The Spring-HATEOAS project aims to assist those writing Spring MVC code in the creation of such links and the assembly of resources returned to the clients.
The example below will cover a simple scenario showing how links are created and returned for the resource, Bet. Each operation on the resource is described below:
- createBet - this POST operation will create a Bet.
- updateBet - this PUT operation will update the Bet.
- getBet - this GET operation will retrieve a Bet.
- cancelBet - this DELETE operation will cancel the Bet.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
| @Controller@RequestMapping("/bets")public class BetController { private BetService betService; private BetResourceAssembler betResourceAssembler; public BetController(BetService betService, BetResourceAssembler betResourceAssembler) { this.betService = betService; this.betResourceAssembler = betResourceAssembler; } @RequestMapping(method = RequestMethod.POST) ResponseEntity@RequestBody Bet body) { Bet bet = betService.createBet(body.getMarketId(), body.getSelectionId(), body.getPrice(), body.getStake(), body.getType()); BetResource resource = betResourceAssembler.toResource(bet); return new ResponseEntity } @RequestMapping(method = RequestMethod.PUT, value = "/{betId}") ResponseEntity@PathVariable Long betId, @RequestBody Bet body) throws BetNotFoundException, BetNotUnmatchedException { Bet bet = betService.updateBet(betId, body); BetResource resource = betResourceAssembler.toResource(bet); return new ResponseEntity } @RequestMapping(method = RequestMethod.GET, value = "/{betId}") ResponseEntity@PathVariable Long betId) throws BetNotFoundException { Bet bet = betService.getBet(betId); BetResource resource = betResourceAssembler.toResource(bet); if (bet.getStatus() == BetStatus.UNMATCHED) { resource.add(linkTo(BetController.class).slash(bet.getId()).withRel("cancel")); } return new ResponseEntity } @RequestMapping(method = RequestMethod.GET) ResponseEntity List List return new ResponseEntity } @RequestMapping(method = RequestMethod.DELETE, value = "/{betId}") ResponseEntity@PathVariable Long betId) { Bet bet = betService.cancelBet(betId); BetResource resource = betResourceAssembler.toResource(bet); return new ResponseEntity } @ExceptionHandler ResponseEntity handleExceptions(Exception ex) { ResponseEntity responseEntity = null; if (ex instanceof BetNotFoundException) { responseEntity = new ResponseEntity(HttpStatus.NOT_FOUND); } else if (ex instanceof BetNotUnmatchedException) { responseEntity = new ResponseEntity(HttpStatus.CONFLICT); } else { responseEntity = new ResponseEntity(HttpStatus.INTERNAL_SERVER_ERROR); } return responseEntity; } } |
1
2
3
4
5
6
7
8
9
10
11
12
13
14
| public class BetResourceAssembler extends ResourceAssemblerSupport public BetResourceAssembler() { super(BetController.class, BetResource.class); } public BetResource toResource(Bet bet) { BetResource resource = instantiateResource(bet); resource.bet = bet; resource.add(linkTo(BetController.class).slash(bet.getId()).withSelfRel()); return resource; }} |
This class extends ResourceAssemblerSupport which requires the implementation of a toResourcemethod as it implements the ResourceAssembler interface. This is where the mapping between Betand BetResource is done. In this case, BetResource is just a wrapper for Bet so it is simply a case of setting the bet attribute. The instantiateResource method will return a BetResource without any links so links can be added at this point if required. In this example a link to self is added. An alternative approach would be to use createResourceWithId which will return a BetResource with the self link.
1
2
3
4
5
| public class BetResource extends ResourceSupport { public Bet bet; } |
Also in this example, links are added to the BetResource within the BetController class to ensure the application of the HATEOAS constraint. If the REST service receives a GET request then a check is made on the status of the Bet. If the Bet is UNMATCHED, then a link to cancel the Betcan be added to the BetResource. This is done in similar fashion to the self link but with the relationship attribute name of cancel.
An alternative approach to this is to build a link to a method as opposed to constructing a URI.
1
2
| resource.add(linkTo(methodOn(BetController.class).cancelBet(betId)).withRel("cancel")); |
The methodOn would create a proxy of the BetController class and as a result the return type of thecancelBet method would have to be capable of proxying. Therefore in this example the return type of cancelBet method would be HttpEntity. If the latter, then the likely exception from the server would be:
Back to the GET request, and the returned JSON for requesting a Bet resource which has a status of UNMATCHED is shown below:
{
"links":[
{"rel":"self","href":http://localhost:8080/hateoas-1-SNAPSHOT/bets/0},
{"rel":"cancel","href":http://localhost:8080/hateoas-1-SNAPSHOT/bets/0} ],
"bet":{"id":0,"marketId":1,"selectionId":22,"price":4.0,"stake":2.0,"type":"BACK","status":"UNMATCHED"}
}
The client can therefore use the self link for retrieving and updating the Bet, and also the cancel link to effectively delete it.
This post describes just some of the functionality of the Spring-HATEOAS project which is evolving all the time. For an up to date and more detailed explanation, visit the GitHub pages.
{
"links":[
{"rel":"self","href":http://localhost:8080/hateoas-1-SNAPSHOT/bets/0},
{"rel":"cancel","href":http://localhost:8080/hateoas-1-SNAPSHOT/bets/0} ],
"bet":{"id":0,"marketId":1,"selectionId":22,"price":4.0,"stake":2.0,"type":"BACK","status":"UNMATCHED"}
}
The client can therefore use the self link for retrieving and updating the Bet, and also the cancel link to effectively delete it.
This post describes just some of the functionality of the Spring-HATEOAS project which is evolving all the time. For an up to date and more detailed explanation, visit the GitHub pages.
Không có nhận xét nào:
Đăng nhận xét