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1   /*
2    * Copyright (C) 2009 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.base;
16  
17  import static com.google.common.base.Preconditions.checkArgument;
18  import static com.google.common.base.Preconditions.checkNotNull;
19  
20  import com.google.common.annotations.Beta;
21  import com.google.common.annotations.GwtCompatible;
22  import com.google.common.annotations.GwtIncompatible;
23  import java.util.ArrayList;
24  import java.util.Collections;
25  import java.util.Iterator;
26  import java.util.LinkedHashMap;
27  import java.util.List;
28  import java.util.Map;
29  import java.util.regex.Pattern;
30  
31  /**
32   * Extracts non-overlapping substrings from an input string, typically by recognizing appearances of
33   * a <i>separator</i> sequence. This separator can be specified as a single {@linkplain #on(char)
34   * character}, fixed {@linkplain #on(String) string}, {@linkplain #onPattern regular expression} or
35   * {@link #on(CharMatcher) CharMatcher} instance. Or, instead of using a separator at all, a
36   * splitter can extract adjacent substrings of a given {@linkplain #fixedLength fixed length}.
37   *
38   * <p>For example, this expression: <pre>   {@code
39   *
40   *   Splitter.on(',').split("foo,bar,qux")}</pre>
41   *
42   * ... produces an {@code Iterable} containing {@code "foo"}, {@code "bar"} and {@code "qux"}, in
43   * that order.
44   *
45   * <p>By default, {@code Splitter}'s behavior is simplistic and unassuming. The following
46   * expression: <pre>   {@code
47   *
48   *   Splitter.on(',').split(" foo,,,  bar ,")}</pre>
49   *
50   * ... yields the substrings {@code [" foo", "", "", "  bar ", ""]}. If this is not the desired
51   * behavior, use configuration methods to obtain a <i>new</i> splitter instance with modified
52   * behavior: <pre>   {@code
53   *
54   *   private static final Splitter MY_SPLITTER = Splitter.on(',')
55   *       .trimResults()
56   *       .omitEmptyStrings();}</pre>
57   *
58   * <p>Now {@code MY_SPLITTER.split("foo,,,  bar ,")} returns just {@code ["foo",
59   * "bar"]}. Note that the order in which these configuration methods are called is never
60   * significant.
61   *
62   * <p><b>Warning:</b> Splitter instances are immutable. Invoking a configuration method has no
63   * effect on the receiving instance; you must store and use the new splitter instance it returns
64   * instead. <pre>   {@code
65   *
66   *   // Do NOT do this
67   *   Splitter splitter = Splitter.on('/');
68   *   splitter.trimResults(); // does nothing!
69   *   return splitter.split("wrong / wrong / wrong");}</pre>
70   *
71   * <p>For separator-based splitters that do not use {@code omitEmptyStrings}, an input string
72   * containing {@code n} occurrences of the separator naturally yields an iterable of size
73   * {@code n + 1}. So if the separator does not occur anywhere in the input, a single substring is
74   * returned containing the entire input. Consequently, all splitters split the empty string to
75   * {@code [""]} (note: even fixed-length splitters).
76   *
77   * <p>Splitter instances are thread-safe immutable, and are therefore safe to store as
78   * {@code static final} constants.
79   *
80   * <p>The {@link Joiner} class provides the inverse operation to splitting, but note that a
81   * round-trip between the two should be assumed to be lossy.
82   *
83   * <p>See the Guava User Guide article on
84   * <a href="https://github.com/google/guava/wiki/StringsExplained#splitter">{@code Splitter}</a>.
85   *
86   * @author Julien Silland
87   * @author Jesse Wilson
88   * @author Kevin Bourrillion
89   * @author Louis Wasserman
90   * @since 1.0
91   */
92  @GwtCompatible(emulated = true)
93  public final class Splitter {
94    private final CharMatcher trimmer;
95    private final boolean omitEmptyStrings;
96    private final Strategy strategy;
97    private final int limit;
98  
99    private Splitter(Strategy strategy) {
100     this(strategy, false, CharMatcher.none(), Integer.MAX_VALUE);
101   }
102 
103   private Splitter(Strategy strategy, boolean omitEmptyStrings, CharMatcher trimmer, int limit) {
104     this.strategy = strategy;
105     this.omitEmptyStrings = omitEmptyStrings;
106     this.trimmer = trimmer;
107     this.limit = limit;
108   }
109 
110   /**
111    * Returns a splitter that uses the given single-character separator. For example,
112    * {@code Splitter.on(',').split("foo,,bar")} returns an iterable containing
113    * {@code ["foo", "", "bar"]}.
114    *
115    * @param separator the character to recognize as a separator
116    * @return a splitter, with default settings, that recognizes that separator
117    */
118   public static Splitter on(char separator) {
119     return on(CharMatcher.is(separator));
120   }
121 
122   /**
123    * Returns a splitter that considers any single character matched by the given {@code CharMatcher}
124    * to be a separator. For example, {@code
125    * Splitter.on(CharMatcher.anyOf(";,")).split("foo,;bar,quux")} returns an iterable containing
126    * {@code ["foo", "", "bar", "quux"]}.
127    *
128    * @param separatorMatcher a {@link CharMatcher} that determines whether a character is a
129    *     separator
130    * @return a splitter, with default settings, that uses this matcher
131    */
132   public static Splitter on(final CharMatcher separatorMatcher) {
133     checkNotNull(separatorMatcher);
134 
135     return new Splitter(
136         new Strategy() {
137           @Override
138           public SplittingIterator iterator(Splitter splitter, final CharSequence toSplit) {
139             return new SplittingIterator(splitter, toSplit) {
140               @Override
141               int separatorStart(int start) {
142                 return separatorMatcher.indexIn(toSplit, start);
143               }
144 
145               @Override
146               int separatorEnd(int separatorPosition) {
147                 return separatorPosition + 1;
148               }
149             };
150           }
151         });
152   }
153 
154   /**
155    * Returns a splitter that uses the given fixed string as a separator. For example,
156    * {@code Splitter.on(", ").split("foo, bar,baz")} returns an iterable containing
157    * {@code ["foo", "bar,baz"]}.
158    *
159    * @param separator the literal, nonempty string to recognize as a separator
160    * @return a splitter, with default settings, that recognizes that separator
161    */
162   public static Splitter on(final String separator) {
163     checkArgument(separator.length() != 0, "The separator may not be the empty string.");
164     if (separator.length() == 1) {
165       return Splitter.on(separator.charAt(0));
166     }
167     return new Splitter(
168         new Strategy() {
169           @Override
170           public SplittingIterator iterator(Splitter splitter, CharSequence toSplit) {
171             return new SplittingIterator(splitter, toSplit) {
172               @Override
173               public int separatorStart(int start) {
174                 int separatorLength = separator.length();
175 
176                 positions:
177                 for (int p = start, last = toSplit.length() - separatorLength; p <= last; p++) {
178                   for (int i = 0; i < separatorLength; i++) {
179                     if (toSplit.charAt(i + p) != separator.charAt(i)) {
180                       continue positions;
181                     }
182                   }
183                   return p;
184                 }
185                 return -1;
186               }
187 
188               @Override
189               public int separatorEnd(int separatorPosition) {
190                 return separatorPosition + separator.length();
191               }
192             };
193           }
194         });
195   }
196 
197   /**
198    * Returns a splitter that considers any subsequence matching {@code pattern} to be a separator.
199    * For example, {@code Splitter.on(Pattern.compile("\r?\n")).split(entireFile)} splits a string
200    * into lines whether it uses DOS-style or UNIX-style line terminators.
201    *
202    * @param separatorPattern the pattern that determines whether a subsequence is a separator. This
203    *     pattern may not match the empty string.
204    * @return a splitter, with default settings, that uses this pattern
205    * @throws IllegalArgumentException if {@code separatorPattern} matches the empty string
206    */
207   @GwtIncompatible // java.util.regex
208   public static Splitter on(Pattern separatorPattern) {
209     return on(new JdkPattern(separatorPattern));
210   }
211 
212   private static Splitter on(final CommonPattern separatorPattern) {
213     checkArgument(
214         !separatorPattern.matcher("").matches(),
215         "The pattern may not match the empty string: %s",
216         separatorPattern);
217 
218     return new Splitter(
219         new Strategy() {
220           @Override
221           public SplittingIterator iterator(final Splitter splitter, CharSequence toSplit) {
222             final CommonMatcher matcher = separatorPattern.matcher(toSplit);
223             return new SplittingIterator(splitter, toSplit) {
224               @Override
225               public int separatorStart(int start) {
226                 return matcher.find(start) ? matcher.start() : -1;
227               }
228 
229               @Override
230               public int separatorEnd(int separatorPosition) {
231                 return matcher.end();
232               }
233             };
234           }
235         });
236   }
237 
238   /**
239    * Returns a splitter that considers any subsequence matching a given pattern (regular expression)
240    * to be a separator. For example, {@code Splitter.onPattern("\r?\n").split(entireFile)} splits a
241    * string into lines whether it uses DOS-style or UNIX-style line terminators. This is equivalent
242    * to {@code Splitter.on(Pattern.compile(pattern))}.
243    *
244    * @param separatorPattern the pattern that determines whether a subsequence is a separator. This
245    *     pattern may not match the empty string.
246    * @return a splitter, with default settings, that uses this pattern
247    * @throws IllegalArgumentException if {@code separatorPattern} matches the empty string or is a
248    *     malformed expression
249    */
250   @GwtIncompatible // java.util.regex
251   public static Splitter onPattern(String separatorPattern) {
252     return on(Platform.compilePattern(separatorPattern));
253   }
254 
255   /**
256    * Returns a splitter that divides strings into pieces of the given length. For example,
257    * {@code Splitter.fixedLength(2).split("abcde")} returns an iterable containing
258    * {@code ["ab", "cd", "e"]}. The last piece can be smaller than {@code length} but will never be
259    * empty.
260    *
261    * <p><b>Exception:</b> for consistency with separator-based splitters, {@code
262    * split("")} does not yield an empty iterable, but an iterable containing {@code ""}. This is the
263    * only case in which {@code
264    * Iterables.size(split(input))} does not equal {@code
265    * IntMath.divide(input.length(), length, CEILING)}. To avoid this behavior, use
266    * {@code omitEmptyStrings}.
267    *
268    * @param length the desired length of pieces after splitting, a positive integer
269    * @return a splitter, with default settings, that can split into fixed sized pieces
270    * @throws IllegalArgumentException if {@code length} is zero or negative
271    */
272   public static Splitter fixedLength(final int length) {
273     checkArgument(length > 0, "The length may not be less than 1");
274 
275     return new Splitter(
276         new Strategy() {
277           @Override
278           public SplittingIterator iterator(final Splitter splitter, CharSequence toSplit) {
279             return new SplittingIterator(splitter, toSplit) {
280               @Override
281               public int separatorStart(int start) {
282                 int nextChunkStart = start + length;
283                 return (nextChunkStart < toSplit.length() ? nextChunkStart : -1);
284               }
285 
286               @Override
287               public int separatorEnd(int separatorPosition) {
288                 return separatorPosition;
289               }
290             };
291           }
292         });
293   }
294 
295   /**
296    * Returns a splitter that behaves equivalently to {@code this} splitter, but automatically omits
297    * empty strings from the results. For example, {@code
298    * Splitter.on(',').omitEmptyStrings().split(",a,,,b,c,,")} returns an iterable containing only
299    * {@code ["a", "b", "c"]}.
300    *
301    * <p>If either {@code trimResults} option is also specified when creating a splitter, that
302    * splitter always trims results first before checking for emptiness. So, for example, {@code
303    * Splitter.on(':').omitEmptyStrings().trimResults().split(": : : ")} returns an empty iterable.
304    *
305    * <p>Note that it is ordinarily not possible for {@link #split(CharSequence)} to return an empty
306    * iterable, but when using this option, it can (if the input sequence consists of nothing but
307    * separators).
308    *
309    * @return a splitter with the desired configuration
310    */
311   public Splitter omitEmptyStrings() {
312     return new Splitter(strategy, true, trimmer, limit);
313   }
314 
315   /**
316    * Returns a splitter that behaves equivalently to {@code this} splitter but stops splitting after
317    * it reaches the limit. The limit defines the maximum number of items returned by the iterator,
318    * or the maximum size of the list returned by {@link #splitToList}.
319    *
320    * <p>For example, {@code Splitter.on(',').limit(3).split("a,b,c,d")} returns an iterable
321    * containing {@code ["a", "b", "c,d"]}. When omitting empty strings, the omitted strings do not
322    * count. Hence, {@code Splitter.on(',').limit(3).omitEmptyStrings().split("a,,,b,,,c,d")} returns
323    * an iterable containing {@code ["a", "b", "c,d"}. When trim is requested, all entries are
324    * trimmed, including the last. Hence
325    * {@code Splitter.on(',').limit(3).trimResults().split(" a , b , c , d ")} results in
326    * {@code ["a", "b", "c , d"]}.
327    *
328    * @param limit the maximum number of items returned
329    * @return a splitter with the desired configuration
330    * @since 9.0
331    */
332   public Splitter limit(int limit) {
333     checkArgument(limit > 0, "must be greater than zero: %s", limit);
334     return new Splitter(strategy, omitEmptyStrings, trimmer, limit);
335   }
336 
337   /**
338    * Returns a splitter that behaves equivalently to {@code this} splitter, but automatically
339    * removes leading and trailing {@linkplain CharMatcher#whitespace whitespace} from each returned
340    * substring; equivalent to {@code trimResults(CharMatcher.whitespace())}. For example, {@code
341    * Splitter.on(',').trimResults().split(" a, b ,c ")} returns an iterable containing
342    * {@code ["a", "b", "c"]}.
343    *
344    * @return a splitter with the desired configuration
345    */
346   public Splitter trimResults() {
347     return trimResults(CharMatcher.whitespace());
348   }
349 
350   /**
351    * Returns a splitter that behaves equivalently to {@code this} splitter, but removes all leading
352    * or trailing characters matching the given {@code
353    * CharMatcher} from each returned substring. For example, {@code
354    * Splitter.on(',').trimResults(CharMatcher.is('_')).split("_a ,_b_ ,c__")} returns an iterable
355    * containing {@code ["a ", "b_ ", "c"]}.
356    *
357    * @param trimmer a {@link CharMatcher} that determines whether a character should be removed from
358    *     the beginning/end of a subsequence
359    * @return a splitter with the desired configuration
360    */
361   // TODO(kevinb): throw if a trimmer was already specified!
362   public Splitter trimResults(CharMatcher trimmer) {
363     checkNotNull(trimmer);
364     return new Splitter(strategy, omitEmptyStrings, trimmer, limit);
365   }
366 
367   /**
368    * Splits {@code sequence} into string components and makes them available through an
369    * {@link Iterator}, which may be lazily evaluated. If you want an eagerly computed {@link List},
370    * use {@link #splitToList(CharSequence)}.
371    *
372    * @param sequence the sequence of characters to split
373    * @return an iteration over the segments split from the parameter
374    */
375   public Iterable<String> split(final CharSequence sequence) {
376     checkNotNull(sequence);
377 
378     return new Iterable<String>() {
379       @Override
380       public Iterator<String> iterator() {
381         return splittingIterator(sequence);
382       }
383 
384       @Override
385       public String toString() {
386         return Joiner.on(", ")
387             .appendTo(new StringBuilder().append('['), this)
388             .append(']')
389             .toString();
390       }
391     };
392   }
393 
394   private Iterator<String> splittingIterator(CharSequence sequence) {
395     return strategy.iterator(this, sequence);
396   }
397 
398   /**
399    * Splits {@code sequence} into string components and returns them as an immutable list. If you
400    * want an {@link Iterable} which may be lazily evaluated, use {@link #split(CharSequence)}.
401    *
402    * @param sequence the sequence of characters to split
403    * @return an immutable list of the segments split from the parameter
404    * @since 15.0
405    */
406   @Beta
407   public List<String> splitToList(CharSequence sequence) {
408     checkNotNull(sequence);
409 
410     Iterator<String> iterator = splittingIterator(sequence);
411     List<String> result = new ArrayList<>();
412 
413     while (iterator.hasNext()) {
414       result.add(iterator.next());
415     }
416 
417     return Collections.unmodifiableList(result);
418   }
419 
420   /**
421    * Returns a {@code MapSplitter} which splits entries based on this splitter, and splits entries
422    * into keys and values using the specified separator.
423    *
424    * @since 10.0
425    */
426   @Beta
427   public MapSplitter withKeyValueSeparator(String separator) {
428     return withKeyValueSeparator(on(separator));
429   }
430 
431   /**
432    * Returns a {@code MapSplitter} which splits entries based on this splitter, and splits entries
433    * into keys and values using the specified separator.
434    *
435    * @since 14.0
436    */
437   @Beta
438   public MapSplitter withKeyValueSeparator(char separator) {
439     return withKeyValueSeparator(on(separator));
440   }
441 
442   /**
443    * Returns a {@code MapSplitter} which splits entries based on this splitter, and splits entries
444    * into keys and values using the specified key-value splitter.
445    *
446    * @since 10.0
447    */
448   @Beta
449   public MapSplitter withKeyValueSeparator(Splitter keyValueSplitter) {
450     return new MapSplitter(this, keyValueSplitter);
451   }
452 
453   /**
454    * An object that splits strings into maps as {@code Splitter} splits iterables and lists. Like
455    * {@code Splitter}, it is thread-safe and immutable. The common way to build instances is by
456    * providing an additional {@linkplain Splitter#withKeyValueSeparator key-value separator} to
457    * {@link Splitter}.
458    *
459    * @since 10.0
460    */
461   @Beta
462   public static final class MapSplitter {
463     private static final String INVALID_ENTRY_MESSAGE = "Chunk [%s] is not a valid entry";
464     private final Splitter outerSplitter;
465     private final Splitter entrySplitter;
466 
467     private MapSplitter(Splitter outerSplitter, Splitter entrySplitter) {
468       this.outerSplitter = outerSplitter; // only "this" is passed
469       this.entrySplitter = checkNotNull(entrySplitter);
470     }
471 
472     /**
473      * Splits {@code sequence} into substrings, splits each substring into an entry, and returns an
474      * unmodifiable map with each of the entries. For example,
475      * {@code Splitter.on(';').trimResults().withKeyValueSeparator("=>").split("a=>b ; c=>b")} will
476      * return a mapping from {@code "a"} to {@code "b"} and {@code "c"} to {@code "b"}.
477      *
478      * <p>The returned map preserves the order of the entries from {@code sequence}.
479      *
480      * @throws IllegalArgumentException if the specified sequence does not split into valid map
481      *     entries, or if there are duplicate keys
482      */
483     public Map<String, String> split(CharSequence sequence) {
484       Map<String, String> map = new LinkedHashMap<>();
485       for (String entry : outerSplitter.split(sequence)) {
486         Iterator<String> entryFields = entrySplitter.splittingIterator(entry);
487 
488         checkArgument(entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry);
489         String key = entryFields.next();
490         checkArgument(!map.containsKey(key), "Duplicate key [%s] found.", key);
491 
492         checkArgument(entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry);
493         String value = entryFields.next();
494         map.put(key, value);
495 
496         checkArgument(!entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry);
497       }
498       return Collections.unmodifiableMap(map);
499     }
500   }
501 
502   private interface Strategy {
503     Iterator<String> iterator(Splitter splitter, CharSequence toSplit);
504   }
505 
506   private abstract static class SplittingIterator extends AbstractIterator<String> {
507     final CharSequence toSplit;
508     final CharMatcher trimmer;
509     final boolean omitEmptyStrings;
510 
511     /**
512      * Returns the first index in {@code toSplit} at or after {@code start} that contains the
513      * separator.
514      */
515     abstract int separatorStart(int start);
516 
517     /**
518      * Returns the first index in {@code toSplit} after {@code
519      * separatorPosition} that does not contain a separator. This method is only invoked after a
520      * call to {@code separatorStart}.
521      */
522     abstract int separatorEnd(int separatorPosition);
523 
524     int offset = 0;
525     int limit;
526 
527     protected SplittingIterator(Splitter splitter, CharSequence toSplit) {
528       this.trimmer = splitter.trimmer;
529       this.omitEmptyStrings = splitter.omitEmptyStrings;
530       this.limit = splitter.limit;
531       this.toSplit = toSplit;
532     }
533 
534     @Override
535     protected String computeNext() {
536       /*
537        * The returned string will be from the end of the last match to the beginning of the next
538        * one. nextStart is the start position of the returned substring, while offset is the place
539        * to start looking for a separator.
540        */
541       int nextStart = offset;
542       while (offset != -1) {
543         int start = nextStart;
544         int end;
545 
546         int separatorPosition = separatorStart(offset);
547         if (separatorPosition == -1) {
548           end = toSplit.length();
549           offset = -1;
550         } else {
551           end = separatorPosition;
552           offset = separatorEnd(separatorPosition);
553         }
554         if (offset == nextStart) {
555           /*
556            * This occurs when some pattern has an empty match, even if it doesn't match the empty
557            * string -- for example, if it requires lookahead or the like. The offset must be
558            * increased to look for separators beyond this point, without changing the start position
559            * of the next returned substring -- so nextStart stays the same.
560            */
561           offset++;
562           if (offset > toSplit.length()) {
563             offset = -1;
564           }
565           continue;
566         }
567 
568         while (start < end && trimmer.matches(toSplit.charAt(start))) {
569           start++;
570         }
571         while (end > start && trimmer.matches(toSplit.charAt(end - 1))) {
572           end--;
573         }
574 
575         if (omitEmptyStrings && start == end) {
576           // Don't include the (unused) separator in next split string.
577           nextStart = offset;
578           continue;
579         }
580 
581         if (limit == 1) {
582           // The limit has been reached, return the rest of the string as the
583           // final item. This is tested after empty string removal so that
584           // empty strings do not count towards the limit.
585           end = toSplit.length();
586           offset = -1;
587           // Since we may have changed the end, we need to trim it again.
588           while (end > start && trimmer.matches(toSplit.charAt(end - 1))) {
589             end--;
590           }
591         } else {
592           limit--;
593         }
594 
595         return toSplit.subSequence(start, end).toString();
596       }
597       return endOfData();
598     }
599   }
600 }