001 /*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017 package com.google.common.base;
018
019 import static com.google.common.base.Preconditions.checkNotNull;
020
021 import com.google.common.annotations.Beta;
022 import com.google.common.annotations.GwtCompatible;
023
024 import java.io.IOException;
025 import java.util.AbstractList;
026 import java.util.Arrays;
027 import java.util.Iterator;
028 import java.util.Map;
029 import java.util.Map.Entry;
030
031 import javax.annotation.CheckReturnValue;
032 import javax.annotation.Nullable;
033
034 /**
035 * An object which joins pieces of text (specified as an array, {@link Iterable}, varargs or even a
036 * {@link Map}) with a separator. It either appends the results to an {@link Appendable} or returns
037 * them as a {@link String}. Example: <pre> {@code
038 *
039 * Joiner joiner = Joiner.on("; ").skipNulls();
040 * . . .
041 * return joiner.join("Harry", null, "Ron", "Hermione");}</pre>
042 *
043 * This returns the string {@code "Harry; Ron; Hermione"}. Note that all input elements are
044 * converted to strings using {@link Object#toString()} before being appended.
045 *
046 * <p>If neither {@link #skipNulls()} nor {@link #useForNull(String)} is specified, the joining
047 * methods will throw {@link NullPointerException} if any given element is null.
048 *
049 * <p><b>Warning: joiner instances are always immutable</b>; a configuration method such as {@code
050 * useForNull} has no effect on the instance it is invoked on! You must store and use the new joiner
051 * instance returned by the method. This makes joiners thread-safe, and safe to store as {@code
052 * static final} constants. <pre> {@code
053 *
054 * // Bad! Do not do this!
055 * Joiner joiner = Joiner.on(',');
056 * joiner.skipNulls(); // does nothing!
057 * return joiner.join("wrong", null, "wrong");}</pre>
058 *
059 * <p>See the Guava User Guide article on <a href=
060 * "http://code.google.com/p/guava-libraries/wiki/StringsExplained#Joiner">{@code Joiner}</a>.
061 *
062 * @author Kevin Bourrillion
063 * @since 2.0 (imported from Google Collections Library)
064 */
065 @GwtCompatible
066 public class Joiner {
067 /**
068 * Returns a joiner which automatically places {@code separator} between consecutive elements.
069 */
070 public static Joiner on(String separator) {
071 return new Joiner(separator);
072 }
073
074 /**
075 * Returns a joiner which automatically places {@code separator} between consecutive elements.
076 */
077 public static Joiner on(char separator) {
078 return new Joiner(String.valueOf(separator));
079 }
080
081 private final String separator;
082
083 private Joiner(String separator) {
084 this.separator = checkNotNull(separator);
085 }
086
087 private Joiner(Joiner prototype) {
088 this.separator = prototype.separator;
089 }
090
091 /**
092 * <b>Deprecated.</b>
093 *
094 * @since 11.0
095 * @deprecated use {@link #appendTo(Appendable, Iterator)} by casting {@code parts} to
096 * {@code Iterator<?>}, or better yet, by implementing only {@code Iterator} and not
097 * {@code Iterable}. <b>This method is scheduled for deletion in June 2013.</b>
098 */
099 @Beta
100 @Deprecated
101 public
102 final <A extends Appendable, I extends Object & Iterable<?> & Iterator<?>> A
103 appendTo(A appendable, I parts) throws IOException {
104 return appendTo(appendable, (Iterator<?>) parts);
105 }
106
107 /**
108 * Appends the string representation of each of {@code parts}, using the previously configured
109 * separator between each, to {@code appendable}.
110 */
111 public <A extends Appendable> A appendTo(A appendable, Iterable<?> parts) throws IOException {
112 return appendTo(appendable, parts.iterator());
113 }
114
115 /**
116 * Appends the string representation of each of {@code parts}, using the previously configured
117 * separator between each, to {@code appendable}.
118 *
119 * @since 11.0
120 */
121 public <A extends Appendable> A appendTo(A appendable, Iterator<?> parts) throws IOException {
122 checkNotNull(appendable);
123 if (parts.hasNext()) {
124 appendable.append(toString(parts.next()));
125 while (parts.hasNext()) {
126 appendable.append(separator);
127 appendable.append(toString(parts.next()));
128 }
129 }
130 return appendable;
131 }
132
133 /**
134 * Appends the string representation of each of {@code parts}, using the previously configured
135 * separator between each, to {@code appendable}.
136 */
137 public final <A extends Appendable> A appendTo(A appendable, Object[] parts) throws IOException {
138 return appendTo(appendable, Arrays.asList(parts));
139 }
140
141 /**
142 * Appends to {@code appendable} the string representation of each of the remaining arguments.
143 */
144 public final <A extends Appendable> A appendTo(
145 A appendable, @Nullable Object first, @Nullable Object second, Object... rest)
146 throws IOException {
147 return appendTo(appendable, iterable(first, second, rest));
148 }
149
150 /**
151 * <b>Deprecated.</b>
152 *
153 * @since 11.0
154 * @deprecated use {@link #appendTo(StringBuilder, Iterator)} by casting {@code parts} to
155 * {@code Iterator<?>}, or better yet, by implementing only {@code Iterator} and not
156 * {@code Iterable}. <b>This method is scheduled for deletion in June 2013.</b>
157 */
158 @Beta
159 @Deprecated
160 public
161 final <I extends Object & Iterable<?> & Iterator<?>> StringBuilder
162 appendTo(StringBuilder builder, I parts) {
163 return appendTo(builder, (Iterator<?>) parts);
164 }
165
166 /**
167 * Appends the string representation of each of {@code parts}, using the previously configured
168 * separator between each, to {@code builder}. Identical to {@link #appendTo(Appendable,
169 * Iterable)}, except that it does not throw {@link IOException}.
170 */
171 public final StringBuilder appendTo(StringBuilder builder, Iterable<?> parts) {
172 return appendTo(builder, parts.iterator());
173 }
174
175 /**
176 * Appends the string representation of each of {@code parts}, using the previously configured
177 * separator between each, to {@code builder}. Identical to {@link #appendTo(Appendable,
178 * Iterable)}, except that it does not throw {@link IOException}.
179 *
180 * @since 11.0
181 */
182 public final StringBuilder appendTo(StringBuilder builder, Iterator<?> parts) {
183 try {
184 appendTo((Appendable) builder, parts);
185 } catch (IOException impossible) {
186 throw new AssertionError(impossible);
187 }
188 return builder;
189 }
190
191 /**
192 * Appends the string representation of each of {@code parts}, using the previously configured
193 * separator between each, to {@code builder}. Identical to {@link #appendTo(Appendable,
194 * Iterable)}, except that it does not throw {@link IOException}.
195 */
196 public final StringBuilder appendTo(StringBuilder builder, Object[] parts) {
197 return appendTo(builder, Arrays.asList(parts));
198 }
199
200 /**
201 * Appends to {@code builder} the string representation of each of the remaining arguments.
202 * Identical to {@link #appendTo(Appendable, Object, Object, Object...)}, except that it does not
203 * throw {@link IOException}.
204 */
205 public final StringBuilder appendTo(
206 StringBuilder builder, @Nullable Object first, @Nullable Object second, Object... rest) {
207 return appendTo(builder, iterable(first, second, rest));
208 }
209
210 /**
211 * <b>Deprecated.</b>
212 *
213 * @since 11.0
214 * @deprecated use {@link #join(Iterator)} by casting {@code parts} to
215 * {@code Iterator<?>}, or better yet, by implementing only {@code Iterator} and not
216 * {@code Iterable}. <b>This method is scheduled for deletion in June 2013.</b>
217 */
218 @Beta
219 @Deprecated
220 public
221 final <I extends Object & Iterable<?> & Iterator<?>> String join(I parts) {
222 return join((Iterator<?>) parts);
223 }
224
225 /**
226 * Returns a string containing the string representation of each of {@code parts}, using the
227 * previously configured separator between each.
228 */
229 public final String join(Iterable<?> parts) {
230 return join(parts.iterator());
231 }
232
233 /**
234 * Returns a string containing the string representation of each of {@code parts}, using the
235 * previously configured separator between each.
236 *
237 * @since 11.0
238 */
239 public final String join(Iterator<?> parts) {
240 return appendTo(new StringBuilder(), parts).toString();
241 }
242
243 /**
244 * Returns a string containing the string representation of each of {@code parts}, using the
245 * previously configured separator between each.
246 */
247 public final String join(Object[] parts) {
248 return join(Arrays.asList(parts));
249 }
250
251 /**
252 * Returns a string containing the string representation of each argument, using the previously
253 * configured separator between each.
254 */
255 public final String join(@Nullable Object first, @Nullable Object second, Object... rest) {
256 return join(iterable(first, second, rest));
257 }
258
259 /**
260 * Returns a joiner with the same behavior as this one, except automatically substituting {@code
261 * nullText} for any provided null elements.
262 */
263 @CheckReturnValue
264 public Joiner useForNull(final String nullText) {
265 checkNotNull(nullText);
266 return new Joiner(this) {
267 @Override CharSequence toString(Object part) {
268 return (part == null) ? nullText : Joiner.this.toString(part);
269 }
270
271 @Override public Joiner useForNull(String nullText) {
272 checkNotNull(nullText); // weird: just to satisfy NullPointerTester.
273 throw new UnsupportedOperationException("already specified useForNull");
274 }
275
276 @Override public Joiner skipNulls() {
277 throw new UnsupportedOperationException("already specified useForNull");
278 }
279 };
280 }
281
282 /**
283 * Returns a joiner with the same behavior as this joiner, except automatically skipping over any
284 * provided null elements.
285 */
286 @CheckReturnValue
287 public Joiner skipNulls() {
288 return new Joiner(this) {
289 @Override public <A extends Appendable> A appendTo(A appendable, Iterator<?> parts)
290 throws IOException {
291 checkNotNull(appendable, "appendable");
292 checkNotNull(parts, "parts");
293 while (parts.hasNext()) {
294 Object part = parts.next();
295 if (part != null) {
296 appendable.append(Joiner.this.toString(part));
297 break;
298 }
299 }
300 while (parts.hasNext()) {
301 Object part = parts.next();
302 if (part != null) {
303 appendable.append(separator);
304 appendable.append(Joiner.this.toString(part));
305 }
306 }
307 return appendable;
308 }
309
310 @Override public Joiner useForNull(String nullText) {
311 checkNotNull(nullText); // weird: just to satisfy NullPointerTester.
312 throw new UnsupportedOperationException("already specified skipNulls");
313 }
314
315 @Override public MapJoiner withKeyValueSeparator(String kvs) {
316 checkNotNull(kvs); // weird: just to satisfy NullPointerTester.
317 throw new UnsupportedOperationException("can't use .skipNulls() with maps");
318 }
319 };
320 }
321
322 /**
323 * Returns a {@code MapJoiner} using the given key-value separator, and the same configuration as
324 * this {@code Joiner} otherwise.
325 */
326 @CheckReturnValue
327 public MapJoiner withKeyValueSeparator(String keyValueSeparator) {
328 return new MapJoiner(this, keyValueSeparator);
329 }
330
331 /**
332 * An object that joins map entries in the same manner as {@code Joiner} joins iterables and
333 * arrays. Like {@code Joiner}, it is thread-safe and immutable.
334 *
335 * <p>In addition to operating on {@code Map} instances, {@code MapJoiner} can operate on {@code
336 * Multimap} entries in two distinct modes:
337 *
338 * <ul>
339 * <li>To output a separate entry for each key-value pair, pass {@code multimap.entries()} to a
340 * {@code MapJoiner} method that accepts entries as input, and receive output of the form
341 * {@code key1=A&key1=B&key2=C}.
342 * <li>To output a single entry for each key, pass {@code multimap.asMap()} to a {@code MapJoiner}
343 * method that accepts a map as input, and receive output of the form {@code
344 * key1=[A, B]&key2=C}.
345 * </ul>
346 *
347 * @since 2.0 (imported from Google Collections Library)
348 */
349 public final static class MapJoiner {
350 private final Joiner joiner;
351 private final String keyValueSeparator;
352
353 private MapJoiner(Joiner joiner, String keyValueSeparator) {
354 this.joiner = joiner; // only "this" is ever passed, so don't checkNotNull
355 this.keyValueSeparator = checkNotNull(keyValueSeparator);
356 }
357
358 /**
359 * Appends the string representation of each entry of {@code map}, using the previously
360 * configured separator and key-value separator, to {@code appendable}.
361 */
362 public <A extends Appendable> A appendTo(A appendable, Map<?, ?> map) throws IOException {
363 return appendTo(appendable, map.entrySet());
364 }
365
366 /**
367 * Appends the string representation of each entry of {@code map}, using the previously
368 * configured separator and key-value separator, to {@code builder}. Identical to {@link
369 * #appendTo(Appendable, Map)}, except that it does not throw {@link IOException}.
370 */
371 public StringBuilder appendTo(StringBuilder builder, Map<?, ?> map) {
372 return appendTo(builder, map.entrySet());
373 }
374
375 /**
376 * Returns a string containing the string representation of each entry of {@code map}, using the
377 * previously configured separator and key-value separator.
378 */
379 public String join(Map<?, ?> map) {
380 return join(map.entrySet());
381 }
382
383 /**
384 * <b>Deprecated.</b>
385 *
386 * @since 11.0
387 * @deprecated use {@link #appendTo(Appendable, Iterator)} by casting {@code entries} to
388 * {@code Iterator<? extends Entry<?, ?>>}, or better yet, by implementing only
389 * {@code Iterator} and not {@code Iterable}. <b>This method is scheduled for deletion
390 * in June 2013.</b>
391 */
392 @Beta
393 @Deprecated
394 public
395 <A extends Appendable,
396 I extends Object & Iterable<? extends Entry<?, ?>> & Iterator<? extends Entry<?, ?>>>
397 A appendTo(A appendable, I entries) throws IOException {
398 Iterator<? extends Entry<?, ?>> iterator = entries;
399 return appendTo(appendable, iterator);
400 }
401
402 /**
403 * Appends the string representation of each entry in {@code entries}, using the previously
404 * configured separator and key-value separator, to {@code appendable}.
405 *
406 * @since 10.0
407 */
408 @Beta
409 public <A extends Appendable> A appendTo(A appendable, Iterable<? extends Entry<?, ?>> entries)
410 throws IOException {
411 return appendTo(appendable, entries.iterator());
412 }
413
414 /**
415 * Appends the string representation of each entry in {@code entries}, using the previously
416 * configured separator and key-value separator, to {@code appendable}.
417 *
418 * @since 11.0
419 */
420 @Beta
421 public <A extends Appendable> A appendTo(A appendable, Iterator<? extends Entry<?, ?>> parts)
422 throws IOException {
423 checkNotNull(appendable);
424 if (parts.hasNext()) {
425 Entry<?, ?> entry = parts.next();
426 appendable.append(joiner.toString(entry.getKey()));
427 appendable.append(keyValueSeparator);
428 appendable.append(joiner.toString(entry.getValue()));
429 while (parts.hasNext()) {
430 appendable.append(joiner.separator);
431 Entry<?, ?> e = parts.next();
432 appendable.append(joiner.toString(e.getKey()));
433 appendable.append(keyValueSeparator);
434 appendable.append(joiner.toString(e.getValue()));
435 }
436 }
437 return appendable;
438 }
439
440 /**
441 * <b>Deprecated.</b>
442 *
443 * @since 11.0
444 * @deprecated use {@link #appendTo(StringBuilder, Iterator)} by casting {@code entries} to
445 * {@code Iterator<? extends Entry<?, ?>>}, or better yet, by implementing only
446 * {@code Iterator} and not {@code Iterable}. <b>This method is scheduled for deletion
447 * in June 2013.</b>
448 */
449 @Beta
450 @Deprecated
451 public
452 <I extends Object & Iterable<? extends Entry<?, ?>> & Iterator<? extends Entry<?, ?>>>
453 StringBuilder appendTo(StringBuilder builder, I entries) throws IOException {
454 Iterator<? extends Entry<?, ?>> iterator = entries;
455 return appendTo(builder, iterator);
456 }
457
458 /**
459 * Appends the string representation of each entry in {@code entries}, using the previously
460 * configured separator and key-value separator, to {@code builder}. Identical to {@link
461 * #appendTo(Appendable, Iterable)}, except that it does not throw {@link IOException}.
462 *
463 * @since 10.0
464 */
465 @Beta
466 public StringBuilder appendTo(StringBuilder builder, Iterable<? extends Entry<?, ?>> entries) {
467 return appendTo(builder, entries.iterator());
468 }
469
470 /**
471 * Appends the string representation of each entry in {@code entries}, using the previously
472 * configured separator and key-value separator, to {@code builder}. Identical to {@link
473 * #appendTo(Appendable, Iterable)}, except that it does not throw {@link IOException}.
474 *
475 * @since 11.0
476 */
477 @Beta
478 public StringBuilder appendTo(StringBuilder builder, Iterator<? extends Entry<?, ?>> entries) {
479 try {
480 appendTo((Appendable) builder, entries);
481 } catch (IOException impossible) {
482 throw new AssertionError(impossible);
483 }
484 return builder;
485 }
486
487 /**
488 * <b>Deprecated.</b>
489 *
490 * @since 11.0
491 * @deprecated use {@link #join(Iterator)} by casting {@code entries} to
492 * {@code Iterator<? extends Entry<?, ?>>}, or better yet, by implementing only
493 * {@code Iterator} and not {@code Iterable}. <b>This method is scheduled for deletion
494 * in June 2013.</b>
495 */
496 @Beta
497 @Deprecated
498 public
499 <I extends Object & Iterable<? extends Entry<?, ?>> & Iterator<? extends Entry<?, ?>>>
500 String join(I entries) throws IOException {
501 Iterator<? extends Entry<?, ?>> iterator = entries;
502 return join(iterator);
503 }
504
505 /**
506 * Returns a string containing the string representation of each entry in {@code entries}, using
507 * the previously configured separator and key-value separator.
508 *
509 * @since 10.0
510 */
511 @Beta
512 public String join(Iterable<? extends Entry<?, ?>> entries) {
513 return join(entries.iterator());
514 }
515
516 /**
517 * Returns a string containing the string representation of each entry in {@code entries}, using
518 * the previously configured separator and key-value separator.
519 *
520 * @since 11.0
521 */
522 @Beta
523 public String join(Iterator<? extends Entry<?, ?>> entries) {
524 return appendTo(new StringBuilder(), entries).toString();
525 }
526
527 /**
528 * Returns a map joiner with the same behavior as this one, except automatically substituting
529 * {@code nullText} for any provided null keys or values.
530 */
531 @CheckReturnValue
532 public MapJoiner useForNull(String nullText) {
533 return new MapJoiner(joiner.useForNull(nullText), keyValueSeparator);
534 }
535 }
536
537 CharSequence toString(Object part) {
538 checkNotNull(part); // checkNotNull for GWT (do not optimize).
539 return (part instanceof CharSequence) ? (CharSequence) part : part.toString();
540 }
541
542 private static Iterable<Object> iterable(
543 final Object first, final Object second, final Object[] rest) {
544 checkNotNull(rest);
545 return new AbstractList<Object>() {
546 @Override public int size() {
547 return rest.length + 2;
548 }
549
550 @Override public Object get(int index) {
551 switch (index) {
552 case 0:
553 return first;
554 case 1:
555 return second;
556 default:
557 return rest[index - 2];
558 }
559 }
560 };
561 }
562 }