How can I parse url query string parameter in java?

[ying lam]

Hi,
If I have a URL string like this:
http://www.javaranch.com

How can I parse the query string parameter?
e.g. parameter 'ubb' is nettopic
parmater 'f' is 1

From the java doc, it only gives me the query string of the url:
http://java.sun.com/j2se/1.4.2/docs/api/java/net/URL.html

Thank you.

[Vijayender Bandaru]

see here

[Freddy Wong]

The easiest way is probably to use the getQuery() from URL class and then parse the result returned by the getQuery(). For example:

    
public static Map<String, String> getQueryMap(String query)
{
    String[] params = query.split("&");
    Map<String, String> map = new HashMap<String, String>();
    for (String param : params)
    {
        String name = param.split("=")[0];
        String value = param.split("=")[1];
        map.put(name, value);
    }
    return map;
}

To iterate the map, you can do this:

    
String query = url.getQuery();
Map<String, String> map = getQueryMap(query);
Set<String> keys = map.keySet();
for (String key : keys)
{
   System.out.println("Name=" + key);
   System.out.println("Value=" + map.get(key));
}

[ August 07, 2007: Message edited by: Freddy Wong ]

[Stan James]

I was a bit surprised the other day when I did getParameterMap().entrySet() from a J2EE Request object, the value in each entry is an array. That supports having the same key more than once in the query string. Think about whether you want to handle that.

[Joe Donahue]

Using request.getParameter("ubb") is significantly easier than iterating through the entire query string.

If, however, you have multiple possible values (which the query string supports, though rarely used) you would have to iterate through.

And the value would be newtopic, not nettopic.

[David Newton]

(Not sure that it's "rarely used"; I see it all the time for checkboxes, multiple selects, etc.)

[Bear Bibeault]

Joe Donahue wrote:If, however, you have multiple possible values (which the query string supports, though rarely used) you would have to iterate through.

Not correct on both counts. It is very common to have multiple parameters with the same name, and the getParameterValues() method gives them to you as an array without the need for dealing with the query string.

[Joe Donahue]

Well played.

BTW - I made your frappacinos. They are fantastic!