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How to split classes to use serveral #Controller

I am learning spring boot, and i developed the below simple example. I would like to annotate a class as Controller using #Controller. this class has constructor and I want to have access to GreetingFromDeuController as shown:
http://localhost:8080:/GreetingFromDeuController?str = "hi"
the error i am receiving is
#RequestMapping is not applicable on a constructor
please let me know how to solve.
code:
#Controller
#RequestMapping("/GreetingFromDeuController")
public class GreetingFromDeuController {
private String str;
#RequestMapping("/GreetingFrom/deu")
GreetingFromDeuController(#RequestParam(value = "str") String str) {
this.str = str;
}
#RequestMapping("/GreetingFromDeuController")
public String getGreetingFromDeu() {
return this.str;
}
}

First of all your constructor gets initialize much before you hit your URL. So you need to work on your design or tell me your business requirement and I will try to provide you a solution. My refactor code solution will help you to achieve that in two steps. First hit POST method which will do work on setting variable and then subsequent hits of GET method will return that set value.
We can refactor code like below. It will explain use of RequestMapping on method and class.
Considering we have to write two API, one for reading and one for writing.
URLS :
1. POST http://localhost:8080/example/greetings (in request body send {str:'hi'})
2. GET http://localhost:8080/example/greetings
#Controller
#RequestMapping("/example")
public class GreetingFromDeuController {
private String str;
#RequestMapping(value="/greetings" , method = RequestMethod.POST)
public void setGreetingFromDeu(#RequestBody(value = "str") String str)
{
this.str = str;
}
#RequestMapping(value="/greetings" , method = RequestMethod.GET)
public String getGreetingFromDeu()
{
return this.str;
}
}

The #RequestMapping documentation says:
Annotation for mapping web requests onto methods in request-handling
classes with flexible method signatures.
Then you can not do that, if you want to initialize your variables or whatever you can use several ways:
1.- Use #PostConstruct
#PostContruct
public void init() {
this.str = "Anything";
}
2.- Use a simple request to set anything only
#RequestMapping(value="/refresh/anythings", method = RequestMethod.PUT)
public void refresh(#RequestBody(value = "str") String str) {
this.str = str;
}
3.- Use #Value
In application.properties / application.yaml
properties.str = anything
In the Controller
#Value("${properties.str:default}") // by default str is "default"
public String str;
#RequestMapping(value="/greetings" , method = RequestMethod.GET)
public String getGreetingFromDeu() {
return this.str;
}

As far I am concerned, #RequestMapping is not meant for constructors. It should be used for annotating methods or classes. Methods that are responsible for handling requests.

#RequestMapping should be used to map request with endPoint. which can be used as class level and method level.
You can use #RestController (improved from #Controller see difference).
The ideal flow for Spring Boot is Controller -> Service -> Repository
Controller -> maps request with endPoint and return response
Service -> perform business logic
Repository -> Handle database operation
Example
#RestController
#RequestMapping("/api")
public class GreetingController {
#Autowired GreetinService greetingService;
// Request http://localhost:8080/api/GreetingFrom
#GetMapping("/GreetingFrom")
public ResponseEntity<String> GreetingRequestParam(#RequestParam(value = "name") String name) {
greetingService.performBusinessLogic(name);
return new ResponseEntity<String>("Greetings from "+name,HttpStatus.OK);
}
// Request http://localhost:8080/api/GreetingFrom/user2121
#GetMapping("/GreetingFrom/{name}")
public ResponseEntity<String> GreetingPathVariable(#PathVariable(value = "name") String name) {
return new ResponseEntity<String>("Greetings from "+name,HttpStatus.OK);
}
}

Error: Ambiguous handler methods mapped for HTTP path in spring data rest

this is the code:
#Import(Appconfig.class)
#RestController
//#RequestMapping("/api/destination/find")
public class RestApi01_Controller {
#Autowired
public CountryRepo Country_Repository;
#Autowired
public CityRepo City_Repository;
#Autowired
public AirportRepo Airport_Repository;
#Autowired
public ResortRepo Resort_Repository;
#RequestMapping(value="/api/destination/find/{city}", method=RequestMethod.GET)
public List<Master_City> getCity(#PathVariable String city) {
return City_Repository.findByCityLikeIgnoreCase(city);
}
#RequestMapping(value="/api/destination/find/{airportname}", method=RequestMethod.GET)
public List<Master_Airport> getAirportname(#PathVariable String airportname) {
return Airport_Repository.findByAirportnameLikeIgnoreCase(airportname);
}
#RequestMapping(value="/api/destination/find/{resortname}", method=RequestMethod.GET)
public List<Master_Resort> getResortname(#PathVariable String resortname) {
return ResortRepository.findByResortnameLikeIgnoreCase(resortname);
}
}

Your REST Endpoints are pointing basically to the same URI pattern.
Taking the first two as an example,
/api/destination/find/{city}
and
/api/destination/find/{airportname}
Since {city} and {airportname} are placeholders, and both the URI are HTTP GET methods, Spring is not able to make out which API to be used when a call to say /api/destination/find/london.
Instead of this, use request parameters. Something like this
/api/destination/find?airport={airportname}
and
/api/destination/find?city={city}

Spring Data Rest / Spring Hateoas Custom Controller - PersistentEntityResourceAssembler

I'm attempting to add some additional business logic to the auto-generated endpoints from the RepositoryRestResource. Please see the code below:
Resource:
#RepositoryRestResource(collectionResourceRel="event", path="event")
public interface EventRepository extends PagingAndSortingRepository<Event, Long> {
}
Controller:
#RepositoryRestController
#RequestMapping(value = "/event")
public class EventController {
#Autowired
private EventRepository eventRepository;
#Autowired
private PagedResourcesAssembler<Event> pagedResourcesAssembler;
#RequestMapping(method = RequestMethod.GET, value = "")
#ResponseBody
public PagedResources<PersistentEntityResource> getEvents(Pageable pageable,
PersistentEntityResourceAssembler persistentEntityResourceAssembler) {
Page<Event> events = eventRepository.findAll(pageable);
return pagedResourcesAssembler.toResource(events, persistentEntityResourceAssembler);
}
}
I've looked at the following two stackoverflow articles:
Can I make a custom controller mirror the formatting of Spring-Data-Rest / Spring-Hateoas generated classes?
Enable HAL serialization in Spring Boot for custom controller method
I feel like I am close, but the problem that I am facing is that:
return pagedResourcesAssembler.toResource(events, persistentEntityResourceAssembler);
returns an error saying:
"The method toResource(Page<Event>, Link) in the type PagedResourcesAssembler<Event> is not applicable
for the arguments (Page<Event>, PersistentEntityResourceAssembler)".
The toResource method has a method signature that accepts a ResourceAssembler, but I'm not sure how to properly implement this and I can't find any documentation on the matter.
Thanks in advance,
- Brian
Edit
My issue was that I thought I could override the controller methods that are auto-created from #RepositoryRestResource annotation without having to create my own resource and resource assembler. After creating the resource and resource assembler I was able to add my business logic to the endpoint.
Resource:
public class EventResource extends ResourceSupport {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
Resource Assembler:
#Component
public class EventResourceAssembler extends ResourceAssemblerSupport<Event, EventResource> {
public EventResourceAssembler() {
super(EventController.class, EventResource.class);
}
#Override
public EventResource toResource(Event entity) {
EventResource eventResource = createResourceWithId(entity.getId(), entity);
eventResource.setName(entity.getName());
return eventResource;
}
}
Updated Controller:
#RepositoryRestController
#RequestMapping(value = "/event")
public class EventController {
#Autowired
private EventRepository eventRepository;
#Autowired
private EventResourceAssembler eventResourceAssembler;
#Autowired
private PagedResourcesAssembler<Event> pageAssembler;
#RequestMapping(method = RequestMethod.GET, value = "")
#ResponseBody
public PagedResources<EventResource> getEvents(Pageable pageable) {
Page<Event> events = eventRepository.findAll(pageable);
// business logic
return pageAssembler.toResource(events, eventResourceAssembler);
}
}
The thing I don't like about this is that it seems to defeat the purpose of having a RepositoryRestResource. The other approach would be to use event handlers that would get called before and/or after the create, save, delete operations.
#RepositoryEventHandler(Event.class)
public class EventRepositoryEventHandler {
#HandleBeforeCreate
private void handleEventCreate(Event event) {
System.out.println("1");
}
}
There doesn't seem to be any events for the findAll or findOne operations. Anyways, both these approaches seem to solve my problem of extending the auto generated controller methods from RepositoryRestResource.

It requires a PagedResourcesAssembler, Spring will inject one for you if you ask.
public PagedResources<Foo> get(Pageable page, PagedResourcesAssembler<Foo> assembler) {
// ...
}
In this case the resource is Foo. It seems in your case the resource you're trying to return is an Event. If that's so, I would expect your code to look something like:
private ResourceAssembler<Event> eventAssembler = ...;
public PagedResources<Event> get(Pageable page, PagedResourcesAssembler<Event> pageAssembler) {
Event event = ...;
return eventAssembler.toResource(event, pageAssembler);
}
You provide the ResourceAssembler<Event> that tells Spring how to turn Event into a Resource. Spring injects the PagedResourcesAssembler<Event> into your controller method to handle the pagination links. Combine them by calling toResource and passing in the injected pageAssembler.
The final result can be returned simply as a body as above. You could also use things like HttpEntity to gain more control over status codes and headers.
Note: The ResourceAssembler you provide can literally be something as simple as wrapping the resource, such as Event, with a Resource object. Generally you'll want to add any relevant links though.

To hack it you can use just PagedResourcesAssembler<Object> like:
#RequestMapping(method = RequestMethod.GET, value = "")
#ResponseBody
public PagedModel<PersistentEntityResource> getEvents(
Pageable pageable,
PersistentEntityResourceAssembler persistentAssembler,
PagedResourcesAssembler<Object> pageableAssembler
) {
return pageableAssembler.toModel(
(Page<Object>) repository.findAll(pageable),
persistentAssembler
);
}

Forward request to another controller in Spring MVC

I'd like to know if there is a way I can forward a request from one controller to another without actually changing the URL in the browser.
#RequestMapping(value= {"/myurl"})
public ModelAndView handleMyURL(){
if(somecondition == true)
//forward to another controller but keep the url in the browser as /myurl
}
examples that I found online were redirecting to another url which was causing other controllers to handle that. I don't want to change the URL.

Try to return a String instead of ModelAndView, and the String being the forward url.
#RequestMapping({"/myurl"})
public String handleMyURL(Model model) {
if(somecondition == true)
return "forward:/forwardURL";
}

Instead of forwarding, you may just call the controller method directly after getting a reference to it via autowiring. Controllers are normal spring beans:
#Controller
public class MainController {
#Autowired OtherController otherController;
#RequestMapping("/myurl")
public String handleMyURL(Model model) {
otherController.doStuff();
return ...;
}
}
#Controller
public class OtherController {
#RequestMapping("/doStuff")
public String doStuff(Model model) {
...
}
}

As far as I know "forward" of a request will be done internally by the servlet, so there will not be a second request and hence the URL should remain the same. Try using the following code.
#RequestMapping(value= {"/myurl"})
public ModelAndView handleMyURL(){
if(somecondition == true){
return new ModelAndView("forward:/targetURL");
}
}

Call method of Controller1 into another method of Controller2 in Spring

I did Google a lot to find my problem but I couldn't and sorry If this question already on the stack overflow because I have not find it.
First let take a look into the code
#Controller
public class Controller1 {
#RequestMapping(value = "URL", method = RequestMethod.GET)
public ModelAndView methodHandler(Parameters) {
}
public int calculation(int i){
//Some Calcucation
return i;
}
}
and second controller is
#Controller
public class Controller2 {
#RequestMapping(value = "URL", method = RequestMethod.GET)
public ModelAndView methodHandler(Parameters) {
//In this I want to call the calculation(1) method of controller1.
}
}
My question is that is there any way to call the method of calculation() of controler1 in to controller2. But remember I don't want to make method static in controller1.Is there anyway to call it without make it static?
Thanks
Yasir

You should create service bean for example in configuration file (or use # one of the annotaions) and inject it into controller. For example ()
#Configuration
public class MyConfig {
#Bean
public MyService myService(){
return new MyService();
}
}
#Controller
public class Controller1 {
#Autowire
private MyService myService;
#RequestMapping(value = "URL", method = RequestMethod.GET)
public ModelAndView First(Parameters) {
myService.calculation();
}
}
#Controller
public class Controller2 {
#Autowire
private MyBean myBean;
#RequestMapping(value = "URL", method = RequestMethod.GET)
public ModelAndView First(Parameters) {
myService.calculation();
}
}

Your controllers should not call each other. If there is a logic which needs to be used by both controllers, it is much better to put that into separate bean, which will be used by both controllers. Then you can simply inject that bean to whicheveer controller neccessary. Try not to put any business logic to controllers, try tu put it to specialized class instead which will be web independent if possible and will accept web agnostic business data as user email, account number etc. No http request or response. This way your class with actual logic is reusable and can be unit tested much more easily. Also, if there is state, it should be contained in your classes outside controllers. Controllers should be stateless and not contail any state at all.
When using MVC pattern and you are deciding where to put your logic, you should separate business logic into model and into controllers you should put only logic regarding user interaction, as explained in this stack overflow post.