Hi all,

I am new for Apex development. So please help me out. Any help will be appreciable.
Currently I am using a function in our application in which I am retrieving data from external web services and storing it in Salesforce database. I am calling this function in a ‘for’ loop because this is getting called multiple times based on the selection of checkboxes. At 1st time, this function is working properly but 2nd time, It's giving exception which is as follows:
ERROR: System.CalloutException: You have uncommitted work pending. Please commit or rollback before calling out.

Below is the function which is getting called multiple times:
WebService static void getContent(String id)
{
    String response = '';
    Http h = new Http();
    HttpRequest req = new HttpRequest();
    String url = 'url of the web service';
    req.setEndpoint(url);
    req.setMethod('GET');
    HttpResponse res=null;
    try {
        res= h.send(req);
    } catch(System.CalloutException e) {
    System.debug('ERROR: '+ e);
}

Thanks,
Manjiri