001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.io.input;
018
019import static org.apache.commons.io.IOUtils.EOF;
020
021import java.io.FilterReader;
022import java.io.IOException;
023import java.io.Reader;
024import java.nio.CharBuffer;
025
026import org.apache.commons.io.IOUtils;
027
028/**
029 * A Proxy stream which acts as expected, that is it passes the method
030 * calls on to the proxied stream and doesn't change which methods are
031 * being called.
032 * <p>
033 * It is an alternative base class to FilterReader
034 * to increase reusability, because FilterReader changes the
035 * methods being called, such as read(char[]) to read(char[], int, int).
036 * </p>
037 */
038public abstract class ProxyReader extends FilterReader {
039
040    /**
041     * Constructs a new ProxyReader.
042     *
043     * @param delegate  the Reader to delegate to
044     */
045    public ProxyReader(final Reader delegate) {
046        // the delegate is stored in a protected superclass variable named 'in'
047        super(delegate);
048    }
049
050    /**
051     * Invoked by the read methods after the proxied call has returned
052     * successfully. The number of chars returned to the caller (or -1 if
053     * the end of stream was reached) is given as an argument.
054     * <p>
055     * Subclasses can override this method to add common post-processing
056     * functionality without having to override all the read methods.
057     * The default implementation does nothing.
058     * <p>
059     * Note this method is <em>not</em> called from {@link #skip(long)} or
060     * {@link #reset()}. You need to explicitly override those methods if
061     * you want to add post-processing steps also to them.
062     *
063     * @since 2.0
064     * @param n number of chars read, or -1 if the end of stream was reached
065     * @throws IOException if the post-processing fails
066     */
067    @SuppressWarnings("unused") // Possibly thrown from subclasses.
068    protected void afterRead(final int n) throws IOException {
069        // noop
070    }
071
072    /**
073     * Invoked by the read methods before the call is proxied. The number
074     * of chars that the caller wanted to read (1 for the {@link #read()}
075     * method, buffer length for {@link #read(char[])}, etc.) is given as
076     * an argument.
077     * <p>
078     * Subclasses can override this method to add common pre-processing
079     * functionality without having to override all the read methods.
080     * The default implementation does nothing.
081     * <p>
082     * Note this method is <em>not</em> called from {@link #skip(long)} or
083     * {@link #reset()}. You need to explicitly override those methods if
084     * you want to add pre-processing steps also to them.
085     *
086     * @since 2.0
087     * @param n number of chars that the caller asked to be read
088     * @throws IOException if the pre-processing fails
089     */
090    @SuppressWarnings("unused") // Possibly thrown from subclasses.
091    protected void beforeRead(final int n) throws IOException {
092        // noop
093    }
094
095    /**
096     * Invokes the delegate's {@code close()} method.
097     * @throws IOException if an I/O error occurs.
098     */
099    @Override
100    public void close() throws IOException {
101        try {
102            in.close();
103        } catch (final IOException e) {
104            handleIOException(e);
105        }
106    }
107
108    /**
109     * Handle any IOExceptions thrown.
110     * <p>
111     * This method provides a point to implement custom exception
112     * handling. The default behavior is to re-throw the exception.
113     * @param e The IOException thrown
114     * @throws IOException if an I/O error occurs.
115     * @since 2.0
116     */
117    protected void handleIOException(final IOException e) throws IOException {
118        throw e;
119    }
120
121    /**
122     * Invokes the delegate's {@code mark(int)} method.
123     * @param idx read ahead limit
124     * @throws IOException if an I/O error occurs.
125     */
126    @Override
127    public synchronized void mark(final int idx) throws IOException {
128        try {
129            in.mark(idx);
130        } catch (final IOException e) {
131            handleIOException(e);
132        }
133    }
134
135    /**
136     * Invokes the delegate's {@code markSupported()} method.
137     * @return true if mark is supported, otherwise false
138     */
139    @Override
140    public boolean markSupported() {
141        return in.markSupported();
142    }
143
144    /**
145     * Invokes the delegate's {@code read()} method.
146     * @return the character read or -1 if the end of stream
147     * @throws IOException if an I/O error occurs.
148     */
149    @Override
150    public int read() throws IOException {
151        try {
152            beforeRead(1);
153            final int c = in.read();
154            afterRead(c != EOF ? 1 : EOF);
155            return c;
156        } catch (final IOException e) {
157            handleIOException(e);
158            return EOF;
159        }
160    }
161
162    /**
163     * Invokes the delegate's {@code read(char[])} method.
164     * @param chr the buffer to read the characters into
165     * @return the number of characters read or -1 if the end of stream
166     * @throws IOException if an I/O error occurs.
167     */
168    @Override
169    public int read(final char[] chr) throws IOException {
170        try {
171            beforeRead(IOUtils.length(chr));
172            final int n = in.read(chr);
173            afterRead(n);
174            return n;
175        } catch (final IOException e) {
176            handleIOException(e);
177            return EOF;
178        }
179    }
180
181    /**
182     * Invokes the delegate's {@code read(char[], int, int)} method.
183     * @param chr the buffer to read the characters into
184     * @param st The start offset
185     * @param len The number of bytes to read
186     * @return the number of characters read or -1 if the end of stream
187     * @throws IOException if an I/O error occurs.
188     */
189    @Override
190    public int read(final char[] chr, final int st, final int len) throws IOException {
191        try {
192            beforeRead(len);
193            final int n = in.read(chr, st, len);
194            afterRead(n);
195            return n;
196        } catch (final IOException e) {
197            handleIOException(e);
198            return EOF;
199        }
200    }
201
202    /**
203     * Invokes the delegate's {@code read(CharBuffer)} method.
204     * @param target the char buffer to read the characters into
205     * @return the number of characters read or -1 if the end of stream
206     * @throws IOException if an I/O error occurs.
207     * @since 2.0
208     */
209    @Override
210    public int read(final CharBuffer target) throws IOException {
211        try {
212            beforeRead(IOUtils.length(target));
213            final int n = in.read(target);
214            afterRead(n);
215            return n;
216        } catch (final IOException e) {
217            handleIOException(e);
218            return EOF;
219        }
220    }
221
222    /**
223     * Invokes the delegate's {@code ready()} method.
224     * @return true if the stream is ready to be read
225     * @throws IOException if an I/O error occurs.
226     */
227    @Override
228    public boolean ready() throws IOException {
229        try {
230            return in.ready();
231        } catch (final IOException e) {
232            handleIOException(e);
233            return false;
234        }
235    }
236
237    /**
238     * Invokes the delegate's {@code reset()} method.
239     * @throws IOException if an I/O error occurs.
240     */
241    @Override
242    public synchronized void reset() throws IOException {
243        try {
244            in.reset();
245        } catch (final IOException e) {
246            handleIOException(e);
247        }
248    }
249
250    /**
251     * Invokes the delegate's {@code skip(long)} method.
252     * @param ln the number of bytes to skip
253     * @return the number of bytes to skipped or EOF if the end of stream
254     * @throws IOException if an I/O error occurs.
255     */
256    @Override
257    public long skip(final long ln) throws IOException {
258        try {
259            return in.skip(ln);
260        } catch (final IOException e) {
261            handleIOException(e);
262            return 0;
263        }
264    }
265
266}