概要

Google Guava提供了如下几大类工具方法类。来简化对应代码逻辑。

Joiner
Splitter
CharMatcher
Charsets
CaseFormat
Strings

此系列笔记将从实际开发使用的角度，来看看Guava String工具类的优点。
本文继续简介一下Guava Splitter。

Splitter

相关Core Java提供的String.split方式。Guava相对功能要靠谱许多。
Core Java中String.split方式有比较坑的地方。

请看如下示例，想一想结果应该是什么。
",a ,,b,".split(",")

A. "", "a ", "", "b", ""
B. null, "a ", null, "b", null
C. "a ", null, "b"
D. "a ", "b"

正确答案为"", "a ", "", "b"。

@Test
void testCoreJavaSplit() {
    String sampleDate = ",a ,,b,";
    String[] actual = sampleData.split(",");
    String[] expected = new String[]{"", "a ", "", "b"};
    // assertJ
    assertThat(actual).usingRecursiveComparison().isEqualTo(expected);
}

说实话，我在看Guava文档之前，认为A是对的。可以看出String.split方法会跳过结尾空字符串。
同时String.split()方法返回的是String[]，不实用。

由此在实际开发过程中，我还是比较推荐使用Guava的Splitter

如果使用Splitter来处理上面CoreJava split对应示例，则会得到答案A

@Test
void testGuavaSplitter() {
    String sampleDate = ",a ,,b,";
    List<String> actual = Splitter.on(",").splitToList(sampleDate);
    List<String> expected = Arrays.asList("", "a ", "", "b", "");
    assertThat(actual).usingRecursiveComparison().isEqualTo(expected);
}

split方法

Guava Splitter提供了三个split方法，对不同返回类型。

split(): Iterable<String>
splitToList(): List<String>
splitToStream(): Stream<String>

Iterable<String>在开发中使用做后续处理没有那么方便
List<String>则相对容易处理，我比较推荐。后续示例也都用splitToList()
Stream<String>对应Lambda解决方案，是比较方便，但是由于splitToStream方法被标记为@Beta，所以现在来说，还是谨慎使用。

处理工具方法

跳过空字符串

@Test
void testGuavaSplitter() {
    String sampleDate = ",a ,,b,";
    List<String> actual = Splitter.on(",")
            .omitEmptyStrings()
            .splitToList(sampleDate);
    List<String> expected = Arrays.asList("a ", "b");
    assertThat(actual).usingRecursiveComparison().isEqualTo(expected);
}

Trim返回结果

Trim空格

@Test
void testGuavaSplitter() {
    String sampleDate = ",a ,,b,";
    List<String> actual = Splitter.on(",")
            .omitEmptyStrings()
            .trimResults()
            .splitToList(sampleDate);
    List<String> expected = Arrays.asList("a", "b");
    assertThat(actual).usingRecursiveComparison().isEqualTo(expected);
}

使用CharMatcher去除其它字符

@Test
void testSplitterTrimResult() {
    String data = "alpha!|beta:|gamma;|omega_1|_sigma_";
    List<String> actual = Splitter
            .on("|")
            .trimResults(CharMatcher.anyOf("!:;_"))
            .splitToList(data);
    List<String> expected = Arrays.asList("alpha", "beta", "gamma", "omega_1", "sigma");
    assertThat(actual).usingRecursiveComparison().isEqualTo(expected);

}

限制分隔次数

@Test
void testSplitterLimit() {
    String data = "alpha|beta|gamma|omega|sigma";
    List<String> actual = Splitter.on("|").limit(3).splitToList(data);
    List<String> expected = Arrays.asList("alpha", "beta", "gamma|omega|sigma");
    assertThat(actual).usingRecursiveComparison().isEqualTo(expected);
}

根据特写字符长度进行分隔

@Test
void testSplitterFixedLength() {
    String data = "001002003911";
    List<String> actual = Splitter.fixedLength(3).splitToList(data);
    List<String> expected = Arrays.asList("001", "002", "003", "911");
    assertThat(actual).usingRecursiveComparison().isEqualTo(expected);
}

CharMatcher匹配多个分隔符

 @Test
void testCharMatcherSplitter() {
    String data = "alpha,beta;gamma_omega|sigma";
    List<String> actual = Splitter.on(CharMatcher.anyOf(",;_|")).splitToList(data);
    List<String> expected = Arrays.asList("alpha", "beta", "gamma", "omega", "sigma");
    assertThat(actual).usingRecursiveComparison().isEqualTo(expected);
}

Split返回Map

此方法被标记为@Beta，生产谨慎使用。

@Test
void testSplitterToMap() {
    String data = "language=java|version=1.8";
    Map<String, String> actual = Splitter
            .on("|")
            .withKeyValueSeparator("=")
            .split(data);
    Map<String, String> expected = Maps.newHashMap();
    expected.put("language", "java");
    expected.put("version", "1.8");
    assertThat(actual).usingRecursiveComparison().isEqualTo(expected);

    actual = Splitter
            .on("|")
            .withKeyValueSeparator(Splitter.on("="))
            .split(data);
    assertThat(actual).usingRecursiveComparison().isEqualTo(expected);
}

大家根据实际场景进行使用

Cheers~

Markfred Chen

Guava String笔记 (2) - Splitter

概要