Source Code Cross Referenced for DeferredFileOutputStream.java in  » Library » apache-common-IO » org » apache » commons » io » output » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Library » apache common IO » org.apache.commons.io.output 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


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.File;
020:        import java.io.FileInputStream;
021:        import java.io.FileOutputStream;
022:        import java.io.IOException;
023:        import java.io.OutputStream;
024:        import org.apache.commons.io.IOUtils;
025:
026:        /**
027:         * An output stream which will retain data in memory until a specified
028:         * threshold is reached, and only then commit it to disk. If the stream is
029:         * closed before the threshold is reached, the data will not be written to
030:         * disk at all.
031:         * <p>
032:         * This class originated in FileUpload processing. In this use case, you do
033:         * not know in advance the size of the file being uploaded. If the file is small
034:         * you want to store it in memory (for speed), but if the file is large you want
035:         * to store it to file (to avoid memory issues).
036:         *
037:         * @author <a href="mailto:martinc@apache.org">Martin Cooper</a>
038:         * @author gaxzerow
039:         *
040:         * @version $Id: DeferredFileOutputStream.java 437567 2006-08-28 06:39:07Z bayard $
041:         */
042:        public class DeferredFileOutputStream extends ThresholdingOutputStream {
043:
044:            // ----------------------------------------------------------- Data members
045:
046:            /**
047:             * The output stream to which data will be written prior to the theshold
048:             * being reached.
049:             */
050:            private ByteArrayOutputStream memoryOutputStream;
051:
052:            /**
053:             * The output stream to which data will be written at any given time. This
054:             * will always be one of <code>memoryOutputStream</code> or
055:             * <code>diskOutputStream</code>.
056:             */
057:            private OutputStream currentOutputStream;
058:
059:            /**
060:             * The file to which output will be directed if the threshold is exceeded.
061:             */
062:            private File outputFile;
063:
064:            /**
065:             * True when close() has been called successfully.
066:             */
067:            private boolean closed = false;
068:
069:            // ----------------------------------------------------------- Constructors
070:
071:            /**
072:             * Constructs an instance of this class which will trigger an event at the
073:             * specified threshold, and save data to a file beyond that point.
074:             *
075:             * @param threshold  The number of bytes at which to trigger an event.
076:             * @param outputFile The file to which data is saved beyond the threshold.
077:             */
078:            public DeferredFileOutputStream(int threshold, File outputFile) {
079:                super (threshold);
080:                this .outputFile = outputFile;
081:
082:                memoryOutputStream = new ByteArrayOutputStream();
083:                currentOutputStream = memoryOutputStream;
084:            }
085:
086:            // --------------------------------------- ThresholdingOutputStream methods
087:
088:            /**
089:             * Returns the current output stream. This may be memory based or disk
090:             * based, depending on the current state with respect to the threshold.
091:             *
092:             * @return The underlying output stream.
093:             *
094:             * @exception IOException if an error occurs.
095:             */
096:            protected OutputStream getStream() throws IOException {
097:                return currentOutputStream;
098:            }
099:
100:            /**
101:             * Switches the underlying output stream from a memory based stream to one
102:             * that is backed by disk. This is the point at which we realise that too
103:             * much data is being written to keep in memory, so we elect to switch to
104:             * disk-based storage.
105:             *
106:             * @exception IOException if an error occurs.
107:             */
108:            protected void thresholdReached() throws IOException {
109:                FileOutputStream fos = new FileOutputStream(outputFile);
110:                memoryOutputStream.writeTo(fos);
111:                currentOutputStream = fos;
112:                memoryOutputStream = null;
113:            }
114:
115:            // --------------------------------------------------------- Public methods
116:
117:            /**
118:             * Determines whether or not the data for this output stream has been
119:             * retained in memory.
120:             *
121:             * @return <code>true</code> if the data is available in memory;
122:             *         <code>false</code> otherwise.
123:             */
124:            public boolean isInMemory() {
125:                return (!isThresholdExceeded());
126:            }
127:
128:            /**
129:             * Returns the data for this output stream as an array of bytes, assuming
130:             * that the data has been retained in memory. If the data was written to
131:             * disk, this method returns <code>null</code>.
132:             *
133:             * @return The data for this output stream, or <code>null</code> if no such
134:             *         data is available.
135:             */
136:            public byte[] getData() {
137:                if (memoryOutputStream != null) {
138:                    return memoryOutputStream.toByteArray();
139:                }
140:                return null;
141:            }
142:
143:            /**
144:             * Returns the same output file specified in the constructor, even when
145:             * threashold has not been reached.
146:             *
147:             * @return The file for this output stream, or <code>null</code> if no such
148:             *         file exists.
149:             */
150:            public File getFile() {
151:                return outputFile;
152:            }
153:
154:            /**
155:             * Closes underlying output stream, and mark this as closed
156:             *
157:             * @exception IOException if an error occurs.
158:             */
159:            public void close() throws IOException {
160:                super .close();
161:                closed = true;
162:            }
163:
164:            /**
165:             * Writes the data from this output stream to the specified output stream,
166:             * after it has been closed.
167:             *
168:             * @param out output stream to write to.
169:             * @exception IOException if this stream is not yet closed or an error occurs.
170:             */
171:            public void writeTo(OutputStream out) throws IOException {
172:                // we may only need to check if this is closed if we are working with a file
173:                // but we should force the habit of closing wether we are working with
174:                // a file or memory.
175:                if (!closed) {
176:                    throw new IOException("Stream not closed");
177:                }
178:
179:                if (isInMemory()) {
180:                    memoryOutputStream.writeTo(out);
181:                } else {
182:                    FileInputStream fis = new FileInputStream(outputFile);
183:                    try {
184:                        IOUtils.copy(fis, out);
185:                    } finally {
186:                        IOUtils.closeQuietly(fis);
187:                    }
188:                }
189:            }
190:        }
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