com.google.common.base.Splitter Maven / Gradle / Ivy
/*
* Copyright (C) 2009 Google Inc.
*
* 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 com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* An object that divides strings (or other instances of {@code CharSequence})
* into substrings, by recognizing a separator (a.k.a. "delimiter")
* which can be expressed as a single character, literal string, regular
* expression, {@code CharMatcher}, or by using a fixed substring length. This
* class provides the complementary functionality to {@link Joiner}.
*
* Here is the most basic example of {@code Splitter} usage:
{@code
*
* Splitter.on(',').split("foo,bar")}
*
* This invocation returns an {@code Iterable} containing {@code "foo"}
* and {@code "bar"}, in that order.
*
* By default {@code Splitter}'s behavior is very simplistic:
{@code
*
* Splitter.on(',').split("foo,,bar, quux")}
*
* This returns an iterable containing {@code ["foo", "", "bar", " quux"]}.
* Notice that the splitter does not assume that you want empty strings removed,
* or that you wish to trim whitespace. If you want features like these, simply
* ask for them: {@code
*
* private static final Splitter MY_SPLITTER = Splitter.on(',')
* .trimResults()
* .omitEmptyStrings();}
*
* Now {@code MY_SPLITTER.split("foo, ,bar, quux,")} returns an iterable
* containing just {@code ["foo", "bar", "quux"]}. Note that the order in which
* the configuration methods are called is never significant; for instance,
* trimming is always applied first before checking for an empty result,
* regardless of the order in which the {@link #trimResults()} and
* {@link #omitEmptyStrings()} methods were invoked.
*
* Warning: splitter instances are always immutable; a configuration
* method such as {@code omitEmptyStrings} has no effect on the instance it
* is invoked on! You must store and use the new splitter instance returned by
* the method. This makes splitters thread-safe, and safe to store as {@code
* static final} constants (as illustrated above).
{@code
*
* // Bad! Do not do this!
* Splitter splitter = Splitter.on('/');
* splitter.trimResults(); // does nothing!
* return splitter.split("wrong / wrong / wrong");}
*
* The separator recognized by the splitter does not have to be a single
* literal character as in the examples above. See the methods {@link
* #on(String)}, {@link #on(Pattern)} and {@link #on(CharMatcher)} for examples
* of other ways to specify separators.
*
* Note: this class does not mimic any of the quirky behaviors of
* similar JDK methods; for instance, it does not silently discard trailing
* separators, as does {@link String#split(String)}, nor does it have a default
* behavior of using five particular whitespace characters as separators, like
* {@link java.util.StringTokenizer}.
*
* @author Julien Silland
* @author Jesse Wilson
* @author Kevin Bourrillion
* @since 1
*/
@GwtCompatible
public final class Splitter {
private final CharMatcher trimmer;
private final boolean omitEmptyStrings;
private final Strategy strategy;
private Splitter(Strategy strategy) {
this(strategy, false, CharMatcher.NONE);
}
private Splitter(Strategy strategy, boolean omitEmptyStrings,
CharMatcher trimmer) {
this.strategy = strategy;
this.omitEmptyStrings = omitEmptyStrings;
this.trimmer = trimmer;
}
/**
* 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,qux")} returns an
* iterable containing {@code ["foo", "bar", "baz,qux"]}.
*
* @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 delimeterLength = separator.length();
positions:
for (int p = start, last = toSplit.length() - delimeterLength;
p <= last; p++) {
for (int i = 0; i < delimeterLength; 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.
*
* @param length the desired length of pieces after splitting
* @return a splitter, with default settings, that can split into fixed sized
* pieces
*/
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
*/
public Splitter omitEmptyStrings() {
return new Splitter(strategy, true, trimmer);
}
/**
* 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: throw if a trimmer was already specified!
public Splitter trimResults(CharMatcher trimmer) {
checkNotNull(trimmer);
return new Splitter(strategy, omitEmptyStrings, trimmer);
}
/**
* Splits the {@link CharSequence} passed in parameter.
*
* @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 strategy.iterator(Splitter.this, sequence);
}
};
}
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;
protected SplittingIterator(Splitter splitter, CharSequence toSplit) {
this.trimmer = splitter.trimmer;
this.omitEmptyStrings = splitter.omitEmptyStrings;
this.toSplit = toSplit;
}
@Override protected String computeNext() {
while (offset != -1) {
int start = offset;
int end;
int separatorPosition = separatorStart(offset);
if (separatorPosition == -1) {
end = toSplit.length();
offset = -1;
} else {
end = separatorPosition;
offset = separatorEnd(separatorPosition);
}
while (start < end && trimmer.matches(toSplit.charAt(start))) {
start++;
}
while (end > start && trimmer.matches(toSplit.charAt(end - 1))) {
end--;
}
if (omitEmptyStrings && start == end) {
continue;
}
return toSplit.subSequence(start, end).toString();
}
return endOfData();
}
}
/*
* Copied from common.collect.AbstractIterator. TODO: un-fork once these
* packages have been combined into a single library.
*/
private static abstract class AbstractIterator implements Iterator {
State state = State.NOT_READY;
enum State {
READY, NOT_READY, DONE, FAILED,
}
T next;
protected abstract T computeNext();
protected final T endOfData() {
state = State.DONE;
return null;
}
public final boolean hasNext() {
checkState(state != State.FAILED);
switch (state) {
case DONE:
return false;
case READY:
return true;
default:
}
return tryToComputeNext();
}
boolean tryToComputeNext() {
state = State.FAILED; // temporary pessimism
next = computeNext();
if (state != State.DONE) {
state = State.READY;
return true;
}
return false;
}
public final T next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
state = State.NOT_READY;
return next;
}
/*@Override*/ public void remove() {
throw new UnsupportedOperationException();
}
}
}