https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * 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.Pattern;


Extracts non-overlapping substrings from an input string, typically by recognizing appearances of
a separator sequence. This separator can be specified as a single 
character, fixed string, regular expression or CharMatcher instance. Or, instead of using a separator at all, a splitter can extract adjacent substrings of a given fixed length. 
For example, this expression:


Splitter.on(',').split("foo,bar,qux")

 ... produces an Iterable containing "foo", "bar" and "qux", in that order. 
By default, Splitter's behavior is simplistic and unassuming. The following expression: 

Splitter.on(',').split(" foo,,,  bar ,")

 ... yields the substrings [" foo", "", "", " bar ", ""]. If this is not the desired behavior, use configuration methods to obtain a new splitter instance with modified
behavior:


private static final Splitter MY_SPLITTER = Splitter.on(',')
    .trimResults()
    .omitEmptyStrings();



Now MY_SPLITTER.split("foo,,, bar ,") returns just ["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.


// 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 omitEmptyStrings, an input string containing n occurrences of the separator naturally yields an iterable of size 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 [""] (note: even fixed-length splitters). 
Splitter instances are thread-safe immutable, and are therefore safe to store as static
final constants. 
The 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 Splitter.

Author:Julien Silland, Jesse Wilson, Kevin Bourrillion, Louis Wasserman
Since:1.0
/**
 * 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, 
Splitter.on(',').split("foo,,bar") returns an iterable containing ["foo", "", "bar"]. 
Params:
  • separator – the character to recognize as a separator
Returns:a splitter, with default settings, that recognizes that separator
/**
   * 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 CharMatcher to be a separator. For example, 
Splitter.on(CharMatcher.anyOf(";,")).split("foo,;bar,quux") returns an iterable containing ["foo", "", "bar", "quux"]. 
Params:
  • separatorMatcher – a CharMatcher that determines whether a character is a separator
Returns:a splitter, with default settings, that uses this matcher
/**
   * 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, 
Splitter.on(", ").split("foo, bar,baz") returns an iterable containing ["foo",
"bar,baz"]. 
Params:
  • separator – the literal, nonempty string to recognize as a separator
Returns:a splitter, with default settings, that recognizes that separator
/**
   * 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 pattern to be a separator. For example, Splitter.on(Pattern.compile("\r?\n")).split(entireFile) splits a string into lines whether it uses DOS-style or UNIX-style line terminators. 
Params:
  • separatorPattern – the pattern that determines whether a subsequence is a separator. This
    pattern may not match the empty string.
Throws:
Returns:a splitter, with default settings, that uses this pattern
/**
   * 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(Pattern separatorPattern) {
    return on(new JdkPattern(separatorPattern));
  }

  private static Splitter on(final CommonPattern 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 CommonMatcher 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, 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 Splitter.on(Pattern.compile(pattern)). 
Params:
  • separatorPattern – the pattern that determines whether a subsequence is a separator. This
    pattern may not match the empty string.
Throws:
Returns:a splitter, with default settings, that uses this pattern
/**
   * 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 IllegalArgumentException if {@code separatorPattern} matches the empty string or is a
   *     malformed expression
   */
  @GwtIncompatible // java.util.regex
  public static Splitter onPattern(String separatorPattern) {
    return on(Platform.compilePattern(separatorPattern));
  }

  
Returns a splitter that divides strings into pieces of the given length. For example, 
Splitter.fixedLength(2).split("abcde") returns an iterable containing ["ab", "cd",
"e"]. The last piece can be smaller than length but will never be empty. 
Exception: for consistency with separator-based splitters, split("") does not yield an empty iterable, but an iterable containing "". This is the only case in which Iterables.size(split(input)) does not equal IntMath.divide(input.length(),
length, CEILING). To avoid this behavior, use omitEmptyStrings. 
Params:
  • length – the desired length of pieces after splitting, a positive integer
Throws:
Returns:a splitter, with default settings, that can split into fixed sized pieces
/**
   * 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
   */
  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 this splitter, but automatically omits empty strings from the results. For example, 
Splitter.on(',').omitEmptyStrings().split(",a,,,b,c,,") returns an iterable containing only ["a", "b", "c"]. 
If either trimResults option is also specified when creating a splitter, that splitter always trims results first before checking for emptiness. So, for example, 
Splitter.on(':').omitEmptyStrings().trimResults().split(": : : ") returns an empty iterable. 
Note that it is ordinarily not possible for split(CharSequence) to return an empty iterable, but when using this option, it can (if the input sequence consists of nothing but separators). 
Returns:a splitter with the desired configuration
/**
   * 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 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 splitToList. 
For example, Splitter.on(',').limit(3).split("a,b,c,d") returns an iterable containing ["a", "b", "c,d"]. When omitting empty strings, the omitted strings do not count. Hence, Splitter.on(',').limit(3).omitEmptyStrings().split("a,,,b,,,c,d") returns an iterable containing ["a", "b", "c,d". When trim is requested, all entries are trimmed, including the last. Hence Splitter.on(',').limit(3).trimResults().split(" a , b
, c , d ") results in ["a", "b", "c , d"]. 
Params:
  • limit – the maximum number of items returned
Returns:a splitter with the desired configuration
Since:9.0
/**
   * 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 not
   * 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 are
   * trimmed, including the last. 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 this splitter, but automatically removes leading and trailing whitespace from each returned substring; equivalent to trimResults(CharMatcher.whitespace()). For example, 
Splitter.on(',').trimResults().split(" a, b ,c ") returns an iterable containing ["a",
"b", "c"]. 
Returns:a splitter with the desired configuration
/**
   * 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 this splitter, but removes all leading or trailing characters matching the given CharMatcher from each returned substring. For example, Splitter.on(',').trimResults(CharMatcher.is('_')).split("_a ,_b_ ,c__") returns an iterable containing ["a ", "b_ ", "c"]. 
Params:
  • trimmer – a CharMatcher that determines whether a character should be removed from the beginning/end of a subsequence
Returns:a splitter with the desired configuration
/**
   * 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 sequence into string components and makes them available through an Iterator, which may be lazily evaluated. If you want an eagerly computed List, use splitToList(CharSequence). 
Params:
  • sequence – the sequence of characters to split
Returns:an iteration over the segments split from the parameter
/**
   * 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 sequence into string components and returns them as an immutable list. If you want an Iterable which may be lazily evaluated, use split(CharSequence). 
Params:
  • sequence – the sequence of characters to split
Returns:an immutable list of the segments split from the parameter
Since:15.0
/**
   * 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 MapSplitter which splits entries based on this splitter, and splits entries into keys and values using the specified separator. 
Since:10.0
/**
   * 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 MapSplitter which splits entries based on this splitter, and splits entries into keys and values using the specified separator. 
Since:14.0
/**
   * 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 MapSplitter which splits entries based on this splitter, and splits entries into keys and values using the specified key-value splitter. 
Since:10.0
/**
   * 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 Splitter splits iterables and lists. Like Splitter, it is thread-safe and immutable. The common way to build instances is by providing an additional key-value separator to Splitter. 
Since:10.0
/**
   * An object that splits strings into maps as {@code Splitter} splits iterables and lists. Like
   * {@code Splitter}, it is thread-safe and immutable. The common way to build instances is by
   * providing an additional {@linkplain Splitter#withKeyValueSeparator key-value separator} to
   * {@link Splitter}.
   *
   * @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 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 "a" to "b" and "c" to "b". 
The returned map preserves the order of the entries from sequence. 
Throws:
  • IllegalArgumentException – if the specified sequence does not split into valid map
    entries, or if there are duplicate keys
/**
     * 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 toSplit at or after start that contains the separator. 
/**
     * 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 toSplit after separatorPosition that does not contain a separator. This method is only invoked after a call to separatorStart. 
/**
     * 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();
    }
  }
}