Android(安卓)NDK开发之JNI基础知识
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 JNICALLJava_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 JNICALLJava_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
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