001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.io;
016
017import static com.google.common.base.Preconditions.checkNotNull;
018import static com.google.common.base.Preconditions.checkPositionIndexes;
019
020import com.google.common.annotations.Beta;
021import com.google.common.annotations.GwtIncompatible;
022import com.google.errorprone.annotations.CanIgnoreReturnValue;
023import java.io.Closeable;
024import java.io.EOFException;
025import java.io.IOException;
026import java.io.Reader;
027import java.io.Writer;
028import java.nio.CharBuffer;
029import java.util.ArrayList;
030import java.util.List;
031
032/**
033 * Provides utility methods for working with character streams.
034 *
035 * <p>All method parameters must be non-null unless documented otherwise.
036 *
037 * <p>Some of the methods in this class take arguments with a generic type of
038 * {@code Readable & Closeable}. A {@link java.io.Reader} implements both of those interfaces.
039 * Similarly for {@code Appendable & Closeable} and {@link java.io.Writer}.
040 *
041 * @author Chris Nokleberg
042 * @author Bin Zhu
043 * @author Colin Decker
044 * @since 1.0
045 */
046@Beta
047@GwtIncompatible
048public final class CharStreams {
049
050  // 2K chars (4K bytes)
051  private static final int DEFAULT_BUF_SIZE = 0x800;
052
053  /**
054   * Creates a new {@code CharBuffer} for buffering reads or writes.
055   */
056  static CharBuffer createBuffer() {
057    return CharBuffer.allocate(DEFAULT_BUF_SIZE);
058  }
059
060  private CharStreams() {}
061
062  /**
063   * Copies all characters between the {@link Readable} and {@link Appendable} objects. Does not
064   * close or flush either object.
065   *
066   * @param from the object to read from
067   * @param to the object to write to
068   * @return the number of characters copied
069   * @throws IOException if an I/O error occurs
070   */
071  @CanIgnoreReturnValue
072  public static long copy(Readable from, Appendable to) throws IOException {
073    // The most common case is that from is a Reader (like InputStreamReader or StringReader) so
074    // take advantage of that.
075    if (from instanceof Reader) {
076      // optimize for common output types which are optimized to deal with char[]
077      if (to instanceof StringBuilder) {
078        return copyReaderToBuilder((Reader) from, (StringBuilder) to);
079      } else {
080        return copyReaderToWriter((Reader) from, asWriter(to));
081      }
082    } else {
083      checkNotNull(from);
084      checkNotNull(to);
085      long total = 0;
086      CharBuffer buf = createBuffer();
087      while (from.read(buf) != -1) {
088        buf.flip();
089        to.append(buf);
090        total += buf.remaining();
091        buf.clear();
092      }
093      return total;
094    }
095  }
096
097  // TODO(lukes): consider allowing callers to pass in a buffer to use, some callers would be able
098  // to reuse buffers, others would be able to size them more appropriately than the constant
099  // defaults
100
101  /**
102   * Copies all characters between the {@link Reader} and {@link StringBuilder} objects. Does not
103   * close or flush the reader.
104   *
105   * <p>This is identical to {@link #copy(Readable, Appendable)} but optimized for these specific
106   * types. CharBuffer has poor performance when being written into or read out of so round tripping
107   * all the bytes through the buffer takes a long time. With these specialized types we can just
108   * use a char array.
109   *
110   * @param from the object to read from
111   * @param to the object to write to
112   * @return the number of characters copied
113   * @throws IOException if an I/O error occurs
114   */
115  @CanIgnoreReturnValue
116  static long copyReaderToBuilder(Reader from, StringBuilder to) throws IOException {
117    checkNotNull(from);
118    checkNotNull(to);
119    char[] buf = new char[DEFAULT_BUF_SIZE];
120    int nRead;
121    long total = 0;
122    while ((nRead = from.read(buf)) != -1) {
123      to.append(buf, 0, nRead);
124      total += nRead;
125    }
126    return total;
127  }
128
129  /**
130   * Copies all characters between the {@link Reader} and {@link Writer} objects. Does not close or
131   * flush the reader or writer.
132   *
133   * <p>This is identical to {@link #copy(Readable, Appendable)} but optimized for these specific
134   * types. CharBuffer has poor performance when being written into or read out of so round tripping
135   * all the bytes through the buffer takes a long time. With these specialized types we can just
136   * use a char array.
137   *
138   * @param from the object to read from
139   * @param to the object to write to
140   * @return the number of characters copied
141   * @throws IOException if an I/O error occurs
142   */
143  @CanIgnoreReturnValue
144  static long copyReaderToWriter(Reader from, Writer to) throws IOException {
145    checkNotNull(from);
146    checkNotNull(to);
147    char[] buf = new char[DEFAULT_BUF_SIZE];
148    int nRead;
149    long total = 0;
150    while ((nRead = from.read(buf)) != -1) {
151      to.write(buf, 0, nRead);
152      total += nRead;
153    }
154    return total;
155  }
156
157  /**
158   * Reads all characters from a {@link Readable} object into a {@link String}. Does not close the
159   * {@code Readable}.
160   *
161   * @param r the object to read from
162   * @return a string containing all the characters
163   * @throws IOException if an I/O error occurs
164   */
165  public static String toString(Readable r) throws IOException {
166    return toStringBuilder(r).toString();
167  }
168
169  /**
170   * Reads all characters from a {@link Readable} object into a new {@link StringBuilder} instance.
171   * Does not close the {@code Readable}.
172   *
173   * @param r the object to read from
174   * @return a {@link StringBuilder} containing all the characters
175   * @throws IOException if an I/O error occurs
176   */
177  private static StringBuilder toStringBuilder(Readable r) throws IOException {
178    StringBuilder sb = new StringBuilder();
179    if (r instanceof Reader) {
180      copyReaderToBuilder((Reader) r, sb);
181    } else {
182      copy(r, sb);
183    }
184    return sb;
185  }
186
187  /**
188   * Reads all of the lines from a {@link Readable} object. The lines do not include
189   * line-termination characters, but do include other leading and trailing whitespace.
190   *
191   * <p>Does not close the {@code Readable}. If reading files or resources you should use the
192   * {@link Files#readLines} and {@link Resources#readLines} methods.
193   *
194   * @param r the object to read from
195   * @return a mutable {@link List} containing all the lines
196   * @throws IOException if an I/O error occurs
197   */
198  public static List<String> readLines(Readable r) throws IOException {
199    List<String> result = new ArrayList<>();
200    LineReader lineReader = new LineReader(r);
201    String line;
202    while ((line = lineReader.readLine()) != null) {
203      result.add(line);
204    }
205    return result;
206  }
207
208  /**
209   * Streams lines from a {@link Readable} object, stopping when the processor returns {@code false}
210   * or all lines have been read and returning the result produced by the processor. Does not close
211   * {@code readable}. Note that this method may not fully consume the contents of {@code readable}
212   * if the processor stops processing early.
213   *
214   * @throws IOException if an I/O error occurs
215   * @since 14.0
216   */
217  @CanIgnoreReturnValue // some processors won't return a useful result
218  public static <T> T readLines(Readable readable, LineProcessor<T> processor) throws IOException {
219    checkNotNull(readable);
220    checkNotNull(processor);
221
222    LineReader lineReader = new LineReader(readable);
223    String line;
224    while ((line = lineReader.readLine()) != null) {
225      if (!processor.processLine(line)) {
226        break;
227      }
228    }
229    return processor.getResult();
230  }
231
232  /**
233   * Reads and discards data from the given {@code Readable} until the end of the stream is
234   * reached. Returns the total number of chars read. Does not close the stream.
235   *
236   * @since 20.0
237   */
238  @CanIgnoreReturnValue
239  public static long exhaust(Readable readable) throws IOException {
240    long total = 0;
241    long read;
242    CharBuffer buf = createBuffer();
243    while ((read = readable.read(buf)) != -1) {
244      total += read;
245      buf.clear();
246    }
247    return total;
248  }
249
250  /**
251   * Discards {@code n} characters of data from the reader. This method will block until the full
252   * amount has been skipped. Does not close the reader.
253   *
254   * @param reader the reader to read from
255   * @param n the number of characters to skip
256   * @throws EOFException if this stream reaches the end before skipping all the characters
257   * @throws IOException if an I/O error occurs
258   */
259  public static void skipFully(Reader reader, long n) throws IOException {
260    checkNotNull(reader);
261    while (n > 0) {
262      long amt = reader.skip(n);
263      if (amt == 0) {
264        throw new EOFException();
265      }
266      n -= amt;
267    }
268  }
269
270  /**
271   * Returns a {@link Writer} that simply discards written chars.
272   *
273   * @since 15.0
274   */
275  public static Writer nullWriter() {
276    return NullWriter.INSTANCE;
277  }
278
279  private static final class NullWriter extends Writer {
280
281    private static final NullWriter INSTANCE = new NullWriter();
282
283    @Override
284    public void write(int c) {}
285
286    @Override
287    public void write(char[] cbuf) {
288      checkNotNull(cbuf);
289    }
290
291    @Override
292    public void write(char[] cbuf, int off, int len) {
293      checkPositionIndexes(off, off + len, cbuf.length);
294    }
295
296    @Override
297    public void write(String str) {
298      checkNotNull(str);
299    }
300
301    @Override
302    public void write(String str, int off, int len) {
303      checkPositionIndexes(off, off + len, str.length());
304    }
305
306    @Override
307    public Writer append(CharSequence csq) {
308      checkNotNull(csq);
309      return this;
310    }
311
312    @Override
313    public Writer append(CharSequence csq, int start, int end) {
314      checkPositionIndexes(start, end, csq.length());
315      return this;
316    }
317
318    @Override
319    public Writer append(char c) {
320      return this;
321    }
322
323    @Override
324    public void flush() {}
325
326    @Override
327    public void close() {}
328
329    @Override
330    public String toString() {
331      return "CharStreams.nullWriter()";
332    }
333  }
334
335  /**
336   * Returns a Writer that sends all output to the given {@link Appendable} target. Closing the
337   * writer will close the target if it is {@link Closeable}, and flushing the writer will flush the
338   * target if it is {@link java.io.Flushable}.
339   *
340   * @param target the object to which output will be sent
341   * @return a new Writer object, unless target is a Writer, in which case the target is returned
342   */
343  public static Writer asWriter(Appendable target) {
344    if (target instanceof Writer) {
345      return (Writer) target;
346    }
347    return new AppendableWriter(target);
348  }
349}