HDFSCommand.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.zeppelin.file;

import java.net.URL;
import java.net.HttpURLConnection;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import javax.ws.rs.core.UriBuilder;
import org.slf4j.Logger;

/**
 * Definition and HTTP invocation methods for all WebHDFS commands
 *
 */
public class HDFSCommand {

  /**
   * Type of HTTP request
   */
  public enum HttpType {
    GET,
    PUT
  }

  /**
   * Definition of WebHDFS operator
   */
  public class Op {
    public String op;
    public HttpType cmd;
    public int minArgs;

    public Op(String op, HttpType cmd, int minArgs) {
      this.op = op;
      this.cmd = cmd;
      this.minArgs = minArgs;
    }
  }

  /**
   * Definition of argument to an operator
   */
  public class Arg {
    public String key;
    public String value;

    public Arg(String key, String value) {
      this.key = key;
      this.value = value;
    }
  }

  // How to connect to WebHDFS
  String url = null;
  String user = null;
  int maxLength = 0;
  Logger logger;

  // Define all the commands available
  public Op getFileStatus = new Op("GETFILESTATUS", HttpType.GET, 0);
  public Op listStatus = new Op("LISTSTATUS", HttpType.GET, 0);

  public HDFSCommand(String url, String user, Logger logger, int maxLength) {
    super();
    this.url = url;
    this.user = user;
    this.maxLength = maxLength;
    this.logger = logger;
  }

  public String checkArgs(Op op, String path, Arg[] args) throws Exception {
    if (op == null ||
        path == null ||
        (op.minArgs > 0 &&
            (args == null ||
                args.length != op.minArgs)))
    {
      String a = "";
      a = (op != null) ? a + op.op + "\n" : a;
      a = (path != null) ? a + path + "\n" : a;
      a = (args != null) ? a + args + "\n" : a;
      return a;
    }
    return null;
  }


  // The operator that runs all commands
  public String runCommand(Op op, String path, Arg[] args) throws Exception {

    // Check arguments
    String error = checkArgs(op, path, args);
    if (error != null) {
      logger.error("Bad arguments to command: " + error);
      return "ERROR: BAD ARGS";
    }

    // Build URI
    UriBuilder builder = UriBuilder
        .fromPath(url)
        .path(path)
        .queryParam("op", op.op);

    if (args != null) {
      for (Arg a : args) {
        builder = builder.queryParam(a.key, a.value);
      }
    }
    java.net.URI uri = builder.build();

    // Connect and get response string
    URL hdfsUrl = uri.toURL();
    HttpURLConnection con = (HttpURLConnection) hdfsUrl.openConnection();

    if (op.cmd == HttpType.GET) {
      con.setRequestMethod("GET");
      int responseCode = con.getResponseCode();
      logger.info("Sending 'GET' request to URL : " + hdfsUrl);
      logger.info("Response Code : " + responseCode);

      BufferedReader in = new BufferedReader(
          new InputStreamReader(con.getInputStream()));
      String inputLine;
      StringBuffer response = new StringBuffer();

      int i = 0;
      while ((inputLine = in.readLine()) != null) {
        if (inputLine.length() < maxLength)
          response.append(inputLine);
        i++;
        if (i >= maxLength)
          break;
      }
      in.close();
      return response.toString();
    }
    return null;
  }
}