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.output;
018
019 import java.io.IOException;
020 import java.io.OutputStream;
021
022
023 /**
024 * An output stream which triggers an event when a specified number of bytes of
025 * data have been written to it. The event can be used, for example, to throw
026 * an exception if a maximum has been reached, or to switch the underlying
027 * stream type when the threshold is exceeded.
028 * <p>
029 * This class overrides all <code>OutputStream</code> methods. However, these
030 * overrides ultimately call the corresponding methods in the underlying output
031 * stream implementation.
032 * <p>
033 * NOTE: This implementation may trigger the event <em>before</em> the threshold
034 * is actually reached, since it triggers when a pending write operation would
035 * cause the threshold to be exceeded.
036 *
037 * @author <a href="mailto:martinc@apache.org">Martin Cooper</a>
038 *
039 * @version $Id: ThresholdingOutputStream.java 540714 2007-05-22 19:39:44Z niallp $
040 */
041 public abstract class ThresholdingOutputStream
042 extends OutputStream
043 {
044
045 // ----------------------------------------------------------- Data members
046
047
048 /**
049 * The threshold at which the event will be triggered.
050 */
051 private int threshold;
052
053
054 /**
055 * The number of bytes written to the output stream.
056 */
057 private long written;
058
059
060 /**
061 * Whether or not the configured threshold has been exceeded.
062 */
063 private boolean thresholdExceeded;
064
065
066 // ----------------------------------------------------------- Constructors
067
068
069 /**
070 * Constructs an instance of this class which will trigger an event at the
071 * specified threshold.
072 *
073 * @param threshold The number of bytes at which to trigger an event.
074 */
075 public ThresholdingOutputStream(int threshold)
076 {
077 this.threshold = threshold;
078 }
079
080
081 // --------------------------------------------------- OutputStream methods
082
083
084 /**
085 * Writes the specified byte to this output stream.
086 *
087 * @param b The byte to be written.
088 *
089 * @exception IOException if an error occurs.
090 */
091 public void write(int b) throws IOException
092 {
093 checkThreshold(1);
094 getStream().write(b);
095 written++;
096 }
097
098
099 /**
100 * Writes <code>b.length</code> bytes from the specified byte array to this
101 * output stream.
102 *
103 * @param b The array of bytes to be written.
104 *
105 * @exception IOException if an error occurs.
106 */
107 public void write(byte b[]) throws IOException
108 {
109 checkThreshold(b.length);
110 getStream().write(b);
111 written += b.length;
112 }
113
114
115 /**
116 * Writes <code>len</code> bytes from the specified byte array starting at
117 * offset <code>off</code> to this output stream.
118 *
119 * @param b The byte array from which the data will be written.
120 * @param off The start offset in the byte array.
121 * @param len The number of bytes to write.
122 *
123 * @exception IOException if an error occurs.
124 */
125 public void write(byte b[], int off, int len) throws IOException
126 {
127 checkThreshold(len);
128 getStream().write(b, off, len);
129 written += len;
130 }
131
132
133 /**
134 * Flushes this output stream and forces any buffered output bytes to be
135 * written out.
136 *
137 * @exception IOException if an error occurs.
138 */
139 public void flush() throws IOException
140 {
141 getStream().flush();
142 }
143
144
145 /**
146 * Closes this output stream and releases any system resources associated
147 * with this stream.
148 *
149 * @exception IOException if an error occurs.
150 */
151 public void close() throws IOException
152 {
153 try
154 {
155 flush();
156 }
157 catch (IOException ignored)
158 {
159 // ignore
160 }
161 getStream().close();
162 }
163
164
165 // --------------------------------------------------------- Public methods
166
167
168 /**
169 * Returns the threshold, in bytes, at which an event will be triggered.
170 *
171 * @return The threshold point, in bytes.
172 */
173 public int getThreshold()
174 {
175 return threshold;
176 }
177
178
179 /**
180 * Returns the number of bytes that have been written to this output stream.
181 *
182 * @return The number of bytes written.
183 */
184 public long getByteCount()
185 {
186 return written;
187 }
188
189
190 /**
191 * Determines whether or not the configured threshold has been exceeded for
192 * this output stream.
193 *
194 * @return <code>true</code> if the threshold has been reached;
195 * <code>false</code> otherwise.
196 */
197 public boolean isThresholdExceeded()
198 {
199 return (written > threshold);
200 }
201
202
203 // ------------------------------------------------------ Protected methods
204
205
206 /**
207 * Checks to see if writing the specified number of bytes would cause the
208 * configured threshold to be exceeded. If so, triggers an event to allow
209 * a concrete implementation to take action on this.
210 *
211 * @param count The number of bytes about to be written to the underlying
212 * output stream.
213 *
214 * @exception IOException if an error occurs.
215 */
216 protected void checkThreshold(int count) throws IOException
217 {
218 if (!thresholdExceeded && (written + count > threshold))
219 {
220 thresholdExceeded = true;
221 thresholdReached();
222 }
223 }
224
225 /**
226 * Resets the byteCount to zero. You can call this from
227 * {@link #thresholdReached()} if you want the event to be triggered again.
228 */
229 protected void resetByteCount()
230 {
231 this.thresholdExceeded = false;
232 this.written = 0;
233 }
234
235 // ------------------------------------------------------- Abstract methods
236
237
238 /**
239 * Returns the underlying output stream, to which the corresponding
240 * <code>OutputStream</code> methods in this class will ultimately delegate.
241 *
242 * @return The underlying output stream.
243 *
244 * @exception IOException if an error occurs.
245 */
246 protected abstract OutputStream getStream() throws IOException;
247
248
249 /**
250 * Indicates that the configured threshold has been reached, and that a
251 * subclass should take whatever action necessary on this event. This may
252 * include changing the underlying output stream.
253 *
254 * @exception IOException if an error occurs.
255 */
256 protected abstract void thresholdReached() throws IOException;
257 }