@Retention(RUNTIME)
@Target(TYPE)
@Documented
public @interface Dispatches

Annotation that should be applied to sub-types of HttpServlet to describe the URI patterns that the servlet can dispatch. These patterns are termed Route patterns and have a specific syntax.

Basic Example

 @Dispatches(@PathTemplate("some/resource"))
 @Provides 
 class ExampleServlet extends HttpServlet { 
 
  @Inject ExampleServlet(Logger log) {
   super();
   this.log = log;
  }
  
  public void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/plain");
    response.getWriter().append("Hello World");
    response.flushBuffer();
    log.fine("Generated Resource");
  }
  
  private final Logger log;
 }

This servlet dispatches the some/resource path.
The servlet must have the Provides annotation to be discoverable. The class must extend HttpServlet directly, or directly implement the Servlet interface.

If the class does not directly extend HttpServlet or directly implement the Servlet interface, then it must express that it provides the Servlet service via the Provides annotation. For example: @Provides(HttpServlet.class) or @Provides(Servlet.class).
The servlet can express any dependencies using a Constructor annotated with the Inject annotation. This servlet injects the Log service.
The set of HTTP methods that the servlet supports is inferred by examining which of the HttpServlet methods the class overrides. This example overrides HttpServlet#doGet(HttpServletRequest,HttpServletResponse).

The override may be public or protected.

Dispatching multiple paths

 @Dispatches({@PathTemplate(name="collection", value="/some/collection/",methods={"GET","POST"),
                   @PathTemplate(name="item", value="/some/collection/:id",methods={"GET","PUT","DELETE")})
 @Provides  
 class ExampleCollectionServlet extends HttpServlet { 
 
  @Inject ExampleServlet(PathTemplates pathTemplates,Logger log) {
   super();
   this.pathTemplates = pathTemplates;
   this.log = log;
  }
  
  public void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
    final PathTemplateMatch matched = pathTemplates.matchedTemplate(request);
    switch ( matched.name() ) {
    case "collection":
     // generate resource for some/collection/ path
     ...
     log.fine("Generated Collection Resource");
     break;
    default:
     // generate resource for some/collection/:id path
     final String id = matched.parameters().get("id");
     ...
     log.fine("Generated Resource for: " +id );
    }
  }
  
  public void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
    // can only be a POST on the collection resource
    ...
  }
  
  public void doPut(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
    // can only be a PUT on an individual resource
    final String id = pathTemplates.matchedTemplate(request).parameters().get("id");
    ...
  }
  
  public void doDelete(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
    // can only be a DELETE on an individual resource
    final String id = pathTemplates.matchedTemplate(request).parameters().get("id");
    ...
  }
  
  private final Logger log;
  private final PathTemplates pathTemplates;
  
 }

A servlet can dispatch for multiple paths by specifying multiple PathTemplate annotations. This example shows a common pattern, consisting of one pattern for a collection resource, and another pattern for individual resources within the collection.
The HTTP methods that a particular pattern supports can be specified via the PathTemplate.methods() property.

In this example the collection resource supports GET for retrieving an enumeration of all resources in the collection, and POST for adding new resources to the collection.

The individual resource supports GET for retrieving the resource, PUT for updating the resource, and DELETE for removing the resource.

Dispatching custom HTTP methods

Name your handler method after the HTTP method, e.g: GET is handled by doGet(HttpServletRequest,HttpServletResponse). For example, to handle the PATCH method, define a doPatch(HttpServletRequest,HttpServletResponse) method. Note that you must override the service(HttpServletRequest,HttpServletResponse) method to cause it to dispatch to the doPatch method, as shown below:

 @Provides
 @Dispatches(@PathTemplate("/examples/custom"))
 class SupportsPatchExample extends HttpServlet {
 
   @Inject
   SupportsPathExample() {
   }
   
   protected void service(HttpServletRequest req, HttpServletResponse resp)
       throws ServletException, IOException {
     final String method = req.getMethod();
     // dispatch to doPatch() method
     if ("PATCH".equalsIgnoreCase(method)) {
       doPatch(req, resp);
     } else {
       super.service(req, resp);
     }
   }
 
   private void doPatch(HttpServletRequest req, HttpServletResponse resp)
       throws ServletException, IOException {
     // handle PATCH ...
   }
 }

Explicitly stating supported HTTP methods

As shown above, supported HTTP methods are discovered by looking for methods starting with do and taking (HttpServletRequest,HttpServletResponse) arguments.

If you prefer you can explicitly enumerate the methods that are supported via the PathTemplate.methods() property:

 @Provides
 @Dispatches(@PathTemplate(value = "/examples/explicit", methods = { "GET",
     "PATCH" }))
 class ExplicitHttpMethods extends HttpServlet {
 
   protected void service(HttpServletRequest req, HttpServletResponse resp)
       throws ServletException, IOException {
     final String method = req.getMethod();
     // dispatch to doPatch() method
     if ("PATCH".equalsIgnoreCase(method)) {
       // handle PATCH
       ...
     } else if ("GET".equalsIgnoreCase(method)) {
       // handle GET
     } else {
       super.service(req, resp);
     }
   }
 }

Author:: cdivilly
See Also:: Route Pattern Syntax

- Required Element Summary
  
  Required Elements
  Modifier and Type Required Element Description
  
  PathTemplate[] value
  Identifies the URI patterns that a type can dispatch:

Element Detail

value

PathTemplate[] value

Identifies the URI patterns that a type can dispatch:

 @Dispatches(@PathTemplate("some/collection/:id")

 @Dispatches({@PathTemplate(value="some/collection/",methods={"GET","POST"),
                 @PathTemplate(value="some/collection/:id",methods={"GET","PUT","DELETE")})

Returns:: The PathTemplates for this servlet

Annotation Type Dispatches