Sure. Thanks for responding. This is the method which i am trying to call from my Custom class. Its part of class AWS_S3_ExampleController which gets installed with AWS S3 toolkit on SalesForce.

Its not necessary i use this. I need any solution which allows me to read a csv file into a String. The conversion to blob is easy enough. I do not want a UI solution as my custom class does not have a UI

    /*
        This method uploads a file from the filesystem and puts it in S3.
        It also supports setting the Access Control policy.
    */
    public pageReference syncFilesystemDoc(){
        try{  
          Datetime now = Datetime.now();
          
          String docBody = EncodingUtil.base64Encode(fileBlob);
          
          //TODO - make sure doc.bodyLength is not greater than 100000 to avoid apex limits
          System.debug('body length: ' + fileSize);
          uploadObjectErrorMsg = 'Error';
          Boolean putObjResult = as3.PutObjectInline_ACL(bucketToUploadObject,fileName,null,docBody,fileSize,accessTypeSelected,as3.key,now,as3.signature('PutObjectInline',now),as3.secret, OwnerId);
          if(putObjResult==true){
                System.debug('putobjectinline successful');
                uploadObjectErrorMsg = 'Success';
          }
          
      
          }catch(System.CalloutException callout){
          System.debug('CALLOUT EXCEPTION: ' + callout);
          uploadObjectErrorMsg =     callout.getMessage();
     
        }catch(Exception ex){
            System.debug('EXCEPTION: ' + ex);
            uploadObjectErrorMsg =     ex.getMessage();
        }
       
      return null;    
    }