[FIXED] How to validate JSON request matched with model/dto entity?

Issue

I have a simple problem in Spring/JPA. Supposedly, I have this format of request:

model/BillDto.java

public class BillDto {
    private String desc;
    private Long id;
    private Integer amount;
    
    public BillDto(String desc, long id, int amount) {
        this.desc = desc;
        this.id = id;
        this.amount = amount;
    }
}

or as this json format

{
    "desc": "String",
    "id": 0,
    "amount": 0
}

And this is the controller

controller/BillController.java

@RequestMapping(method = RequestMethod.POST)
public void create(@RequestBody BillDto billDto) {
    billService.create(billDto); // some service to execute
}

However when I accidentally request with wrong format, the generated SQL won't execute, hence it returns 500 code. For example,

{
    "desc": "String",
    "id": 0
}

How do I handle this error in shortest lines of codes? How do I validate the json request to match the model/dto before passing it to service?

Solution

You can use @Valid annotation to the BillDto parameter annotated with @RequestBody. This will tell Spring to process validation before making an actual method call. In case validation fails, Spring will throw a MethodArgument NotValidException which, by default, will return a 400 (Bad Request) response.

@RequestMapping(method = RequestMethod.POST)
public void create(@Valid @RequestBody BillDto billDto) {
    billService.create(billDto); // some service to execute
}

In POST or PUT requests, when we pass JSON payload, Spring automatically converts it into a Java object and now it can validate the resulting object.

Answered By - user10260739
Answer Checked By - Gilberto Lyons (JavaFixing Admin)