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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.commons.io.input;

import static org.apache.commons.io.IOUtils.EOF;

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.
 * 

* 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). *

* See the protected methods for ways in which a subclass can easily decorate * a stream with custom pre-, post- or error processing functionality. * */ public abstract class ProxyInputStream extends FilterInputStream { /** * Constructs a new ProxyInputStream. * * @param proxy the InputStream to delegate to */ public ProxyInputStream(final InputStream proxy) { super(proxy); // the proxy is stored in a protected superclass variable named 'in' } /** * Invokes the delegate's read() 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); final int b = in.read(); afterRead(b != EOF ? 1 : EOF); return b; } catch (final IOException e) { handleIOException(e); return EOF; } } /** * Invokes the delegate's read(byte[]) method. * @param bts the buffer to read the bytes into * @return the number of bytes read or EOF if the end of stream * @throws IOException if an I/O error occurs */ @Override public int read(final byte[] bts) throws IOException { try { beforeRead(bts != null ? bts.length : 0); final int n = in.read(bts); afterRead(n); return n; } catch (final IOException e) { handleIOException(e); return EOF; } } /** * Invokes the delegate's read(byte[], int, int) 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(final byte[] bts, final int off, final int len) throws IOException { try { beforeRead(len); final int n = in.read(bts, off, len); afterRead(n); return n; } catch (final IOException e) { handleIOException(e); return EOF; } } /** * Invokes the delegate's skip(long) 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(final long ln) throws IOException { try { return in.skip(ln); } catch (final IOException e) { handleIOException(e); return 0; } } /** * Invokes the delegate's available() 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 (final IOException e) { handleIOException(e); return 0; } } /** * Invokes the delegate's close() method. * @throws IOException if an I/O error occurs */ @Override public void close() throws IOException { try { in.close(); } catch (final IOException e) { handleIOException(e); } } /** * Invokes the delegate's mark(int) method. * @param readlimit read ahead limit */ @Override public synchronized void mark(final int readlimit) { in.mark(readlimit); } /** * Invokes the delegate's reset() method. * @throws IOException if an I/O error occurs */ @Override public synchronized void reset() throws IOException { try { in.reset(); } catch (final IOException e) { handleIOException(e); } } /** * Invokes the delegate's markSupported() 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. *

* Subclasses can override this method to add common pre-processing * functionality without having to override all the read methods. * The default implementation does nothing. *

* Note this method is not 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 2.0 * @param n number of bytes that the caller asked to be read * @throws IOException if the pre-processing fails */ protected void beforeRead(final int n) throws IOException { // no-op } /** * 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. *

* Subclasses can override this method to add common post-processing * functionality without having to override all the read methods. * The default implementation does nothing. *

* Note this method is not 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 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(final int n) throws IOException { // no-op } /** * Handle any IOExceptions thrown. *

* 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 2.0 */ protected void handleIOException(final IOException e) throws IOException { throw e; } }





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