24.2. The Seam object
Client-side component interaction is performed with the
Seam
JavaScript object defined in remote.js
. This is used to make asynchronous calls against your component. It is split into two areas of functionality: Seam.Component
contains methods for working with components and Seam.Remoting
contains methods for executing remote requests. The easiest way to become familiar with this object is to start with a simple example.
24.2.1. A Hello World example
Procedure 24.1. Hello World Example
- To show you how the
Seam
object works, we will first create a new Seam component calledhelloAction
:@Stateless @Name("helloAction") public class HelloAction implements HelloLocal { public String sayHello(String name) { return "Hello, " + name; } }
- We will also need to create a local interface for our new component. In particular, note the
@WebRemote
annotation, as this is required to make our method accessible via remoting:@Local public interface HelloLocal { @WebRemote public String sayHello(String name); }
- This is all the server-side code we require. Next, create a new web page and import the
helloAction
component:<s:remote include="helloAction"/>
- Add a button to the page to make this an interactive user experience:
<button onclick="javascript:sayHello()">Say Hello</button>
- You will also need script that performs an action when the button is clicked:
<script type="text/javascript"> function sayHello() { var name = prompt("What is your name?"); Seam.Component.getInstance("helloAction").sayHello(name, sayHelloCallback); } function sayHelloCallback(result) { alert(result); } </script>
- Now deploy your application and browse to your page. Click the button, and enter a name when prompted. A message box will display the "Hello" message, confirming the call's success. (You can find the full source code for this Hello World example in Seam's
/examples/remoting/helloworld
directory.)
You can see from the JavaScript code listing that we have implemented two methods. The first method prompts the user for their name, and makes a remote request. Look at the following line:
Seam.Component.getInstance("helloAction").sayHello(name, sayHelloCallback);
The first section of this line (
Seam.Component.getInstance("helloAction")
) returns a proxy, or stub, for our helloAction
component. The remainder of the line (sayHello(name,sayHelloCallback);
) invokes our component methods against the stub.
The whole line invokes the
sayHello
method of our component, passing in name
as a parameter. The second parameter, sayHelloCallback
, is not a parameter of our component's sayHello
method — it tells the Seam Remoting framework that, once a response to the request is received, the response should be passed to the sayHelloCallback
JavaScript method. (This callback parameter is optional; you can leave it out if you are calling a method with a void
return type, or if the result of the request is not important.)
When the
sayHelloCallback
method receives the response to our remote request, it displays an alert message with the result of our method call.