匹配右括号时Android中的正则表达式模式错误 [英] Regex pattern error in Android when matching closing brace

问题描述

我正在使用java.util.regex.Pattern类来匹配Android程序中的字符串.

I am using java.util.regex.Pattern class to match a string in a Android program.

if(Pattern.matches("\\{\\{.*?}}", element.getValue())) {
   ...             
} else {
   ...
}

然后出现以下错误.

 Caused by: java.util.regex.PatternSyntaxException: Syntax error in regexp pattern near index 8
                                                                  \{\{.*?}}

我正在使用Android Studio和Open JDK.为了测试正则表达式，我在Netbeans中编写了一个简单的程序，它运行良好. Netbeans也使用openjdk.

I am using Android studio and Open JDK. To test the regex expression I wrote a simple program in Netbeans and it works fine. Netbeans also use openjdk.

System.out.println(Pattern.matches("\\{\\{.*?}}", "{{hello:sdf}}"));

为什么正则表达式在android项目中给出错误?

Why the regular expression is giving an error in android project?

推荐答案

使用

"\\{\\{.*?\\}\\}"

问题在于，Android中使用的正则表达式引擎是 ICU引擎，即与Java不同，表示文字打开/关闭花括号的 和都必须在ICU正则表达式模式中转义.

The issue is that the regex engine used in Android is an ICU engine that is different from Java one, and both { and } that represent literal open/close curly braces must be escaped in ICU regex patterns.

在绝大多数的正则表达式中，不必逃避}，但是ICU regex引擎不是这种情况，它不能基于模式上下文来推断}的含义.例如. PCRE，.NET，Python，Java正则表达式以[a-z]}模式找到}，并且由于之前没有{，因此他们知道"它不是

In the overwhelming majority of regex flavors } does not have to be escaped, but it is not the case with the ICU regex engine that cannot deduce the } meaning based on the pattern context. E.g. PCRE, .NET, Python, Java regexes find } in [a-z]} pattern and as there is no { before, they "know" it is not a part of the limiting quantifier construct. ICU is not that smart. It still thinks there must be a { that is followed with digit(s) before } and reports an error if it is unescaped.

这篇关于匹配右括号时Android中的正则表达式模式错误的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！