Example with jax-rs error mapper (#2742)

Motivation:

Add an example of how error mapping can be done with jax-rs to help users debug development and/or not issues.

Results:

Better example base

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

@@ -0,0 +1,30 @@
+/*
+ * Copyright © 2023 Apple Inc. and the ServiceTalk project authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.servicetalk.examples.http.jaxrs;
+
+import javax.ws.rs.core.Response;
+import javax.ws.rs.ext.ExceptionMapper;
+
+public class HelloWorldExceptionMapper implements ExceptionMapper<Throwable> {
+    @Override
+    public Response toResponse(final Throwable exception) {
+        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/HelloWorldJaxRsApplication.java

@@ -31,7 +31,8 @@ public final class HelloWorldJaxRsApplication extends Application {
     public Set<Class<?>> getClasses() {
         return new HashSet<>(asList(
                 MultiPartFeature.class,
-                HelloWorldJaxRsResource.class
+                HelloWorldJaxRsResource.class,
+                HelloWorldExceptionMapper.class
             )
         );
     }

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 Single.<String>failed(mapped ? new IllegalStateException() : new Exception()).toCompletionStage();
+    }
+
     /**
      * 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,