCharMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jchar       (*CallCharMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jshort      (*CallShortMethod)(JNIEnv*, jobject, jmethodID, ...);
    jshort      (*CallShortMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jshort      (*CallShortMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jint        (*CallIntMethod)(JNIEnv*, jobject, jmethodID, ...);
    jint        (*CallIntMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jint        (*CallIntMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jlong       (*CallLongMethod)(JNIEnv*, jobject, jmethodID, ...);
    jlong       (*CallLongMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    jlong       (*CallLongMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);
    jfloat      (*CallFloatMethod)(JNIEnv*, jobject, jmethodID, ...) __NDK_FPABI__;
    jfloat      (*CallFloatMethodV)(JNIEnv*, jobject, jmethodID, va_list) __NDK_FPABI__;
    jfloat      (*CallFloatMethodA)(JNIEnv*, jobject, jmethodID, jvalue*) __NDK_FPABI__;
    jdouble     (*CallDoubleMethod)(JNIEnv*, jobject, jmethodID, ...) __NDK_FPABI__;
    jdouble     (*CallDoubleMethodV)(JNIEnv*, jobject, jmethodID, va_list) __NDK_FPABI__;
    jdouble     (*CallDoubleMethodA)(JNIEnv*, jobject, jmethodID, jvalue*) __NDK_FPABI__;
    void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
    void        (*CallVoidMethodV)(JNIEnv*, jobject, jmethodID, va_list);
    void        (*CallVoidMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);

    jobject     (*CallNonvirtualObjectMethod)(JNIEnv*, jobject, jclass,
                        jmethodID, ...);
    jobject     (*CallNonvirtualObjectMethodV)(JNIEnv*, jobject, jclass,
                        jmethodID, va_list);
    jobject     (*CallNonvirtualObjectMethodA)(JNIEnv*, jobject, jclass,
                        jmethodID, jvalue*);
    jboolean    (*CallNonvirtualBooleanMethod)(JNIEnv*, jobject, jclass,
                        jmethodID, ...);
    jboolean    (*CallNonvirtualBooleanMethodV)(JNIEnv*, jobject, jclass,
                         jmethodID, va_list);
    jboolean    (*CallNonvirtualBooleanMethodA)(JNIEnv*, jobject, jclass,
                         jmethodID, jvalue*);
    jbyte       (*CallNonvirtualByteMethod)(JNIEnv*, jobject, jclass,
                        jmethodID, ...);
    jbyte       (*CallNonvirtualByteMethodV)(JNIEnv*, jobject, jclass,
                        jmethodID, va_list);
    jbyte       (*CallNonvirtualByteMethodA)(JNIEnv*, jobject, jclass,
                        jmethodID, jvalue*);
    jchar       (*CallNonvirtualCharMethod)(JNIEnv*, jobject, jclass,
                        jmethodID, ...);
    jchar       (*CallNonvirtualCharMethodV)(JNIEnv*, jobject, jclass,
                        jmethodID, va_list);
    jchar       (*CallNonvirtualCharMethodA)(JNIEnv*, jobject, jclass,
                        jmethodID, jvalue*);
    jshort      (*CallNonvirtualShortMethod)(JNIEnv*, jobject, jclass,
                        jmethodID, ...);
    jshort      (*CallNonvirtualShortMethodV)(JNIEnv*, jobject, jclass,
                        jmethodID, va_list);
    jshort      (*CallNonvirtualShortMethodA)(JNIEnv*, jobject, jclass,
                        jmethodID, jvalue*);
    jint        (*CallNonvirtualIntMethod)(JNIEnv*, jobject, jclass,
                        jmethodID, ...);
    jint        (*CallNonvirtualIntMethodV)(JNIEnv*, jobject, jclass,
                        jmethodID, va_list);
    jint        (*CallNonvirtualIntMethodA)(JNIEnv*, jobject, jclass,
                        jmethodID, jvalue*);
    jlong       (*CallNonvirtualLongMethod)(JNIEnv*, jobject, jclass,
                        jmethodID, ...);
    jlong       (*CallNonvirtualLongMethodV)(JNIEnv*, jobject, jclass,
                        jmethodID, va_list);
    jlong       (*CallNonvirtualLongMethodA)(JNIEnv*, jobject, jclass,
                        jmethodID, jvalue*);
    jfloat      (*CallNonvirtualFloatMethod)(JNIEnv*, jobject, jclass,
                        jmethodID, ...) __NDK_FPABI__;
    jfloat      (*CallNonvirtualFloatMethodV)(JNIEnv*, jobject, jclass,
                        jmethodID, va_list) __NDK_FPABI__;
    jfloat      (*CallNonvirtualFloatMethodA)(JNIEnv*, jobject, jclass,
                        jmethodID, jvalue*) __NDK_FPABI__;
    jdouble     (*CallNonvirtualDoubleMethod)(JNIEnv*, jobject, jclass,
                        jmethodID, ...) __NDK_FPABI__;
    jdouble     (*CallNonvirtualDoubleMethodV)(JNIEnv*, jobject, jclass,
                        jmethodID, va_list) __NDK_FPABI__;
    jdouble     (*CallNonvirtualDoubleMethodA)(JNIEnv*, jobject, jclass,
                        jmethodID, jvalue*) __NDK_FPABI__;
    void        (*CallNonvirtualVoidMethod)(JNIEnv*, jobject, jclass,
                        jmethodID, ...);
    void        (*CallNonvirtualVoidMethodV)(JNIEnv*, jobject, jclass,
                        jmethodID, va_list);
    void        (*CallNonvirtualVoidMethodA)(JNIEnv*, jobject, jclass,
                        jmethodID, jvalue*);

    jfieldID    (*GetFieldID)(JNIEnv*, jclass, const char*, const char*);

    jobject     (*GetObjectField)(JNIEnv*, jobject, jfieldID);
    jboolean    (*GetBooleanField)(JNIEnv*, jobject, jfieldID);
    jbyte       (*GetByteField)(JNIEnv*, jobject, jfieldID);
    jchar       (*GetCharField)(JNIEnv*, jobject, jfieldID);
    jshort      (*GetShortField)(JNIEnv*, jobject, jfieldID);
    jint        (*GetIntField)(JNIEnv*, jobject, jfieldID);
    jlong       (*GetLongField)(JNIEnv*, jobject, jfieldID);
    jfloat      (*GetFloatField)(JNIEnv*, jobject, jfieldID) __NDK_FPABI__;
    jdouble     (*GetDoubleField)(JNIEnv*, jobject, jfieldID) __NDK_FPABI__;

    void        (*SetObjectField)(JNIEnv*, jobject, jfieldID, jobject);
    void        (*SetBooleanField)(JNIEnv*, jobject, jfieldID, jboolean);
    void        (*SetByteField)(JNIEnv*, jobject, jfieldID, jbyte);
    void        (*SetCharField)(JNIEnv*, jobject, jfieldID, jchar);
    void        (*SetShortField)(JNIEnv*, jobject, jfieldID, jshort);
    void        (*SetIntField)(JNIEnv*, jobject, jfieldID, jint);
    void        (*SetLongField)(JNIEnv*, jobject, jfieldID, jlong);
    void        (*SetFloatField)(JNIEnv*, jobject, jfieldID, jfloat) __NDK_FPABI__;
    void        (*SetDoubleField)(JNIEnv*, jobject, jfieldID, jdouble) __NDK_FPABI__;

    jmethodID   (*GetStaticMethodID)(JNIEnv*, jclass, const char*, const char*);

    jobject     (*CallStaticObjectMethod)(JNIEnv*, jclass, jmethodID, ...);
    jobject     (*CallStaticObjectMethodV)(JNIEnv*, jclass, jmethodID, va_list);
    jobject     (*CallStaticObjectMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
    jboolean    (*CallStaticBooleanMethod)(JNIEnv*, jclass, jmethodID, ...);
    jboolean    (*CallStaticBooleanMethodV)(JNIEnv*, jclass, jmethodID,
                        va_list);
    jboolean    (*CallStaticBooleanMethodA)(JNIEnv*, jclass, jmethodID,
                        jvalue*);
    jbyte       (*CallStaticByteMethod)(JNIEnv*, jclass, jmethodID, ...);
    jbyte       (*CallStaticByteMethodV)(JNIEnv*, jclass, jmethodID, va_list);
    jbyte       (*CallStaticByteMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
    jchar       (*CallStaticCharMethod)(JNIEnv*, jclass, jmethodID, ...);
    jchar       (*CallStaticCharMethodV)(JNIEnv*, jclass, jmethodID, va_list);
    jchar       (*CallStaticCharMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
    jshort      (*CallStaticShortMethod)(JNIEnv*, jclass, jmethodID, ...);
    jshort      (*CallStaticShortMethodV)(JNIEnv*, jclass, jmethodID, va_list);
    jshort      (*CallStaticShortMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
    jint        (*CallStaticIntMethod)(JNIEnv*, jclass, jmethodID, ...);
    jint        (*CallStaticIntMethodV)(JNIEnv*, jclass, jmethodID, va_list);
    jint        (*CallStaticIntMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
    jlong       (*CallStaticLongMethod)(JNIEnv*, jclass, jmethodID, ...);
    jlong       (*CallStaticLongMethodV)(JNIEnv*, jclass, jmethodID, va_list);
    jlong       (*CallStaticLongMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);
    jfloat      (*CallStaticFloatMethod)(JNIEnv*, jclass, jmethodID, ...) __NDK_FPABI__;
    jfloat      (*CallStaticFloatMethodV)(JNIEnv*, jclass, jmethodID, va_list) __NDK_FPABI__;
    jfloat      (*CallStaticFloatMethodA)(JNIEnv*, jclass, jmethodID, jvalue*) __NDK_FPABI__;
    jdouble     (*CallStaticDoubleMethod)(JNIEnv*, jclass, jmethodID, ...) __NDK_FPABI__;
    jdouble     (*CallStaticDoubleMethodV)(JNIEnv*, jclass, jmethodID, va_list) __NDK_FPABI__;
    jdouble     (*CallStaticDoubleMethodA)(JNIEnv*, jclass, jmethodID, jvalue*) __NDK_FPABI__;
    void        (*CallStaticVoidMethod)(JNIEnv*, jclass, jmethodID, ...);
    void        (*CallStaticVoidMethodV)(JNIEnv*, jclass, jmethodID, va_list);
    void        (*CallStaticVoidMethodA)(JNIEnv*, jclass, jmethodID, jvalue*);

    jfieldID    (*GetStaticFieldID)(JNIEnv*, jclass, const char*,
                        const char*);

    jobject     (*GetStaticObjectField)(JNIEnv*, jclass, jfieldID);
    jboolean    (*GetStaticBooleanField)(JNIEnv*, jclass, jfieldID);
    jbyte       (*GetStaticByteField)(JNIEnv*, jclass, jfieldID);
    jchar       (*GetStaticCharField)(JNIEnv*, jclass, jfieldID);
    jshort      (*GetStaticShortField)(JNIEnv*, jclass, jfieldID);
    jint        (*GetStaticIntField)(JNIEnv*, jclass, jfieldID);
    jlong       (*GetStaticLongField)(JNIEnv*, jclass, jfieldID);
    jfloat      (*GetStaticFloatField)(JNIEnv*, jclass, jfieldID) __NDK_FPABI__;
    jdouble     (*GetStaticDoubleField)(JNIEnv*, jclass, jfieldID) __NDK_FPABI__;

    void        (*SetStaticObjectField)(JNIEnv*, jclass, jfieldID, jobject);
    void        (*SetStaticBooleanField)(JNIEnv*, jclass, jfieldID, jboolean);
    void        (*SetStaticByteField)(JNIEnv*, jclass, jfieldID, jbyte);
    void        (*SetStaticCharField)(JNIEnv*, jclass, jfieldID, jchar);
    void        (*SetStaticShortField)(JNIEnv*, jclass, jfieldID, jshort);
    void        (*SetStaticIntField)(JNIEnv*, jclass, jfieldID, jint);
    void        (*SetStaticLongField)(JNIEnv*, jclass, jfieldID, jlong);
    void        (*SetStaticFloatField)(JNIEnv*, jclass, jfieldID, jfloat) __NDK_FPABI__;
    void        (*SetStaticDoubleField)(JNIEnv*, jclass, jfieldID, jdouble) __NDK_FPABI__;

    jstring     (*NewString)(JNIEnv*, const jchar*, jsize);
    jsize       (*GetStringLength)(JNIEnv*, jstring);
    const jchar* (*GetStringChars)(JNIEnv*, jstring, jboolean*);
    void        (*ReleaseStringChars)(JNIEnv*, jstring, const jchar*);
    jstring     (*NewStringUTF)(JNIEnv*, const char*);
    jsize       (*GetStringUTFLength)(JNIEnv*, jstring);
    /* JNI spec says this returns const jbyte*, but that's inconsistent */
    const char* (*GetStringUTFChars)(JNIEnv*, jstring, jboolean*);
    void        (*ReleaseStringUTFChars)(JNIEnv*, jstring, const char*);
    jsize       (*GetArrayLength)(JNIEnv*, jarray);
    jobjectArray (*NewObjectArray)(JNIEnv*, jsize, jclass, jobject);
    jobject     (*GetObjectArrayElement)(JNIEnv*, jobjectArray, jsize);
    void        (*SetObjectArrayElement)(JNIEnv*, jobjectArray, jsize, jobject);

    jbooleanArray (*NewBooleanArray)(JNIEnv*, jsize);
    jbyteArray    (*NewByteArray)(JNIEnv*, jsize);
    jcharArray    (*NewCharArray)(JNIEnv*, jsize);
    jshortArray   (*NewShortArray)(JNIEnv*, jsize);
    jintArray     (*NewIntArray)(JNIEnv*, jsize);
    jlongArray    (*NewLongArray)(JNIEnv*, jsize);
    jfloatArray   (*NewFloatArray)(JNIEnv*, jsize);
    jdoubleArray  (*NewDoubleArray)(JNIEnv*, jsize);

    jboolean*   (*GetBooleanArrayElements)(JNIEnv*, jbooleanArray, jboolean*);
    jbyte*      (*GetByteArrayElements)(JNIEnv*, jbyteArray, jboolean*);
    jchar*      (*GetCharArrayElements)(JNIEnv*, jcharArray, jboolean*);
    jshort*     (*GetShortArrayElements)(JNIEnv*, jshortArray, jboolean*);
    jint*       (*GetIntArrayElements)(JNIEnv*, jintArray, jboolean*);
    jlong*      (*GetLongArrayElements)(JNIEnv*, jlongArray, jboolean*);
    jfloat*     (*GetFloatArrayElements)(JNIEnv*, jfloatArray, jboolean*);
    jdouble*    (*GetDoubleArrayElements)(JNIEnv*, jdoubleArray, jboolean*);

    void        (*ReleaseBooleanArrayElements)(JNIEnv*, jbooleanArray,
                        jboolean*, jint);
    void        (*ReleaseByteArrayElements)(JNIEnv*, jbyteArray,
                        jbyte*, jint);
    void        (*ReleaseCharArrayElements)(JNIEnv*, jcharArray,
                        jchar*, jint);
    void        (*ReleaseShortArrayElements)(JNIEnv*, jshortArray,
                        jshort*, jint);
    void        (*ReleaseIntArrayElements)(JNIEnv*, jintArray,
                        jint*, jint);
    void        (*ReleaseLongArrayElements)(JNIEnv*, jlongArray,
                        jlong*, jint);
    void        (*ReleaseFloatArrayElements)(JNIEnv*, jfloatArray,
                        jfloat*, jint);
    void        (*ReleaseDoubleArrayElements)(JNIEnv*, jdoubleArray,
                        jdouble*, jint);

    void        (*GetBooleanArrayRegion)(JNIEnv*, jbooleanArray,
                        jsize, jsize, jboolean*);
    void        (*GetByteArrayRegion)(JNIEnv*, jbyteArray,
                        jsize, jsize, jbyte*);
    void        (*GetCharArrayRegion)(JNIEnv*, jcharArray,
                        jsize, jsize, jchar*);
    void        (*GetShortArrayRegion)(JNIEnv*, jshortArray,
                        jsize, jsize, jshort*);
    void        (*GetIntArrayRegion)(JNIEnv*, jintArray,
                        jsize, jsize, jint*);
    void        (*GetLongArrayRegion)(JNIEnv*, jlongArray,
                        jsize, jsize, jlong*);
    void        (*GetFloatArrayRegion)(JNIEnv*, jfloatArray,
                        jsize, jsize, jfloat*);
    void        (*GetDoubleArrayRegion)(JNIEnv*, jdoubleArray,
                        jsize, jsize, jdouble*);

    /* spec shows these without const; some jni.h do, some don't */
    void        (*SetBooleanArrayRegion)(JNIEnv*, jbooleanArray,
                        jsize, jsize, const jboolean*);
    void        (*SetByteArrayRegion)(JNIEnv*, jbyteArray,
                        jsize, jsize, const jbyte*);
    void        (*SetCharArrayRegion)(JNIEnv*, jcharArray,
                        jsize, jsize, const jchar*);
    void        (*SetShortArrayRegion)(JNIEnv*, jshortArray,
                        jsize, jsize, const jshort*);
    void        (*SetIntArrayRegion)(JNIEnv*, jintArray,
                        jsize, jsize, const jint*);
    void        (*SetLongArrayRegion)(JNIEnv*, jlongArray,
                        jsize, jsize, const jlong*);
    void        (*SetFloatArrayRegion)(JNIEnv*, jfloatArray,
                        jsize, jsize, const jfloat*);
    void        (*SetDoubleArrayRegion)(JNIEnv*, jdoubleArray,
                        jsize, jsize, const jdouble*);

    jint        (*RegisterNatives)(JNIEnv*, jclass, const JNINativeMethod*,
                        jint);
    jint        (*UnregisterNatives)(JNIEnv*, jclass);
    jint        (*MonitorEnter)(JNIEnv*, jobject);
    jint        (*MonitorExit)(JNIEnv*, jobject);
    jint        (*GetJavaVM)(JNIEnv*, JavaVM**);

    void        (*GetStringRegion)(JNIEnv*, jstring, jsize, jsize, jchar*);
    void        (*GetStringUTFRegion)(JNIEnv*, jstring, jsize, jsize, char*);

    void*       (*GetPrimitiveArrayCritical)(JNIEnv*, jarray, jboolean*);
    void        (*ReleasePrimitiveArrayCritical)(JNIEnv*, jarray, void*, jint);

    const jchar* (*GetStringCritical)(JNIEnv*, jstring, jboolean*);
    void        (*ReleaseStringCritical)(JNIEnv*, jstring, const jchar*);

    jweak       (*NewWeakGlobalRef)(JNIEnv*, jobject);
    void        (*DeleteWeakGlobalRef)(JNIEnv*, jweak);

    jboolean    (*ExceptionCheck)(JNIEnv*);

    jobject     (*NewDirectByteBuffer)(JNIEnv*, void*, jlong);
    void*       (*GetDirectBufferAddress)(JNIEnv*, jobject);
    jlong       (*GetDirectBufferCapacity)(JNIEnv*, jobject);

    /* added in JNI 1.6 */
    jobjectRefType (*GetObjectRefType)(JNIEnv*, jobject);

JNI层访问和修改JAVA实例变量与静态变量

由于JNI函数是直接操作JVM中的数据结构，不受Java访问修饰符的限制。即，在本地代码中可以调用JNI函数可以访问Java对象中的非public属性和方法

访问和修改实例变量操作步聚

调用GetObjectClass函数获取实例对象的Class引用
调用GetFieldID函数获取Class引用中某个实例变量的ID
调用GetXXXField（如GetObjectField）函数获取变量的值，需要传入实例变量所属对象和变量ID
调用SetXXXField（如SetObjectField）函数修改变量的值，需要传入实例变量所属对象、变量ID和变量的值

访问和修改静态变量操作步聚

调用FindClass函数获取类的Class引用
调用GetStaticFieldID函数获取Class引用中某个静态变量ID
调用GetStaticXXXField（如GetStaticIntField）函数获取静态变量的值，需要传入变量所属Class的引用和变量ID
调用SetStaticXXXField（SetStaticIntField）函数设置静态变量的值，需要传入变量所属Class的引用、变量ID和变量的值

JNI层访问和修改JAVA实例方法与静态方法

调用静态方法使用CallStaticXXXMethod/V/A函数，XXX代表返回值的数据类型。如：CallStaticIntMethod

void (JNICALL *CallStaticVoidMethod)  
 (JNIEnv *env, jclass cls, jmethodID methodID, ...);  
void (JNICALL *CallStaticVoidMethodV)  
 (JNIEnv *env, jclass cls, jmethodID methodID, va_list args);  
void (JNICALL *CallStaticVoidMethodA)  
 (JNIEnv *env, jclass cls, jmethodID methodID, const jvalue * args);

调用实例方法使用CallXXXMethod/V/A函数，XXX代表返回的数据类型，如：CallIntMethod

void        (*CallVoidMethod)(JNIEnv*, jobject, jmethodID, ...);
void        (*CallVoidMethodV)(JNIEnv*, jobject, jmethodID, va_list);
void        (*CallVoidMethodA)(JNIEnv*, jobject, jmethodID, jvalue*);

获取一个实例方法的ID，使用GetMethodID函数，传入方法名称和方法签名

jmethodID   (*GetMethodID)(JNIEnv*, jclass, const char*, const char*);

获以一个静态方法的ID，使用GetStaticMethodID函数，传入方法名称和方法签名

jmethodID   (*GetStaticMethodID)(JNIEnv*, jclass, const char*, const char*);

获取构造方法ID，方法名称使用”<init>”，比如获取默认构造方法

(*env)->GetMethodID(env,clazz, "<init>","()V");

获取一个类的Class实例，使用FindClass函数，传入类描述符。JVM会从classpath目录下开始搜索。

jclass      (*FindClass)(JNIEnv*, const char*);

创建一个类的实例，使用NewObject函数，传入Class引用和构造方法ID

    jobject     (*NewObject)(JNIEnv*, jclass, jmethodID, ...);
    jobject     (*NewObjectV)(JNIEnv*, jclass, jmethodID, va_list);
    jobject     (*NewObjectA)(JNIEnv*, jclass, jmethodID, jvalue*);

删除局部变量引用，使用DeleteLocalRef，传入引用变量

    void DeleteLocalRef(jobject localRef)
    { functions->DeleteLocalRef(this, localRef); }

方法签名格式：(形参参数列表)返回值类型。注意：形参参数列表之间不需要用空格或其它字符分隔
类描述符格式：L包名路径/类名;，包名之间用/分隔。如：Ljava/lang/String;
调用GetMethodID获取方法ID和调用FindClass获取Class实例后，要做异常判断，判断返回值是否为NULL