1 /*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14
15 package com.google.common.io;
16
17 import static com.google.common.base.Preconditions.checkNotNull;
18 import static com.google.common.base.Preconditions.checkPositionIndexes;
19
20 import com.google.common.annotations.Beta;
21 import com.google.common.annotations.GwtIncompatible;
22 import com.google.errorprone.annotations.CanIgnoreReturnValue;
23 import java.io.Closeable;
24 import java.io.EOFException;
25 import java.io.IOException;
26 import java.io.Reader;
27 import java.io.Writer;
28 import java.nio.CharBuffer;
29 import java.util.ArrayList;
30 import java.util.List;
31 import javax.annotation.CheckForNull;
32 import org.checkerframework.checker.nullness.qual.Nullable;
33
34 /**
35 * Provides utility methods for working with character streams.
36 *
37 * <p>All method parameters must be non-null unless documented otherwise.
38 *
39 * <p>Some of the methods in this class take arguments with a generic type of {@code Readable &
40 * Closeable}. A {@link java.io.Reader} implements both of those interfaces. Similarly for {@code
41 * Appendable & Closeable} and {@link java.io.Writer}.
42 *
43 * @author Chris Nokleberg
44 * @author Bin Zhu
45 * @author Colin Decker
46 * @since 1.0
47 */
48 @GwtIncompatible
49 @ElementTypesAreNonnullByDefault
50 public final class CharStreams {
51
52 // 2K chars (4K bytes)
53 private static final int DEFAULT_BUF_SIZE = 0x800;
54
55 /** Creates a new {@code CharBuffer} for buffering reads or writes. */
56 static CharBuffer createBuffer() {
57 return CharBuffer.allocate(DEFAULT_BUF_SIZE);
58 }
59
60 private CharStreams() {}
61
62 /**
63 * Copies all characters between the {@link Readable} and {@link Appendable} objects. Does not
64 * close or flush either object.
65 *
66 * @param from the object to read from
67 * @param to the object to write to
68 * @return the number of characters copied
69 * @throws IOException if an I/O error occurs
70 */
71 @CanIgnoreReturnValue
72 public static long copy(Readable from, Appendable to) throws IOException {
73 // The most common case is that from is a Reader (like InputStreamReader or StringReader) so
74 // take advantage of that.
75 if (from instanceof Reader) {
76 // optimize for common output types which are optimized to deal with char[]
77 if (to instanceof StringBuilder) {
78 return copyReaderToBuilder((Reader) from, (StringBuilder) to);
79 } else {
80 return copyReaderToWriter((Reader) from, asWriter(to));
81 }
82 }
83
84 checkNotNull(from);
85 checkNotNull(to);
86 long total = 0;
87 CharBuffer buf = createBuffer();
88 while (from.read(buf) != -1) {
89 Java8Compatibility.flip(buf);
90 to.append(buf);
91 total += buf.remaining();
92 Java8Compatibility.clear(buf);
93 }
94 return total;
95 }
96
97 // TODO(lukes): consider allowing callers to pass in a buffer to use, some callers would be able
98 // to reuse buffers, others would be able to size them more appropriately than the constant
99 // 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 {@link
192 * 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 @Beta
199 public static List<String> readLines(Readable r) throws IOException {
200 List<String> result = new ArrayList<>();
201 LineReader lineReader = new LineReader(r);
202 String line;
203 while ((line = lineReader.readLine()) != null) {
204 result.add(line);
205 }
206 return result;
207 }
208
209 /**
210 * Streams lines from a {@link Readable} object, stopping when the processor returns {@code false}
211 * or all lines have been read and returning the result produced by the processor. Does not close
212 * {@code readable}. Note that this method may not fully consume the contents of {@code readable}
213 * if the processor stops processing early.
214 *
215 * @throws IOException if an I/O error occurs
216 * @since 14.0
217 */
218 @Beta
219 @CanIgnoreReturnValue // some processors won't return a useful result
220 @ParametricNullness
221 public static <T extends @Nullable Object> T readLines(
222 Readable readable, LineProcessor<T> processor) throws IOException {
223 checkNotNull(readable);
224 checkNotNull(processor);
225
226 LineReader lineReader = new LineReader(readable);
227 String line;
228 while ((line = lineReader.readLine()) != null) {
229 if (!processor.processLine(line)) {
230 break;
231 }
232 }
233 return processor.getResult();
234 }
235
236 /**
237 * Reads and discards data from the given {@code Readable} until the end of the stream is reached.
238 * Returns the total number of chars read. Does not close the stream.
239 *
240 * @since 20.0
241 */
242 @Beta
243 @CanIgnoreReturnValue
244 public static long exhaust(Readable readable) throws IOException {
245 long total = 0;
246 long read;
247 CharBuffer buf = createBuffer();
248 while ((read = readable.read(buf)) != -1) {
249 total += read;
250 Java8Compatibility.clear(buf);
251 }
252 return total;
253 }
254
255 /**
256 * Discards {@code n} characters of data from the reader. This method will block until the full
257 * amount has been skipped. Does not close the reader.
258 *
259 * @param reader the reader to read from
260 * @param n the number of characters to skip
261 * @throws EOFException if this stream reaches the end before skipping all the characters
262 * @throws IOException if an I/O error occurs
263 */
264 @Beta
265 public static void skipFully(Reader reader, long n) throws IOException {
266 checkNotNull(reader);
267 while (n > 0) {
268 long amt = reader.skip(n);
269 if (amt == 0) {
270 throw new EOFException();
271 }
272 n -= amt;
273 }
274 }
275
276 /**
277 * Returns a {@link Writer} that simply discards written chars.
278 *
279 * @since 15.0
280 */
281 @Beta
282 public static Writer nullWriter() {
283 return NullWriter.INSTANCE;
284 }
285
286 private static final class NullWriter extends Writer {
287
288 private static final NullWriter INSTANCE = new NullWriter();
289
290 @Override
291 public void write(int c) {}
292
293 @Override
294 public void write(char[] cbuf) {
295 checkNotNull(cbuf);
296 }
297
298 @Override
299 public void write(char[] cbuf, int off, int len) {
300 checkPositionIndexes(off, off + len, cbuf.length);
301 }
302
303 @Override
304 public void write(String str) {
305 checkNotNull(str);
306 }
307
308 @Override
309 public void write(String str, int off, int len) {
310 checkPositionIndexes(off, off + len, str.length());
311 }
312
313 @Override
314 public Writer append(@CheckForNull CharSequence csq) {
315 return this;
316 }
317
318 @Override
319 public Writer append(@CheckForNull CharSequence csq, int start, int end) {
320 checkPositionIndexes(start, end, csq == null ? "null".length() : csq.length());
321 return this;
322 }
323
324 @Override
325 public Writer append(char c) {
326 return this;
327 }
328
329 @Override
330 public void flush() {}
331
332 @Override
333 public void close() {}
334
335 @Override
336 public String toString() {
337 return "CharStreams.nullWriter()";
338 }
339 }
340
341 /**
342 * Returns a Writer that sends all output to the given {@link Appendable} target. Closing the
343 * writer will close the target if it is {@link Closeable}, and flushing the writer will flush the
344 * target if it is {@link java.io.Flushable}.
345 *
346 * @param target the object to which output will be sent
347 * @return a new Writer object, unless target is a Writer, in which case the target is returned
348 */
349 @Beta
350 public static Writer asWriter(Appendable target) {
351 if (target instanceof Writer) {
352 return (Writer) target;
353 }
354 return new AppendableWriter(target);
355 }
356 }