Java PatternSyntaxException：字符串替换的非法重复？

问题描述

我正在尝试编写一个接受 String 的方法，检查某些令牌的实例（例如 $ {fizz} code>， $ {buzz} ， $ {foo} 等），并将每个令牌替换为一个新的字符串，从 Map< String，String> 中获取。

I am trying to write a method that will accept a String, inspect it for instances of certain tokens (e.g. ${fizz}, ${buzz}, ${foo}, etc.) and replace each token with a new string that is fetched from a Map<String,String>.

例如，如果我通过方法以下字符串：

For example, if I pass this method the following string:

如果该方法查询了以下 Map< String，String> ：

And if the method consulted the following Map<String,String>:

Key             Value
==========================
"fizz"          "brown"
"buzz"          "arsonist"
"foo"           "feet"

然后结果字符串将是：

这是我的方法：

String substituteAllTokens(Map<String,String> tokensMap, String toInspect) {
    String regex = "\\$\\{([^}]*)\\}";
    Pattern pattern = Pattern.compile(regex);
    Matcher matcher = pattern.matcher(toInspect);
    while(matcher.find()) {
        String token = matcher.group();     // Ex: ${fizz}
        String tokenKey = matcher.group(1); // Ex: fizz
        String replacementValue = null;

        if(tokensMap.containsKey(tokenKey))
            replacementValue = tokensMap.get(tokenKey);
        else
            throw new RuntimeException("String contained an unsupported token.");

        toInspect = toInspect.replaceFirst(token, replacementValue);
    }

    return toInspect;
}

当我运行这个，我得到以下异常：

When I run this, I get the following exception:

Exception in thread "main" java.util.regex.PatternSyntaxException: Illegal repetition near index 0
${fizz}
^
    at java.util.regex.Pattern.error(Pattern.java:1730)
    at java.util.regex.Pattern.closure(Pattern.java:2792)
    at java.util.regex.Pattern.sequence(Pattern.java:1906)
    at java.util.regex.Pattern.expr(Pattern.java:1769)
    at java.util.regex.Pattern.compile(Pattern.java:1477)
    at java.util.regex.Pattern.<init>(Pattern.java:1150)
    at java.util.regex.Pattern.compile(Pattern.java:840)
    at java.lang.String.replaceFirst(String.java:2158)
    ...rest of stack trace omitted for brevity (but available upon request!)

为什么我得到这个？

Why am I getting this? And what is the correct fix? Thanks in advance!

推荐答案

在 $ {fizz }

{是正在启动的正则表达式引擎的指标重复指示符，如 {2,4} ，这意味着前一个令牌的2到4倍。但是， {f 是非法的，因为它必须跟随一个数字，所以它会抛出一个例外。

{ is an indicator to the regex engine that you are about to start a repetition indicator, like {2,4} which means '2 to 4 times of the previous token'. But {f is illegal, because it has to be followed by a number, so it throws an exception.

您需要逃避所有正则表达式元字符（在这种情况下 $ ， {和} ）（尝试使用）或使用不同的替代方法字符串的字符串，而不是字符串的正则表达式。

You need to escape all regex metacharacters (in this case $, { and }) (try using http://docs.oracle.com/javase/6/docs/api/java/util/regex/Pattern.html#quote(java.lang.String) ) or use a different method that substitutes a string for a string, not a regex for a string.

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