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 */
017 package org.apache.commons.io.input;
018
019 import java.io.FilterReader;
020 import java.io.IOException;
021 import java.io.Reader;
022 import java.nio.CharBuffer;
023
024 /**
025 * A Proxy stream which acts as expected, that is it passes the method
026 * calls on to the proxied stream and doesn't change which methods are
027 * being called.
028 * <p>
029 * It is an alternative base class to FilterReader
030 * to increase reusability, because FilterReader changes the
031 * methods being called, such as read(char[]) to read(char[], int, int).
032 *
033 * @version $Id: ProxyReader.java 1304052 2012-03-22 20:55:29Z ggregory $
034 */
035 public abstract class ProxyReader extends FilterReader {
036
037 /**
038 * Constructs a new ProxyReader.
039 *
040 * @param proxy the Reader to delegate to
041 */
042 public ProxyReader(Reader proxy) {
043 super(proxy);
044 // the proxy is stored in a protected superclass variable named 'in'
045 }
046
047 /**
048 * Invokes the delegate's <code>read()</code> method.
049 * @return the character read or -1 if the end of stream
050 * @throws IOException if an I/O error occurs
051 */
052 @Override
053 public int read() throws IOException {
054 try {
055 beforeRead(1);
056 int c = in.read();
057 afterRead(c != -1 ? 1 : -1);
058 return c;
059 } catch (IOException e) {
060 handleIOException(e);
061 return -1;
062 }
063 }
064
065 /**
066 * Invokes the delegate's <code>read(char[])</code> method.
067 * @param chr the buffer to read the characters into
068 * @return the number of characters read or -1 if the end of stream
069 * @throws IOException if an I/O error occurs
070 */
071 @Override
072 public int read(char[] chr) throws IOException {
073 try {
074 beforeRead(chr != null ? chr.length : 0);
075 int n = in.read(chr);
076 afterRead(n);
077 return n;
078 } catch (IOException e) {
079 handleIOException(e);
080 return -1;
081 }
082 }
083
084 /**
085 * Invokes the delegate's <code>read(char[], int, int)</code> method.
086 * @param chr the buffer to read the characters into
087 * @param st The start offset
088 * @param len The number of bytes to read
089 * @return the number of characters read or -1 if the end of stream
090 * @throws IOException if an I/O error occurs
091 */
092 @Override
093 public int read(char[] chr, int st, int len) throws IOException {
094 try {
095 beforeRead(len);
096 int n = in.read(chr, st, len);
097 afterRead(n);
098 return n;
099 } catch (IOException e) {
100 handleIOException(e);
101 return -1;
102 }
103 }
104
105 /**
106 * Invokes the delegate's <code>read(CharBuffer)</code> method.
107 * @param target the char buffer to read the characters into
108 * @return the number of characters read or -1 if the end of stream
109 * @throws IOException if an I/O error occurs
110 * @since 2.0
111 */
112 @Override
113 public int read(CharBuffer target) throws IOException {
114 try {
115 beforeRead(target != null ? target.length() : 0);
116 int n = in.read(target);
117 afterRead(n);
118 return n;
119 } catch (IOException e) {
120 handleIOException(e);
121 return -1;
122 }
123 }
124
125 /**
126 * Invokes the delegate's <code>skip(long)</code> method.
127 * @param ln the number of bytes to skip
128 * @return the number of bytes to skipped or -1 if the end of stream
129 * @throws IOException if an I/O error occurs
130 */
131 @Override
132 public long skip(long ln) throws IOException {
133 try {
134 return in.skip(ln);
135 } catch (IOException e) {
136 handleIOException(e);
137 return 0;
138 }
139 }
140
141 /**
142 * Invokes the delegate's <code>ready()</code> method.
143 * @return true if the stream is ready to be read
144 * @throws IOException if an I/O error occurs
145 */
146 @Override
147 public boolean ready() throws IOException {
148 try {
149 return in.ready();
150 } catch (IOException e) {
151 handleIOException(e);
152 return false;
153 }
154 }
155
156 /**
157 * Invokes the delegate's <code>close()</code> method.
158 * @throws IOException if an I/O error occurs
159 */
160 @Override
161 public void close() throws IOException {
162 try {
163 in.close();
164 } catch (IOException e) {
165 handleIOException(e);
166 }
167 }
168
169 /**
170 * Invokes the delegate's <code>mark(int)</code> method.
171 * @param idx read ahead limit
172 * @throws IOException if an I/O error occurs
173 */
174 @Override
175 public synchronized void mark(int idx) throws IOException {
176 try {
177 in.mark(idx);
178 } catch (IOException e) {
179 handleIOException(e);
180 }
181 }
182
183 /**
184 * Invokes the delegate's <code>reset()</code> method.
185 * @throws IOException if an I/O error occurs
186 */
187 @Override
188 public synchronized void reset() throws IOException {
189 try {
190 in.reset();
191 } catch (IOException e) {
192 handleIOException(e);
193 }
194 }
195
196 /**
197 * Invokes the delegate's <code>markSupported()</code> method.
198 * @return true if mark is supported, otherwise false
199 */
200 @Override
201 public boolean markSupported() {
202 return in.markSupported();
203 }
204
205 /**
206 * Invoked by the read methods before the call is proxied. The number
207 * of chars that the caller wanted to read (1 for the {@link #read()}
208 * method, buffer length for {@link #read(char[])}, etc.) is given as
209 * an argument.
210 * <p>
211 * Subclasses can override this method to add common pre-processing
212 * functionality without having to override all the read methods.
213 * The default implementation does nothing.
214 * <p>
215 * Note this method is <em>not</em> called from {@link #skip(long)} or
216 * {@link #reset()}. You need to explicitly override those methods if
217 * you want to add pre-processing steps also to them.
218 *
219 * @since 2.0
220 * @param n number of chars that the caller asked to be read
221 * @throws IOException if the pre-processing fails
222 */
223 protected void beforeRead(int n) throws IOException {
224 }
225
226 /**
227 * Invoked by the read methods after the proxied call has returned
228 * successfully. The number of chars returned to the caller (or -1 if
229 * the end of stream was reached) is given as an argument.
230 * <p>
231 * Subclasses can override this method to add common post-processing
232 * functionality without having to override all the read methods.
233 * The default implementation does nothing.
234 * <p>
235 * Note this method is <em>not</em> called from {@link #skip(long)} or
236 * {@link #reset()}. You need to explicitly override those methods if
237 * you want to add post-processing steps also to them.
238 *
239 * @since 2.0
240 * @param n number of chars read, or -1 if the end of stream was reached
241 * @throws IOException if the post-processing fails
242 */
243 protected void afterRead(int n) throws IOException {
244 }
245
246 /**
247 * Handle any IOExceptions thrown.
248 * <p>
249 * This method provides a point to implement custom exception
250 * handling. The default behaviour is to re-throw the exception.
251 * @param e The IOException thrown
252 * @throws IOException if an I/O error occurs
253 * @since 2.0
254 */
255 protected void handleIOException(IOException e) throws IOException {
256 throw e;
257 }
258
259 }