Java正则表达式示例

柔情只为你懂 2023-02-15 05:13 31阅读 0赞

Java 8流和正则表达式示例。

> **注意**  
> 在[Wikipedia上][Wikipedia]学习基本的正则表达式

## 1. String.matches（regex） ##

1.1在此示例中，检查字符串是否为数字。

JavaRegEx1.java

package com.mkyong.regex;
    
    import java.util.Arrays;
    import java.util.List;
    
    public class JavaRegEx1 {
    
        public static void main(String[] args) {
    
            List<String> numbers = Arrays.asList("1", "20", "A1", "333", "A2A211");
    
            for (String number : numbers) {
    		
                if (number.matches("\\d+")) {
                    System.out.println(number);		// 1, 20, 333
                }
            }
    
            // Java 8 stream example
            numbers.stream()
                    .filter(x -> x.matches("\\d+"))
                    .forEach(System.out::println);
    
        }
    }

输出量

1
    20
    333
    
    1
    20
    333

## 2. String.replaceAll（正则表达式，替换） ##

2.1本示例将所有数字替换为`#`

JavaRegEx2.java

package com.mkyong.regex;
    
    import java.util.Arrays;
    import java.util.List;
    
    public class JavaRegEx2 {
    
        public static void main(String[] args) {
    
            List<String> numbers = Arrays.asList("1", "20", "A1", "333", "A2A211");
    
            for (String number : numbers) {
                System.out.println(number.replaceAll("\\d", "#"));
            }
    
            // Java 8 stream example
            numbers.stream()
                    .map(x -> x.replaceAll("\\d", "#"))
                    .forEach(System.out::println);
    
        }
    }

输出量

#
    ##
    A#
    ###
    A#A###
    
    #
    ##
    A#
    ###
    A#A###

## 3.模式和匹配器 ##

3.1从“字符串”列表中查找所有数字。

JavaRegEx3.java

package com.mkyong.regex;
    
    import java.util.Arrays;
    import java.util.List;
    import java.util.regex.Matcher;
    import java.util.regex.Pattern;
    
    public class JavaRegEx3 {
    
        public static void main(String[] args) {
    
            List<String> numbers = Arrays.asList("1", "20", "A1", "333", "A2A211");
    
            Pattern pattern = Pattern.compile("\\d+");
    
            for (String number : numbers) {
    
                Matcher matcher = pattern.matcher(number);
                while (matcher.find()) {
                    System.out.println(matcher.group(0));
                }
    
            }
    	
    	}
    }

输出量

1
    20
    1
    333
    2
    211

3.2对于Java 8流，首先我们尝试进行如下转换：

numbers.stream()
    		.map(x -> pattern.matcher(x))
    		.filter(Matcher::find)          // A2A211, will it loop?
    		.map(x -> x.group())
    		.forEach(x -> System.out.println(x));

输出，最后的211是否丢失？

1
    20
    1
    333
    2

流无法循环`.filter`来获取所有组，我们需要使用自定义的`Spliterators`进行破解

JavaRegEx4.java

package com.mkyong.regex;
    
    import java.util.Arrays;
    import java.util.List;
    import java.util.Spliterators;
    import java.util.function.Consumer;
    import java.util.regex.Matcher;
    import java.util.regex.Pattern;
    import java.util.stream.StreamSupport;
    
    public class JavaRegEx4 {
    
        public static void main(String[] args) {
    
            List<String> numbers = Arrays.asList("1", "20", "A1", "333", "A2A211");
    
            Pattern pattern = Pattern.compile("\\d+");
    
            numbers.stream()
                    .flatMap(x ->
                            StreamSupport.stream(new MatchItr(pattern.matcher(x)), false))
                    .forEach(x -> System.out.println(x));
    
    
        }
    
        final static class MatchItr extends Spliterators.AbstractSpliterator<String> {
            private final Matcher matcher;
    
            MatchItr(Matcher m) {
                super(m.regionEnd() - m.regionStart(), ORDERED | NONNULL);
                matcher = m;
            }
    
            public boolean tryAdvance(Consumer<? super String> action) {
                if (!matcher.find()) return false;
                action.accept(matcher.group());
                return true;
            }
        }
    
    }

输出量

1
    20
    1
    333
    2
    211

## 4. Java 9，Scanner.findAll（regex） ##

4.1 Java 9，我们可以使用`Scanner.findAll(regex)`返回与提供的正则表达式匹配的匹配结果流。

Scanner scan = new Scanner("A2A211");
    	List<String> collect = scan
    			.findAll("\\d+")
    			.map(m -> m.group())
    			.collect(Collectors.toList());
    	collect.forEach(x -> System.out.println(x));

输出量

2
    211

最终版本，带有Java 9。

JavaRegEx5.java

package com.mkyong.regex;
    
    import java.util.Arrays;
    import java.util.List;
    import java.util.Scanner;
    import java.util.regex.Pattern;
    import java.util.stream.Collectors;
    
    public class JavaRegEx5 {
    
        public static void main(String[] args) {
    
            List<String> numbers = Arrays.asList("1", "20", "A1", "333", "A2A211");
    
            Pattern pattern = Pattern.compile("\\d+");
    
            List<String> collect = numbers.stream()
                    .map(x -> new Scanner(x).findAll(pattern)
                            .map(m -> m.group())
                            .collect(Collectors.toList())
                    )
                    .flatMap(List::stream)
                    .collect(Collectors.toList());
    
            collect.forEach(x -> System.out.println(x));
    
        }
    
    }

输出量

1
    20
    1
    333
    2
    211

## 参考文献 ##

*  [Scanner.find所有JavaDocs][Scanner.find_JavaDocs]
 *  [维基百科-RegEx][Wikipedia]

标签： [flatMap][] [Java 8][] [Java 9][] [正则表达式][Link 1] [流][Link 2]

> 翻译自: [https://mkyong.com/java/java-regular-expression-examples/][https_mkyong.com_java_java-regular-expression-examples]

[Wikipedia]: https://en.wikipedia.org/wiki/Regular_expression
[Scanner.find_JavaDocs]: https://docs.oracle.com/javase/9/docs/api/java/util/Scanner.html#findAll-java.lang.String-
[flatMap]: https://mkyong.com/tag/flatmap/
[Java 8]: https://mkyong.com/tag/java-8/
[Java 9]: https://mkyong.com/tag/java-9/
[Link 1]: https://mkyong.com/tag/regex/
[Link 2]: https://mkyong.com/tag/stream/
[https_mkyong.com_java_java-regular-expression-examples]: https://mkyong.com/java/java-regular-expression-examples/