使用正则表达式匹配查询字符串中的重复模式

Question

I have a series of URL params and I need extract some of them that are repeated. For example:

Required params "m"

I have a string how this:

m=123456789&reset=true&color=blue&getppm=1112&comparechars=yes&alternatem=5&.....

This repeats about 10 times with different values.

I have this regex:

m=(.*?)&

But my problem is that other params are entering too ( getppm , alternatem ).

m is the first in some cases. It could vary in some cases, and I can't use &m= in such cases.

How can I solve this problem?

EDIT: The m param normally is continued by a serie of numbers and uppercase letters on this type:

m=1A2B3C4D6D8A7D5S.32D4D1D5D3D6D8D&nextparam=...

I was trying with {x,x} variations without successfull

Answer 1

The key to solving this is using the "word boundary" regex \\b .

To extract the value of the "m" parameter:

String m = str.replaceAll(".*?\\bm=([^&]+).*", "$1");

Answer 2

GET parameter key-value pairs are delimited by & (prepended by ? for the first key-value pair in the URL).

You could simply use a lookbehind to limit the parameter to actual m instead of [something]m .

For instance:

String params = "myUrl?m=123456789&reset=true&color=blue&getppm=1112&comparechars=yes&alternatem=5&...";
// Pattern improved as per Pschemo's suggestion
Pattern pattern = Pattern.compile("(?<=&|\\?)m=([^&?]+)");
Matcher matcher = pattern.matcher(params);
while (matcher.find()) {
    System.out.println(matcher.group(1));
}

Output

123456789