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