Can we add validation to the request body based on the request Parameter

I have an REST endpoint, which takes an object in the request body and a request parameter. When the request parameter is passed, I need to validate all the attributes of the object, if not the parameter
takes the default value assigned and only 2 attributes needs to be validated. The path needs to be same for both the case. How can this be achieved?

Currently I have pattern, length and possibles values check for the objects, validated with the help of annotations.

----- Updating the Class -------

@ValidateParent(parent = "parent ", child= "child")
public class anClass{

    @NotNull(groups = {FrstValidator.class, SndValidator.class})
    @Pattern(regexp = "^[a-zA-Z]{3}$",
            groups = {FrstValidator.class, SndValidator.class})
    String str1;

    @NotNull(groups = {FrstValidator.class, SndValidator.class})
    @Pattern(regexp = "^[a-zA-Z]{3}$",
            groups = {FrstValidator.class, SndValidator.class})
    String str2;

    @Pattern(regexp = "^[a-zA-Z]{10}$",
            groups =  SndValidator.class)
    String child;

    @Pattern(regexp = "^[a-zA-Z]{10}$",
            groups = SndValidator.class)
    String parent;

    @Pattern(regexp = "^[a-zA-Z]{10}$",
            groups = SndValidator.class)
    String str3;


}

ValidateParent, checks if the parent is also passed when the child is passed in the request body.

You can achieve your goal in an elegant "Spring way", using validation groups and two separate endpoints, distinguished by presence of the request parameter:

Validation groups:

// Validation groups are just marker interfaces
private interface PartialValidation {}
private interface FullValidation {}

Request DTO:

@Data
private static class Request {
    // This field will be validated only for FullValidation validation group
    @NotNull(groups = FullValidation.class)
    String field1;
    // This field will be validated for both validation groups
    @NotNull(groups = {FullValidation.class, PartialValidation.class})
    String field2;
}

Controller:

// This endpoint is executed only if there is no myParam preprovided
@PostMapping(
    value = "/validation",
    params = "!myParam")
public void partialValidation(
    @RequestParam(defaultValue = "DEFAULT") String myParam,
    // Request is validated against the PartialValidation group
    @RequestBody @Validated(PartialValidation.class) Request request) {

    System.out.println("Partial validation");
}

// This endpoint is executed only if there is myParam preprovided
@PostMapping(
    value = "/validation",
    params = "myParam")
public void fullValidation(
    @RequestParam String myParam,
    // Request is validated against the FullValidation group
    @RequestBody @Validated(FullValidation.class) Request request) {

    System.out.println("Full validation");
}