文档首页/ MapReduce服务 MRS/ 开发指南（普通版_3.x）/ HDFS开发指南（普通模式）/ HDFS应用开发常见问题/ HDFS常用API介绍/ HDFS C API接口介绍
更新时间：2024-10-23 GMT+08:00
查看PDF
分享

HDFS C API接口介绍

功能简介

C语言应用开发代码样例中所涉及的文件操作主要包括创建文件、读写文件、追加文件、删除文件。完整和详细的接口请直接参考官网上的描述以了解其使用方法：

http://hadoop.apache.org/docs/r3.1.1/hadoop-project-dist/hadoop-hdfs/LibHdfs.html

代码样例

下面代码片段仅为演示，具体代码请参见样例代码解压目录中HDFS的C样例代码“hdfs-c-example/hdfs_test.c”文件。

  1. 设置HDFS NameNode参数，建立HDFS文件系统连接。 
    hdfsFS fs = hdfsConnect("default", 0);
fprintf(stderr, "hdfsConnect- SUCCESS!\n");
  2. 创建HDFS目录。 
    const char* dir = "/tmp/nativeTest";
int exitCode = hdfsCreateDirectory(fs, dir);
if( exitCode == -1 ){
     fprintf(stderr, "Failed to create directory %s \n", dir );
     exit(-1);
}
fprintf(stderr, "hdfsCreateDirectory- SUCCESS! : %s\n", dir);
  3. 写文件。 
    const char* file = "/tmp/nativeTest/testfile.txt";
hdfsFile writeFile = openFile(fs, (char*)file, O_WRONLY |O_CREAT, 0, 0, 0);
fprintf(stderr, "hdfsOpenFile- SUCCESS! for write : %s\n", file);

if(!hdfsFileIsOpenForWrite(writeFile)){
    fprintf(stderr, "Failed to open %s for writing.\n", file);
    exit(-1);
}

char* buffer = "Hadoop HDFS Native file write!";

hdfsWrite(fs, writeFile, (void*)buffer, strlen(buffer)+1);
fprintf(stderr, "hdfsWrite- SUCCESS! : %s\n", file);

printf("Flushing file data ....\n");
if (hdfsFlush(fs, writeFile)) {
     fprintf(stderr, "Failed to 'flush' %s\n", file);
     exit(-1);
}
hdfsCloseFile(fs, writeFile);
fprintf(stderr, "hdfsCloseFile- SUCCESS! : %s\n", file);
  4. 读文件。 
    hdfsFile readFile = openFile(fs, (char*)file, O_RDONLY, 100, 0, 0);
fprintf(stderr, "hdfsOpenFile- SUCCESS! for read : %s\n", file);

if(!hdfsFileIsOpenForRead(readFile)){
    fprintf(stderr, "Failed to open %s for reading.\n", file);
    exit(-1);
}

buffer = (char *) malloc(100);
tSize num_read = hdfsRead(fs, readFile, (void*)buffer, 100);
fprintf(stderr, "hdfsRead- SUCCESS!, Byte read : %d, File contant : %s \n", num_read ,buffer);
hdfsCloseFile(fs, readFile);
  5. 指定位置开始读文件。 
    buffer = (char *) malloc(100);
readFile = openFile(fs, file, O_RDONLY, 100, 0, 0);
if (hdfsSeek(fs, readFile, 10)) {
     fprintf(stderr, "Failed to 'seek' %s\n", file);
     exit(-1);
}
num_read = hdfsRead(fs, readFile, (void*)buffer, 100);
fprintf(stderr, "hdfsSeek- SUCCESS!, Byte read : %d, File seek contant : %s \n", num_read ,buffer);
hdfsCloseFile(fs, readFile);
  6. 复制文件。 
    const char* destfile = "/tmp/nativeTest/testfile1.txt";
if (hdfsCopy(fs, file, fs, destfile)) {
    fprintf(stderr, "File copy failed, src : %s, des : %s \n", file, destfile);
    exit(-1);
}
fprintf(stderr, "hdfsCopy- SUCCESS!, File copied, src : %s, des : %s \n", file, destfile);
  7. 移动文件。 
    const char* mvfile = "/tmp/nativeTest/testfile2.txt";
if (hdfsMove(fs, destfile, fs, mvfile )) {
    fprintf(stderr, "File move failed, src : %s, des : %s \n", destfile , mvfile);
    exit(-1);
}
fprintf(stderr, "hdfsMove- SUCCESS!, File moved, src : %s, des : %s \n", destfile , mvfile);
  8. 重命名文件。 
    const char* renamefile = "/tmp/nativeTest/testfile3.txt";
if (hdfsRename(fs, mvfile, renamefile)) {
     fprintf(stderr, "File rename failed, Old name : %s, New name : %s \n", mvfile, renamefile);
     exit(-1);
}
fprintf(stderr, "hdfsRename- SUCCESS!, File renamed, Old name : %s, New name : %s \n", mvfile, renamefile);
  9. 删除文件。 
    if (hdfsDelete(fs, renamefile, 0)) {
    fprintf(stderr, "File delete failed : %s \n", renamefile);
    exit(-1);
}
fprintf(stderr, "hdfsDelete- SUCCESS!, File deleted : %s\n",renamefile);
  10. 设置副本数。 
    if (hdfsSetReplication(fs, file, 10)) {
    fprintf(stderr, "Failed to set replication : %s \n", file );
    exit(-1);
}
fprintf(stderr, "hdfsSetReplication- SUCCESS!, Set replication 10 for %s\n",file);
  11. 设置用户、用户组。 
    if (hdfsChown(fs, file, "root", "root")) {
   fprintf(stderr, "Failed to set chown : %s \n", file );
   exit(-1);
}
fprintf(stderr, "hdfsChown- SUCCESS!, Chown success for %s\n",file);
  12. 设置权限。 
    if (hdfsChmod(fs, file, S_IRWXU | S_IRWXG | S_IRWXO)) {
   fprintf(stderr, "Failed to set chmod: %s \n", file );
   exit(-1);
}
fprintf(stderr, "hdfsChmod- SUCCESS!, Chmod success for %s\n",file);
  13. 设置文件时间。 
    struct timeval now;
gettimeofday(&now, NULL);
if (hdfsUtime(fs, file, now.tv_sec, now.tv_sec)) {
   fprintf(stderr, "Failed to set time: %s \n", file );
   exit(-1);
}
fprintf(stderr, "hdfsUtime- SUCCESS!, Set time success for %s\n",file);
  14. 获取文件信息。 
    hdfsFileInfo *fileInfo = NULL;
if((fileInfo = hdfsGetPathInfo(fs, file)) != NULL) {
   printFileInfo(fileInfo);
   hdfsFreeFileInfo(fileInfo, 1);
   fprintf(stderr, "hdfsGetPathInfo - SUCCESS!\n");
}
  15. 遍历目录。 
    hdfsFileInfo *fileList = 0;
int numEntries = 0;
if((fileList = hdfsListDirectory(fs, dir, &numEntries)) != NULL) {
   int i = 0;
   for(i=0; i < numEntries; ++i) {
       printFileInfo(fileList+i);
   }
   hdfsFreeFileInfo(fileList, numEntries);
}
fprintf(stderr, "hdfsListDirectory- SUCCESS!, %s\n", dir);
  16. stream builder接口。 
    buffer = (char *) malloc(100);
struct hdfsStreamBuilder *builder= hdfsStreamBuilderAlloc(fs, (char*)file, O_RDONLY);
hdfsStreamBuilderSetBufferSize(builder,100);
hdfsStreamBuilderSetReplication(builder,20);
hdfsStreamBuilderSetDefaultBlockSize(builder,10485760);
readFile = hdfsStreamBuilderBuild(builder);
num_read = hdfsRead(fs, readFile, (void*)buffer, 100);
fprintf(stderr, "hdfsStreamBuilderBuild- SUCCESS! File read success. Byte read : %d, File contant : %s \n", num_read ,buffer);
free(buffer);

struct hdfsReadStatistics *stats = NULL;
hdfsFileGetReadStatistics(readFile, &stats);
fprintf(stderr, "hdfsFileGetReadStatistics- SUCCESS! totalBytesRead : %" PRId64 ", totalLocalBytesRead : %" PRId64 ", totalShortCircuitBytesRead : %" PRId64 ", totalZeroCopyBytesRead : %" PRId64 "\n", stats->totalBytesRead , stats->totalLocalBytesRead, stats->totalShortCircuitBytesRead,  stats->totalZeroCopyBytesRead);
hdfsFileFreeReadStatistics(stats);
  17. 断开HDFS文件系统连接。 
    hdfsDisconnect(fs);

准备运行环境

在节点上安装客户端，例如安装到“/opt/client”目录。

Linux中编译并运行程序

  1. 进入Linux客户端目录，运行如下命令导入公共环境变量：

    cd/opt/client

    sourcebigdata_env

  2. 进入“/opt/client/HDFS/hadoop/hdfs-c-example”目录下，运行如下命令导入C客户端环境变量。

    cd/opt/client/HDFS/hadoop/hdfs-c-example

    sourcecomponent_env_C_example

  3. 清除之前运行生成的目标文件和可执行文件，运行如下命令。

    make clean

    执行结果如下：

    [root@10-120-85-2 hdfs-c-example]# make clean
rm -f hdfs_test.o
rm -f hdfs_test
  4. 编译生成新的目标和可执行文件，运行如下命令。

    make（或make all）

    执行结果如下：

    [root@10-120-85-2 hdfs-c-example]# make
cc -c -I/opt/client/HDFS/hadoop/include -Wall -o hdfs_test.o hdfs_test.c
cc -o hdfs_test hdfs_test.o -lhdfs
  5. 运行文件以实现创建文件、读写追加文件和删除文件的功能，运行如下命令。

    make run

    执行结果如下：

    [root@10-120-85-2 hdfs-c-example]# make run
./hdfs_test
hdfsConnect- SUCCESS!
hdfsCreateDirectory- SUCCESS! : /tmp/nativeTest
hdfsOpenFile- SUCCESS! for write : /tmp/nativeTest/testfile.txt
hdfsWrite- SUCCESS! : /tmp/nativeTest/testfile.txt
Flushing file data ....
hdfsCloseFile- SUCCESS! : /tmp/nativeTest/testfile.txt
hdfsOpenFile- SUCCESS! for read : /tmp/nativeTest/testfile.txt
hdfsRead- SUCCESS!, Byte read : 31, File contant : Hadoop HDFS Native file write! 
hdfsSeek- SUCCESS!, Byte read : 21, File seek contant : S Native file write! 
hdfsPread- SUCCESS!, Byte read : 10, File pead contant : S Native f  
hdfsCopy- SUCCESS!, File copied, src : /tmp/nativeTest/testfile.txt, des : /tmp/nativeTest/testfile1.txt 
hdfsMove- SUCCESS!, File moved, src : /tmp/nativeTest/testfile1.txt, des : /tmp/nativeTest/testfile2.txt 
hdfsRename- SUCCESS!, File renamed, Old name : /tmp/nativeTest/testfile2.txt, New name : /tmp/nativeTest/testfile3.txt 
hdfsDelete- SUCCESS!, File deleted : /tmp/nativeTest/testfile3.txt
hdfsSetReplication- SUCCESS!, Set replication 10 for /tmp/nativeTest/testfile.txt
hdfsChown- SUCCESS!, Chown success for /tmp/nativeTest/testfile.txt
hdfsChmod- SUCCESS!, Chmod success for /tmp/nativeTest/testfile.txt
hdfsUtime- SUCCESS!, Set time success for /tmp/nativeTest/testfile.txt

Name: hdfs://hacluster/tmp/nativeTest/testfile.txt, Type: F, Replication: 10, BlockSize: 134217728, Size: 31, LastMod: 1500345260, Owner: root, Group: root, Permissions: 511 (rwxrwxrwx)
hdfsGetPathInfo - SUCCESS!

Name: hdfs://hacluster/tmp/nativeTest/testfile.txt, Type: F, Replication: 10, BlockSize: 134217728, Size: 31, LastMod: 1500345260, Owner: root, Group: root, Permissions: 511 (rwxrwxrwx)
hdfsListDirectory- SUCCESS!, /tmp/nativeTest
hdfsTruncateFile- SUCCESS!, /tmp/nativeTest/testfile.txt
Block Size : 134217728 
hdfsGetDefaultBlockSize- SUCCESS!
Block Size : 134217728 for file /tmp/nativeTest/testfile.txt
hdfsGetDefaultBlockSizeAtPath- SUCCESS!
HDFS Capacity : 102726873909
hdfsGetCapacity- SUCCESS!
HDFS Used : 4767076324
hdfsGetCapacity- SUCCESS!
hdfsExists- SUCCESS! /tmp/nativeTest/testfile.txt
hdfsConfGetStr- SUCCESS : hdfs://hacluster 
hdfsStreamBuilderBuild- SUCCESS! File read success. Byte read : 31, File contant : Hadoop HDFS Native file write! 
hdfsFileGetReadStatistics- SUCCESS! totalBytesRead : 31, totalLocalBytesRead : 0, totalShortCircuitBytesRead : 0, totalZeroCopyBytesRead : 0
  6. 进入debug模式(可选)

    make gdb

    执行结果如下：

    [root@10-120-85-2 hdfs-c-example]# make gdb
gdb hdfs_test
GNU gdb (GDB) SUSE (7.5.1-0.7.29)
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-suse-linux".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /opt/client/HDFS/hadoop/hdfs-c-example/hdfs_test...done.
(gdb)
父主题： HDFS常用API介绍