Fix exception handler lookup logic (#90)

* Fix exception handler lookup logic. Fixes #88

* Fix tests

http-server-jetty/src/test/groovy/io/micronaut/servlet/jetty/JettyExceptionHandlerSpec.groovy

@@ -0,0 +1,81 @@
+package io.micronaut.servlet.jetty
+
+import groovy.transform.InheritConstructors
+import io.micronaut.context.annotation.Property
+import io.micronaut.context.annotation.Requires
+import io.micronaut.http.HttpRequest
+import io.micronaut.http.HttpResponse
+import io.micronaut.http.HttpStatus
+import io.micronaut.http.MutableHttpResponse
+import io.micronaut.http.annotation.Controller
+import io.micronaut.http.annotation.Get
+import io.micronaut.http.client.HttpClient
+import io.micronaut.http.client.annotation.Client
+import io.micronaut.http.client.exceptions.HttpClientResponseException
+import io.micronaut.http.server.exceptions.ExceptionHandler
+import io.micronaut.test.extensions.spock.annotation.MicronautTest
+import spock.lang.Specification
+
+import javax.inject.Inject
+import javax.inject.Singleton
+
+@MicronautTest
+@Property(name = "spec.name", value = "JettyExceptionHandlerSpec")
+class JettyExceptionHandlerSpec extends Specification {
+
+    @Inject
+    @Client("/")
+    HttpClient client
+
+    void "test an exception handler for mutable request works"() {
+        when:
+        def resp = client.toBlocking().exchange("/exception")
+
+        then:
+        resp.status() == HttpStatus.OK
+    }
+
+    void "test an exception handler returning the body"() {
+        when:
+        client.toBlocking().retrieve("/exception/my")
+
+        then:
+        def ex = thrown(HttpClientResponseException)
+        ex.response.status() == HttpStatus.INTERNAL_SERVER_ERROR
+        ex.response.getBody().get() == "hello"
+    }
+
+    @Controller("/exception")
+    static class ExceptionController {
+
+        @Get
+        void throwsEx() {
+            throw new RuntimeException("bad")
+        }
+
+        @Get("/my")
+        void throwsMy() {
+            throw new MyException("bad")
+        }
+    }
+
+    @Singleton
+    static class MyExceptionHandler implements ExceptionHandler<MyException, String> {
+        @Override
+        String handle(HttpRequest request, MyException exception) {
+            "hello"
+        }
+    }
+
+    @Singleton
+    @Requires(property = "spec.name", value = "JettyExceptionHandlerSpec")
+    static class RuntimeExceptionHandler implements ExceptionHandler<RuntimeException, MutableHttpResponse<?>> {
+        @Override
+        MutableHttpResponse<?> handle(HttpRequest request, RuntimeException exception) {
+            return HttpResponse.ok()
+        }
+    }
+
+    @InheritConstructors
+    static class MyException extends Exception {}
+}

servlet-core/src/main/java/io/micronaut/servlet/http/ServletHttpHandler.java

@@ -825,7 +825,7 @@ private JsonError newJsonError(HttpRequest<Object> req, String message) {
     @SuppressWarnings("unchecked")
     private ExceptionHandler<Throwable, ?> lookupExceptionHandler(Throwable e) {
         final Class<? extends Throwable> type = e.getClass();
-        return applicationContext.findBean(ExceptionHandler.class, Qualifiers.byTypeArgumentsClosest(type, HttpResponse.class))
+        return applicationContext.findBean(ExceptionHandler.class, Qualifiers.byTypeArgumentsClosest(type, Object.class))
                 .orElse(null);
     }