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Thrift is a software framework for scalable cross-language services development.
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/*
 * 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.thrift.server;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Map;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.thrift.TException;
import org.apache.thrift.TProcessor;
import org.apache.thrift.protocol.TProtocol;
import org.apache.thrift.protocol.TProtocolFactory;
import org.apache.thrift.transport.TIOStreamTransport;
import org.apache.thrift.transport.TTransport;

/**
 * Servlet implementation class ThriftServer, that allows {@link TProcessor} and
 * {@link TProtocolFactory} to be supplied after the {@link #init()} method has
 * finished. 

 * Subclasses must implement the abstract methods that return the TProcessor and
 * two TProtocolFactory. Those methods are guaranteed to be called exactly once,
 * and that {@link ServletContext} is available.
 */
public abstract class TExtensibleServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;

  private TProcessor processor;

  private TProtocolFactory inFactory;

  private TProtocolFactory outFactory;

  private Collection> customHeaders;

  /**
   * Returns the appropriate {@link TProcessor}. This will be called once just
   * after the {@link #init()} method
   * 
   * @return
   */
  protected abstract TProcessor getProcessor();

  /**
   * Returns the appropriate in {@link TProtocolFactory}. This will be called
   * once just after the {@link #init()} method
   * 
   * @return
   */
  protected abstract TProtocolFactory getInProtocolFactory();

  /**
   * Returns the appropriate out {@link TProtocolFactory}. This will be called
   * once just after the {@link #init()} method
   * 
   * @return
   */
  protected abstract TProtocolFactory getOutProtocolFactory();

  @Override
  public final void init(ServletConfig config) throws ServletException {
    super.init(config); //no-args init() happens here
    this.processor = getProcessor();
    this.inFactory = getInProtocolFactory();
    this.outFactory = getOutProtocolFactory();
    this.customHeaders = new ArrayList>();

    if (processor == null) {
      throw new ServletException("processor must be set");
    }
    if (inFactory == null) {
      throw new ServletException("inFactory must be set");
    }
    if (outFactory == null) {
      throw new ServletException("outFactory must be set");
    }
  }

  /**
   * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
   *      response)
   */
  @Override
  protected void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    TTransport inTransport = null;
    TTransport outTransport = null;

    try {
      response.setContentType("application/x-thrift");

      if (null != this.customHeaders) {
	for (Map.Entry header : this.customHeaders) {
	  response.addHeader(header.getKey(), header.getValue());
	}
      }

      InputStream in = request.getInputStream();
      OutputStream out = response.getOutputStream();

      TTransport transport = new TIOStreamTransport(in, out);
      inTransport = transport;
      outTransport = transport;

      TProtocol inProtocol = inFactory.getProtocol(inTransport);
      TProtocol outProtocol = inFactory.getProtocol(outTransport);

      processor.process(inProtocol, outProtocol);
      out.flush();
    } catch (TException te) {
      throw new ServletException(te);
    }
  }

  /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
   *      response)
   */
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    doPost(req, resp);
  }

  public void addCustomHeader(final String key, final String value) {
    this.customHeaders.add(new Map.Entry() {
      public String getKey() {
	return key;
      }

      public String getValue() {
	return value;
      }

      public String setValue(String value) {
	return null;
      }
    });
  }

  public void setCustomHeaders(Collection> headers) {
    this.customHeaders.clear();
    this.customHeaders.addAll(headers);
  }
}