http stauts code handling

restful-web-service/src/main/java/com/example/restfulwebservice/user/UserController.java

@@ -1,7 +1,10 @@
 package com.example.restfulwebservice.user;
 
+import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.*;
+import org.springframework.web.servlet.support.ServletUriComponentsBuilder;
 
+import java.net.URI;
 import java.util.List;
 
 @RestController
@@ -19,12 +22,24 @@ public class UserController {
 
     @GetMapping("/users/{id}")
     public User retrieveUser(@PathVariable int id) {
-        return userDaoService.findOne(id);
+        User user = userDaoService.findOne(id);
 
+        if (user == null) {
+            throw new UserNotFoundException(String.format("ID[%s] not found", id));
+        }
+
+        return user;
     }
 
     @PostMapping("/users")
-    public void createUser(@RequestBody User user) {
+    public ResponseEntity<User> createUser(@RequestBody User user) {
         User savedUser = userDaoService.save(user);
+
+        URI location = ServletUriComponentsBuilder.fromCurrentRequest()
+                .path("/{id}")
+                .buildAndExpand(savedUser.getId())
+                .toUri();
+
+        return ResponseEntity.created(location).build();
     }
 }

restful-web-service/src/main/java/com/example/restfulwebservice/user/UserNotFoundException.java

@@ -0,0 +1,15 @@
+package com.example.restfulwebservice.user;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.web.bind.annotation.ResponseStatus;
+
+// HTTP Status code
+// 2XX -> OK
+// 4XX -> Client error
+// 5XX -> Server error
+@ResponseStatus(HttpStatus.NOT_FOUND)
+public class UserNotFoundException extends RuntimeException {
+    public UserNotFoundException(String message) {
+        super(message);
+    }
+}