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Java > Open Source Codes > org > apache > commons > fileupload > DeferredFileOutputStream


1 /*
2  * $Header: /home/cvs/jakarta-commons/fileupload/src/java/org/apache/commons/fileupload/DeferredFileOutputStream.java,v 1.2 2003/05/31 22:31:08 martinc Exp $
3  * $Revision: 1.2 $
4  * $Date: 2003/05/31 22:31:08 $
5  *
6  * ====================================================================
7  *
8  * The Apache Software License, Version 1.1
9  *
10  * Copyright (c) 2001-2003 The Apache Software Foundation. All rights
11  * reserved.
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14  * modification, are permitted provided that the following conditions
15  * are met:
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18  * notice, this list of conditions and the following disclaimer.
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26  * any, must include the following acknowlegement:
27  * "This product includes software developed by the
28  * Apache Software Foundation (http://www.apache.org/)."
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30  * if and wherever such third-party acknowlegements normally appear.
31  *
32  * 4. The names "The Jakarta Project", "Commons", and "Apache Software
33  * Foundation" must not be used to endorse or promote products derived
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55  * This software consists of voluntary contributions made by many
56  * individuals on behalf of the Apache Software Foundation. For more
57  * information on the Apache Software Foundation, please see
58  * <http://www.apache.org/>.
59  *
60  */
61
62
63 package org.apache.commons.fileupload;
64
65 import java.io.ByteArrayOutputStream JavaDoc;
66 import java.io.File JavaDoc;
67 import java.io.FileOutputStream JavaDoc;
68 import java.io.IOException JavaDoc;
69 import java.io.OutputStream JavaDoc;
70
71 /**
72  * <p>An output stream which will retain data in memory until a specified
73  * threshold is reached, and only then commit it to disk. If the stream is
74  * closed before the threshold is reached, the data will not be written to
75  * disk at all.</p>
76  *
77  * @author <a HREF="mailto:martinc@apache.org">Martin Cooper</a>
78  *
79  * @version $Id: DeferredFileOutputStream.java,v 1.2 2003/05/31 22:31:08 martinc Exp $
80  */
81 public class DeferredFileOutputStream
82     extends ThresholdingOutputStream
83 {
84
85     // ----------------------------------------------------------- Data members
86
87
88     /**
89      * The output stream to which data will be written prior to the theshold
90      * being reached.
91      */
92     private ByteArrayOutputStream JavaDoc memoryOutputStream;
93
94
95     /**
96      * The output stream to which data will be written after the theshold is
97      * reached.
98      */
99     private FileOutputStream JavaDoc diskOutputStream;
100
101
102     /**
103      * The output stream to which data will be written at any given time. This
104      * will always be one of <code>memoryOutputStream</code> or
105      * <code>diskOutputStream</code>.
106      */
107     private OutputStream JavaDoc currentOutputStream;
108
109
110     /**
111      * The file to which output will be directed if the threshold is exceeded.
112      */
113     private File JavaDoc outputFile;
114
115
116     // ----------------------------------------------------------- Constructors
117
118
119     /**
120      * Constructs an instance of this class which will trigger an event at the
121      * specified threshold, and save data to a file beyond that point.
122      *
123      * @param threshold The number of bytes at which to trigger an event.
124      * @param outputFile The file to which data is saved beyond the threshold.
125      */
126     public DeferredFileOutputStream(int threshold, File JavaDoc outputFile)
127     {
128         super(threshold);
129         this.outputFile = outputFile;
130
131         memoryOutputStream = new ByteArrayOutputStream JavaDoc(threshold);
132         currentOutputStream = memoryOutputStream;
133     }
134
135
136     // --------------------------------------- ThresholdingOutputStream methods
137
138
139     /**
140      * Returns the current output stream. This may be memory based or disk
141      * based, depending on the current state with respect to the threshold.
142      *
143      * @return The underlying output stream.
144      *
145      * @exception IOException if an error occurs.
146      */
147     protected OutputStream JavaDoc getStream() throws IOException JavaDoc
148     {
149         return currentOutputStream;
150     }
151
152
153     /**
154      * Switches the underlying output stream from a memory based stream to one
155      * that is backed by disk. This is the point at which we realise that too
156      * much data is being written to keep in memory, so we elect to switch to
157      * disk-based storage.
158      *
159      * @exception IOException if an error occurs.
160      */
161     protected void thresholdReached() throws IOException JavaDoc
162     {
163         byte[] data = memoryOutputStream.toByteArray();
164         FileOutputStream JavaDoc fos = new FileOutputStream JavaDoc(outputFile);
165         fos.write(data);
166         diskOutputStream = fos;
167         currentOutputStream = fos;
168         memoryOutputStream = null;
169     }
170
171
172     // --------------------------------------------------------- Public methods
173
174
175     /**
176      * Determines whether or not the data for this output stream has been
177      * retained in memory.
178      *
179      * @return <code>true</code> if the data is available in memory;
180      * <code>false</code> otherwise.
181      */
182     public boolean isInMemory()
183     {
184         return (!isThresholdExceeded());
185     }
186
187
188     /**
189      * Returns the data for this output stream as an array of bytes, assuming
190      * that the data has been retained in memory. If the data was written to
191      * disk, this method returns <code>null</code>.
192      *
193      * @return The data for this output stream, or <code>null</code> if no such
194      * data is available.
195      */
196     public byte[] getData()
197     {
198         if (memoryOutputStream != null)
199         {
200             return memoryOutputStream.toByteArray();
201         }
202         return null;
203     }
204
205
206     /**
207      * Returns the data for this output stream as a <code>File</code>, assuming
208      * that the data was written to disk. If the data was retained in memory,
209      * this method returns <code>null</code>.
210      *
211      * @return The file for this output stream, or <code>null</code> if no such
212      * file exists.
213      */
214     public File JavaDoc getFile()
215     {
216         return outputFile;
217     }
218 }
219
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