Match repeated pattern in a query string using a regex

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

Isn't m always preceded by some specific character? Define "vary in some cases"! — Maarten Bodewes
– Maarten Bodewes, Commented Jun 29, 2014 at 14:10
Sometimes m is preceded by &, others by ", others by blank space, others by comma,.... its difficult because this varies. — Genaut
– Genaut, Commented Jun 29, 2014 at 14:22

Bohemian · Accepted Answer · 2014-06-29 14:29:09Z

2

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");

answered Jun 29, 2014 at 14:29

Bohemian♦

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Mena · Accepted Answer · 2014-06-29 14:29:08Z

1

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

edited Jun 29, 2014 at 14:29

answered Jun 29, 2014 at 14:23

Mena

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1 Comment

Pshemo Over a year ago

Maybe instead of .+? consider using [^&?]+. This way you wouldn't need to check (.+?)(?=&|\\?) conditions - which probably should also contain end of string $ if m=... would be last parameter).

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