code: /*
   * 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.commons.io.output;
  
  import java.io.FilterOutputStream;
  import java.io.IOException;
  import java.io.OutputStream;
  
  /**
   * A Proxy stream which acts as expected, that is it passes the method 
   * calls on to the proxied stream and doesn't change which methods are 
   * being called. It is an alternative base class to FilterOutputStream
   * to increase reusability.
   * <p>
   * See the protected methods for ways in which a subclass can easily decorate
   * a stream with custom pre-, post- or error processing functionality.
   * 
   * @author Stephen Colebourne
   * @version $Id: ProxyOutputStream.java 1003340 2010-10-01 00:31:53Z sebb $
   */
  public class ProxyOutputStream extends FilterOutputStream {
  
      /**
       * Constructs a new ProxyOutputStream.
       * 
       * @param proxy  the OutputStream to delegate to
       */
      public ProxyOutputStream(OutputStream proxy) {
          super(proxy);
          // the proxy is stored in a protected superclass variable named 'out'
      }
  
      /**
       * Invokes the delegate's <code>write(int)</code> method.
       * @param idx the byte to write
       * @throws IOException if an I/O error occurs
       */
      @Override
      public void write(int idx) throws IOException {
          try {
              beforeWrite(1);
              out.write(idx);
              afterWrite(1);
          } catch (IOException e) {
              handleIOException(e);
          }
      }
  
      /**
       * Invokes the delegate's <code>write(byte[])</code> method.
       * @param bts the bytes to write
       * @throws IOException if an I/O error occurs
       */
      @Override
      public void write(byte[] bts) throws IOException {
          try {
              int len = bts != null ? bts.length : 0;
              beforeWrite(len);
              out.write(bts);
              afterWrite(len);
          } catch (IOException e) {
              handleIOException(e);
          }
      }
  
      /**
       * Invokes the delegate's <code>write(byte[])</code> method.
       * @param bts the bytes to write
       * @param st The start offset
       * @param end The number of bytes to write
       * @throws IOException if an I/O error occurs
       */
      @Override
      public void write(byte[] bts, int st, int end) throws IOException {
          try {
              beforeWrite(end);
              out.write(bts, st, end);
              afterWrite(end);
          } catch (IOException e) {
              handleIOException(e);
          }
      }
  
      /**
       * Invokes the delegate's <code>flush()</code> method.
       * @throws IOException if an I/O error occurs
       */
      @Override
      public void flush() throws IOException {
          try {
              out.flush();
          } catch (IOException e) {
              handleIOException(e);
          }
      }
  
      /**
       * Invokes the delegate's <code>close()</code> method.
       * @throws IOException if an I/O error occurs
       */
      @Override
      public void close() throws IOException {
          try {
              out.close();
          } catch (IOException e) {
              handleIOException(e);
          }
      }
  
      /**
       * Invoked by the write methods before the call is proxied. The number
       * of bytes to be written (1 for the {@link #write(int)} method, buffer
       * length for {@link #write(byte[])}, etc.) is given as an argument.
       * <p>
       * Subclasses can override this method to add common pre-processing
       * functionality without having to override all the write methods.
       * The default implementation does nothing.
       *
       * @since Commons IO 2.0
       * @param n number of bytes to be written
       * @throws IOException if the pre-processing fails
       */
      protected void beforeWrite(int n) throws IOException {
      }
  
      /**
       * Invoked by the write methods after the proxied call has returned
       * successfully. The number of bytes written (1 for the
       * {@link #write(int)} method, buffer length for {@link #write(byte[])},
       * etc.) is given as an argument.
       * <p>
       * Subclasses can override this method to add common post-processing
       * functionality without having to override all the write methods.
       * The default implementation does nothing.
       *
       * @since Commons IO 2.0
       * @param n number of bytes written
       * @throws IOException if the post-processing fails
       */
      protected void afterWrite(int n) throws IOException {
      }
  
      /**
       * Handle any IOExceptions thrown.
       * <p>
       * This method provides a point to implement custom exception
       * handling. The default behaviour is to re-throw the exception.
       * @param e The IOException thrown
       * @throws IOException if an I/O error occurs
       * @since Commons IO 2.0
       */
      protected void handleIOException(IOException e) throws IOException {
          throw e;
      }
  
  }
  