Java tutorial
/* * Copyright (C) 2009 The Guava Authors * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.google.common.base; import static com.google.common.base.Preconditions.checkArgument; import static com.google.common.base.Preconditions.checkNotNull; import com.google.common.annotations.Beta; import com.google.common.annotations.GwtCompatible; import com.google.common.annotations.GwtIncompatible; import java.util.ArrayList; import java.util.Collections; import java.util.Iterator; import java.util.LinkedHashMap; import java.util.List; import java.util.Map; import java.util.regex.Matcher; import java.util.regex.Pattern; import javax.annotation.CheckReturnValue; /** * Extracts non-overlapping substrings from an input string, typically by * recognizing appearances of a <i>separator</i> sequence. This separator can be * specified as a single {@linkplain #on(char) character}, fixed {@linkplain * #on(String) string}, {@linkplain #onPattern regular expression} or {@link * #on(CharMatcher) CharMatcher} instance. Or, instead of using a separator at * all, a splitter can extract adjacent substrings of a given {@linkplain * #fixedLength fixed length}. * * <p>For example, this expression: <pre> {@code * * Splitter.on(',').split("foo,bar,qux")}</pre> * * ... produces an {@code Iterable} containing {@code "foo"}, {@code "bar"} and * {@code "qux"}, in that order. * * <p>By default, {@code Splitter}'s behavior is simplistic and unassuming. The * following expression: <pre> {@code * * Splitter.on(',').split(" foo,,, bar ,")}</pre> * * ... yields the substrings {@code [" foo", "", "", " bar ", ""]}. If this * is not the desired behavior, use configuration methods to obtain a <i>new</i> * splitter instance with modified behavior: <pre> {@code * * private static final Splitter MY_SPLITTER = Splitter.on(',') * .trimResults() * .omitEmptyStrings();}</pre> * * <p>Now {@code MY_SPLITTER.split("foo,,, bar ,")} returns just {@code ["foo", * "bar"]}. Note that the order in which these configuration methods are called * is never significant. * * <p><b>Warning:</b> Splitter instances are immutable. Invoking a configuration * method has no effect on the receiving instance; you must store and use the * new splitter instance it returns instead. <pre> {@code * * // Do NOT do this * Splitter splitter = Splitter.on('/'); * splitter.trimResults(); // does nothing! * return splitter.split("wrong / wrong / wrong");}</pre> * * <p>For separator-based splitters that do not use {@code omitEmptyStrings}, an * input string containing {@code n} occurrences of the separator naturally * yields an iterable of size {@code n + 1}. So if the separator does not occur * anywhere in the input, a single substring is returned containing the entire * input. Consequently, all splitters split the empty string to {@code [""]} * (note: even fixed-length splitters). * * <p>Splitter instances are thread-safe immutable, and are therefore safe to * store as {@code static final} constants. * * <p>The {@link Joiner} class provides the inverse operation to splitting, but * note that a round-trip between the two should be assumed to be lossy. * * <p>See the Guava User Guide article on <a href= * "https://github.com/google/guava/wiki/StringsExplained#splitter"> * {@code Splitter}</a>. * * @author Julien Silland * @author Jesse Wilson * @author Kevin Bourrillion * @author Louis Wasserman * @since 1.0 */ @GwtCompatible(emulated = true) public final class Splitter { private final CharMatcher trimmer; private final boolean omitEmptyStrings; private final Strategy strategy; private final int limit; private Splitter(Strategy strategy) { this(strategy, false, CharMatcher.NONE, Integer.MAX_VALUE); } private Splitter(Strategy strategy, boolean omitEmptyStrings, CharMatcher trimmer, int limit) { this.strategy = strategy; this.omitEmptyStrings = omitEmptyStrings; this.trimmer = trimmer; this.limit = limit; } /** * Returns a splitter that uses the given single-character separator. For * example, {@code Splitter.on(',').split("foo,,bar")} returns an iterable * containing {@code ["foo", "", "bar"]}. * * @param separator the character to recognize as a separator * @return a splitter, with default settings, that recognizes that separator */ @CheckReturnValue public static Splitter on(char separator) { return on(CharMatcher.is(separator)); } /** * Returns a splitter that considers any single character matched by the * given {@code CharMatcher} to be a separator. For example, {@code * Splitter.on(CharMatcher.anyOf(";,")).split("foo,;bar,quux")} returns an * iterable containing {@code ["foo", "", "bar", "quux"]}. * * @param separatorMatcher a {@link CharMatcher} that determines whether a * character is a separator * @return a splitter, with default settings, that uses this matcher */ @CheckReturnValue public static Splitter on(final CharMatcher separatorMatcher) { checkNotNull(separatorMatcher); return new Splitter(new Strategy() { @Override public SplittingIterator iterator(Splitter splitter, final CharSequence toSplit) { return new SplittingIterator(splitter, toSplit) { @Override int separatorStart(int start) { return separatorMatcher.indexIn(toSplit, start); } @Override int separatorEnd(int separatorPosition) { return separatorPosition + 1; } }; } }); } /** * Returns a splitter that uses the given fixed string as a separator. For * example, {@code Splitter.on(", ").split("foo, bar,baz")} returns an * iterable containing {@code ["foo", "bar,baz"]}. * * @param separator the literal, nonempty string to recognize as a separator * @return a splitter, with default settings, that recognizes that separator */ @CheckReturnValue public static Splitter on(final String separator) { checkArgument(separator.length() != 0, "The separator may not be the empty string."); if (separator.length() == 1) { return Splitter.on(separator.charAt(0)); } return new Splitter(new Strategy() { @Override public SplittingIterator iterator(Splitter splitter, CharSequence toSplit) { return new SplittingIterator(splitter, toSplit) { @Override public int separatorStart(int start) { int separatorLength = separator.length(); positions: for (int p = start, last = toSplit.length() - separatorLength; p <= last; p++) { for (int i = 0; i < separatorLength; i++) { if (toSplit.charAt(i + p) != separator.charAt(i)) { continue positions; } } return p; } return -1; } @Override public int separatorEnd(int separatorPosition) { return separatorPosition + separator.length(); } }; } }); } /** * Returns a splitter that considers any subsequence matching {@code * pattern} to be a separator. For example, {@code * Splitter.on(Pattern.compile("\r?\n")).split(entireFile)} splits a string * into lines whether it uses DOS-style or UNIX-style line terminators. * * @param separatorPattern the pattern that determines whether a subsequence * is a separator. This pattern may not match the empty string. * @return a splitter, with default settings, that uses this pattern * @throws IllegalArgumentException if {@code separatorPattern} matches the * empty string */ @CheckReturnValue @GwtIncompatible("java.util.regex") public static Splitter on(final Pattern separatorPattern) { checkNotNull(separatorPattern); checkArgument(!separatorPattern.matcher("").matches(), "The pattern may not match the empty string: %s", separatorPattern); return new Splitter(new Strategy() { @Override public SplittingIterator iterator(final Splitter splitter, CharSequence toSplit) { final Matcher matcher = separatorPattern.matcher(toSplit); return new SplittingIterator(splitter, toSplit) { @Override public int separatorStart(int start) { return matcher.find(start) ? matcher.start() : -1; } @Override public int separatorEnd(int separatorPosition) { return matcher.end(); } }; } }); } /** * Returns a splitter that considers any subsequence matching a given * pattern (regular expression) to be a separator. For example, {@code * Splitter.onPattern("\r?\n").split(entireFile)} splits a string into lines * whether it uses DOS-style or UNIX-style line terminators. This is * equivalent to {@code Splitter.on(Pattern.compile(pattern))}. * * @param separatorPattern the pattern that determines whether a subsequence * is a separator. This pattern may not match the empty string. * @return a splitter, with default settings, that uses this pattern * @throws java.util.regex.PatternSyntaxException if {@code separatorPattern} * is a malformed expression * @throws IllegalArgumentException if {@code separatorPattern} matches the * empty string */ @CheckReturnValue @GwtIncompatible("java.util.regex") public static Splitter onPattern(String separatorPattern) { return on(Pattern.compile(separatorPattern)); } /** * Returns a splitter that divides strings into pieces of the given length. * For example, {@code Splitter.fixedLength(2).split("abcde")} returns an * iterable containing {@code ["ab", "cd", "e"]}. The last piece can be * smaller than {@code length} but will never be empty. * * <p><b>Exception:</b> for consistency with separator-based splitters, {@code * split("")} does not yield an empty iterable, but an iterable containing * {@code ""}. This is the only case in which {@code * Iterables.size(split(input))} does not equal {@code * IntMath.divide(input.length(), length, CEILING)}. To avoid this behavior, * use {@code omitEmptyStrings}. * * @param length the desired length of pieces after splitting, a positive * integer * @return a splitter, with default settings, that can split into fixed sized * pieces * @throws IllegalArgumentException if {@code length} is zero or negative */ @CheckReturnValue public static Splitter fixedLength(final int length) { checkArgument(length > 0, "The length may not be less than 1"); return new Splitter(new Strategy() { @Override public SplittingIterator iterator(final Splitter splitter, CharSequence toSplit) { return new SplittingIterator(splitter, toSplit) { @Override public int separatorStart(int start) { int nextChunkStart = start + length; return (nextChunkStart < toSplit.length() ? nextChunkStart : -1); } @Override public int separatorEnd(int separatorPosition) { return separatorPosition; } }; } }); } /** * Returns a splitter that behaves equivalently to {@code this} splitter, but * automatically omits empty strings from the results. For example, {@code * Splitter.on(',').omitEmptyStrings().split(",a,,,b,c,,")} returns an * iterable containing only {@code ["a", "b", "c"]}. * * <p>If either {@code trimResults} option is also specified when creating a * splitter, that splitter always trims results first before checking for * emptiness. So, for example, {@code * Splitter.on(':').omitEmptyStrings().trimResults().split(": : : ")} returns * an empty iterable. * * <p>Note that it is ordinarily not possible for {@link #split(CharSequence)} * to return an empty iterable, but when using this option, it can (if the * input sequence consists of nothing but separators). * * @return a splitter with the desired configuration */ @CheckReturnValue public Splitter omitEmptyStrings() { return new Splitter(strategy, true, trimmer, limit); } /** * Returns a splitter that behaves equivalently to {@code this} splitter but * stops splitting after it reaches the limit. * The limit defines the maximum number of items returned by the iterator, or * the maximum size of the list returned by {@link #splitToList}. * * <p>For example, * {@code Splitter.on(',').limit(3).split("a,b,c,d")} returns an iterable * containing {@code ["a", "b", "c,d"]}. When omitting empty strings, the * omitted strings do no count. Hence, * {@code Splitter.on(',').limit(3).omitEmptyStrings().split("a,,,b,,,c,d")} * returns an iterable containing {@code ["a", "b", "c,d"}. * When trim is requested, all entries, including the last are trimmed. Hence * {@code Splitter.on(',').limit(3).trimResults().split(" a , b , c , d ")} * results in {@code ["a", "b", "c , d"]}. * * @param limit the maximum number of items returned * @return a splitter with the desired configuration * @since 9.0 */ @CheckReturnValue public Splitter limit(int limit) { checkArgument(limit > 0, "must be greater than zero: %s", limit); return new Splitter(strategy, omitEmptyStrings, trimmer, limit); } /** * Returns a splitter that behaves equivalently to {@code this} splitter, but * automatically removes leading and trailing {@linkplain * CharMatcher#WHITESPACE whitespace} from each returned substring; equivalent * to {@code trimResults(CharMatcher.WHITESPACE)}. For example, {@code * Splitter.on(',').trimResults().split(" a, b ,c ")} returns an iterable * containing {@code ["a", "b", "c"]}. * * @return a splitter with the desired configuration */ @CheckReturnValue public Splitter trimResults() { return trimResults(CharMatcher.WHITESPACE); } /** * Returns a splitter that behaves equivalently to {@code this} splitter, but * removes all leading or trailing characters matching the given {@code * CharMatcher} from each returned substring. For example, {@code * Splitter.on(',').trimResults(CharMatcher.is('_')).split("_a ,_b_ ,c__")} * returns an iterable containing {@code ["a ", "b_ ", "c"]}. * * @param trimmer a {@link CharMatcher} that determines whether a character * should be removed from the beginning/end of a subsequence * @return a splitter with the desired configuration */ // TODO(kevinb): throw if a trimmer was already specified! @CheckReturnValue public Splitter trimResults(CharMatcher trimmer) { checkNotNull(trimmer); return new Splitter(strategy, omitEmptyStrings, trimmer, limit); } /** * Splits {@code sequence} into string components and makes them available * through an {@link Iterator}, which may be lazily evaluated. If you want * an eagerly computed {@link List}, use {@link #splitToList(CharSequence)}. * * @param sequence the sequence of characters to split * @return an iteration over the segments split from the parameter. */ @CheckReturnValue public Iterable<String> split(final CharSequence sequence) { checkNotNull(sequence); return new Iterable<String>() { @Override public Iterator<String> iterator() { return splittingIterator(sequence); } @Override public String toString() { return Joiner.on(", ").appendTo(new StringBuilder().append('['), this).append(']').toString(); } }; } private Iterator<String> splittingIterator(CharSequence sequence) { return strategy.iterator(this, sequence); } /** * Splits {@code sequence} into string components and returns them as * an immutable list. If you want an {@link Iterable} which may be lazily * evaluated, use {@link #split(CharSequence)}. * * @param sequence the sequence of characters to split * @return an immutable list of the segments split from the parameter * @since 15.0 */ @CheckReturnValue @Beta public List<String> splitToList(CharSequence sequence) { checkNotNull(sequence); Iterator<String> iterator = splittingIterator(sequence); List<String> result = new ArrayList<String>(); while (iterator.hasNext()) { result.add(iterator.next()); } return Collections.unmodifiableList(result); } /** * Returns a {@code MapSplitter} which splits entries based on this splitter, * and splits entries into keys and values using the specified separator. * * @since 10.0 */ @CheckReturnValue @Beta public MapSplitter withKeyValueSeparator(String separator) { return withKeyValueSeparator(on(separator)); } /** * Returns a {@code MapSplitter} which splits entries based on this splitter, * and splits entries into keys and values using the specified separator. * * @since 14.0 */ @CheckReturnValue @Beta public MapSplitter withKeyValueSeparator(char separator) { return withKeyValueSeparator(on(separator)); } /** * Returns a {@code MapSplitter} which splits entries based on this splitter, * and splits entries into keys and values using the specified key-value * splitter. * * @since 10.0 */ @CheckReturnValue @Beta public MapSplitter withKeyValueSeparator(Splitter keyValueSplitter) { return new MapSplitter(this, keyValueSplitter); } /** * An object that splits strings into maps as {@code Splitter} splits * iterables and lists. Like {@code Splitter}, it is thread-safe and * immutable. * * @since 10.0 */ @Beta public static final class MapSplitter { private static final String INVALID_ENTRY_MESSAGE = "Chunk [%s] is not a valid entry"; private final Splitter outerSplitter; private final Splitter entrySplitter; private MapSplitter(Splitter outerSplitter, Splitter entrySplitter) { this.outerSplitter = outerSplitter; // only "this" is passed this.entrySplitter = checkNotNull(entrySplitter); } /** * Splits {@code sequence} into substrings, splits each substring into * an entry, and returns an unmodifiable map with each of the entries. For * example, <code> * Splitter.on(';').trimResults().withKeyValueSeparator("=>") * .split("a=>b ; c=>b") * </code> will return a mapping from {@code "a"} to {@code "b"} and * {@code "c"} to {@code b}. * * <p>The returned map preserves the order of the entries from * {@code sequence}. * * @throws IllegalArgumentException if the specified sequence does not split * into valid map entries, or if there are duplicate keys */ @CheckReturnValue public Map<String, String> split(CharSequence sequence) { Map<String, String> map = new LinkedHashMap<String, String>(); for (String entry : outerSplitter.split(sequence)) { Iterator<String> entryFields = entrySplitter.splittingIterator(entry); checkArgument(entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry); String key = entryFields.next(); checkArgument(!map.containsKey(key), "Duplicate key [%s] found.", key); checkArgument(entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry); String value = entryFields.next(); map.put(key, value); checkArgument(!entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry); } return Collections.unmodifiableMap(map); } } private interface Strategy { Iterator<String> iterator(Splitter splitter, CharSequence toSplit); } private abstract static class SplittingIterator extends AbstractIterator<String> { final CharSequence toSplit; final CharMatcher trimmer; final boolean omitEmptyStrings; /** * Returns the first index in {@code toSplit} at or after {@code start} * that contains the separator. */ abstract int separatorStart(int start); /** * Returns the first index in {@code toSplit} after {@code * separatorPosition} that does not contain a separator. This method is only * invoked after a call to {@code separatorStart}. */ abstract int separatorEnd(int separatorPosition); int offset = 0; int limit; protected SplittingIterator(Splitter splitter, CharSequence toSplit) { this.trimmer = splitter.trimmer; this.omitEmptyStrings = splitter.omitEmptyStrings; this.limit = splitter.limit; this.toSplit = toSplit; } @Override protected String computeNext() { /* * The returned string will be from the end of the last match to the * beginning of the next one. nextStart is the start position of the * returned substring, while offset is the place to start looking for a * separator. */ int nextStart = offset; while (offset != -1) { int start = nextStart; int end; int separatorPosition = separatorStart(offset); if (separatorPosition == -1) { end = toSplit.length(); offset = -1; } else { end = separatorPosition; offset = separatorEnd(separatorPosition); } if (offset == nextStart) { /* * This occurs when some pattern has an empty match, even if it * doesn't match the empty string -- for example, if it requires * lookahead or the like. The offset must be increased to look for * separators beyond this point, without changing the start position * of the next returned substring -- so nextStart stays the same. */ offset++; if (offset >= toSplit.length()) { offset = -1; } continue; } while (start < end && trimmer.matches(toSplit.charAt(start))) { start++; } while (end > start && trimmer.matches(toSplit.charAt(end - 1))) { end--; } if (omitEmptyStrings && start == end) { // Don't include the (unused) separator in next split string. nextStart = offset; continue; } if (limit == 1) { // The limit has been reached, return the rest of the string as the // final item. This is tested after empty string removal so that // empty strings do not count towards the limit. end = toSplit.length(); offset = -1; // Since we may have changed the end, we need to trim it again. while (end > start && trimmer.matches(toSplit.charAt(end - 1))) { end--; } } else { limit--; } return toSplit.subSequence(start, end).toString(); } return endOfData(); } } }