references

• https://www.baeldung.com/rest-with-spring-series
• web filter : https://chatgpt.com/c/34abc85f-eabb-47ac-b525-7c2c6af8023a

---

REST Actions

1 actions list-1

• https://chatgpt.com/c/0471007c-7d4e-4a04-bd37-d6262d5f9aaf - REST Actions
• create
• logging interceptor/filter --> not doing, having common logging.
• Content Negotiation - Support different representations : produces/consumes = MediaType.APPLICATION_JSON
• API versioning
• API DOC
• security - using OAuth2.0
• Validation - using hibernate JSR validator + custom validator anno.
• Formatting - using jackson - custom serialization/de-S..
• CORS setup - add frontend url
• Pagination and Sorting - pageable and page

2 more actions list-2 (pending)

• Async Controllers:
• Use @Async("taskExecutor-1") and CompletableFuture to handle long-running requests asynchronously
• AsyncController.java
• @EnableAsync - enable

• create @Bean(name = "taskExecutor-1") ThreadPoolTaskExecutor : AsyncConfig.java

• HATEOS

• https://chatgpt.com/c/67414b1b-9018-800d-a683-8a632932177a
• return EntityModel from api method.
• use WebMvcLinkBuilder to create Link

  User user1 = new User(id, "John Doe", "john.doe@example.com"); // current api result
  ...
  Link allUsersLink = WebMvcLinkBuilder
   .linkTo(
       WebMvcLinkBuilder
          .methodOn(UserController.class)
          .getAllUsers())                     <<< another controller/api method
   .withRel("all-users");
   ...
   return EntityModel<User>.of(user1, allUsersLink);
  

• sample response : _links

  {
    "id": 1,
    "name": "John Doe",
    "email": "john.doe@example.com",
  
    "_links": {
        "all-users": {
            "href": "http://localhost:8080/api/users"
        }
    }
  }
  

---

A Create API

• check JewelleryController.java
• @ResponseBody + @Controller =@RestController
• Modify HttpResponse
• inject HttpServletResponse response as method arg directly and manipulate response.
• ResponseEntity<?> ResponseEntityBuilder --> statusCode, headers and body.
• @ResponseBody - serialized into JSON
• Bind Map<String,String> with
• RequestHeader
• RequestBody
• PathVariable
• RequestParam
• can make above input optional. can set default value for above input.
• eg: @PathVariable(value="pathVariable2", required = false) String pathVariable2_optional :

---

B. Validation / JSR 380

• apply on DTO/Bean/ENTITY
• https://chatgpt.com/c/a04dc001-e879-43e0-a39d-acd01b9ef2c7
• Add dependeny : spring-boot-starter-validation
• annotation: @email, @size, @NotBlank(""), etc
• use @Valid annotation to trigger validation in Controller or where ever binding happens:
  • @Valid @ResquestBody dto //method arg
  • Apply on method return.
• validate response: https://chatgpt.com/c/b8c60911-2df5-478b-9804-67c3ecf9506d

Custom validator

• check hibernate_validator
• can inject BindingResult as well.
• just implement ConstraintValidator<Anno,feildType>
• ``` // Apply @NameCheckAnnotation_1 on feilds

public class NameValidator implements ConstraintValidator { @Override public boolean isValid(String value, ConstraintValidatorContext context) { return true; } } ```

• implement ResponseBodyAdvice class
• The default Spring validation mechanism does not automatically validate objects wrapped in ResponseEntity.
• However, you can achieve this by creating a custom ResponseBodyAdvice implementation.
• @Valid / @validated :: cannot perform on ResponseEntity.
• check : https://chatgpt.com/c/591c7b06-4ac0-4f03-a328-038cde9cf7ca

---

C. Formatting ( Serialize / De-serialize)

• more: 05_Jackson.md
• binding happens with internal Serialize/De-serialize by jackson,
• has inbuilt serializer and de-serializer
• can create custom ones too.
• customize objectMapper, check JacksonConfig.java
• note: String to LocalDateTime : @DateTimeFormat (From SB, not jackson)
• HttpMessageConverter
• new MappingJackson2HttpMessageConverter()

---

D. Version

• https://chatgpt.com/c/7fa2c12d-eada-4991-944f-cfad8d084805
• @RequestMapping("/api/v1")
• @GetMapping(value = "/users", params = "version=1")
  • while consuming, set requestParam : version=1

• @GetMapping(value = "/users", headers = "X-API-VERSION=1")

  • while consuming, set header : X-API-VERSION=1

• @GetMapping(value = "/users", produces = "application/vnd.company.app-v1+json")

  • while consuming, set header : Accept=application/vnd.company.app-v1+json

• Choosing the Right API versioning Approach:

  • URI Path Versioning: Clear and straightforward, widely used.
  • Request Parameter Versioning: Useful for flexibility in request parameters.
  • Header Versioning: Keeps the URL clean, suitable for clients that can easily add headers.
  • Content Negotiation Versioning: Good for complex API evolution but can be harder to debug.

---

E. REST : consume Pending...

• https://chatgpt.com/c/9719e1f6-c4e4-4fac-8941-178c26acc484

RestTemplate

webClient

---

F. HATEOAS Pending...

• add hypermedia links to the API responses, enabling clients to navigate the API dynamically
• hands-on pending.

project : Pending...

• SetTimeouts API
• API to download file.
• Filters and Interceptors / InterceptorRegistry
• webClient and RestTemplate
• custom Binder
• ResponseBodyAdvice program
• @WebFilter
• Send response other than JSON