JNI
简介
JNI是JAVA和C/C++相互调用的桥梁
文档 官方文档
类型映射
Jni中定义了原始类型和java中的类型一一对应
| Java 类型 | 原始类型 |
|---|---|
| boolean | jboolean |
| byte | jbyte |
| char | jchar |
| short | jshort |
| int | jint |
| long | jlong |
| float | jfloat |
| double | jdouble |
| void | void |
| true | JNI_TRUE |
| false | JNI_FALSE |
types4.gif
类型签名
当Jni获取java中方法时，由于java有重载，Jni不知道具体调哪个方法，所以存在签名
| 签名 | Java类型 |
|---|---|
| Z | boolean |
| B | byte |
| C | char |
| S | short |
| I | int |
| J | long |
| F | float |
| D | double |
| L fully-qualified-class ; | fully-qualified-class |
| [ type | type[] |
| ( arg-types ) ret-type | method type |
| V | void |
示例
long f (int n, String s, int[] arr);
签名为 (ILjava/lang/String;[I)J
extern "C"
JNIEXPORT void JNICALL
Java_com_example_mynative_MainActivity_start(JNIEnv *env, jobject thiz, jint type,
jobject on_click_listener) {
jclass pJclass = env->GetObjectClass(on_click_listener);
//通过object获取到Class
// jclass pJclass = env->FindClass("com/example/mynative/MyListener");
__android_log_print(ANDROID_LOG_DEBUG, "C", "pJclass is haha");
if (pJclass != 0) {
jmethodID pId = env->GetMethodID(pJclass, "onSuccess", "(I)V");
//通过方法名和方法签名获取到class中的方法id
if (pId != 0) {
jint step = 100;
__android_log_print(ANDROID_LOG_DEBUG, "C", "I am here");
env->CallVoidMethod(on_click_listener, pId, step);
// 调用之前获取到的方法
}
}
}
- 注意：getMethodID时的方法签名，是前一步获取class的方法签名 不是java中的native方法
- javac com/example/mynative/MyListener.java
- javap -s -p com/example/mynative/MyListener
- 可以通过上述方法获取签名
接口函数表
Code Example 4-1
const struct JNINativeInterface ... = {
NULL,
NULL,
NULL,
NULL,
GetVersion,
DefineClass,
FindClass,
FromReflectedMethod,
FromReflectedField,
ToReflectedMethod,
GetSuperclass,
IsAssignableFrom,
ToReflectedField,
Throw,
ThrowNew,
ExceptionOccurred,
ExceptionDescribe,
ExceptionClear,
FatalError,
PushLocalFrame,
PopLocalFrame,
NewGlobalRef,
DeleteGlobalRef,
DeleteLocalRef,
IsSameObject,
NewLocalRef,
EnsureLocalCapacity,
AllocObject,
NewObject,
NewObjectV,
NewObjectA,
GetObjectClass,
IsInstanceOf,
GetMethodID,
CallObjectMethod,
CallObjectMethodV,
CallObjectMethodA,
CallBooleanMethod,
CallBooleanMethodV,
CallBooleanMethodA,
CallByteMethod,
CallByteMethodV,
CallByteMethodA,
CallCharMethod,
CallCharMethodV,
CallCharMethodA,
CallShortMethod,
CallShortMethodV,
CallShortMethodA,
CallIntMethod,
CallIntMethodV,
CallIntMethodA,
CallLongMethod,
CallLongMethodV,
CallLongMethodA,
CallFloatMethod,
CallFloatMethodV,
CallFloatMethodA,
CallDoubleMethod,
CallDoubleMethodV,
CallDoubleMethodA,
CallVoidMethod,
CallVoidMethodV,
CallVoidMethodA,
CallNonvirtualObjectMethod,
CallNonvirtualObjectMethodV,
CallNonvirtualObjectMethodA,
CallNonvirtualBooleanMethod,
CallNonvirtualBooleanMethodV,
CallNonvirtualBooleanMethodA,
CallNonvirtualByteMethod,
CallNonvirtualByteMethodV,
CallNonvirtualByteMethodA,
CallNonvirtualCharMethod,
CallNonvirtualCharMethodV,
CallNonvirtualCharMethodA,
CallNonvirtualShortMethod,
CallNonvirtualShortMethodV,
CallNonvirtualShortMethodA,
CallNonvirtualIntMethod,
CallNonvirtualIntMethodV,
CallNonvirtualIntMethodA,
CallNonvirtualLongMethod,
CallNonvirtualLongMethodV,
CallNonvirtualLongMethodA,
CallNonvirtualFloatMethod,
CallNonvirtualFloatMethodV,
CallNonvirtualFloatMethodA,
CallNonvirtualDoubleMethod,
CallNonvirtualDoubleMethodV,
CallNonvirtualDoubleMethodA,
CallNonvirtualVoidMethod,
CallNonvirtualVoidMethodV,
CallNonvirtualVoidMethodA,
GetFieldID,
GetObjectField,
GetBooleanField,
GetByteField,
GetCharField,
GetShortField,
GetIntField,
GetLongField,
GetFloatField,
GetDoubleField,
SetObjectField,
SetBooleanField,
SetByteField,
SetCharField,
SetShortField,
SetIntField,
SetLongField,
SetFloatField,
SetDoubleField,
GetStaticMethodID,
CallStaticObjectMethod,
CallStaticObjectMethodV,
CallStaticObjectMethodA,
CallStaticBooleanMethod,
CallStaticBooleanMethodV,
CallStaticBooleanMethodA,
CallStaticByteMethod,
CallStaticByteMethodV,
CallStaticByteMethodA,
CallStaticCharMethod,
CallStaticCharMethodV,
CallStaticCharMethodA,
CallStaticShortMethod,
CallStaticShortMethodV,
CallStaticShortMethodA,
CallStaticIntMethod,
CallStaticIntMethodV,
CallStaticIntMethodA,
CallStaticLongMethod,
CallStaticLongMethodV,
CallStaticLongMethodA,
CallStaticFloatMethod,
CallStaticFloatMethodV,
CallStaticFloatMethodA,
CallStaticDoubleMethod,
CallStaticDoubleMethodV,
CallStaticDoubleMethodA,
CallStaticVoidMethod,
CallStaticVoidMethodV,
CallStaticVoidMethodA,
GetStaticFieldID,
GetStaticObjectField,
GetStaticBooleanField,
GetStaticByteField,
GetStaticCharField,
GetStaticShortField,
GetStaticIntField,
GetStaticLongField,
GetStaticFloatField,
GetStaticDoubleField,
SetStaticObjectField,
SetStaticBooleanField,
SetStaticByteField,
SetStaticCharField,
SetStaticShortField,
SetStaticIntField,
SetStaticLongField,
SetStaticFloatField,
SetStaticDoubleField,
NewString,
GetStringLength,
GetStringChars,
ReleaseStringChars,
NewStringUTF,
GetStringUTFLength,
GetStringUTFChars,
ReleaseStringUTFChars,
GetArrayLength,
NewObjectArray,
GetObjectArrayElement,
SetObjectArrayElement,
NewBooleanArray,
NewByteArray,
NewCharArray,
NewShortArray,
NewIntArray,
NewLongArray,
NewFloatArray,
NewDoubleArray,
GetBooleanArrayElements,
GetByteArrayElements,
GetCharArrayElements,
GetShortArrayElements,
GetIntArrayElements,
GetLongArrayElements,
GetFloatArrayElements,
GetDoubleArrayElements,
ReleaseBooleanArrayElements,
ReleaseByteArrayElements,
ReleaseCharArrayElements,
ReleaseShortArrayElements,
ReleaseIntArrayElements,
ReleaseLongArrayElements,
ReleaseFloatArrayElements,
ReleaseDoubleArrayElements,
GetBooleanArrayRegion,
GetByteArrayRegion,
GetCharArrayRegion,
GetShortArrayRegion,
GetIntArrayRegion,
GetLongArrayRegion,
GetFloatArrayRegion,
GetDoubleArrayRegion,
SetBooleanArrayRegion,
SetByteArrayRegion,
SetCharArrayRegion,
SetShortArrayRegion,
SetIntArrayRegion,
SetLongArrayRegion,
SetFloatArrayRegion,
SetDoubleArrayRegion,
RegisterNatives,
UnregisterNatives,
MonitorEnter,
MonitorExit,
GetJavaVM,
GetStringRegion,
GetStringUTFRegion,
GetPrimitiveArrayCritical,
ReleasePrimitiveArrayCritical,
GetStringCritical,
ReleaseStringCritical,
NewWeakGlobalRef,
DeleteWeakGlobalRef,
ExceptionCheck,
NewDirectByteBuffer,
GetDirectBufferAddress,
GetDirectBufferCapacity,
GetObjectRefType
};
