Extracting attributes

Introduction

Extracting values from query, entity, cookies into the request’s attributesis a common need that is supported by the Extractor class.

When routing URIs to Resource instances or Restlet, you can decide to transfer data from query, entity or cookies into the request’s list of attributes.
This mechanism is declarative and has been implemented at the level of the “routes” (see the code below for more information). This mechanism transfers data from the query (method “extractQuery”), the entity (method “extractEntity”) or the Cookies (method “extractCookies”) to the request’s list of parameters.

For example, when implementing your Application, assuming that the posted web form contains a select input field (called “selectField”) and a text field ( called “textField”). If you want to transfer them respectively to attributes named “selectAttribute” and “textAttribute”, just proceed as follow.

@Override
public Restlet createInboundRoot() {
     Extractor extractor = new Extractor(getContext()); 
     extractor.extractFromEntity("selectAttribute", "selectField", true);
     extractor.extractFromEntity("textAttribute", "textField", false);

     extractor.setNext(...)

     return extractor;
}

You will get a String value in the “selectAttribute” (the selected option), and a Form object which is a collection of key/value pairs (key=”textField” in this case) with the “textAttribute” attribute.

Here is sample code which helps to retrieve some attributes:

// Get the map of request attributes
Map<String, Object> map = request.getAttributes();

// Retrieve the "selectAttribute" value
String stringValue = (String) map.get("selectAttribute");
System.out.println(" value => " + stringValue);

// Retrieve the "textAttribute" collection of parameters
Object object = map.get("textAttribute");
if(object != null){
    if(object instanceof Form){
        Form form = (Form) object;
        for (Parameter parameter : form) {
            System.out.print("parameter " + parameter.getName());
            System.out.println("/ " + parameter.getValue());
        }
    }
}