Android NDK开发之JNI基础知识，ndkjni
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Android NDK开发之JNI基础知识，ndkjni
JNI层方法命名规范
在java层对应的native方法的声明，test方法是一个本地方法，其参数是字符串类型，返回值是字符串类型。
package com.kltz88.jnidemo;
public class Test {
static {
System.loadLibrary("test");
}
public native String test(String name);
}
由android studio自动生成的native层的方法如下。
#include <jni.h>
JNIEXPORT jstring JNICALL
Java_com_kltz88_car_jnidemo_Test_test(JNIEnv *env, jobject instance, jstring name_) {
const char *name = (*env)->GetStringUTFChars(env, name_, 0);
// TODO
(*env)->ReleaseStringUTFChars(env, name_, name);
return (*env)->NewStringUTF(env, returnValue);
}函数的命名规则
函数命名规则为：Java_类全路径方法名。如Java_com_kltz88_jnidemo_Test_test，其中Java是函数的前缀，com_kltz88_jnidemo_Test是类名，test是方法名，它们之间用 _(下划线) 连接。
函数参数
JNIEXPORT jstring JNICALL Java_com_kltz88_jnidemo_Test_test(JNIEnv *, jclass, jstring );
- 第一个参数：JNIEnv* 是定义任意native函数的第一个参数（包括调用JNI的RegisterNatives函数注册的函数），指向JVM函数表的指针，函数表中的每一个入口指向一个JNI函数，每个函数用于访问JVM中特定的数据结构。
- 第二个参数：调用java中native方法的实例或Class对象，如果这个native方法是实例方法，则该参数是jobject，如果是静态方法，则是jclass
- 第三个参数：Java对应JNI中的数据类型，Java中String类型对应JNI的jstring 类型。
函数返回值类型
夹在JNIEXPORT和JNICALL宏中间的jstring ，表示函数的返回值类型，对应Java的void类型
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
访问和修改静态变量操作步聚
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
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