better example

servicetalk-examples/http/jaxrs/src/main/java/io/servicetalk/examples/http/jaxrs/HelloWorldExceptionMapper.java

@@ -21,7 +21,10 @@
 public class HelloWorldExceptionMapper implements ExceptionMapper<Throwable> {
     @Override
     public Response toResponse(final Throwable exception) {
-        exception.printStackTrace();
+        if (exception instanceof IllegalStateException) {
+            return Response.status(Response.Status.BAD_REQUEST).build();
+        }
+
         return Response.serverError().build();
     }
 }

servicetalk-examples/http/jaxrs/src/main/java/io/servicetalk/examples/http/jaxrs/HelloWorldJaxRsResource.java

@@ -145,6 +145,28 @@ public CompletionStage<String> slowHello(@DefaultValue("world") @QueryParam("who
         return delayedResponse;
     }
 
+    /**
+     * Resource that uses Java's CompletionStage to produce an error response.
+     * Note that the {@link ConnectionContext} could also be injected into a class-level {@code @Context} field.
+     * <p>
+     * Test with:
+     * <pre>
+     * curl -v http://localhost:8080/greetings/error-hello
+     * curl -v http://localhost:8080/greetings/error-hello?mapped=false
+     * </pre>
+     *
+     * @param mapped whether the exception is mapped or not.
+     * @param ctx the {@link ConnectionContext}.
+     * @return future greetings as a {@link CompletionStage} of {@link String}.
+     */
+    @GET
+    @Path("error-hello")
+    @Produces(TEXT_PLAIN)
+    public CompletionStage<String> errorHello(@DefaultValue("true") @QueryParam("mapped") final boolean mapped,
+                                              @Context final ConnectionContext ctx) {
+        return CompletableFuture.failedFuture(mapped ? new IllegalStateException() : new Exception());
+    }
+
     /**
      * Resource that only relies on {@link Single}s for consuming and producing data, and operators for processing it.
      * No OIO adaptation is involved when requests are dispatched to it,