Annotation Type Dispatches
-
@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 extendHttpServlet
directly, or directly implement theServlet
interface.If the class does not directly extend
HttpServlet
or directly implement theServlet
interface, then it must express that it provides theServlet
service via theProvides
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 theLog
service. -
The set of HTTP methods that the servlet supports is inferred by examining which of the
HttpServlet
methods the class overrides. This example overridesHttpServlet#doGet(HttpServletRequest,HttpServletResponse)
.The override may be
public
orprotected
.
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 bydoGet(HttpServletRequest,HttpServletResponse)
. For example, to handle thePATCH
method, define adoPatch(HttpServletRequest,HttpServletResponse)
method. Note that you must override theservice(HttpServletRequest,HttpServletResponse)
method to cause it to dispatch to thedoPatch
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
- This servlet dispatches the
-
-
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
PathTemplate
s for this servlet
-
-