Java 正则表达式的命名捕获组

一、正则分组查询

1. 普通捕获组

从正则表达式左侧开始，每出现一个左括号 “(” 记做一个分组，分组编号从 1 开始。0 代表整个表达式。

public static void main(String[] args) {
    String text = "2021-12-31";
    Pattern pattern = Pattern.compile("(\\d{4})-(\\d{2})-(\\d{2})");
    Matcher matcher = pattern.matcher(text);
    matcher.find(); // 必须要有这句
    System.out.println(matcher.group(1));
    System.out.println(matcher.group(2));
    System.out.println(matcher.group(3));
}

2. 命名捕获组

每个以左括号开始的捕获组，都紧跟着 ?\，而后才是正则表达式。

例如：2021-12-31 的正则表达式如下

public static void main(String[] args) {
    String text = "2021-12-31";
    Pattern pattern = Pattern.compile("(?<year>\\d{4})-(?<month>\\d{2})-(?<day>\\d{2})");
    Matcher matcher = pattern.matcher(text);
    matcher.find(); // 必须要有这句
    System.out.println(matcher.group("year"));
    System.out.println(matcher.group("month"));
    System.out.println(matcher.group("day"));
}

二、RegularUtils 工具类

package io.github.talelin.latticy.utils;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;

import java.util.Collections;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

public class RegularUtils {
    private static Pattern namedGroupCompile = Pattern.compile("\\(\\?<([a-zA-Z][a-zA-Z0-9]*)>");

    public static JSONObject matchByGroupName(String text, String regex) {
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher = pattern.matcher(text);
        JSONObject jsonObject = new JSONObject(true);
        Set<String> namedGroupCandidates = getNamedGroupCandidates(regex);
        List<String> collect = namedGroupCandidates.stream().sorted(Collections.reverseOrder()).collect(Collectors.toList());
        if (matcher.find()) {
            for (String groupName : collect) {
                jsonObject.put(groupName, matcher.group(groupName));
            }
            return jsonObject;
        } else {
            return jsonObject;
        }
    }

    /**
     * 命名捕获组
     * 正则编写好，可以直接匹配到需要的内容，不用多处理
     *
     * @param regex
     * @param content
     * @param group
     * @return
     */
    public static String matchStr(String content, String regex, String group) {
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher = pattern.matcher(content);
        if (matcher.find()) {
            return matcher.group(group);
        }
        return null;
    }

    /**
     * 获取正则表达式对应的命名捕获组（name capture）
     * 输入："(?<year>\\\\d{4})-(?<month>\\\\d{2})-(?<day>\\\\d{2}))"
     * 输出：[year,month,day]
     *
     * @param regex
     * @return
     */
    private static Set<String> getNamedGroupCandidates(String regex) {
        Set<String> namedGroups = new TreeSet<String>();
        Matcher m = namedGroupCompile.matcher(regex);
        while (m.find()) {
            namedGroups.add(m.group(1));
        }
        return namedGroups;
    }

    public static void main(String[] args) {
        String email = "2021-12-31";
        String regex = "(?<year>\\d{4})-(?<month>\\d{2})-(?<day>\\d{2})";
        JSONObject jsonObject = matchByGroupName(email, regex);
        System.out.println(JSON.toJSONString(jsonObject, true));
        System.out.println(jsonObject.get("year"));
        System.out.println(jsonObject.get("month"));
        System.out.println(jsonObject.get("day"));
    }
}

三、参考资料

• Get group names in java regex
  https://newbedev.com/get-group-names-in-java-regex
• Java 正则表达式的捕获组(capture group) | 菜鸟教程
  https://www.runoob.com/w3cnote/java-capture-group.html