Let's create a custom exception and throw it from a service. Take a look at the following code:

    public class TodoNotFoundException extends RuntimeException {
      public TodoNotFoundException(String msg) {
        super(msg);
      }
    }

It's a very simple piece of code that defines ;TodoNotFoundException .

Now let's enhance our TodoController ;class to throw TodoNotFoundException when a todo with a given ID is not found:

    @GetMapping(path = "/users/{name}/todos/{id}")
    public Todo retrieveTodo(@PathVariable String name, 
    @PathVariable int id) {
      Todo todo = todoService.retrieveTodo(id);
      if (todo == null) {
        throw new TodoNotFoundException("Todo Not Found");
       }

     return todo;
    }

If todoService returns a null todo, we throw ;TodoNotFoundException.

When we execute the service with a GET request to a nonexistent ;todo (http://localhost:8080/users/Jack/todos/222), we get the response shown in the following code snippet:

    {
      "timestamp": 1484029048788,
      "status": 500,
      "error": "Internal Server Error",
      "exception":    
      "com.mastering.spring.springboot.bean.TodoNotFoundException",
      "message": "Todo Not Found",
      "path": "/users/Jack/todos/222"
    }

As we can see, a clear exception response is sent back to the service consumer. However, there is one thing that can be improved further--the response status. When a resource is not found, it is recommended that you return a 404 - Resource Not Found status. We will look at how to customize the response ;status ;in the next example.