如何验证 pojo 集合

Question

I have a collection of pojo objects

public class Assignment {
    Date entrydate;
    Date exitdate;
    String team, 
    double allocation;
    String username,
    //getters and setters
}

The example values are Object 1 :

entrydate: "2000-01-01", exitdate: "2019-03-31", team: "team1", allocation: 0.5 username: "user1"

Object 2:

entrydate: "2000-01-01", exitdate: "2019-03-31", team: "team2", allocation: 0.5 username: "user1"

Object 3:

entrydate: "2019-04-01", exitdate: "2019-07-31", team: "team3", allocation: 0.6 username: "user1"

Object 4:

entrydate: "2019-05-01", exitdate: "2019-07-31", team: "team4", allocation: 0.6 username: "user1"

My criterion is for a specified user and for a specific date period the count of total allocation should be 1 => logical explanation will be the engineer should not work more than 100% or less than 100% for a specified period.

We need a function in which we pass a collection of the above pojo objects and if it does not meet this criterion it should throw an error with proper explanation - like for this date range already allocation is over 1 for specified teams. Also this method should check for date gaps if any present -- logical explanation for this feature will be - the engineer should not be idle for a specified period

Method signature will be

List<String> getValidation(List<Assignment > assignments);

(suppose we know that all the assignments belong to a specific user --> no need to worry aboubt username for now)

How to properly implement this

Answer 1

There are several ways to tackle it. There are existing annotations already in the javax-validation-api like NotNull , Min , Max , ...

You have simply use these annotations on your pojo variables for your case as specified below.

public class Assignment {
    Date entrydate;
    Date exitdate;
    String team, 
    @Min(0)
    @Max(1)
    double allocation;
    String username,
    //getters and setters
}

You need to instruct your controller that you will need validations on request body through @Valid annotation as below.

@PostMapping("someEndPoint")
public ResponseEntity getSomeThing(@Valid @RequestBody requestBody)
{
}

In the cases where you have to validate @PathVariable you have to use @Validated on the controller class itself like

@Api("AssignmentController")
@RestController
@Validated
@RequestMapping(value = "/api/admin")
public class AssignmentController {
}

In the case where you need custom validations on the fields which are not provided by javax validations , you can implement your custom validator and custom annotation for that purpose.

Let's look an example where you want to create an annotation @ValidAllocation which will validate your allocation field.

Creating custom annotation:

@Documented
@Retention(RUNTIME)
@Target({FIELD, ANNOTATION_TYPE, PARAMETER})
@Constraint(validatedBy = AllocationValidator.class)
public @interface ValidAssignment {
    String message() default "Assignment should be between 0 and 1";
    Class<?>[] groups() default { };
    Class<? extends Payload>[] payload() default { };
}

Creating custom validator which is used by the annotation:

@Component
public class AllocationValidator implements ConstraintValidator<ValidAssignment, Double> {

    @Override
    public boolean isValid(Double value, ConstraintValidatorContext constraintValidatorContext) {
        return (value >=0 && value <=1);
    }

    @Override
    public void initialize(ValidAssignment validAssignment)  {}
}

You Pojo will look like as specified below

public class Assignment {
    Date entrydate;
    Date exitdate;
    String team, 
    @ValidAllocation
    double allocation;
    String username,
    //getters and setters
}

Let me know if you have any questions :)