com.google.common.base.Splitter Maven / Gradle / Ivy
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/*
* 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 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}.
*
* For example, this expression:
{@code
*
* Splitter.on(',').split("foo,bar,qux")}
*
* ... produces an {@code Iterable} containing {@code "foo"}, {@code "bar"} and
* {@code "qux"}, in that order.
*
* By default, {@code Splitter}'s behavior is simplistic and unassuming. The
* following expression:
{@code
*
* Splitter.on(',').split(" foo,,, bar ,")}
*
* ... yields the substrings {@code [" foo", "", "", " bar ", ""]}. If this
* is not the desired behavior, use configuration methods to obtain a new
* splitter instance with modified behavior: {@code
*
* private static final Splitter MY_SPLITTER = Splitter.on(',')
* .trimResults()
* .omitEmptyStrings();}
*
* 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.
*
*
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.
{@code
*
* // Do NOT do this
* Splitter splitter = Splitter.on('/');
* splitter.trimResults(); // does nothing!
* return splitter.split("wrong / wrong / wrong");}
*
* 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).
*
*
Splitter instances are thread-safe immutable, and are therefore safe to
* store as {@code static final} constants.
*
*
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.
*
*
See the Guava User Guide article on
* {@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.");
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.
*
*
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"]}.
*
*
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.
*
*
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.
*
*
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 returns
* @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.
*/
public Iterable split(final CharSequence sequence) {
checkNotNull(sequence);
return new Iterable() {
@Override public Iterator iterator() {
return splittingIterator(sequence);
}
@Override public String toString() {
return Joiner.on(", ")
.appendTo(new StringBuilder().append('['), this)
.append(']')
.toString();
}
};
}
private Iterator 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 splitToList(CharSequence sequence) {
checkNotNull(sequence);
Iterator iterator = splittingIterator(sequence);
List 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
*/
@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,
* 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}.
*
* 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 split(CharSequence sequence) {
Map map = new LinkedHashMap();
for (String entry : outerSplitter.split(sequence)) {
Iterator 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 iterator(Splitter splitter, CharSequence toSplit);
}
private abstract static class SplittingIterator extends AbstractIterator {
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();
}
}
}