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.input;
  
  import java.io.FilterInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  
  /**
   * 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.
   * <p>
   * It is an alternative base class to FilterInputStream
   * to increase reusability, because FilterInputStream changes the
   * methods being called, such as read(byte[]) to read(byte[], int, int).
   * <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: ProxyInputStream.java 934041 2010-04-14 17:37:24Z jukka $
   */
  public abstract class ProxyInputStream extends FilterInputStream {
  
      /**
       * Constructs a new ProxyInputStream.
       *
       * @param proxy  the InputStream to delegate to
       */
      public ProxyInputStream(InputStream proxy) {
          super(proxy);
          // the proxy is stored in a protected superclass variable named 'in'
      }
  
      /**
       * Invokes the delegate's <code>read()</code> method.
       * @return the byte read or -1 if the end of stream
       * @throws IOException if an I/O error occurs
       */
      @Override
      public int read() throws IOException {
          try {
              beforeRead(1);
              int b = in.read();
              afterRead(b != -1 ? 1 : -1);
              return b;
          } catch (IOException e) {
              handleIOException(e);
              return -1;
          }
      }
  
      /**
       * Invokes the delegate's <code>read(byte[])</code> method.
       * @param bts the buffer to read the bytes into
       * @return the number of bytes read or -1 if the end of stream
       * @throws IOException if an I/O error occurs
       */
      @Override
      public int read(byte[] bts) throws IOException {
          try {
              beforeRead(bts != null ? bts.length : 0);
              int n = in.read(bts);
              afterRead(n);
              return n;
          } catch (IOException e) {
              handleIOException(e);
              return -1;
          }
      }
  
      /**
       * Invokes the delegate's <code>read(byte[], int, int)</code> method.
       * @param bts the buffer to read the bytes into
       * @param off The start offset
       * @param len The number of bytes to read
       * @return the number of bytes read or -1 if the end of stream
       * @throws IOException if an I/O error occurs
       */
      @Override
      public int read(byte[] bts, int off, int len) throws IOException {
          try {
              beforeRead(len);
              int n = in.read(bts, off, len);
              afterRead(n);
              return n;
          } catch (IOException e) {
              handleIOException(e);
              return -1;
          }
      }
  
      /**
       * Invokes the delegate's <code>skip(long)</code> method.
       * @param ln the number of bytes to skip
       * @return the actual number of bytes skipped
       * @throws IOException if an I/O error occurs
       */
      @Override
      public long skip(long ln) throws IOException {
          try {
              return in.skip(ln);
          } catch (IOException e) {
              handleIOException(e);
              return 0;
          }
      }
  
      /**
       * Invokes the delegate's <code>available()</code> method.
       * @return the number of available bytes
       * @throws IOException if an I/O error occurs
       */
      @Override
      public int available() throws IOException {
          try {
              return super.available();
          } catch (IOException e) {
              handleIOException(e);
              return 0;
          }
      }
  
      /**
       * Invokes the delegate's <code>close()</code> method.
       * @throws IOException if an I/O error occurs
       */
      @Override
      public void close() throws IOException {
          try {
              in.close();
          } catch (IOException e) {
              handleIOException(e);
          }
      }
  
      /**
       * Invokes the delegate's <code>mark(int)</code> method.
       * @param readlimit read ahead limit
       */
      @Override
      public synchronized void mark(int readlimit) {
          in.mark(readlimit);
      }
  
      /**
       * Invokes the delegate's <code>reset()</code> method.
       * @throws IOException if an I/O error occurs
       */
      @Override
      public synchronized void reset() throws IOException {
          try {
              in.reset();
          } catch (IOException e) {
              handleIOException(e);
          }
      }
  
      /**
       * Invokes the delegate's <code>markSupported()</code> method.
       * @return true if mark is supported, otherwise false
       */
      @Override
      public boolean markSupported() {
          return in.markSupported();
      }
  
      /**
       * Invoked by the read methods before the call is proxied. The number
       * of bytes that the caller wanted to read (1 for the {@link #read()}
       * method, buffer length for {@link #read(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 read methods.
       * The default implementation does nothing.
       * <p>
       * Note this method is <em>not</em> called from {@link #skip(long)} or
       * {@link #reset()}. You need to explicitly override those methods if
       * you want to add pre-processing steps also to them.
       *
       * @since Commons IO 2.0
       * @param n number of bytes that the caller asked to be read
       * @throws IOException if the pre-processing fails
       */
      protected void beforeRead(int n) throws IOException {
      }
  
      /**
       * Invoked by the read methods after the proxied call has returned
       * successfully. The number of bytes returned to the caller (or -1 if
       * the end of stream was reached) is given as an argument.
       * <p>
       * Subclasses can override this method to add common post-processing
       * functionality without having to override all the read methods.
       * The default implementation does nothing.
       * <p>
       * Note this method is <em>not</em> called from {@link #skip(long)} or
       * {@link #reset()}. You need to explicitly override those methods if
       * you want to add post-processing steps also to them.
       *
       * @since Commons IO 2.0
       * @param n number of bytes read, or -1 if the end of stream was reached
       * @throws IOException if the post-processing fails
       */
      protected void afterRead(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;
      }
  
  }
  