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.FilterWriter;
  import java.io.IOException;
  import java.io.Writer;
  
  /**
   * 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 FilterWriter
   * to increase reusability, because FilterWriter changes the 
   * methods being called, such as write(char[]) to write(char[], int, int)
   * and write(String) to write(String, int, int).
   * 
   * @author Stephen Colebourne
   * @version $Id: ProxyWriter.java 1003647 2010-10-01 20:53:59Z niallp $
   */
  public class ProxyWriter extends FilterWriter {
  
      /**
       * Constructs a new ProxyWriter.
       * 
       * @param proxy  the Writer to delegate to
       */
      public ProxyWriter(Writer proxy) {
          super(proxy);
          // the proxy is stored in a protected superclass variable named 'out'
      }
  
      /**
       * Invokes the delegate's <code>append(char)</code> method.
       * @param c The character to write
       * @return this writer
       * @throws IOException if an I/O error occurs
       * @since Commons IO 2.0
       */
      @Override
      public Writer append(char c) throws IOException {
          try {
              beforeWrite(1);
              out.append(c);
              afterWrite(1);
          } catch (IOException e) {
              handleIOException(e);
          }
          return this;
      }
  
      /**
       * Invokes the delegate's <code>append(CharSequence, int, int)</code> method.
       * @param csq The character sequence to write
       * @param start The index of the first character to write
       * @param end  The index of the first character to write (exclusive)
       * @return this writer
       * @throws IOException if an I/O error occurs
       * @since Commons IO 2.0
       */
      @Override
      public Writer append(CharSequence csq, int start, int end) throws IOException {
          try {
              beforeWrite(end - start);
              out.append(csq, start, end);
              afterWrite(end - start);
          } catch (IOException e) {
              handleIOException(e);
          }
          return this;
      }
  
      /**
       * Invokes the delegate's <code>append(CharSequence)</code> method.
       * @param csq The character sequence to write
       * @return this writer
       * @throws IOException if an I/O error occurs
       * @since Commons IO 2.0
       */
      @Override
      public Writer append(CharSequence csq) throws IOException {
          try {
              int len = 0;
              if (csq != null) {
                  len = csq.length();
              }
  
              beforeWrite(len);
              out.append(csq);
              afterWrite(len);
          } catch (IOException e) {
              handleIOException(e);
          }
          return this;
      }
  
      /**
       * Invokes the delegate's <code>write(int)</code> method.
       * @param idx the character 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(char[])</code> method.
       * @param chr the characters to write
       * @throws IOException if an I/O error occurs
       */
      @Override
      public void write(char[] chr) throws IOException {
          try {
              int len = 0;
              if (chr != null) {
                  len = chr.length;
              }
  
              beforeWrite(len);
              out.write(chr);
              afterWrite(len);
          } catch (IOException e) {
              handleIOException(e);
          }
      }
  
      /**
       * Invokes the delegate's <code>write(char[], int, int)</code> method.
       * @param chr the characters to write
       * @param st The start offset
       * @param len The number of characters to write
       * @throws IOException if an I/O error occurs
       */
      @Override
      public void write(char[] chr, int st, int len) throws IOException {
          try {
              beforeWrite(len);
              out.write(chr, st, len);
              afterWrite(len);
          } catch (IOException e) {
              handleIOException(e);
          }
      }
  
      /**
       * Invokes the delegate's <code>write(String)</code> method.
       * @param str the string to write
       * @throws IOException if an I/O error occurs
       */
      @Override
      public void write(String str) throws IOException {
          try {
              int len = 0;
              if (str != null) {
                  len = str.length();
              }
  
              beforeWrite(len);
              out.write(str);
              afterWrite(len);
          } catch (IOException e) {
              handleIOException(e);
          }
      }
  
      /**
       * Invokes the delegate's <code>write(String)</code> method.
       * @param str the string to write
       * @param st The start offset
       * @param len The number of characters to write
       * @throws IOException if an I/O error occurs
       */
      @Override
      public void write(String str, int st, int len) throws IOException {
          try {
              beforeWrite(len);
              out.write(str, st, len);
              afterWrite(len);
          } 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 chars to be written (1 for the {@link #write(int)} method, buffer
       * length for {@link #write(char[])}, 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 chars 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 chars written (1 for the
       * {@link #write(int)} method, buffer length for {@link #write(char[])},
       * 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 chars 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;
      }
  
  }
  