用逗号分隔一个字符串，但避免转义逗号和反斜杠 [英] split a string at comma but avoid escaped comma and backslash

问题描述

我想用逗号分开一个字符串。该字符串包含转义的逗号\，和转义反斜杠\\。开头和结尾的逗号以及连续的几个逗号应该会导致空字符串。

I'd like to split a string at comma ",". The string contains escaped commas "\," and escaped backslashs "\\". Commas at the beginning and end as well as several commas in a row should lead to empty strings.

所以,, \，\ \ ,,应该成为，，\，\\，，

So ",,\,\\,," should become "", "", "\,\\", "", ""

请注意，我的示例字符串显示为单个\的反斜杠。 Java字符串会使它们翻倍。

Note that my example strings show backslash as single "\". Java strings would have them doubled.

我尝试过几个包，但没有成功。我的最后一个想法是写我自己的解析器。

I tried with several packages but had no success. My last idea would be to write my own parser.

推荐答案

虽然一个专门的库是一个好主意以下将工作

While certainly a dedicated library is a good idea the following will work

    public static String[] splitValues(final String input) {
        final ArrayList<String> result = new ArrayList<String>();
        // (?:\\\\)* matches any number of \-pairs
        // (?<!\\) ensures that the \-pairs aren't preceded by a single \
        final Pattern pattern = Pattern.compile("(?<!\\\\)(?:\\\\\\\\)*,");
        final Matcher matcher = pattern.matcher(input);
        int previous = 0;
        while (matcher.find()) {
            result.add(input.substring(previous, matcher.end() - 1));
            previous = matcher.end();
        }
        result.add(input.substring(previous, input.length()));
        return result.toArray(new String[result.size()]);
    }

想法是找到，以没有或偶数编号的 \ （即不转义，）以及$ code>，是在 end（） - 1 之前的模式的最后一部分，它刚刚在之前， / code>。

Idea is to find , prefixed by no or even-numbered \ (i.e. not escaped ,) and as the , is the last part of the pattern cut at end()-1 which is just before the ,.

除了 null - 输入。如果你喜欢处理 List< String> 更好，你当然可以改变回报;我刚刚采用在 split（）中实现的模式来处理转义。

Function is tested against most odds I can think of except for null-input. If you like handling List<String> better you can of course change the return; I just adopted the pattern implemented in split() to handle escapes.

示例类使用此功能： p>

Example class uitilizing this function:

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

public class Print {
    public static void main(final String[] args) {
        String input = ",,\\,\\\\,,";
        final String[] strings = splitValues(input);
        System.out.print("\""+input+"\" => ");
        printQuoted(strings);
    }

    public static String[] splitValues(final String input) {
        final ArrayList<String> result = new ArrayList<String>();
        // (?:\\\\)* matches any number of \-pairs
        // (?<!\\) ensures that the \-pairs aren't preceded by a single \
        final Pattern pattern = Pattern.compile("(?<!\\\\)(?:\\\\\\\\)*,");
        final Matcher matcher = pattern.matcher(input);
        int previous = 0;
        while (matcher.find()) {
            result.add(input.substring(previous, matcher.end() - 1));
            previous = matcher.end();
        }
        result.add(input.substring(previous, input.length()));
        return result.toArray(new String[result.size()]);
    }

    public static void printQuoted(final String[] strings) {
        if (strings.length > 0) {
            System.out.print("[\"");
            System.out.print(strings[0]);
            for(int i = 1; i < strings.length; i++) {
                System.out.print("\", \"");
                System.out.print(strings[i]);
            }
            System.out.println("\"]");
        } else {
            System.out.println("[]");
        }
    }
}

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