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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.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.
 * 

* See the protected methods for ways in which a subclass can easily decorate * a stream with custom pre-, post- or error processing functionality. * */ public class ProxyOutputStream extends FilterOutputStream { /** * Constructs a new ProxyOutputStream. * * @param proxy the OutputStream to delegate to */ public ProxyOutputStream(final OutputStream proxy) { super(proxy); // the proxy is stored in a protected superclass variable named 'out' } /** * Invokes the delegate's write(int) method. * @param idx the byte to write * @throws IOException if an I/O error occurs */ @Override public void write(final int idx) throws IOException { try { beforeWrite(1); out.write(idx); afterWrite(1); } catch (final IOException e) { handleIOException(e); } } /** * Invokes the delegate's write(byte[]) method. * @param bts the bytes to write * @throws IOException if an I/O error occurs */ @Override public void write(final byte[] bts) throws IOException { try { final int len = bts != null ? bts.length : 0; beforeWrite(len); out.write(bts); afterWrite(len); } catch (final IOException e) { handleIOException(e); } } /** * Invokes the delegate's write(byte[]) 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(final byte[] bts, final int st, final int end) throws IOException { try { beforeWrite(end); out.write(bts, st, end); afterWrite(end); } catch (final IOException e) { handleIOException(e); } } /** * Invokes the delegate's flush() method. * @throws IOException if an I/O error occurs */ @Override public void flush() throws IOException { try { out.flush(); } catch (final IOException e) { handleIOException(e); } } /** * Invokes the delegate's close() method. * @throws IOException if an I/O error occurs */ @Override public void close() throws IOException { try { out.close(); } catch (final 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. *

* 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 2.0 * @param n number of bytes to be written * @throws IOException if the pre-processing fails */ protected void beforeWrite(final 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. *

* 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 2.0 * @param n number of bytes written * @throws IOException if the post-processing fails */ protected void afterWrite(final int n) throws IOException { } /** * 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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