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;
031import org.checkerframework.checker.nullness.qual.Nullable;
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@GwtIncompatible
048public final class CharStreams {
049
050  // 2K chars (4K bytes)
051  private static final int DEFAULT_BUF_SIZE = 0x800;
052
053  /** Creates a new {@code CharBuffer} for buffering reads or writes. */
054  static CharBuffer createBuffer() {
055    return CharBuffer.allocate(DEFAULT_BUF_SIZE);
056  }
057
058  private CharStreams() {}
059
060  /**
061   * Copies all characters between the {@link Readable} and {@link Appendable} objects. Does not
062   * close or flush either object.
063   *
064   * @param from the object to read from
065   * @param to the object to write to
066   * @return the number of characters copied
067   * @throws IOException if an I/O error occurs
068   */
069  @CanIgnoreReturnValue
070  public static long copy(Readable from, Appendable to) throws IOException {
071    // The most common case is that from is a Reader (like InputStreamReader or StringReader) so
072    // take advantage of that.
073    if (from instanceof Reader) {
074      // optimize for common output types which are optimized to deal with char[]
075      if (to instanceof StringBuilder) {
076        return copyReaderToBuilder((Reader) from, (StringBuilder) to);
077      } else {
078        return copyReaderToWriter((Reader) from, asWriter(to));
079      }
080    } else {
081      checkNotNull(from);
082      checkNotNull(to);
083      long total = 0;
084      CharBuffer buf = createBuffer();
085      while (from.read(buf) != -1) {
086        Java8Compatibility.flip(buf);
087        to.append(buf);
088        total += buf.remaining();
089        Java8Compatibility.clear(buf);
090      }
091      return total;
092    }
093  }
094
095  // TODO(lukes): consider allowing callers to pass in a buffer to use, some callers would be able
096  // to reuse buffers, others would be able to size them more appropriately than the constant
097  // defaults
098
099  /**
100   * Copies all characters between the {@link Reader} and {@link StringBuilder} objects. Does not
101   * close or flush the reader.
102   *
103   * <p>This is identical to {@link #copy(Readable, Appendable)} but optimized for these specific
104   * types. CharBuffer has poor performance when being written into or read out of so round tripping
105   * all the bytes through the buffer takes a long time. With these specialized types we can just
106   * use a char array.
107   *
108   * @param from the object to read from
109   * @param to the object to write to
110   * @return the number of characters copied
111   * @throws IOException if an I/O error occurs
112   */
113  @CanIgnoreReturnValue
114  static long copyReaderToBuilder(Reader from, StringBuilder to) throws IOException {
115    checkNotNull(from);
116    checkNotNull(to);
117    char[] buf = new char[DEFAULT_BUF_SIZE];
118    int nRead;
119    long total = 0;
120    while ((nRead = from.read(buf)) != -1) {
121      to.append(buf, 0, nRead);
122      total += nRead;
123    }
124    return total;
125  }
126
127  /**
128   * Copies all characters between the {@link Reader} and {@link Writer} objects. Does not close or
129   * flush the reader or writer.
130   *
131   * <p>This is identical to {@link #copy(Readable, Appendable)} but optimized for these specific
132   * types. CharBuffer has poor performance when being written into or read out of so round tripping
133   * all the bytes through the buffer takes a long time. With these specialized types we can just
134   * use a char array.
135   *
136   * @param from the object to read from
137   * @param to the object to write to
138   * @return the number of characters copied
139   * @throws IOException if an I/O error occurs
140   */
141  @CanIgnoreReturnValue
142  static long copyReaderToWriter(Reader from, Writer to) throws IOException {
143    checkNotNull(from);
144    checkNotNull(to);
145    char[] buf = new char[DEFAULT_BUF_SIZE];
146    int nRead;
147    long total = 0;
148    while ((nRead = from.read(buf)) != -1) {
149      to.write(buf, 0, nRead);
150      total += nRead;
151    }
152    return total;
153  }
154
155  /**
156   * Reads all characters from a {@link Readable} object into a {@link String}. Does not close the
157   * {@code Readable}.
158   *
159   * @param r the object to read from
160   * @return a string containing all the characters
161   * @throws IOException if an I/O error occurs
162   */
163  public static String toString(Readable r) throws IOException {
164    return toStringBuilder(r).toString();
165  }
166
167  /**
168   * Reads all characters from a {@link Readable} object into a new {@link StringBuilder} instance.
169   * Does not close the {@code Readable}.
170   *
171   * @param r the object to read from
172   * @return a {@link StringBuilder} containing all the characters
173   * @throws IOException if an I/O error occurs
174   */
175  private static StringBuilder toStringBuilder(Readable r) throws IOException {
176    StringBuilder sb = new StringBuilder();
177    if (r instanceof Reader) {
178      copyReaderToBuilder((Reader) r, sb);
179    } else {
180      copy(r, sb);
181    }
182    return sb;
183  }
184
185  /**
186   * Reads all of the lines from a {@link Readable} object. The lines do not include
187   * line-termination characters, but do include other leading and trailing whitespace.
188   *
189   * <p>Does not close the {@code Readable}. If reading files or resources you should use the {@link
190   * Files#readLines} and {@link Resources#readLines} methods.
191   *
192   * @param r the object to read from
193   * @return a mutable {@link List} containing all the lines
194   * @throws IOException if an I/O error occurs
195   */
196  @Beta
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  @Beta
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 reached.
234   * Returns the total number of chars read. Does not close the stream.
235   *
236   * @since 20.0
237   */
238  @Beta
239  @CanIgnoreReturnValue
240  public static long exhaust(Readable readable) throws IOException {
241    long total = 0;
242    long read;
243    CharBuffer buf = createBuffer();
244    while ((read = readable.read(buf)) != -1) {
245      total += read;
246      Java8Compatibility.clear(buf);
247    }
248    return total;
249  }
250
251  /**
252   * Discards {@code n} characters of data from the reader. This method will block until the full
253   * amount has been skipped. Does not close the reader.
254   *
255   * @param reader the reader to read from
256   * @param n the number of characters to skip
257   * @throws EOFException if this stream reaches the end before skipping all the characters
258   * @throws IOException if an I/O error occurs
259   */
260  @Beta
261  public static void skipFully(Reader reader, long n) throws IOException {
262    checkNotNull(reader);
263    while (n > 0) {
264      long amt = reader.skip(n);
265      if (amt == 0) {
266        throw new EOFException();
267      }
268      n -= amt;
269    }
270  }
271
272  /**
273   * Returns a {@link Writer} that simply discards written chars.
274   *
275   * @since 15.0
276   */
277  @Beta
278  public static Writer nullWriter() {
279    return NullWriter.INSTANCE;
280  }
281
282  private static final class NullWriter extends Writer {
283
284    private static final NullWriter INSTANCE = new NullWriter();
285
286    @Override
287    public void write(int c) {}
288
289    @Override
290    public void write(char[] cbuf) {
291      checkNotNull(cbuf);
292    }
293
294    @Override
295    public void write(char[] cbuf, int off, int len) {
296      checkPositionIndexes(off, off + len, cbuf.length);
297    }
298
299    @Override
300    public void write(String str) {
301      checkNotNull(str);
302    }
303
304    @Override
305    public void write(String str, int off, int len) {
306      checkPositionIndexes(off, off + len, str.length());
307    }
308
309    @Override
310    public Writer append(@Nullable CharSequence csq) {
311      return this;
312    }
313
314    @Override
315    public Writer append(@Nullable CharSequence csq, int start, int end) {
316      checkPositionIndexes(start, end, csq == null ? "null".length() : csq.length());
317      return this;
318    }
319
320    @Override
321    public Writer append(char c) {
322      return this;
323    }
324
325    @Override
326    public void flush() {}
327
328    @Override
329    public void close() {}
330
331    @Override
332    public String toString() {
333      return "CharStreams.nullWriter()";
334    }
335  }
336
337  /**
338   * Returns a Writer that sends all output to the given {@link Appendable} target. Closing the
339   * writer will close the target if it is {@link Closeable}, and flushing the writer will flush the
340   * target if it is {@link java.io.Flushable}.
341   *
342   * @param target the object to which output will be sent
343   * @return a new Writer object, unless target is a Writer, in which case the target is returned
344   */
345  @Beta
346  public static Writer asWriter(Appendable target) {
347    if (target instanceof Writer) {
348      return (Writer) target;
349    }
350    return new AppendableWriter(target);
351  }
352}