JNIHelp.c 遗漏的部分

从网上下载的Android源代码少了一些函数，但是从google code search里面却能看到遗漏的部分:

 

static struct CachedFields {
    jclass fileDescriptorClass;
    jmethodID fileDescriptorCtor;
    jfieldID descriptorField;
} gCachedFields;

int registerJniHelp(JNIEnv* env) {
    gCachedFields.fileDescriptorClass =
            (*env)->NewGlobalRef(env, (*env)->FindClass(env, "java/io/FileDescriptor"));
    if (gCachedFields.fileDescriptorClass == NULL) {
        return -1;
    }

    gCachedFields.fileDescriptorCtor =
            (*env)->GetMethodID(env, gCachedFields.fileDescriptorClass, "<init>", "()V");
    if (gCachedFields.fileDescriptorCtor == NULL) {
        return -1;
    }

    gCachedFields.descriptorField =
            (*env)->GetFieldID(env, gCachedFields.fileDescriptorClass, "descriptor", "I");
    if (gCachedFields.descriptorField == NULL) {
        return -1;
    }

    return 0;
}

/*
 * Create a java.io.FileDescriptor given an integer fd
 */
jobject jniCreateFileDescriptor(JNIEnv* env, int fd) {
    jobject fileDescriptor = (*env)->NewObject(env,
            gCachedFields.fileDescriptorClass, gCachedFields.fileDescriptorCtor);
    jniSetFileDescriptorOfFD(env, fileDescriptor, fd);
    return fileDescriptor;
}

/*
 * Get an int file descriptor from a java.io.FileDescriptor
 */
int jniGetFDFromFileDescriptor(JNIEnv* env, jobject fileDescriptor) {
    return (*env)->GetIntField(env, fileDescriptor, gCachedFields.descriptorField);
}

/*
 * Set the descriptor of a java.io.FileDescriptor
 */
void jniSetFileDescriptorOfFD(JNIEnv* env, jobject fileDescriptor, int value) {
    (*env)->SetIntField(env, fileDescriptor, gCachedFields.descriptorField, value);
}