The Splitter.java Java example source code
/*
* 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;
/**
* Extracts non-overlapping substrings from an input string, typically by recognizing appearances of
* a <i>separator 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: {@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 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>Warning: 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}.
*
* @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
*/
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
*/
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
*/
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
*/
@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
*/
@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>Exception: 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
*/
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
*/
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
*/
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
*/
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!
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.
*/
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
*/
@Beta
public List<String> splitToList(CharSequence sequence) {
checkNotNull(sequence);
Iterator<String> iterator = splittingIterator(sequence);
List<String> result = new ArrayList();
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
*/
@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
*/
@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
*/
@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")} 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
*/
public Map<String, String> split(CharSequence sequence) {
Map<String, String> map = new LinkedHashMap();
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();
}
}
}
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