HDFS API 操作实例(一) HDFS读写操作

1. 读取HDFS文件

1.1 字符读取HDFS上的文件

   Configuration conf = new Configuration();
   Path path = new Path(pathstr); 
   FileSystem fs = FileSystem.get(conf);
   FSDataInputStream fsin= fs.open(path); 
   BufferedReader br =null;
   String line ;
   try{
    br = new BufferedReader(new InputStreamReader(fsin));
       while ((line = br.readLine()) != null) {
         System.out.println(line);
        } 
   }finally{
    br.close();
}

1.2 字节流读取HDFS文件内容(API)

1.2.1 字节数组读取

 public void readFileByAPI() throws Exception {
        Configuration conf = new Configuration();
        conf.set("fs.default.name", "hdfs://192.168.8.156:9000/");
        FileSystem fileSystem = FileSystem.get(conf);
        Path path = new Path("/user/compass/readme.txt");
 
        FSDataInputStream fsDataInputStream = fileSystem.open(path);
        byte[] bytes = new byte[1024];
        int len = -1;
        ByteArrayOutputStream stream = new ByteArrayOutputStream();
 
        while ((len = fsDataInputStream.read(bytes)) != -1) {
            stream.write(bytes, 0, len);
        }
        fsDataInputStream.close();
        stream.close();
        System.out.println(new String(stream.toByteArray()));
 
    }

1.2.1 hadoop工具类读取

public void readFileByAPI() throws Exception {
        Configuration conf = new Configuration();
        conf.set("fs.default.name", "hdfs://192.168.8.156:9000/");
        FileSystem fileSystem = FileSystem.get(conf);
        Path path = new Path("/user/compass/readme.txt");
        FSDataInputStream fsDataInputStream = fileSystem.open(path);
        ByteArrayOutputStream stream = new ByteArrayOutputStream();
        IOUtils.copyBytes(fsDataInputStream, stream, 1024);
        System.out.println(new String(stream.toByteArray()));

    }

1.3 URL流读取HDFS文件(不常用)

public void readFileByURL() throws Exception {
        //url流处理器工程
        URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());
        URL url = new URL("hdfs://192.168.8.156:9000/user/readme.txt");
        URLConnection connection = url.openConnection();
        InputStream inputStream = connection.getInputStream();
       // 返回这个输入流中可以被读的剩下的bytes字节的估计值
        byte[] b = new byte[inputStream.available()];
        while (inputStream.read(b) != -1)
            inputStream.read(b);
        inputStream.close();
        String string = new String(b);
        System.out.println(string);
    }

2. 写入HDFS文件

2.1 字节写入HDFS文件

  Configuration conf = new Configuration();
  Path path = new Path(path); 
  FileSystem fs = FileSystem.get(conf); 
  FSDataOutputStream out = fs.create(src);
  out.write(sb.toString().getBytes());
  out.close();

2.2 HDFS 文件中追加（append）数据

public static boolean appendRTData(String src, String drc) { // src源文件 drc 追加文件
    boolean flag = false;
 
    Configuration conf = new Configuration();
    FileSystem fs = null;
    try {
      fs = FileSystem.get(URI.create(src), conf);
      InputStream in = new BufferedInputStream(new FileInputStream(drc));
      OutputStream out = fs.append(new Path(src));
      IOUtils.copyBytes(in, out, 4096, true);
    } catch (IOException e) {
      e.printStackTrace();
    }
 
    return flag;
  }