Operation System : Windows 10

IDE : IntelliJ

Requirements : Java 8 > , Postman ( For Testing)

Book | Tutorial : youtube tutorial

Java version : 12

Git Project : Here

Parts: Part 1


Learn how to indicate erroneous actions and objects in the REST Service


Main Changes


During my research I encountered the use of validation annotations such as @NotNull, @NotEmpty etc, but I could not seem to get them to function as desired. However I will definitely look more into that in the nearer future and update this solution.

With that being said, in this solution the Todo bean/object was extended with a static method which confirms the validity of the provided arguments and returns a boolean value accordingly.

package com.example.demo.model;
import java.util.regex.Pattern;
import java.util.UUID;

public class Todo {
    private final UUID id;
    private  String title;

    public static boolean validateTodo(String title){
        if(title == null) {
            return false;
        boolean isValid = true;
        String pattern = "\\w+";
        Pattern p = Pattern.compile(pattern);
       return p.matcher(title).find();


Since the Todo class has a validateTodo function, the TodoService will use this to check the correctness of the title value before a new Todo object is created. Hence both the addTodo and patchTodo methods are to be modified.

public class TodoService implements ITodoService {
    private List<Todo> todos = new ArrayList<>();

    public Todo addTodo(@JsonProperty("title") String title, @JsonProperty("isCompleted") boolean isCompleted) {
        if(Todo.validateTodo(title) == false){
            return null;
        Todo todo = new Todo(UUID.randomUUID(), title, isCompleted);
        return todo;

    public Todo patchTodo(UUID id, Todo patch) {
        if(Todo.validateTodo(patch.getTitle()) == false){
            return null;
        Todo update = new Todo(id, patch.getTitle(), patch.getIsComplete());
        List<Todo> newtodos = this.todos.stream().map(todo -> todo.getId().equals(id)? update : todo).collect(Collectors.toList());
        this.todos = newtodos;
        return patch;


These functions return either a valid Todo object or a null object depending on the validity of the given title.


One last modification is the <PATCH> and <POST> APIs. Since the TodoService returns either a valid Todo object or a Null object when creating a todo, the respective controllers should accommodate the changes and react accordingly. This means if the returned value is null, the controllers throw an exception indicating that something went wrong ( “title is invalid”) . Otherwise the todo object is returned along with a status 200.


public class TodoController {

    public ResponseEntity<Todo> addTodo(@RequestBody Todo todo){
        Todo newtodo =  this.todoService.addTodo(todo.getTitle(), todo.getIsComplete());
        if(newtodo == null){
            throw new TodoInvalidException();
        return new ResponseEntity<Todo>(newtodo, HttpStatus.OK);
    public ResponseEntity<Todo> patchTodo(@PathVariable("id") UUID id, @RequestBody Todo patch ){
        Todo updateTodo = this.todoService.patchTodo(id,patch);
        if(updateTodo == null){
            throw new TodoInvalidException();
        return new ResponseEntity<Todo>(updateTodo, HttpStatus.OK);


Author Notes

This is most likely not the cleanest implementation, just a heads up.


  1. Validating Form Input
  2. Validation in Spring Boot
  3. Practice RegEXP
  4. Using Spring ResponseEntity to Manipulate the HTTP Response
  5. Interface BindingResult
  6. getAllErrors
  7. ObjectError
  8. Regular expressions in Java – Tutorial
  9. RuntimeException
  10. Exception Handling in Spring MVC
  11. How to use Regex in Java to pattern match?
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