String replaceAll 中的 Java 正则表达式:负面展望未按预期工作 [英] Java regex in String replaceAll: negative look ahead does not work as expected

问题描述

我正在尝试处理文本并替换所有以www"开头的出现.用某个词(在这种情况下为香蕉")，但我想排除在www"之前有http://"的所有情况.

I am trying to process text and replace all the occurence that start with "www." with a certain word (in this cases "Banana"), but I want to exclude all the cases in which there is "http://" before the "www".

当我使用正向前瞻时它可以工作(只有 http://www 案例更改)，但是当我使用负面展望 - 两个词都发生了变化.

When I use a positive lookahead it works (only the http://www case changes), but when I use a negative lookahead - both words change.

你能帮我解决这个问题吗?

Can you help me with this one?

String baseString = "replace this: www.q.com and not this:http://www.q.com";
String positiveLookahead = baseString.replaceAll("(?:http://)www([^ \n\t]*)", "Banana");
String negativeLookahead = baseString.replaceAll("(?!http://)www([^ \n\t]*)", "Banana");

//positiveLookahead works (changes only the scond phrase), but positiveLookahead does not (changes both)

推荐答案

使用否定的 回顾, (?:

String negativeLookahead = baseString.replaceAll("(?<!http://)www[^ \n\t]*", "Banana");

(?<!http://)www[^ \n\t]* 模式匹配:

• (?<!http://) - 字符串中没有紧跟在 http://
前面的位置
• www - 文字 www 子字符串
• [^ \n\t]* - 除了空格、换行符和回车之外的任何 0+ 个字符(可能你想试​​试 \\S* 代替).

• (?<!http://) - a location in the string that is not immediately preceded with http://
• www - a literal www substring
• [^ \n\t]* - any 0+ chars other than space, newline and carriage return (probably you want to try \\S* instead).

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