Spring RestController

1. Create a package call controllers (could be anything, but this name make it clear) under your project root package.
2. Create a class call Home (could be anything, but this name make it clear) in the controllers package.

3. package com.example.demo.controllers
   
   import com.example.demo.domain.Cat
   import org.springframework.web.bind.annotation.GetMapping
   import org.springframework.web.bind.annotation.RequestParam
   import org.springframework.web.bind.annotation.RestController
   
   @RestController
   class Home {
       @GetMapping("/")
       String index() {
           return "Return as plain text"
       }
   
       @GetMapping("/cat")
       Cat something() {
           return new Cat()
       }
   
       @GetMapping("/param")
       String param(@RequestParam(value = "param1", defaultValue = "param1") String param1) {
           return param1
       }
   }

4. Above your class name, add @RestController to tell spring that it is a rest controller class
5. To map url get path to a method, put @GetMapping with the corresponding path eg:@GetMapping(“/”) above the method. This example mapped the root path to the method index()
6. If the thing return is a string, it will return a plain text to the http client.
7. If the thing return is an object, it will return a JSON that represent that Object. It depends in the getter of that Object.
8. We can take parameter from user by using @RequestParam. We can map it to the parameter with the method parameter, and give it a default value if the user do not supply one.
9. For this example, we have links http://127.0.0.1:8080/, http://127.0.0.1:8080/cat, and http://127.0.0.1:8080/param?param1=type%20anything

We have all kind of mapping, and we can map the same path with different http method to a different functions.

1. @GetMapping
2. @PostMapping
3. @PutMapping
4. @DeleteMapping
5. @PatchMapping

We can add @RequestMapping(“something”) to the class so that any mapping under this class will become /something/…