how to call rest apex class "AdobeConnectEvents from "CommandButtonParamController " class for passing the details.

<apex:page standardController="LightiningEd__Login__c"
           extensions="CommandButtonParamController">
<apex:form >
<apex:pageBlock title="Login To Adobe">
   <apex:pageBlockSection >
       <apex:inputField value="{!LightiningEd__Login__c.LightiningEd__Username__c}"/><br/>
       <apex:inputField value="{!LightiningEd__Login__c.LightiningEd__Password__c}"/><br/>
       <apex:inputField value="{!LightiningEd__Login__c.LightiningEd__URL__c}"/>
   </apex:pageBlockSection>

      <center>
         <apex:commandButton id="saveBtn" value="Login" action="{!processButtonClick}" />
              <apex:param name="username" value="{!LightiningEd__Login__c.LightiningEd__Username__c}" assignTo="{!username}"/>
              <apex:param name="password" value="{!LightiningEd__Login__c.LightiningEd__Password__c}" assignTo="{!password}"/>
              <apex:param name = "url" value="{!LightiningEd__Login__c.LightiningEd__URL__c}" assignTo="{!url}"/>
      </center><br/>
</apex:pageBlock>
</apex:form>

private ApexPages.StandardController controller {get; set;}
private LightiningEd__Login__c login {get;set;}
public String username{
    get;

    set {
        username= value;
        System.debug('value: '+value);
    }
}
  public String password{
    get;

    set {
        password= value;
        System.debug('value: '+value);
    }
}
  public String url{
    get;

    set {
        url= value;
        System.debug('value: '+value);
    }
}

public CommandButtonParamController(ApexPages.StandardController controller) {
    this.controller = controller;
    this.login= (LightiningEd__Login__c)controller.getRecord();

}

public PageReference processButtonClick() {
    System.debug('username: '+username);
    System.debug('password: '+username);
    System.debug('url: '+username);
    PageReference pageref = new PageReference('/apex/Display_All_Webinars');

    return pageref;
}

@future (callout=true)
global static void getParticipants(String username, String password,String url){

    Http http = new Http();
    HttpRequest req =  new HttpRequest();
    HttpResponse res =  new HttpResponse();
    Blob headerValue = Blob.valueOf(username + ':' + password);
    String authorizationHeader = 'BASIC ' +
    EncodingUtil.base64Encode(headerValue);
    req.setHeader('Authorization', authorizationHeader);
    req.setEndpoint(url+'/api/xml?action=report-my-events&account-id=1309160790&&session=apac1breezdhqaxms9bksbrsmt');
    req.setMethod('GET');
    req.setHeader('Content-Type', 'application/json');
    req.setHeader('Accept','application/json');
    try {
        res = http.send(req);
        System.debug('MyResult == :'+res.getBody());
        XMLParserCopy s = new XMLParserCopy(res.getBody());
        System.debug('Response value'+s);

    }catch(System.CalloutException e){
           System.debug('Callout error: '+ e);
}//return res;