refactor: change RestController to controller

src/main/java/com/guide/server/StudentController.java

 package com.guide.server;
 
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.stereotype.Controller;
 import org.springframework.web.bind.annotation.*;
 
 import java.util.List;
 import java.util.Optional;
 
-@RestController
+@Controller
 public class StudentController {
     private final StudentService studentService;
 
@@ -16,45 +19,48 @@ public class StudentController {
     }
 
     @PostMapping("/student/add")
-    public String createStudent(
+    public ResponseEntity<?> createStudent(
             @RequestParam String name,
             @RequestParam String stdId,
             @RequestParam Integer grade,
             @RequestParam String major) {
+        System.out.println("실행중1");
         studentService.saveStudent(Student.builder().name(name).stdId(stdId).grade(grade).major(major).build());
-        return "success";
+        return new ResponseEntity<>("success", HttpStatus.OK);
     }
     @PutMapping("/student/update")
-    public String updateStudent(
+    public ResponseEntity<?> updateStudent(
             @RequestParam Long id,
             @RequestParam String major) {
+        System.out.println("실행중3");
         Optional<Student> student = studentService.findOne(id);
         if(student.isPresent()){
             Student newStudent = student.get();
             newStudent.setMajor(major);
             studentService.saveStudent(newStudent);
-            return "success";
+            return new ResponseEntity<>("success", HttpStatus.OK);
         }
-        return "fail";
+        return new ResponseEntity<>("fail", HttpStatus.OK);
     }
 
     @GetMapping("/student/stdId")
-    public Student getStudentByStdId(@RequestParam String stdId){
-        return studentService.findOne(stdId).orElse(null);
+    public ResponseEntity<?> getStudentByStdId(@RequestParam String stdId){
+        return new ResponseEntity<>(studentService.findOne(stdId).orElse(null), HttpStatus.OK);
     }
 
     @GetMapping("/student/list")
-    public List<Student> getStudentList(){
-        return studentService.findStudents();
+    public ResponseEntity<?> getStudentList(){
+        System.out.println("실행중2");
+        return new ResponseEntity<>(studentService.findStudents(), HttpStatus.OK);
     }
 
     @DeleteMapping("/student/delete")
-    public String deleteStudent(@RequestParam Long id){
+    public ResponseEntity<?> deleteStudent(@RequestParam Long id){
         Optional<Student> student = studentService.findOne(id);
         if(student.isPresent()){
             studentService.deleteStudent(id);
-            return "success";
+            return new ResponseEntity<>("success", HttpStatus.OK);
         }
-        return "fail";
+        return new ResponseEntity<>("fail", HttpStatus.OK);
     }
 }