Simplify command/query bus

rgomezcasas · rgomezcasas · commit 4fba49403fa3 · 2019-12-23T18:57:49.000+01:00
diff --git a/apps/main/tv/codely/apps/backoffice/backend/controller/courses/CoursesGetController.java b/apps/main/tv/codely/apps/backoffice/backend/controller/courses/CoursesGetController.java
@@ -8,7 +8,6 @@
 import tv.codely.shared.domain.bus.command.CommandBus;
 import tv.codely.shared.domain.bus.query.QueryBus;
 import tv.codely.shared.domain.bus.query.QueryHandlerExecutionError;
-import tv.codely.shared.domain.bus.query.QueryNotRegisteredError;
 import tv.codely.shared.infrastructure.spring.ApiController;
 
 import java.io.Serializable;
@@ -28,7 +27,7 @@ public CoursesGetController(QueryBus queryBus, CommandBus commandBus) {
     @GetMapping("/courses")
     public List<HashMap<String, String>> index(
         @RequestParam HashMap<String, Serializable> params
-    ) throws QueryNotRegisteredError, QueryHandlerExecutionError {
+    ) throws QueryHandlerExecutionError {
         BackofficeCoursesResponse courses = ask(
             new SearchBackofficeCoursesByCriteriaQuery(
                 parseFilters(params),
diff --git a/apps/main/tv/codely/apps/backoffice/backend/middleware/BasicHttpAuthMiddleware.java b/apps/main/tv/codely/apps/backoffice/backend/middleware/BasicHttpAuthMiddleware.java
@@ -5,7 +5,6 @@
 import tv.codely.backoffice.auth.domain.InvalidAuthUsername;
 import tv.codely.shared.domain.bus.command.CommandBus;
 import tv.codely.shared.domain.bus.command.CommandHandlerExecutionError;
-import tv.codely.shared.domain.bus.command.CommandNotRegisteredError;
 
 import javax.servlet.*;
 import javax.servlet.http.HttpServletRequest;
@@ -55,7 +54,7 @@ private void authenticate(
             request.setAttribute("authentication_username", user);
 
             chain.doFilter(request, response);
-        } catch (InvalidAuthUsername | InvalidAuthCredentials | CommandHandlerExecutionError | CommandNotRegisteredError error) {
+        } catch (InvalidAuthUsername | InvalidAuthCredentials | CommandHandlerExecutionError error) {
             setInvalidCredentials(response);
         }
     }
diff --git a/apps/main/tv/codely/apps/backoffice/frontend/controller/courses/CoursesGetWebController.java b/apps/main/tv/codely/apps/backoffice/frontend/controller/courses/CoursesGetWebController.java
@@ -8,7 +8,6 @@
 import tv.codely.mooc.courses_counter.application.find.FindCoursesCounterQuery;
 import tv.codely.shared.domain.bus.query.QueryBus;
 import tv.codely.shared.domain.bus.query.QueryHandlerExecutionError;
-import tv.codely.shared.domain.bus.query.QueryNotRegisteredError;
 
 import java.io.Serializable;
 import java.util.HashMap;
@@ -27,7 +26,7 @@ public CoursesGetWebController(QueryBus bus) {
     public ModelAndView index(
         @ModelAttribute("inputs") HashMap<String, Serializable> inputs,
         @ModelAttribute("errors") HashMap<String, List<String>> errors
-    ) throws QueryNotRegisteredError, QueryHandlerExecutionError {
+    ) throws QueryHandlerExecutionError {
         CoursesCounterResponse counterResponse = bus.ask(new FindCoursesCounterQuery());
 
         return new ModelAndView("pages/courses/courses", new HashMap<String, Serializable>() {{
diff --git a/apps/main/tv/codely/apps/backoffice/frontend/controller/courses/CoursesPostWebController.java b/apps/main/tv/codely/apps/backoffice/frontend/controller/courses/CoursesPostWebController.java
@@ -9,7 +9,6 @@
 import tv.codely.mooc.courses.application.create.CreateCourseCommand;
 import tv.codely.shared.domain.bus.command.CommandBus;
 import tv.codely.shared.domain.bus.command.CommandHandlerExecutionError;
-import tv.codely.shared.domain.bus.command.CommandNotRegisteredError;
 import tv.codely.shared.infrastructure.validation.ValidationResponse;
 import tv.codely.shared.infrastructure.validation.Validator;
 
@@ -33,7 +32,7 @@ public CoursesPostWebController(CommandBus bus) {
     public RedirectView index(
         @RequestParam HashMap<String, Serializable> request,
         RedirectAttributes attributes
-    ) throws Exception, CommandHandlerExecutionError {
+    ) throws Exception {
         ValidationResponse validationResponse = Validator.validate(request, rules);
 
         return validationResponse.hasErrors()
@@ -52,7 +51,7 @@ private RedirectView redirectWithErrors(
         return new RedirectView("/courses");
     }
 
-    private RedirectView createCourse(HashMap<String, Serializable> request) throws CommandNotRegisteredError, CommandHandlerExecutionError {
+    private RedirectView createCourse(HashMap<String, Serializable> request) throws CommandHandlerExecutionError {
         bus.dispatch(new CreateCourseCommand(
             request.get("id").toString(),
             request.get("name").toString(),
diff --git a/apps/main/tv/codely/apps/mooc/backend/controller/courses/CourseGetController.java b/apps/main/tv/codely/apps/mooc/backend/controller/courses/CourseGetController.java
@@ -7,11 +7,11 @@
 import org.springframework.web.bind.annotation.RestController;
 import tv.codely.mooc.courses.application.CourseResponse;
 import tv.codely.mooc.courses.application.find.FindCourseQuery;
+import tv.codely.mooc.courses.domain.CourseNotExist;
 import tv.codely.shared.domain.DomainError;
 import tv.codely.shared.domain.bus.command.CommandBus;
 import tv.codely.shared.domain.bus.query.QueryBus;
 import tv.codely.shared.domain.bus.query.QueryHandlerExecutionError;
-import tv.codely.shared.domain.bus.query.QueryNotRegisteredError;
 import tv.codely.shared.infrastructure.spring.ApiController;
 
 import java.io.Serializable;
@@ -27,7 +27,7 @@ public CourseGetController(
     }
 
     @GetMapping("/courses/{id}")
-    public ResponseEntity<HashMap<String, Serializable>> index(@PathVariable String id) throws QueryHandlerExecutionError, QueryNotRegisteredError {
+    public ResponseEntity<HashMap<String, Serializable>> index(@PathVariable String id) throws QueryHandlerExecutionError {
         CourseResponse course = ask(new FindCourseQuery(id));
 
         return ResponseEntity.ok().body(new HashMap<String, Serializable>() {{
@@ -39,6 +39,8 @@ public ResponseEntity<HashMap<String, Serializable>> index(@PathVariable String
 
     @Override
     protected HashMap<Class<? extends DomainError>, HttpStatus> errorMapping() {
-        return null;
+        return new HashMap<Class<? extends DomainError>, HttpStatus>() {{
+            put(CourseNotExist.class, HttpStatus.NOT_FOUND);
+        }};
     }
 }
diff --git a/apps/main/tv/codely/apps/mooc/backend/controller/courses/CoursesPutController.java b/apps/main/tv/codely/apps/mooc/backend/controller/courses/CoursesPutController.java
@@ -10,7 +10,6 @@
 import tv.codely.shared.domain.DomainError;
 import tv.codely.shared.domain.bus.command.CommandBus;
 import tv.codely.shared.domain.bus.command.CommandHandlerExecutionError;
-import tv.codely.shared.domain.bus.command.CommandNotRegisteredError;
 import tv.codely.shared.domain.bus.query.QueryBus;
 import tv.codely.shared.infrastructure.spring.ApiController;
 
@@ -29,7 +28,7 @@ public CoursesPutController(
     public ResponseEntity<String> index(
         @PathVariable String id,
         @RequestBody Request request
-    ) throws CommandNotRegisteredError, CommandHandlerExecutionError {
+    ) throws CommandHandlerExecutionError {
         dispatch(new CreateCourseCommand(id, request.name(), request.duration()));
 
         return new ResponseEntity<>(HttpStatus.CREATED);
diff --git a/apps/main/tv/codely/apps/mooc/backend/controller/courses_counter/CoursesCounterGetController.java b/apps/main/tv/codely/apps/mooc/backend/controller/courses_counter/CoursesCounterGetController.java
@@ -9,7 +9,6 @@
 import tv.codely.shared.domain.bus.command.CommandBus;
 import tv.codely.shared.domain.bus.query.QueryBus;
 import tv.codely.shared.domain.bus.query.QueryHandlerExecutionError;
-import tv.codely.shared.domain.bus.query.QueryNotRegisteredError;
 import tv.codely.shared.infrastructure.spring.ApiController;
 
 import java.util.HashMap;
@@ -21,7 +20,7 @@ public CoursesCounterGetController(QueryBus queryBus, CommandBus commandBus) {
     }
 
     @GetMapping("/courses-counter")
-    public HashMap<String, Integer> index() throws QueryNotRegisteredError, QueryHandlerExecutionError {
+    public HashMap<String, Integer> index() throws QueryHandlerExecutionError {
         CoursesCounterResponse response = ask(new FindCoursesCounterQuery());
 
         return new HashMap<String, Integer>() {{
diff --git a/apps/main/tv/codely/apps/mooc/backend/controller/notifications/NewsletterNotificationPutController.java b/apps/main/tv/codely/apps/mooc/backend/controller/notifications/NewsletterNotificationPutController.java
@@ -27,7 +27,7 @@ public NewsletterNotificationPutController(
     @PutMapping(value = "/newsletter/{id}")
     public ResponseEntity<String> index(
         @PathVariable String id
-    ) throws CommandNotRegisteredError, CommandHandlerExecutionError {
+    ) throws CommandHandlerExecutionError {
         dispatch(new SendNewCoursesNewsletterCommand(id));
 
         return new ResponseEntity<>(HttpStatus.CREATED);
diff --git a/src/mooc/main/tv/codely/mooc/courses/application/find/FindCourseQueryHandler.java b/src/mooc/main/tv/codely/mooc/courses/application/find/FindCourseQueryHandler.java
@@ -15,11 +15,7 @@ public FindCourseQueryHandler(CourseFinder finder) {
     }
 
     @Override
-    public CourseResponse handle(FindCourseQuery query) {
-        try {
-            return finder.find(new CourseId(query.id()));
-        } catch (CourseNotExist error) {
-            return null;
-        }
+    public CourseResponse handle(FindCourseQuery query) throws CourseNotExist {
+        return finder.find(new CourseId(query.id()));
     }
 }
diff --git a/src/mooc/main/tv/codely/mooc/notifications/application/send_new_courses_newsletter/NewCoursesNewsletterSender.java b/src/mooc/main/tv/codely/mooc/notifications/application/send_new_courses_newsletter/NewCoursesNewsletterSender.java
@@ -11,8 +11,6 @@
 import tv.codely.shared.domain.UuidGenerator;
 import tv.codely.shared.domain.bus.event.EventBus;
 import tv.codely.shared.domain.bus.query.QueryBus;
-import tv.codely.shared.domain.bus.query.QueryHandlerExecutionError;
-import tv.codely.shared.domain.bus.query.QueryNotRegisteredError;
 
 @Service
 public final class NewCoursesNewsletterSender {
@@ -34,7 +32,7 @@ public NewCoursesNewsletterSender(
         this.eventBus      = eventBus;
     }
 
-    public void send() throws QueryNotRegisteredError, QueryHandlerExecutionError {
+    public void send() {
         CoursesResponse courses = queryBus.ask(new SearchLastCoursesQuery(TOTAL_COURSES));
 
         if (courses.courses().size() > 0) {
diff --git a/src/mooc/main/tv/codely/mooc/notifications/application/send_new_courses_newsletter/SendNewCoursesNewsletterCommandHandler.java b/src/mooc/main/tv/codely/mooc/notifications/application/send_new_courses_newsletter/SendNewCoursesNewsletterCommandHandler.java
@@ -2,7 +2,6 @@
 
 import tv.codely.shared.domain.Service;
 import tv.codely.shared.domain.bus.command.CommandHandler;
-import tv.codely.shared.domain.bus.command.CommandHandlerExecutionError;
 
 @Service
 public final class SendNewCoursesNewsletterCommandHandler implements CommandHandler<SendNewCoursesNewsletterCommand> {
@@ -13,11 +12,7 @@ public SendNewCoursesNewsletterCommandHandler(NewCoursesNewsletterSender sender)
     }
 
     @Override
-    public void handle(SendNewCoursesNewsletterCommand command) throws CommandHandlerExecutionError {
-        try {
-            sender.send();
-        } catch (Throwable error) {
-            throw new CommandHandlerExecutionError(error);
-        }
+    public void handle(SendNewCoursesNewsletterCommand command) {
+        sender.send();
     }
 }
diff --git a/src/mooc/test/tv/codely/mooc/notifications/application/send_new_courses_newsletter/SendNewCoursesNewsletterCommandHandlerShould.java b/src/mooc/test/tv/codely/mooc/notifications/application/send_new_courses_newsletter/SendNewCoursesNewsletterCommandHandlerShould.java
@@ -19,7 +19,6 @@
 import tv.codely.mooc.students.application.search_all.SearchAllStudentsQueryMother;
 import tv.codely.shared.domain.bus.command.CommandHandlerExecutionError;
 import tv.codely.shared.domain.bus.query.QueryHandlerExecutionError;
-import tv.codely.shared.domain.bus.query.QueryNotRegisteredError;
 
 import java.util.Arrays;
 
@@ -36,7 +35,7 @@ protected void setUp() {
     }
 
     @Test
-    void not_send_the_newsletter_when_there_are_no_courses() throws QueryNotRegisteredError, QueryHandlerExecutionError, CommandHandlerExecutionError {
+    void not_send_the_newsletter_when_there_are_no_courses() throws QueryHandlerExecutionError, CommandHandlerExecutionError {
         SendNewCoursesNewsletterCommand command = SendNewCoursesNewsletterCommandMother.random();
 
         SearchLastCoursesQuery coursesQuery    = SearchLastCoursesQueryMother.create(3);
@@ -48,7 +47,7 @@ void not_send_the_newsletter_when_there_are_no_courses() throws QueryNotRegister
     }
 
     @Test
-    void not_send_the_newsletter_when_there_are_no_students() throws QueryNotRegisteredError, QueryHandlerExecutionError, CommandHandlerExecutionError {
+    void not_send_the_newsletter_when_there_are_no_students() throws QueryHandlerExecutionError, CommandHandlerExecutionError {
         SendNewCoursesNewsletterCommand command = SendNewCoursesNewsletterCommandMother.random();
 
         SearchLastCoursesQuery coursesQuery    = SearchLastCoursesQueryMother.create(3);
@@ -64,7 +63,7 @@ void not_send_the_newsletter_when_there_are_no_students() throws QueryNotRegiste
     }
 
     @Test
-    void send_the_new_courses_newsletter() throws QueryNotRegisteredError, QueryHandlerExecutionError, CommandHandlerExecutionError {
+    void send_the_new_courses_newsletter() throws QueryHandlerExecutionError, CommandHandlerExecutionError {
         SendNewCoursesNewsletterCommand command = SendNewCoursesNewsletterCommandMother.random();
 
         SearchLastCoursesQuery coursesQuery    = SearchLastCoursesQueryMother.create(3);
diff --git a/src/shared/main/tv/codely/shared/domain/DomainError.java b/src/shared/main/tv/codely/shared/domain/DomainError.java
@@ -1,6 +1,6 @@
 package tv.codely.shared.domain;
 
-public abstract class DomainError extends Throwable {
+public abstract class DomainError extends RuntimeException {
     private final String errorCode;
     private final String errorMessage;
 
@@ -11,11 +11,11 @@ public DomainError(String errorCode, String errorMessage) {
         this.errorMessage = errorMessage;
     }
 
-    public String getErrorCode() {
+    public String errorCode() {
         return errorCode;
     }
 
-    public String getErrorMessage() {
+    public String errorMessage() {
         return errorMessage;
     }
 }
diff --git a/src/shared/main/tv/codely/shared/domain/bus/command/CommandBus.java b/src/shared/main/tv/codely/shared/domain/bus/command/CommandBus.java
@@ -1,5 +1,5 @@
 package tv.codely.shared.domain.bus.command;
 
 public interface CommandBus {
-    void dispatch(Command command) throws CommandNotRegisteredError, CommandHandlerExecutionError;
+    void dispatch(Command command) throws CommandHandlerExecutionError;
 }
diff --git a/src/shared/main/tv/codely/shared/domain/bus/command/CommandHandler.java b/src/shared/main/tv/codely/shared/domain/bus/command/CommandHandler.java
@@ -1,5 +1,5 @@
 package tv.codely.shared.domain.bus.command;
 
 public interface CommandHandler<T extends Command> {
-    void handle(T command) throws CommandHandlerExecutionError;
+    void handle(T command);
 }
diff --git a/src/shared/main/tv/codely/shared/domain/bus/command/CommandHandlerExecutionError.java b/src/shared/main/tv/codely/shared/domain/bus/command/CommandHandlerExecutionError.java
@@ -1,6 +1,6 @@
 package tv.codely.shared.domain.bus.command;
 
-public final class CommandHandlerExecutionError extends Throwable {
+public final class CommandHandlerExecutionError extends RuntimeException {
     public CommandHandlerExecutionError(Throwable cause) {
         super(cause);
     }
diff --git a/src/shared/main/tv/codely/shared/domain/bus/query/QueryBus.java b/src/shared/main/tv/codely/shared/domain/bus/query/QueryBus.java
@@ -1,5 +1,5 @@
 package tv.codely.shared.domain.bus.query;
 
 public interface QueryBus {
-    <R> R ask(Query query) throws QueryNotRegisteredError, QueryHandlerExecutionError;
+    <R> R ask(Query query) throws QueryHandlerExecutionError;
 }
diff --git a/src/shared/main/tv/codely/shared/domain/bus/query/QueryHandler.java b/src/shared/main/tv/codely/shared/domain/bus/query/QueryHandler.java
@@ -1,5 +1,5 @@
 package tv.codely.shared.domain.bus.query;
 
 public interface QueryHandler<Q extends Query, R extends Response> {
-    R handle(Q query) throws QueryHandlerExecutionError;
+    R handle(Q query);
 }
diff --git a/src/shared/main/tv/codely/shared/domain/bus/query/QueryHandlerExecutionError.java b/src/shared/main/tv/codely/shared/domain/bus/query/QueryHandlerExecutionError.java
@@ -1,6 +1,6 @@
 package tv.codely.shared.domain.bus.query;
 
-public final class QueryHandlerExecutionError extends Throwable {
+public final class QueryHandlerExecutionError extends RuntimeException {
     public QueryHandlerExecutionError(Throwable cause) {
         super(cause);
     }
diff --git a/src/shared/main/tv/codely/shared/infrastructure/bus/command/InMemoryCommandBus.java b/src/shared/main/tv/codely/shared/infrastructure/bus/command/InMemoryCommandBus.java
@@ -2,7 +2,10 @@
 
 import org.springframework.context.ApplicationContext;
 import tv.codely.shared.domain.Service;
-import tv.codely.shared.domain.bus.command.*;
+import tv.codely.shared.domain.bus.command.Command;
+import tv.codely.shared.domain.bus.command.CommandBus;
+import tv.codely.shared.domain.bus.command.CommandHandler;
+import tv.codely.shared.domain.bus.command.CommandHandlerExecutionError;
 
 @Service
 public final class InMemoryCommandBus implements CommandBus {
@@ -15,11 +18,15 @@ public InMemoryCommandBus(CommandHandlersInformation information, ApplicationCon
     }
 
     @Override
-    public void dispatch(Command command) throws CommandNotRegisteredError, CommandHandlerExecutionError {
-        Class<? extends CommandHandler> commandHandlerClass = information.search(command.getClass());
+    public void dispatch(Command command) throws CommandHandlerExecutionError {
+        try {
+            Class<? extends CommandHandler> commandHandlerClass = information.search(command.getClass());
 
-        CommandHandler handler = context.getBean(commandHandlerClass);
+            CommandHandler handler = context.getBean(commandHandlerClass);
 
-        handler.handle(command);
+            handler.handle(command);
+        } catch (Throwable error) {
+            throw new CommandHandlerExecutionError(error);
+        }
     }
 }
diff --git a/src/shared/main/tv/codely/shared/infrastructure/bus/query/InMemoryQueryBus.java b/src/shared/main/tv/codely/shared/infrastructure/bus/query/InMemoryQueryBus.java
@@ -15,11 +15,15 @@ public InMemoryQueryBus(QueryHandlersInformation information, ApplicationContext
     }
 
     @Override
-    public Response ask(Query query) throws QueryNotRegisteredError, QueryHandlerExecutionError {
-        Class<? extends QueryHandler> queryHandlerClass = information.search(query.getClass());
+    public Response ask(Query query) throws QueryHandlerExecutionError {
+        try {
+            Class<? extends QueryHandler> queryHandlerClass = information.search(query.getClass());
 
-        QueryHandler handler = context.getBean(queryHandlerClass);
+            QueryHandler handler = context.getBean(queryHandlerClass);
 
-        return handler.handle(query);
+            return handler.handle(query);
+        } catch (Throwable error) {
+            throw new QueryHandlerExecutionError(error);
+        }
     }
 }
diff --git a/src/shared/main/tv/codely/shared/infrastructure/spring/ApiController.java b/src/shared/main/tv/codely/shared/infrastructure/spring/ApiController.java
@@ -5,11 +5,9 @@
 import tv.codely.shared.domain.bus.command.Command;
 import tv.codely.shared.domain.bus.command.CommandBus;
 import tv.codely.shared.domain.bus.command.CommandHandlerExecutionError;
-import tv.codely.shared.domain.bus.command.CommandNotRegisteredError;
 import tv.codely.shared.domain.bus.query.Query;
 import tv.codely.shared.domain.bus.query.QueryBus;
 import tv.codely.shared.domain.bus.query.QueryHandlerExecutionError;
-import tv.codely.shared.domain.bus.query.QueryNotRegisteredError;
 
 import java.util.HashMap;
 
@@ -22,11 +20,11 @@ public ApiController(QueryBus queryBus, CommandBus commandBus) {
         this.commandBus = commandBus;
     }
 
-    protected void dispatch(Command command) throws CommandNotRegisteredError, CommandHandlerExecutionError {
+    protected void dispatch(Command command) throws CommandHandlerExecutionError {
         commandBus.dispatch(command);
     }
 
-    protected <R> R ask(Query query) throws QueryNotRegisteredError, QueryHandlerExecutionError {
+    protected <R> R ask(Query query) throws QueryHandlerExecutionError {
         return queryBus.ask(query);
     }
 
diff --git a/src/shared/test/tv/codely/shared/infrastructure/UnitTestCase.java b/src/shared/test/tv/codely/shared/infrastructure/UnitTestCase.java
@@ -39,7 +39,7 @@ public void shouldGenerateUuids(String uuid, String... others) {
         when(uuidGenerator.generate()).thenReturn(uuid, others);
     }
 
-    public void shouldAsk(Query query, Response response) throws QueryHandlerExecutionError, QueryNotRegisteredError {
+    public void shouldAsk(Query query, Response response) {
         when(queryBus.ask(query)).thenReturn(response);
     }
 }

Original file line number	Diff line number	Diff line change
`@@ -5,7 +5,6 @@`
`5`	`5`	`import tv.codely.backoffice.auth.domain.InvalidAuthUsername;`
`6`	`6`	`import tv.codely.shared.domain.bus.command.CommandBus;`
`7`	`7`	`import tv.codely.shared.domain.bus.command.CommandHandlerExecutionError;`
`8`		`-import tv.codely.shared.domain.bus.command.CommandNotRegisteredError;`
`9`	`8`
`10`	`9`	`import javax.servlet.*;`
`11`	`10`	`import javax.servlet.http.HttpServletRequest;`
`@@ -55,7 +54,7 @@ private void authenticate(`
`55`	`54`	`request.setAttribute("authentication_username", user);`
`56`	`55`
`57`	`56`	`chain.doFilter(request, response);`
`58`		`- } catch (InvalidAuthUsername \| InvalidAuthCredentials \| CommandHandlerExecutionError \| CommandNotRegisteredError error) {`
	`57`	`+ } catch (InvalidAuthUsername \| InvalidAuthCredentials \| CommandHandlerExecutionError error) {`
`59`	`58`	`setInvalidCredentials(response);`
`60`	`59`	`}`
`61`	`60`	`}`
Original file line number	Diff line number	Diff line change
`@@ -15,11 +15,7 @@ public FindCourseQueryHandler(CourseFinder finder) {`
`15`	`15`	`}`
`16`	`16`
`17`	`17`	`@Override`
`18`		`- public CourseResponse handle(FindCourseQuery query) {`
`19`		`- try {`
`20`		`- return finder.find(new CourseId(query.id()));`
`21`		`- } catch (CourseNotExist error) {`
`22`		`- return null;`
`23`		`- }`
	`18`	`+ public CourseResponse handle(FindCourseQuery query) throws CourseNotExist {`
	`19`	`+ return finder.find(new CourseId(query.id()));`
`24`	`20`	`}`
`25`	`21`	`}`