本文主要介紹一下內容:
- 配合NDK NativeActivity封裝jni調用需要的環境參數
- 獲取靜態和非靜態java方法信息的封裝
- 調用靜態和非靜態java方法的封裝
- 獲取apk簽名的jni調用封裝
#include <android/native_activity.h>
#include <stdbool.h>
extern ANativeActivity* nativeActivity;
static inline JNIEnv* GetEnvPtr()
{
static JNIEnv* envPtr = NULL;
if (envPtr == NULL)
{
(*nativeActivity->vm)->AttachCurrentThread(nativeActivity->vm, &envPtr, NULL);
}
return envPtr;
}
ANativeActivity來自於NDK直接提供的接口。需要注意的是,JNIEnv*是和線程綁定的,所以需要在同一個線程獲取並使用。static inline jclass GetClass(char *className)
{
JNIEnv* envPtr = GetEnvPtr();
static jobject classLoaderObj = NULL;
static jmethodID loadClassId = NULL;
if (classLoaderObj == NULL)
{
jclass activityCls = (*envPtr)->FindClass(envPtr, "android/app/NativeActivity");
jclass loaderCls = (*envPtr)->FindClass(envPtr, "java/lang/ClassLoader");
jmethodID getClassLoaderId = (*envPtr)->GetMethodID
(
envPtr,
activityCls,
"getClassLoader",
"()Ljava/lang/ClassLoader;"
);
classLoaderObj = (*envPtr)->CallObjectMethod(envPtr, nativeActivity->clazz, getClassLoaderId);
loadClassId = (*envPtr)->GetMethodID
(
envPtr,
loaderCls,
"loadClass",
"(Ljava/lang/String;)Ljava/lang/Class;"
);
}
jstring classNameStr = (*envPtr)->NewStringUTF (envPtr, className);
jclass cls = (jclass) (*envPtr)->CallObjectMethod(envPtr, classLoaderObj, loadClassId, classNameStr);
ALogA(cls != NULL, "JniTool GetClass can not load class = %s", className);
(*envPtr)->DeleteLocalRef(envPtr, classNameStr);
return cls;
}
這裏,我們使用了內置類android/app/NativeActivity的類加載器,來載入指定的類。接下來,有了以上兩個方法,就可以封裝獲取java靜態和非靜態方法信息函數了。有了方法信息就可以調用這個方法了。
static inline void GetJniMethodInfo(bool isStatic, char* className, char* methodName, char* paramCode, JniMethodInfo* outJniMethodInfo)
{
JNIEnv* envPtr = GetEnvPtr();
jclass cls = GetClass(className);
jmethodID methodID;
if (isStatic)
{
methodID = (*envPtr)->GetStaticMethodID(envPtr, cls, methodName, paramCode);
}
else
{
methodID = (*envPtr)->GetMethodID(envPtr, cls, methodName, paramCode);
}
ALogA
(
methodID != NULL,
"JniTool %s can not get methodID, className = %s, methodName = %s, paramCode = %s",
isStatic ? "GetStaticMethodID" : "GetMethodID",
className,
methodName,
paramCode
);
outJniMethodInfo->envPtr = envPtr;
outJniMethodInfo->cls = cls;
outJniMethodInfo->methodID = methodID;
}
static void GetMethodInfo(char* className, char* methodName, char* paramCode, JniMethodInfo* outJniMethodInfo)
{
GetJniMethodInfo(false, className, methodName, paramCode,outJniMethodInfo);
}
static void GetStaticMethodInfo(char* className, char* methodName, char* paramCode, JniMethodInfo* outJniMethodInfo)
{
GetJniMethodInfo(true, className, methodName, paramCode,outJniMethodInfo);
}
這兩個方法,是方便自己調用java方法的時候使用的。使用時候返回值需要自己處理,參數主要根據函數自己傳入不定參數。static jvalue CallObjectMethod(jobject object, char* methodName, char* paramCode, ...)
{
JNIEnv* envPtr = GetEnvPtr();
jclass cls = (*envPtr)->GetObjectClass(envPtr, object);
jmethodID methodId = (*envPtr)->GetMethodID (envPtr, cls, methodName, paramCode);
ALogA
(
methodId != NULL,
"JniTool CallObjectMethod can not get methodID, methodName = %s, paramCode = %s",
methodName,
paramCode
);
char* p = paramCode;
// skip '()' to find out the return type
while (*p != ')')
{
p++;
}
// skip ')'
p++;
va_list args;
va_start(args, paramCode);
jvalue value;
switch (*p)
{
case 'V':
(*envPtr)->CallVoidMethodV (envPtr, object, methodId, args);
break;
case '[':
case 'L':
value.l = (*envPtr)->CallObjectMethodV (envPtr, object, methodId, args);
break;
case 'Z':
value.z = (*envPtr)->CallBooleanMethodV(envPtr, object, methodId, args);
break;
case 'B':
value.b = (*envPtr)->CallByteMethodV (envPtr, object, methodId, args);
break;
case 'C':
value.c = (*envPtr)->CallCharMethodV (envPtr, object, methodId, args);
break;
case 'S':
value.s = (*envPtr)->CallShortMethodV (envPtr, object, methodId, args);
break;
case 'I':
value.i = (*envPtr)->CallIntMethodV (envPtr, object, methodId, args);
break;
case 'J':
value.j = (*envPtr)->CallLongMethodV (envPtr, object, methodId, args);
break;
case 'F':
value.f = (*envPtr)->CallFloatMethodV (envPtr, object, methodId, args);
break;
case 'D':
value.d = (*envPtr)->CallDoubleMethodV (envPtr, object, methodId, args);
break;
default:
ALogA(false, "JniTool CallObjectMethod paramCode = %s, illegal", paramCode);
}
va_end(args);
return value;
}
static inline jvalue CallClassMethodV(jclass cls, char* methodName, char* paramCode, va_list args)
{
JNIEnv* envPtr = GetEnvPtr();
jmethodID methodId = (*envPtr)->GetStaticMethodID(envPtr, cls, methodName, paramCode);
ALogA
(
methodId != NULL,
"JniTool CallClassMethodV can not get methodID, methodName = %s, paramCode = %s",
methodName,
paramCode
);
char* p = paramCode;
// skip '()' to find out the return type
while (*p != ')')
{
p++;
}
// skip ')'
p++;
jvalue value;
switch (*p)
{
case 'V':
(*envPtr)->CallStaticVoidMethodV (envPtr, cls, methodId, args);
break;
case '[':
case 'L':
value.l = (*envPtr)->CallStaticObjectMethodV (envPtr, cls, methodId, args);
break;
case 'Z':
value.z = (*envPtr)->CallStaticBooleanMethodV(envPtr, cls, methodId, args);
break;
case 'B':
value.b = (*envPtr)->CallStaticByteMethodV (envPtr, cls, methodId, args);
break;
case 'C':
value.c = (*envPtr)->CallStaticCharMethodV (envPtr, cls, methodId, args);
break;
case 'S':
value.s = (*envPtr)->CallStaticShortMethodV (envPtr, cls, methodId, args);
break;
case 'I':
value.i = (*envPtr)->CallStaticIntMethodV (envPtr, cls, methodId, args);
break;
case 'J':
value.j = (*envPtr)->CallStaticLongMethodV (envPtr, cls, methodId, args);
break;
case 'F':
value.f = (*envPtr)->CallStaticFloatMethodV (envPtr, cls, methodId, args);
break;
case 'D':
value.d = (*envPtr)->CallStaticDoubleMethodV (envPtr, cls, methodId, args);
break;
default:
ALogA(false, "JniTool CallClassMethod paramCode = %s, illegal", paramCode);
}
return value;
}
static inline jvalue CallClassMethod(jclass cls, char* methodName, char* paramCode, ...)
{
va_list args;
va_start(args, paramCode);
jvalue value = CallClassMethodV(cls, methodName, paramCode, args);
va_end(args);
return value;
}
static jvalue CallStaticMethod(char* className, char* methodName, char* paramCode, ...)
{
va_list args;
va_start(args, paramCode);
jvalue value = CallClassMethodV(GetClass(className), methodName, paramCode, args);
va_end(args);
return value;
}
說明幾點:- 參數使用了變參,因爲調用的java方法不確定參數個數和類型,需要依次傳入。
- 返回值當然也是不確定類型的,所以使用了jValue這個union類型存放。
- 這兩個方法,只需要給出字符串類型的,類路徑,方法名,參數列表
static int GetSignHashCode()
{
JNIEnv* envPtr = GetEnvPtr();
jobject packageManager = CallObjectMethod
(
nativeActivity->clazz,
"getPackageManager",
"()Landroid/content/pm/PackageManager;"
).l;
jstring packageName = (jstring) CallObjectMethod
(
nativeActivity->clazz,
"getPackageName",
"()Ljava/lang/String;"
).l;
jobject packageInfo = CallObjectMethod
(
packageManager,
"getPackageInfo",
"(Ljava/lang/String;I)Landroid/content/pm/PackageInfo;",
packageName,
64
).l;
jclass packageInfoCls = (*envPtr)->GetObjectClass(envPtr, packageInfo);
jfieldID signaturesFid = (*envPtr)->GetFieldID
(
envPtr,
packageInfoCls,
"signatures",
"[Landroid/content/pm/Signature;"
);
jobjectArray signatureArr = (*envPtr)->GetObjectField (envPtr, packageInfo, signaturesFid);
jobject signature = (*envPtr)->GetObjectArrayElement(envPtr, signatureArr, 0);
return CallObjectMethod(signature, "hashCode", "()I").i;
}
可以看到,函數的實現,就是使用jni調用各種java已有的代碼來實現的。當然也可以獲得簽名的md5值,只是我懶得寫了。另外需要注意的是,jni提供的New開頭的函數,都需要調用Delete開頭的函數釋放內存。比如,NewStringUTF,DeleteLocalRef。