Google Guava之Splitter

前言

我们上篇文章讲述了Joiner相关API使用，其中提到了Splitter，它与Joiner操作相反，它是根据给定的分隔符，把一个字符串分隔成若个子字符串，那么本篇我们来看看Splitter都有哪些操作的方式。

Splitter

它与Joiner操作相反，它是根据给定的分隔符，把一个字符串分隔成若个子字符串，我们可以在com.google.common.base下找到它，如下：

package com.google.common.base;

import ....;
/**
 * 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;
  }
  //..
}

on

• Splitter指定分隔符的方法，如果你的字符串为"1，2，3"，那么你的是分隔符就是","

    public static void main(String[] args) throws Exception {

        List<String> ints = Splitter.on("|").splitToList("1|2|3");

        // [1, 2, 3]
        System.out.println(ints);
    }

split

• Splitter的切割的方法，可以通过on指定分隔符，由split指定切割的字符串。

    public static void main(String[] args) throws Exception {

        // [1, 2, 3]
        System.out.println(Splitter.on("|").split("1|2|3"));

        // 1
        // 2
        // 3
        Splitter.on("|").split("1|2|3").forEach(System.out::println);
    }

splitToList

• Splitter的切割为list的方法，可以通过on指定分隔符，由split指定切割的字符串。

   public static void main(String[] args) throws Exception {

        List<String> ints = Splitter.on("|").splitToList("1|2|3");

        // [1, 2, 3]
        System.out.println(ints);
    }

trimResults

• Splitter的处理结果的前后空白的方法。

    public static void main(String[] args) throws Exception {

        // [1, 2, 3]
        System.out.println(Splitter.on("|").trimResults().split("1 |2 | 3"));
    }

omitEmptyStrings

• Splitter的去掉空串的方法。

    public static void main(String[] args) throws Exception {

        // [1, 2, 3]
        System.out.println(Splitter.on("|").trimResults().omitEmptyStrings().split("1 |2 ||3"));
        // [1 , 2 , 3]
        System.out.println(Splitter.on("|").omitEmptyStrings().split("1 |2 ||3"));
    }

withKeyValueSeparator

• 它主要是针对的Map的KV，返回一个MapSplitter ，基于MapSplitter以分隔符分隔，此方法用来解析url参数在合适不过了。

    public static void main(String[] args) throws Exception {

        Map<String, String> splitMap = Splitter.on("|").withKeyValueSeparator("=").split("name=小明|age=22");

        // {name=小明, age=22}
        System.out.println(splitMap);
    }

Example

    // 分隔转换
    public static void main(String[] args) throws Exception {

        String userIds = "10001,10002,a56,b123421";

        List<Long> ids = Splitter.on(',').splitToList(userIds)
                .stream()
                .filter(StringUtils::isNumeric) // import org.apache.commons.lang3.StringUtils;
                .map(Long::parseLong)
                .collect(Collectors.toList());
        // [10001, 10002]
        System.out.println(ids);
    }