Regex pattern for query string

Question

I need a help finding java regex pattern to get one query information from the URI. For instance URI here is

"GET /6.2/calculateroute.xml?routeattributes=sm,wp,lg,bb&legattributes=mn&maneuverattributes=ac,po,tt,le,-rn,-sp,-di,no,nu,nr,sh&instructionFormat=html&language=en_US&mode=fastest;car;traffic:default&waypoint0=37.79548,-122.392025&waypoint1=36.0957717,-115.1745167&resolution=786&app_id=D4KnHBzGYyJtbM8lVfYX&token=TRKB7vnBguWLam5rdWshTA HTTP/1.1"

I need to extract 4 value out of it which I manage to do it:

GET

/6.2/calculateroute.xml

routeattributes=sm,wp,lg,bb&legattributes=mn&maneuverattributes=ac,po,tt,le,-rn,-sp,-di,no,nu,nr,sh&instructionFormat=html&language=en_US&mode=fastest;car;traffic:default&waypoint0=37.79548,-122.392025&waypoint1=36.0957717,-115.1745167&resolution=786&app_id=D4KnHBzGYyJtbM8lVfYX&token=TRKB7vnBguWLam5rdWshTA

HTTP/1.1

Now the question is how do I write a regex for app_id value from the query string. Note app_id do not appear in all the pattern, so it should be generic and regex should not fail if app_id is missing. Please help...

can you give a sample string from which app_id id to be extracted? [app_id]* means 0 or more times maybe this will help — Bhavik Shah
– Bhavik Shah, Commented Nov 2, 2012 at 10:44
Does it have to be a regex? Could you use an existing helper method instead such as this one from Apache HTTPClient? — Ian Roberts
– Ian Roberts, Commented Nov 2, 2012 at 10:44

Bohemian · Accepted Answer · 2012-11-02 10:53:39Z

2

Your question can be simplified to: "How do I extract an optional query parameter from a string". Here's how:

String appId = input.replaceAll("(.*(app_id=(\\w+)).*)|.*", "$3");

The appId variable will contain the app_id value if it's present or be blank otherwise.

Here's some test code with the code bundled as a utility method:

public static String getParameterValue(String input, String parameter) {
    return input.replaceAll("(.*("+parameter+"=(\\w+)).*)|.*", "$3"));
}

public static void main(String[] args) {
    String input1 = "foo=bar&app_id=D4KnHBzGYyJtbM8lVfYX&x=y";
    String input2 = "foo=bar&XXXXXX=D4KnHBzGYyJtbM8lVfYX&x=y";

    System.out.println("app_id1:" + getParameterValue(input1, "app_id"));
    System.out.println("app_id2:" + getParameterValue(input2, "app_id"));
}

Output:

app_id1:D4KnHBzGYyJtbM8lVfYX
app_id2:

edited Nov 2, 2012 at 10:53

answered Nov 2, 2012 at 10:47

Bohemian♦

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1 Comment

user1793943 Over a year ago

This is regex pattern ^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(?([^#]*))?(#(.*))?

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