1/*
2 * Copyright (C) 2008 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.io;
18
19import com.google.common.annotations.Beta;
20import com.google.common.annotations.VisibleForTesting;
21
22import java.io.ByteArrayInputStream;
23import java.io.ByteArrayOutputStream;
24import java.io.File;
25import java.io.FileInputStream;
26import java.io.FileOutputStream;
27import java.io.IOException;
28import java.io.InputStream;
29import java.io.OutputStream;
30
31/**
32 * An {@link OutputStream} that starts buffering to a byte array, but
33 * switches to file buffering once the data reaches a configurable size.
34 *
35 * <p>This class is thread-safe.
36 *
37 * @author Chris Nokleberg
38 * @since 1.0
39 */
40@Beta
41public final class FileBackedOutputStream extends OutputStream {
42
43  private final int fileThreshold;
44  private final boolean resetOnFinalize;
45  private final InputSupplier<InputStream> supplier;
46
47  private OutputStream out;
48  private MemoryOutput memory;
49  private File file;
50
51  /** ByteArrayOutputStream that exposes its internals. */
52  private static class MemoryOutput extends ByteArrayOutputStream {
53    byte[] getBuffer() {
54      return buf;
55    }
56
57    int getCount() {
58      return count;
59    }
60  }
61
62  /** Returns the file holding the data (possibly null). */
63  @VisibleForTesting synchronized File getFile() {
64    return file;
65  }
66
67  /**
68   * Creates a new instance that uses the given file threshold, and does
69   * not reset the data when the {@link InputSupplier} returned by
70   * {@link #getSupplier} is finalized.
71   *
72   * @param fileThreshold the number of bytes before the stream should
73   *     switch to buffering to a file
74   */
75  public FileBackedOutputStream(int fileThreshold) {
76    this(fileThreshold, false);
77  }
78
79  /**
80   * Creates a new instance that uses the given file threshold, and
81   * optionally resets the data when the {@link InputSupplier} returned
82   * by {@link #getSupplier} is finalized.
83   *
84   * @param fileThreshold the number of bytes before the stream should
85   *     switch to buffering to a file
86   * @param resetOnFinalize if true, the {@link #reset} method will
87   *     be called when the {@link InputSupplier} returned by {@link
88   *     #getSupplier} is finalized
89   */
90  public FileBackedOutputStream(int fileThreshold, boolean resetOnFinalize) {
91    this.fileThreshold = fileThreshold;
92    this.resetOnFinalize = resetOnFinalize;
93    memory = new MemoryOutput();
94    out = memory;
95
96    if (resetOnFinalize) {
97      supplier = new InputSupplier<InputStream>() {
98        @Override
99        public InputStream getInput() throws IOException {
100          return openStream();
101        }
102
103        @Override protected void finalize() {
104          try {
105            reset();
106          } catch (Throwable t) {
107            t.printStackTrace(System.err);
108          }
109        }
110      };
111    } else {
112      supplier = new InputSupplier<InputStream>() {
113        @Override
114        public InputStream getInput() throws IOException {
115          return openStream();
116        }
117      };
118    }
119  }
120
121  /**
122   * Returns a supplier that may be used to retrieve the data buffered
123   * by this stream.
124   */
125  public InputSupplier<InputStream> getSupplier() {
126    return supplier;
127  }
128
129  private synchronized InputStream openStream() throws IOException {
130    if (file != null) {
131      return new FileInputStream(file);
132    } else {
133      return new ByteArrayInputStream(
134          memory.getBuffer(), 0, memory.getCount());
135    }
136  }
137
138  /**
139   * Calls {@link #close} if not already closed, and then resets this
140   * object back to its initial state, for reuse. If data was buffered
141   * to a file, it will be deleted.
142   *
143   * @throws IOException if an I/O error occurred while deleting the file buffer
144   */
145  public synchronized void reset() throws IOException {
146    try {
147      close();
148    } finally {
149      if (memory == null) {
150        memory = new MemoryOutput();
151      } else {
152        memory.reset();
153      }
154      out = memory;
155      if (file != null) {
156        File deleteMe = file;
157        file = null;
158        if (!deleteMe.delete()) {
159          throw new IOException("Could not delete: " + deleteMe);
160        }
161      }
162    }
163  }
164
165  @Override public synchronized void write(int b) throws IOException {
166    update(1);
167    out.write(b);
168  }
169
170  @Override public synchronized void write(byte[] b) throws IOException {
171    write(b, 0, b.length);
172  }
173
174  @Override public synchronized void write(byte[] b, int off, int len)
175      throws IOException {
176    update(len);
177    out.write(b, off, len);
178  }
179
180  @Override public synchronized void close() throws IOException {
181    out.close();
182  }
183
184  @Override public synchronized void flush() throws IOException {
185    out.flush();
186  }
187
188  /**
189   * Checks if writing {@code len} bytes would go over threshold, and
190   * switches to file buffering if so.
191   */
192  private void update(int len) throws IOException {
193    if (file == null && (memory.getCount() + len > fileThreshold)) {
194      File temp = File.createTempFile("FileBackedOutputStream", null);
195      if (resetOnFinalize) {
196        // Finalizers are not guaranteed to be called on system shutdown;
197        // this is insurance.
198        temp.deleteOnExit();
199      }
200      FileOutputStream transfer = new FileOutputStream(temp);
201      transfer.write(memory.getBuffer(), 0, memory.getCount());
202      transfer.flush();
203
204      // We've successfully transferred the data; switch to writing to file
205      out = transfer;
206      file = temp;
207      memory = null;
208    }
209  }
210}
211