java中正则表达式的group用法

group查询

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Client {

  public static void main(String[] args) {
    String content = "java123python456go";
    Matcher matcher = Pattern.compile("([a-z]+)([0-9]+)").matcher(content);
    while (matcher.find()) {
      System.out.println(matcher.group(0) + " " + matcher.group(1) + " " + matcher.group(2));
    }
  }

}

group(0)表示匹配到的完整字符串，group(1)表示第一个括号中的内容，依次类推。
输出为

java123 java 123
python456 python 456

group替换

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.function.Function;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Client2 {

  public static void main(String[] args) {
    String content = "java123python456go";
    String regex = "([a-z]+)([0-9]+)";
    System.out.println(replaceOfMatchGroup(content, regex, 1, word -> word.toUpperCase()));
    System.out.println(replaceOfMatchGroup(content, regex, 1, word -> word + "good"));
  }

  public static String replaceOfMatchGroup(String sourceString, String pattern,
      int groupToReplace, Function<String, String> replaceStrategy) {
    //模拟栈，保存所有group的起始和结束位置
    Deque<Integer> startPositions = new ArrayDeque<>();
    Deque<Integer> endPositions = new ArrayDeque<>();
    Matcher matcher = Pattern.compile(pattern).matcher(sourceString);
    while (matcher.find()) {
      startPositions.addLast(matcher.start(groupToReplace));
      endPositions.addLast(matcher.end(groupToReplace));
    }
    StringBuilder sb = new StringBuilder(sourceString);
    while (!startPositions.isEmpty()) {
      int start = startPositions.removeLast();
      int end = endPositions.removeLast();
      if (start >= 0 && end >= 0) {
        //在区间[start,end)中使用replaceStrategy策略替换
        sb.replace(start, end, replaceStrategy.apply(sourceString.substring(start, end)));
      }
    }
    return sb.toString();
  }
}

输出为

JAVA123PYTHON456go
javagood123pythongood456go

Matcher类中只有replaceAll()和replaceFirst()方法，只能替换完整的匹配字符串，这里实现一个可以替换任意group的方法。

参考

java Matcher中的group
Java Pattern和Matcher用法
Can I replace groups in Java regex?