I am learning Java in 2020 – Beginner - Simple Spring REST Service Setup and basic Validation (Part 2)

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

Goal

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

Solution

Main Changes

Model

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();
    }
}

Service

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.

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

    @Override
    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);
        todos.add(todo);
        return todo;
    }

    @Override
    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.

Controller

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.

....

@RestController
@RequestMapping("/api/v1/todos")
public class TodoController {
   ....

    @PostMapping("/")
    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);
    }
    @PatchMapping("/{id}")
    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);
    }
    ....


}