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   /*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project 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.jboss.netty.example.factorial;
  
  import org.jboss.netty.channel.ChannelEvent;
  import org.jboss.netty.channel.ChannelHandlerContext;
  import org.jboss.netty.channel.ChannelStateEvent;
  import org.jboss.netty.channel.ExceptionEvent;
  import org.jboss.netty.channel.MessageEvent;
  import org.jboss.netty.channel.SimpleChannelUpstreamHandler;
  
  import java.math.BigInteger;
  import java.util.Formatter;
  
  /**
   * Handler for a server-side channel.  This handler maintains stateful
   * information which is specific to a certain channel using member variables.
   * Therefore, an instance of this handler can cover only one channel.  You have
   * to create a new handler instance whenever you create a new channel and insert
   * this handler  to avoid a race condition.
   */
  public class FactorialServerHandler extends SimpleChannelUpstreamHandler {
  
      // Stateful properties.
      private int lastMultiplier = 1;
      private BigInteger factorial = new BigInteger(new byte[] { 1 });
  
      @Override
      public void handleUpstream(ChannelHandlerContext ctx, ChannelEvent e) throws Exception {
          if (e instanceof ChannelStateEvent) {
              System.err.println(e);
          }
          super.handleUpstream(ctx, e);
      }
  
      @Override
      public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
          // Calculate the cumulative factorial and send it to the client.
          BigInteger number;
          if (e.getMessage() instanceof BigInteger) {
              number = (BigInteger) e.getMessage();
          } else {
              number = new BigInteger(e.getMessage().toString());
          }
          lastMultiplier = number.intValue();
          factorial = factorial.multiply(number);
          e.getChannel().write(factorial);
      }
  
      @Override
      public void channelDisconnected(ChannelHandlerContext ctx, ChannelStateEvent e) {
          System.err.println(new Formatter().format("Factorial of %,d is: %,d", lastMultiplier, factorial));
      }
  
      @Override
      public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) {
          e.getCause().printStackTrace();
          e.getChannel().close();
      }
  }