Guava CharMatcher – 番石榴的CharMatcher

In this quick tutorial we’ll explore the CharMatcher utility class in Guava.

在这个快速教程中，我们将探索Guava中的CharMatcher实用类。

1. Remove Special Characters from a String

1.从一个字符串中删除特殊字符

Let’s start by removing all special characters from a String.

让我们先从字符串中删除所有特殊字符。

In the following example, we remove all characters that aren’t digit or letter using retainFrom():

在下面的例子中，我们使用retainFrom()删除所有非数字或字母的字符。

@Test
public void whenRemoveSpecialCharacters_thenRemoved(){
    String input = "H*el.lo,}12";
    CharMatcher matcher = CharMatcher.javaLetterOrDigit();
    String result = matcher.retainFrom(input);

    assertEquals("Hello12", result);
}

2. Remove Non ASCII Characters From String

2.删除字符串中的非ASCII字符

We can also use CharMatcher to remove non ASCII characters from a String as in the following example:

我们还可以使用CharMatcher从String中删除非ASCII字符，如下例所示。

@Test
public void whenRemoveNonASCIIChars_thenRemoved() {
    String input = "あhello₤";

    String result = CharMatcher.ascii().retainFrom(input);
    assertEquals("hello", result);

    result = CharMatcher.inRange('0', 'z').retainFrom(input);
    assertEquals("hello", result);
}

3. Remove Characters Not in the Charset

3.删除不在字符集的字符

Now – let’s see how to remove Characters that don’t belong to a given Charset. In the following example – we’ll remove characters that don’t belong to the “cp437” Charset:

现在–让我们看看如何删除不属于某个字符集的字符。在下面的例子中–我们将删除不属于 “cp437” Charset的字符。

@Test
public void whenRemoveCharsNotInCharset_thenRemoved() {
    Charset charset = Charset.forName("cp437");
    CharsetEncoder encoder = charset.newEncoder();

    Predicate<Character> inRange = new Predicate<Character>() {
        @Override
        public boolean apply(Character c) {
            return encoder.canEncode(c);
        }
    };

    String result = CharMatcher.forPredicate(inRange)
                               .retainFrom("helloは");
    assertEquals("hello", result);
}

Note: We used CharsetEncoder to create a Predicate that check if the given Character can be encoded to the given Charset.

注意：我们使用CharsetEncoder来创建一个Predicate，检查给定的Character是否可以被编码到给定的Charset。

4. Validate String

4.验证字符串

Next – let’s see how to validate a String using CharMatcher.

接下来–让我们看看如何使用CharMatcher验证一个String。

We can use matchesAllOf() to check if all characters match a condition. And we can make use of matchesNoneOf() to check if a condition doesn’t apply on any of the String characters.

我们可以使用matchesAllOf()来检查所有字符是否符合条件。我们还可以使用matchesNoneOf()来检查条件是否不适用于任何String字符。

In the following example, we check if our String is lowercase, contains at least one ‘e‘ character and doesn’t contain any digits:

在下面的例子中，我们检查我们的String是否是小写的，至少包含一个’e‘字符，并且不包含任何数字。

@Test
public void whenValidateString_thenValid(){
    String input = "hello";

    boolean result = CharMatcher.javaLowerCase().matchesAllOf(input);
    assertTrue(result);

    result = CharMatcher.is('e').matchesAnyOf(input);
    assertTrue(result);

    result = CharMatcher.javaDigit().matchesNoneOf(input);
    assertTrue(result);
}

5. Trim String

5.修剪字符串

Now – let’s see how trim a String using CharMatcher.

现在–让我们看看如何使用CharMatcher修剪一个字符串。

In the following example, we use trimLeading(), trimTrailing and trimFrom() to trim our String:

在下面的例子中，我们使用trimLeading(), trimTrailing 和 trimFrom() 来修剪我们的String。

@Test
public void whenTrimString_thenTrimmed() {
    String input = "---hello,,,";

    String result = CharMatcher.is('-').trimLeadingFrom(input);
    assertEquals("hello,,,", result);

    result = CharMatcher.is(',').trimTrailingFrom(input);
    assertEquals("---hello", result);

    result = CharMatcher.anyOf("-,").trimFrom(input);
    assertEquals("hello", result);
}

6. Collapse a String

6.折叠一个字符串

Next – let’s see how to collapse a String using CharMatcher.

接下来–让我们看看如何使用CharMatcher来折叠一个String。

In the following example, we use collapseFrom() to replace consecutive spaces with ‘–‘:

在下面的例子中，我们使用collapseFrom()来用’–‘替换连续的空格。

@Test
public void whenCollapseFromString_thenCollapsed() {
    String input = "       hel    lo      ";

    String result = CharMatcher.is(' ').collapseFrom(input, '-');
    assertEquals("-hel-lo-", result);

    result = CharMatcher.is(' ').trimAndCollapseFrom(input, '-');
    assertEquals("hel-lo", result);
}

7. Replace from String

7.从字符串替换

We can use CharMatcher to replace specific characters from a String as in the following example:

我们可以使用CharMatcher来替换String中的特定字符，如下例所示。

@Test
public void whenReplaceFromString_thenReplaced() {
    String input = "apple-banana.";

    String result = CharMatcher.anyOf("-.").replaceFrom(input, '!');
    assertEquals("apple!banana!", result);

    result = CharMatcher.is('-').replaceFrom(input, " and ");
    assertEquals("apple and banana.", result);
}

8. Count Character Occurrences

8.计算字符出现的次数

Finally – let’s see how to count the occurrences of characters using CharMatcher.

最后–让我们看看如何使用CharMatcher计算字符的出现次数。

In the following example, we count the commas and characters between ‘a‘:’h‘:

在下面的例子中，我们计算’a‘:’h‘之间的逗号和字符。

@Test
public void whenCountCharInString_thenCorrect() {
    String input = "a, c, z, 1, 2";

    int result = CharMatcher.is(',').countIn(input);
    assertEquals(4, result);

    result = CharMatcher.inRange('a', 'h').countIn(input);
    assertEquals(2, result);
}

9. Conclusion

9.结论

In this article we illustrated some of the more useful APIs and real-world usage examples of using Guava for Strings.

在这篇文章中，我们说明了一些比较有用的API和使用Guava的字符串的真实使用例子。

The full source code is available over on GitHub.

完整的源代码可在GitHub上获得，。