如何通过使用replaceAll（）方法在regex表达式的帮助下从字符串中忽略特殊字符（$ ^ +（）{}等）

Question

I am using java replaceAll() method to replace part of String with another String and its working great but, the problem comes when my file name contains characters like $ ^ + ( ) { } [ ] etc. In this case pattern matching fails and the original String remains as it is. Sample code to show case my use case is as follow:

String messageBody = "src=\"http://thinconnect.interactcrm.com:36061/FileDownloader/4/outbound/31358/file+name.jpeg\" style=\"height:225px\"";
messageBody =  messageBody.replaceAll("(http|https)://(?:[^\\s]*)/FileDownloader/4/outbound/31358/file+name.jpeg", "cid: 14890411127853");
System.out.println(messageBody);

The expected output is:

src="cid: 14890411127853" style="height:225px"

but it gives:

src="http://thinconnect.interactcrm.com:36061/FileDownloader/4/outbound/31358/file+name.jpeg" style="height:225px"

How can I get it working by ignoring special characters that we use to form regex expression from my file name.

Thanks in advance!

Answer 1

You have unescaped metacharacters in your URL pattern, including a plus and a literal dot. Escape them, using the following pattern:

(http|https)://(?:[^\\s]*)/FileDownloader/4/outbound/31358/file\\+name\\.jpeg
                                                               ^^^ escape dot and plus sign

Full code:

String messageBody = "src=\"http://thinconnect.interactcrm.com:36061/FileDownloader/4/outbound/31358/file+name.jpeg\" style=\"height:225px\"";
messageBody =  messageBody.replaceAll("(http|https)://(?:[^\\s]*)/FileDownloader/4/outbound/31358/file\\+name\\.jpeg", "cid: 14890411127853");
System.out.println(messageBody);

Output:

src="cid: 14890411127853" style="height:225px"

Update:

If you don't know in advance what the exact pattern will be, but you know it might have metacharacters, which would require escaping for use in a replacement, then Java provides a method for this: Pattern.quote()

To see how it works, we can split your pattern into two parts:

String part1 = "(http|https)://(?:[^\\s]*)";
String part2 = Pattern.quote("/FileDownloader/4/outbound/31358/file+name.jpeg");
messageBody =  messageBody.replaceAll(part1 + part2, "cid: 14890411127853");

From the documentation for Pattern.quote() :

This method produces a String that can be used to create a Pattern that would match the string s as if it were a literal pattern.
Metacharacters or escape sequences in the input sequence will be given no special meaning.

Answer 2

You just have to escape those characters using a backslash ( \\ )

example:

String messageBody = "src=\"http://thinconnect.interactcrm.com:36061/FileDownloader/4/outbound/31358/file+name.jpeg\" style=\"height:225px\"";
messageBody =  messageBody.replaceAll("(http|https)://(?:[^\\s]*)/FileDownloader/4/outbound/31358/file\\+name\\.jpeg", "cid: 14890411127853");

similarly

String messageBody = "src=\"http://thinconnect.interactcrm.com:36061/FileDownloader/4/outbound/31358/file$name.jpeg\" style=\"height:225px\"";
messageBody =  messageBody.replaceAll("(http|https)://(?:[^\\s]*)/FileDownloader/4/outbound/31358/file\\$name\\.jpeg", "cid: 14890411127853");

Answer 3

Did it this way.

    final String[] metaCharacters = {"^","$","{","}","[","]","(",")",".","+","-","&"};
    String filePath = "/4/outbound/31358/file+name.jpeg";
    for(String c: metaCharacters){
        if(filePath.contains(c)){
            filePath = filePath.replace(c, "\\"+c);
        }
    }
    String messageBody = "src=\"http://thinconnect.interactcrm.com:36061/FileDownloader/4/outbound/31358/file+name.jpeg\" style=\"height:225px\"";
    System.out.println(messageBody);
    messageBody =  messageBody.replaceAll("(http|https)://(?:[^\\s]*)/FileDownloader"+filePath, "cid: 14890411127853");
    System.out.println(messageBody);