Spring Boot with REST API

Spring MVC with Spring Boot

• MVC (Model-View-Controller)

  • View
    • Displays data received from the Controller
    • UI presentation
    • JSP, Thymeleaf, React, Angular, etc.
  • Controller
    • Maps HTTP requests to specific handler methods
    • Validates input data (optional, but often delegated to validation mechanisms)
    • Calls the service layer for business logic execution
    • Returns responses (JSON, XML, View)
  • Model
    • @Service
      • Implements business logic
      • Calls data access layer (repository/DAO)
      • Ensures transaction management (e.g., @Transactional)
    • @Repository
      • Interacting with the database
      • Spring JDBC, Hibernate, Spring Data JPA, etc.
    • @Component
      • Representing and managing application data

• Spring Boot MVC has an embedded Tomcat server

• Work flow

  • [Client] → [DispatcherServlet] → [Controller] → [Service] → [DAO] → [Database]
                  ↓
          [View Resolver] → [View]

• Annotation	Description
  @Controller	Defines a web controller
  @RestController	Handles RESTful APIs
  @RequestMapping("/path")	Maps request URLs
  @GetMapping("/path")	Maps GET requests
  @PostMapping("/path")	Maps POST requests
  @PutMapping("/path")	Maps PUT requests
  @DeleteMapping("/path")	Maps DELETE requests
  @RequestParam	Gets request parameters
  @PathVariable	Extracts values from URL
  @ResponseBody	Sends data as JSON

• Controller for view (skipped)

  • ModelAndView class
  • JSP is a servlet in the end

REST API

• REpresentational State Transfer

• REST API article written by Postman

• A key difference between a traditional MVC controller and the RESTful web service controller is the way that the HTTP response body is created

• Rather than relying on a view technology to perform server-side rendering of the greeting data to HTML, this RESTful web service controller populates and returns an object. The object data will be written directly to the HTTP response as JSON

• jackson library converts Java objects to JSON

• URI syntax

• @RestController
  @RequestMapping("/posts")		// Base URI for all endpoints
  @CrossOrigin(origins = "http://localhost:3000")
  public class JobController {
  
      private JobService service;
  
      @Autowired
      public JobController(JobService service) {
          this.service = service;
      }
  
      public JobController() {
      }
  
    	@GetMapping
      public List<JobPost> getAllJobs() {
          return service.getAllJobs();
      }
  
      // You can specify which format you want to produce or consume
      @GetMapping(path = "/{postId}", produces = {"application/json"})
    	// @PathVariable indicates that a method parameter should be bound to a URI template variable
    	// If the path variable name is the same as the parameter name, you don't have to specify it
      public ResponseEntity<JobPost> getJobById(@PathVariable int postId) {
          JobPost job = service.getJobById(postId);
        	return job != null ? new ResponseEntity<JobPost>(job, HttpStatus.OK) :
                                  new ResponseEntity<>(HttpStatus.NOT_FOUND);
      }
  
    	// If @GetMapping is differentiated by @RequestParam only, then add params element specifying which query parameters are gonna be received
    	@GetMapping(params = "keyword")
      public List<JobPost> searchJob(@RequestParam(name = "keyword", defaultValue = "nothing") String keyword) {
          return service.search(keyword);
      }
  
      @PostMapping(consumes = {"application/json"})
      public JobPost addJob(@RequestBody JobPost job) {
          service.addJob(job);
          return job;
      }
  
      // @RequestBody read the request body and deserialised it into an Object
    	@PutMapping("/{postId}")
      public JobPost updateJob(@RequestBody JobPost job) {
          service.updateJob(job);
          return service.getJobById(job.getPostId());
      }
  
      // @RequestParam binds the value of the query String parameter into the method parameter
    	// If the query parameter is absent in the request, then defaultValue is used
    	// Type conversion is automatically applied if the target method parameter type is not String
    	// If the conversion is falied, then respond bad request
    	@DeleteMapping
      public void deleteJob(@RequestParam(name = "id", defaultValue = "1") int jobId) {
          service.deleteJob(jobId);
      }
  }