001/*
002 * Copyright (C) 2009 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
017package com.google.common.base;
018
019import static com.google.common.base.Preconditions.checkArgument;
020import static com.google.common.base.Preconditions.checkNotNull;
021import static com.google.common.base.Preconditions.checkState;
022
023import com.google.common.annotations.Beta;
024import com.google.common.annotations.GwtCompatible;
025import com.google.common.annotations.GwtIncompatible;
026
027import java.util.Iterator;
028import java.util.NoSuchElementException;
029import java.util.regex.Matcher;
030import java.util.regex.Pattern;
031
032/**
033 * An object that divides strings (or other instances of {@code CharSequence})
034 * into substrings, by recognizing a <i>separator</i> (a.k.a. "delimiter")
035 * which can be expressed as a single character, literal string, regular
036 * expression, {@code CharMatcher}, or by using a fixed substring length. This
037 * class provides the complementary functionality to {@link Joiner}.
038 *
039 * <p>Here is the most basic example of {@code Splitter} usage: <pre>   {@code
040 *
041 *   Splitter.on(',').split("foo,bar")}</pre>
042 *
043 * This invocation returns an {@code Iterable<String>} containing {@code "foo"}
044 * and {@code "bar"}, in that order.
045 *
046 * <p>By default {@code Splitter}'s behavior is very simplistic: <pre>   {@code
047 *
048 *   Splitter.on(',').split("foo,,bar, quux")}</pre>
049 *
050 * This returns an iterable containing {@code ["foo", "", "bar", " quux"]}.
051 * Notice that the splitter does not assume that you want empty strings removed,
052 * or that you wish to trim whitespace. If you want features like these, simply
053 * ask for them: <pre> {@code
054 *
055 *   private static final Splitter MY_SPLITTER = Splitter.on(',')
056 *       .trimResults()
057 *       .omitEmptyStrings();}</pre>
058 *
059 * Now {@code MY_SPLITTER.split("foo, ,bar, quux,")} returns an iterable
060 * containing just {@code ["foo", "bar", "quux"]}. Note that the order in which
061 * the configuration methods are called is never significant; for instance,
062 * trimming is always applied first before checking for an empty result,
063 * regardless of the order in which the {@link #trimResults()} and
064 * {@link #omitEmptyStrings()} methods were invoked.
065 *
066 * <p><b>Warning: splitter instances are always immutable</b>; a configuration
067 * method such as {@code omitEmptyStrings} has no effect on the instance it
068 * is invoked on! You must store and use the new splitter instance returned by
069 * the method. This makes splitters thread-safe, and safe to store as {@code
070 * static final} constants (as illustrated above). <pre>   {@code
071 *
072 *   // Bad! Do not do this!
073 *   Splitter splitter = Splitter.on('/');
074 *   splitter.trimResults(); // does nothing!
075 *   return splitter.split("wrong / wrong / wrong");}</pre>
076 *
077 * The separator recognized by the splitter does not have to be a single
078 * literal character as in the examples above. See the methods {@link
079 * #on(String)}, {@link #on(Pattern)} and {@link #on(CharMatcher)} for examples
080 * of other ways to specify separators.
081 *
082 * <p><b>Note:</b> this class does not mimic any of the quirky behaviors of
083 * similar JDK methods; for instance, it does not silently discard trailing
084 * separators, as does {@link String#split(String)}, nor does it have a default
085 * behavior of using five particular whitespace characters as separators, like
086 * {@link java.util.StringTokenizer}.
087 *
088 * @author Julien Silland
089 * @author Jesse Wilson
090 * @author Kevin Bourrillion
091 * @since 1
092 */
093@GwtCompatible(emulated = true)
094public final class Splitter {
095  private final CharMatcher trimmer;
096  private final boolean omitEmptyStrings;
097  private final Strategy strategy;
098  private final int limit;
099
100  private Splitter(Strategy strategy) {
101    this(strategy, false, CharMatcher.NONE, Integer.MAX_VALUE);
102  }
103
104  private Splitter(Strategy strategy, boolean omitEmptyStrings,
105      CharMatcher trimmer, int limit) {
106    this.strategy = strategy;
107    this.omitEmptyStrings = omitEmptyStrings;
108    this.trimmer = trimmer;
109    this.limit = limit;
110  }
111
112  /**
113   * Returns a splitter that uses the given single-character separator. For
114   * example, {@code Splitter.on(',').split("foo,,bar")} returns an iterable
115   * containing {@code ["foo", "", "bar"]}.
116   *
117   * @param separator the character to recognize as a separator
118   * @return a splitter, with default settings, that recognizes that separator
119   */
120  public static Splitter on(char separator) {
121    return on(CharMatcher.is(separator));
122  }
123
124  /**
125   * Returns a splitter that considers any single character matched by the
126   * given {@code CharMatcher} to be a separator. For example, {@code
127   * Splitter.on(CharMatcher.anyOf(";,")).split("foo,;bar,quux")} returns an
128   * iterable containing {@code ["foo", "", "bar", "quux"]}.
129   *
130   * @param separatorMatcher a {@link CharMatcher} that determines whether a
131   *     character is a separator
132   * @return a splitter, with default settings, that uses this matcher
133   */
134  public static Splitter on(final CharMatcher separatorMatcher) {
135    checkNotNull(separatorMatcher);
136
137    return new Splitter(new Strategy() {
138      @Override public SplittingIterator iterator(
139          Splitter splitter, final CharSequence toSplit) {
140        return new SplittingIterator(splitter, toSplit) {
141          @Override int separatorStart(int start) {
142            return separatorMatcher.indexIn(toSplit, start);
143          }
144
145          @Override int separatorEnd(int separatorPosition) {
146            return separatorPosition + 1;
147          }
148        };
149      }
150    });
151  }
152
153  /**
154   * Returns a splitter that uses the given fixed string as a separator. For
155   * example, {@code Splitter.on(", ").split("foo, bar, baz,qux")} returns an
156   * iterable containing {@code ["foo", "bar", "baz,qux"]}.
157   *
158   * @param separator the literal, nonempty string to recognize as a separator
159   * @return a splitter, with default settings, that recognizes that separator
160   */
161  public static Splitter on(final String separator) {
162    checkArgument(separator.length() != 0,
163        "The separator may not be the empty string.");
164
165    return new Splitter(new Strategy() {
166      @Override public SplittingIterator iterator(
167          Splitter splitter, CharSequence toSplit) {
168        return new SplittingIterator(splitter, toSplit) {
169          @Override public int separatorStart(int start) {
170            int delimeterLength = separator.length();
171
172            positions:
173            for (int p = start, last = toSplit.length() - delimeterLength;
174                p <= last; p++) {
175              for (int i = 0; i < delimeterLength; i++) {
176                if (toSplit.charAt(i + p) != separator.charAt(i)) {
177                  continue positions;
178                }
179              }
180              return p;
181            }
182            return -1;
183          }
184
185          @Override public int separatorEnd(int separatorPosition) {
186            return separatorPosition + separator.length();
187          }
188        };
189      }
190    });
191  }
192
193  /**
194   * Returns a splitter that considers any subsequence matching {@code
195   * pattern} to be a separator. For example, {@code
196   * Splitter.on(Pattern.compile("\r?\n")).split(entireFile)} splits a string
197   * into lines whether it uses DOS-style or UNIX-style line terminators.
198   *
199   * @param separatorPattern the pattern that determines whether a subsequence
200   *     is a separator. This pattern may not match the empty string.
201   * @return a splitter, with default settings, that uses this pattern
202   * @throws IllegalArgumentException if {@code separatorPattern} matches the
203   *     empty string
204   */
205  @GwtIncompatible("java.util.regex")
206  public static Splitter on(final Pattern separatorPattern) {
207    checkNotNull(separatorPattern);
208    checkArgument(!separatorPattern.matcher("").matches(),
209        "The pattern may not match the empty string: %s", separatorPattern);
210
211    return new Splitter(new Strategy() {
212      @Override public SplittingIterator iterator(
213          final Splitter splitter, CharSequence toSplit) {
214        final Matcher matcher = separatorPattern.matcher(toSplit);
215        return new SplittingIterator(splitter, toSplit) {
216          @Override public int separatorStart(int start) {
217            return matcher.find(start) ? matcher.start() : -1;
218          }
219
220          @Override public int separatorEnd(int separatorPosition) {
221            return matcher.end();
222          }
223        };
224      }
225    });
226  }
227
228  /**
229   * Returns a splitter that considers any subsequence matching a given
230   * pattern (regular expression) to be a separator. For example, {@code
231   * Splitter.onPattern("\r?\n").split(entireFile)} splits a string into lines
232   * whether it uses DOS-style or UNIX-style line terminators. This is
233   * equivalent to {@code Splitter.on(Pattern.compile(pattern))}.
234   *
235   * @param separatorPattern the pattern that determines whether a subsequence
236   *     is a separator. This pattern may not match the empty string.
237   * @return a splitter, with default settings, that uses this pattern
238   * @throws java.util.regex.PatternSyntaxException if {@code separatorPattern}
239   *     is a malformed expression
240   * @throws IllegalArgumentException if {@code separatorPattern} matches the
241   *     empty string
242   */
243  @GwtIncompatible("java.util.regex")
244  public static Splitter onPattern(String separatorPattern) {
245    return on(Pattern.compile(separatorPattern));
246  }
247
248  /**
249   * Returns a splitter that divides strings into pieces of the given length.
250   * For example, {@code Splitter.fixedLength(2).split("abcde")} returns an
251   * iterable containing {@code ["ab", "cd", "e"]}. The last piece can be
252   * smaller than {@code length} but will never be empty.
253   *
254   * @param length the desired length of pieces after splitting
255   * @return a splitter, with default settings, that can split into fixed sized
256   *     pieces
257   */
258  public static Splitter fixedLength(final int length) {
259    checkArgument(length > 0, "The length may not be less than 1");
260
261    return new Splitter(new Strategy() {
262      @Override public SplittingIterator iterator(
263          final Splitter splitter, CharSequence toSplit) {
264        return new SplittingIterator(splitter, toSplit) {
265          @Override public int separatorStart(int start) {
266            int nextChunkStart = start + length;
267            return (nextChunkStart < toSplit.length() ? nextChunkStart : -1);
268          }
269
270          @Override public int separatorEnd(int separatorPosition) {
271            return separatorPosition;
272          }
273        };
274      }
275    });
276  }
277
278  /**
279   * Returns a splitter that behaves equivalently to {@code this} splitter, but
280   * automatically omits empty strings from the results. For example, {@code
281   * Splitter.on(',').omitEmptyStrings().split(",a,,,b,c,,")} returns an
282   * iterable containing only {@code ["a", "b", "c"]}.
283   *
284   * <p>If either {@code trimResults} option is also specified when creating a
285   * splitter, that splitter always trims results first before checking for
286   * emptiness. So, for example, {@code
287   * Splitter.on(':').omitEmptyStrings().trimResults().split(": : : ")} returns
288   * an empty iterable.
289   *
290   * <p>Note that it is ordinarily not possible for {@link #split(CharSequence)}
291   * to return an empty iterable, but when using this option, it can (if the
292   * input sequence consists of nothing but separators).
293   *
294   * @return a splitter with the desired configuration
295   */
296  public Splitter omitEmptyStrings() {
297    return new Splitter(strategy, true, trimmer, limit);
298  }
299
300  /**
301   * Returns a splitter that behaves equivalently to {@code this} splitter but
302   * stops splitting after it reaches the limit.
303   * The limit defines the maximum number of items returned by the iterator.
304   *
305   * <p>For example,
306   * {@code Splitter.on(',').limit(3).split("a,b,c,d")} returns an iterable
307   * containing {@code ["a", "b", "c,d"]}.  When omitting empty strings, the
308   * omitted strings do no count.  Hence,
309   * {@code Splitter.on(',').limit(3).omitEmptyStrings().split("a,,,b,,,c,d")}
310   * returns an iterable containing {@code ["a", "b", "c,d"}.
311   * When trim is requested, all entries, including the last are trimmed.  Hence
312   * {@code Splitter.on(',').limit(3).trimResults().split(" a , b , c , d ")}
313   * results in @{code ["a", "b", "c , d"]}.
314   *
315   * @param limit the maximum number of items returns
316   * @return a splitter with the desired configuration
317   * @since 9
318   */
319  @Beta
320  public Splitter limit(int limit) {
321    checkArgument(limit > 0, "must be greater then zero: %s", limit);
322    return new Splitter(strategy, omitEmptyStrings, trimmer, limit);
323  }
324
325  /**
326   * Returns a splitter that behaves equivalently to {@code this} splitter, but
327   * automatically removes leading and trailing {@linkplain
328   * CharMatcher#WHITESPACE whitespace} from each returned substring; equivalent
329   * to {@code trimResults(CharMatcher.WHITESPACE)}. For example, {@code
330   * Splitter.on(',').trimResults().split(" a, b ,c ")} returns an iterable
331   * containing {@code ["a", "b", "c"]}.
332   *
333   * @return a splitter with the desired configuration
334   */
335  public Splitter trimResults() {
336    return trimResults(CharMatcher.WHITESPACE);
337  }
338
339  /**
340   * Returns a splitter that behaves equivalently to {@code this} splitter, but
341   * removes all leading or trailing characters matching the given {@code
342   * CharMatcher} from each returned substring. For example, {@code
343   * Splitter.on(',').trimResults(CharMatcher.is('_')).split("_a ,_b_ ,c__")}
344   * returns an iterable containing {@code ["a ", "b_ ", "c"]}.
345   *
346   * @param trimmer a {@link CharMatcher} that determines whether a character
347   *     should be removed from the beginning/end of a subsequence
348   * @return a splitter with the desired configuration
349   */
350  // TODO(kevinb): throw if a trimmer was already specified!
351  public Splitter trimResults(CharMatcher trimmer) {
352    checkNotNull(trimmer);
353    return new Splitter(strategy, omitEmptyStrings, trimmer, limit);
354  }
355
356  /**
357   * Splits {@code sequence} into string components and makes them available
358   * through an {@link Iterator}, which may be lazily evaluated.
359   *
360   * @param sequence the sequence of characters to split
361   * @return an iteration over the segments split from the parameter.
362   */
363  public Iterable<String> split(final CharSequence sequence) {
364    checkNotNull(sequence);
365
366    return new Iterable<String>() {
367      @Override public Iterator<String> iterator() {
368        return strategy.iterator(Splitter.this, sequence);
369      }
370    };
371  }
372
373  private interface Strategy {
374    Iterator<String> iterator(Splitter splitter, CharSequence toSplit);
375  }
376
377  private abstract static class SplittingIterator
378      extends AbstractIterator<String> {
379    final CharSequence toSplit;
380    final CharMatcher trimmer;
381    final boolean omitEmptyStrings;
382
383    /**
384     * Returns the first index in {@code toSplit} at or after {@code start}
385     * that contains the separator.
386     */
387    abstract int separatorStart(int start);
388
389    /**
390     * Returns the first index in {@code toSplit} after {@code
391     * separatorPosition} that does not contain a separator. This method is only
392     * invoked after a call to {@code separatorStart}.
393     */
394    abstract int separatorEnd(int separatorPosition);
395
396    int offset = 0;
397    int limit;
398
399    protected SplittingIterator(Splitter splitter, CharSequence toSplit) {
400      this.trimmer = splitter.trimmer;
401      this.omitEmptyStrings = splitter.omitEmptyStrings;
402      this.limit = splitter.limit;
403      this.toSplit = toSplit;
404    }
405
406    @Override protected String computeNext() {
407      while (offset != -1) {
408        int start = offset;
409        int end;
410
411        int separatorPosition = separatorStart(offset);
412        if (separatorPosition == -1) {
413          end = toSplit.length();
414          offset = -1;
415        } else {
416          end = separatorPosition;
417          offset = separatorEnd(separatorPosition);
418        }
419
420        while (start < end && trimmer.matches(toSplit.charAt(start))) {
421          start++;
422        }
423        while (end > start && trimmer.matches(toSplit.charAt(end - 1))) {
424          end--;
425        }
426
427        if (omitEmptyStrings && start == end) {
428          continue;
429        }
430
431        if (limit == 1) {
432          // The limit has been reached, return the rest of the string as the
433          // final item.  This is tested after empty string removal so that
434          // empty strings do not count towards the limit.
435          end = toSplit.length();
436          offset = -1;
437          // Since we may have changed the end, we need to trim it again.
438          while (end > start && trimmer.matches(toSplit.charAt(end - 1))) {
439            end--;
440          }
441        } else {
442          limit--;
443        }
444
445        return toSplit.subSequence(start, end).toString();
446      }
447      return endOfData();
448    }
449  }
450
451  /*
452   * Copied from common.collect.AbstractIterator. TODO(kevinb): un-fork if these
453   * packages are ever combined into a single library.
454   */
455  private abstract static class AbstractIterator<T> implements Iterator<T> {
456    State state = State.NOT_READY;
457
458    enum State {
459      READY, NOT_READY, DONE, FAILED,
460    }
461
462    T next;
463
464    protected abstract T computeNext();
465
466    protected final T endOfData() {
467      state = State.DONE;
468      return null;
469    }
470
471    @Override
472    public final boolean hasNext() {
473      checkState(state != State.FAILED);
474      switch (state) {
475        case DONE:
476          return false;
477        case READY:
478          return true;
479        default:
480      }
481      return tryToComputeNext();
482    }
483
484    boolean tryToComputeNext() {
485      state = State.FAILED; // temporary pessimism
486      next = computeNext();
487      if (state != State.DONE) {
488        state = State.READY;
489        return true;
490      }
491      return false;
492    }
493
494    @Override
495    public final T next() {
496      if (!hasNext()) {
497        throw new NoSuchElementException();
498      }
499      state = State.NOT_READY;
500      return next;
501    }
502
503    @Override public void remove() {
504      throw new UnsupportedOperationException();
505    }
506  }
507}