Salesforce To dropbox file upload

Hello All,

I am trying to upload a file from salesforce to Dropbox.

I have created a class in salesforce as per suggestions from the internet.

My code is:

public class dropBoxApi{
Public String code ;
Public String accesstoken;
public String fileBody{get;set;}


public dropBoxApi()
{
code = ApexPages.currentPage().getParameters().get('code') ;
System.debug('Code='+code);
if(code != '' && code != null)
{
AccessToken() ;
}
}

public PageReference DropAuth()
{

system.debug('UPLOAD'+accessToken );
//Authenticating
PageReference pg = new PageReference('https://www.dropbox.com/1/oauth2/authorize?response_type=code&client_id={clientId}&redirect_uri=https://c.na46.visual.force.com/apex/DropBoxPage&state=Mytesting') ;

return null;
}

public void AccessToken()
{
//Getting access token from dropbox


String appKey='************';
String appSecreatKey='**********';
String tokenuri = 'https://api.dropbox.com/oauth2/token?grant_type=authorization_code&code='+code+'&redirect_uri=https://c.na46.visual.force.com/apex/DropBoxPage';
//https://api.dropbox.com/1/oauth2/token?grant_type=authorization_code&code='+code+'&redirect_uri=https://c.ap1.visual.force.com/apex/DropboxPage';
HttpRequest req = new HttpRequest();
req.setEndpoint(tokenuri);
req.setMethod('POST');
req.setTimeout(60*1000);

Blob headerValue = Blob.valueOf('{appKey}' + ':' + '{appSecreatKey}');
String authorizationHeader = 'BASIC ' + EncodingUtil.base64Encode(headerValue);
req.setHeader('Authorization', authorizationHeader);
Http h = new Http();
String resp;
HttpResponse res = h.send(req);
resp = res.getBody();
System.debug('response='+resp);
JSONParser parser = JSON.createParser(resp);
while (parser.nextToken() != null) {
if ((parser.getCurrentToken() == JSONToken.FIELD_NAME)){
String fieldName = parser.getText();
parser.nextToken();
if(fieldName == 'access_token') {
accesstoken = parser.getText();
System.debug('accesstoken='+accesstoken);
}
}
}
system.debug('accessToken:'+accessToken );
System.debug(' You can parse the response to get the access token ::: ' + resp);

}
}

can anybody tell me what is 'code' value at line 

code = ApexPages.currentPage().getParameters().get('code') ;

Help is highly appreciated.