一、拆分文件

//获取文件大小
long get_file_size(char *path) {
    FILE *fp = fopen(path, "rb");
    fseek(fp, 0, SEEK_END);
    return ftell(fp);
}

JNIEXPORT void JNICALL Java_com_binzi_ndkfile_NDKFileUtils_split
  (JNIEnv *env, jclass jcls, jstring path_jstr,jstring path_pattern_jstr, jint file_num){
    //jstring -> char*
    //需要分割的文件路径
    const char* path = (*env)->GetStringUTFChars(env,path_jstr,NULL);
    const char* path_pattern = (*env)->GetStringUTFChars(env,path_pattern_jstr,NULL);

    //得到分割之后的子文件的路径列表
    char **patches = malloc(sizeof(char*) * file_num);
    int i = 0;
    for (; i < file_num; i++) {
        patches[i] = malloc(sizeof(char) * 100);
        //元素赋值
        sprintf(patches[i], path_pattern, (i+1));
        LOGI("patch path:%s",patches[i]);
    }

    //不断读取path文件，循环写入file_num个文件中
    //  整除
    //  文件大小：90，分成9个文件，每个文件10
    //  不整除
    //  文件大小：110，分成9个文件，
    //  前(9-1)个文件为(110/(9-1))=13
    //  最后一个文件(110%(9-1))=6
    int filesize = get_file_size(path);
    FILE *fpr = fopen(path,"rb");
    //整除
    if(filesize % file_num == 0){
        //单个文件大小
        int part = filesize / file_num;
        i = 0;
        //逐一写入不同的分割子文件中
        for (; i < file_num; i++) {
            FILE *fpw = fopen(patches[i], "wb");
            int j = 0;
            for(; j < part; j++){
                //边读边写
                fputc(fgetc(fpr),fpw);
            }
            fclose(fpw);
        }
    } else {
        //不整除
        int part = filesize / (file_num - 1);
        i = 0;
        //逐一写入不同的分割子文件中
        for (; i < file_num - 1; i++) {
            FILE *fpw = fopen(patches[i], "wb");
            int j = 0;
            for(; j < part; j++){
                //边读边写
                fputc(fgetc(fpr),fpw);
            }
            fclose(fpw);
        }
        //the last one
        FILE *fpw = fopen(patches[file_num - 1], "wb");
        i = 0;
        for(; i < filesize % (file_num - 1); i++){
            fputc(fgetc(fpr),fpw);
        }
        fclose(fpw);
    }

    //关闭被分割的文件
    fclose(fpr);

    //释放
    i = 0;
    for(; i < file_num; i++){
        free(patches[i]);
    }
    free(patches);

    (*env)->ReleaseStringUTFChars(env,path_jstr,path);
    (*env)->ReleaseStringUTFChars(env,path_pattern_jstr,path_pattern);
}

二、文件合并

JNIEXPORT void JNICALL Java_com_binzi_ndkfile_NDKFileUtils_merge
  (JNIEnv *env, jclass jcls,jstring path_pattern_jstr, jint file_num,jstring merge_path_jstr){
    //合并之后的文件
    const char* merge_path = (*env)->GetStringUTFChars(env,merge_path_jstr,NULL);
    //分割子文件的pattern
    const char* path_pattern = (*env)->GetStringUTFChars(env,path_pattern_jstr,NULL);

    //得到分割之后的子文件的路径列表
    char **patches = malloc(sizeof(char*) * file_num);
    int i = 0;
    for (; i < file_num; i++) {
        patches[i] = malloc(sizeof(char) * 100);
        //元素赋值
        sprintf(patches[i], path_pattern, (i+1));
        LOGI("patch path:%s",patches[i]);
    }

    FILE *fpw = fopen(merge_path,"wb");
    //把所有的分割文件读取一遍，写入一个总的文件中
    i = 0;
    for(; i < file_num; i++){
        //每个子文件的大小
        int filesize = get_file_size(patches[i]);
        FILE *fpr = fopen(patches[i], "rb");
        int j = 0;
        for (; j < filesize; j++) {
            fputc(fgetc(fpr),fpw);
        }
        fclose(fpr);
    }
    fclose(fpw);

    //释放
    i = 0;
    for(; i < file_num; i++){
        free(patches[i]);
    }
    free(patches);

    (*env)->ReleaseStringUTFChars(env,path_pattern_jstr,path_pattern);
    (*env)->ReleaseStringUTFChars(env,merge_path_jstr,merge_path);
}