java - 拆分返回 PatternSyntaxException : Illegal/unsupported escape sequence

Question

当用户输入包含 Unicode 字符(例如 ' 或 ” )时，以下操作将失败:

String[] unicodeStrings = answerText.split("((?<=\\R)|(?=\\R))");

我尝试过调试 split 方法，但没有找到根本原因。我有预感这与表达式中的问号(?)有关。

我还尝试了在线 java 正则表达式工具，并将表达式应用于具有以下字符 ‘” 的某些文本。没有显示任何错误。

我还尝试在在线java编译器中编写一个简单的测试方法，其中我传递了带有‘”字符的测试字符串并执行了上述拆分。也没有错误。

代码:

String answerText = uiq.getAnswerText();
            if (answerText.matches("[\\x00-\\x7F]*")) //if the answerString consists only of ascii characters we encode it
                sb.append("<String name=\"answerText\">")
                        .append(wrapCdata(uiq.isDate() ? formatDate(uiq.getAnswerText(), sourceFormat, targetFormat) : answerText)).append("</String>");
            else { //if the answerString consists of unicode characters we encode only the Linebreakers (the \R)
                String answerNonEscapedText = "";
                String[] unicodeStrings = answerText.split("((?<=\\R)|(?=\\R))");//This regex splits the string to its linebreak-delimiters, including them. i.e. ("$$$\r\n" ---> [$,$,$,\r\n])
                for (String str : unicodeStrings) {
                    if (str.matches("\\R"))
                        str = StringEscapeUtils.escapeJava(str);

                    answerNonEscapedText += str;
                }

错误:

java.util.regex.PatternSyntaxException: Illegal/unsupported escape sequence near index 6 
((?<=\R)|(?=\R)) 
 ^ 
 at java.util.regex.Pattern.error(Pattern.java:1924) 
 at java.util.regex.Pattern.escape(Pattern.java:2416) 
 at java.util.regex.Pattern.atom(Pattern.java:2164) 
 at java.util.regex.Pattern.sequence(Pattern.java:2046) 
 at java.util.regex.Pattern.expr(Pattern.java:1964) 
 at java.util.regex.Pattern.group0(Pattern.java:2807) 
 at java.util.regex.Pattern.sequence(Pattern.java:2018) 
 at java.util.regex.Pattern.expr(Pattern.java:1964) 
 at java.util.regex.Pattern.group0(Pattern.java:2854) 
 at java.util.regex.Pattern.sequence(Pattern.java:2018) 
 at java.util.regex.Pattern.expr(Pattern.java:1964) 
 at java.util.regex.Pattern.compile(Pattern.java:1665) 
 at java.util.regex.Pattern.<init>(Pattern.java:1337) 
 at java.util.regex.Pattern.compile(Pattern.java:1022) 
 at java.lang.String.split(String.java:2313) 
 at java.lang.String.split(String.java:2355)

您能帮我找出失败的根本原因吗？

Answer 1

        String answerText = uiq.getAnswerText();
        if (answerText.matches("[\\x00-\\x7F]*")) {
            sb.append("<String name=\"answerText\">")
              .append(wrapCdata(uiq.isDate()
                      ? formatDate(uiq.getAnswerText(), sourceFormat, targetFormat)
                      : answerText))
              .append("</String>");
        } else {
            String[] unicodeStrings = answerText.split("\\R"); // Splits on linebreaks.
            // This looses the exact line delimiter.
            String answerNonEscapedText = ""; // Better StringBuilder too.
            for (String str : unicodeStrings) {
                answerNonEscapedText += str + "\\r\\n";
            }

对于某些情况，上述原始行分隔符的丢失很重要:存在 CSV，其中字段值可能包含行分隔符 \n 而行以 \r\n。或者这样。

更简单的解决方案:

        // Java >= 9
        String answerText = Pattern.compile("\\R").matcher(uiq.getAnswerText())
            .replaceAll(mr -> StringEscapeUtils.escapeJava(mr.group()));


        // Java < 9 (only for \r and \n)
        String answerText = uiq.getAnswerText()
            .replace("\r", "\\r").replace("\n", "\\n");