Getting parameter values

Introduction

This is a common need to retrieve data, especially "key=value" pairs from the query, the entity, or the cookies.
Here are some sample lines of code wich illustrate this feature.

Getting values from a web form

The web form is in fact the entity of the POST request sent to the server, thus you have access to it via request.getEntity().
There is a shortcut which allows to have a list of all input fields :

Form form = request.getEntityAsForm();
for (Parameter parameter : form) {
  System.out.print("parameter " + parameter.getName());
  System.out.println("/" + parameter.getValue());
}

Getting values from a query

The query is a part of the identifier (the URI) of the request resource. Thus, you have access to it via request.getResourceRef().getQuery().
There is a shortcut which allows to have a list of all "key=value" pairs :
Form form = request.getResourceRef().getQueryAsForm();
for (Parameter parameter : form) {
  System.out.print("parameter " + parameter.getName());
  System.out.println("/" + parameter.getValue());
}

Getting values from the cookies

Cookies are directly available from the request via the request.getCookies() method. It returns a collection of "Cookie" objects which extends the Parameter class and contains additional attributes:

for (Cookie cookie : request.getCookies()) {
    System.out.println("name = " + cookie.getName());
    System.out.println("value = " + cookie.getValue());
    System.out.println("domain = " + cookie.getDomain());
    System.out.println("path = " + cookie.getPath());
    System.out.println("version = " + cookie.getVersion());
}

Extracting values from query, entity, cookies into the request's attributes

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 createRoot() {
     Router router = new Router(getContext());
     Route route = router.attachDefault(MyResource.class);
     route.extractEntity("selectAttribute", "selectField", true);
     route.extractEntity("textAttribute", "textField", false);
     return router;
}

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());
        }
    }
}