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Spring Boot - how to validate fields that depend on each other?

Is there some way in Spring Boot that I can perform validation on properties that depend on each other's values, and have the error message be associated with the property?
I want to return the errors to the user in a nice JSON structure:
{
"errors": {
"name": "is required if flag is true"
}
}
Example:
#Entity
public class MyEntity {
private boolean nameRequiredFlag;
// Required if "nameRequiredFlag" is set to true:
private String name;
}
One solution that doesn't solve my problem of associating the error message with the name property is to create a validator annotation for the entity:
#ValidEntity
public class MyEntity {
private boolean nameRequiredFlag;
// Required if "nameRequiredFlag" is set to true:
private String name;
}
#Constraint( validatedBy = { MyEntityValidator.class } )
#Documented
#Target( { ElementType.TYPE } )
#Retention( RetentionPolicy.RUNTIME )
public #interface ValidEntity{
Class<?>[] groups () default {};
String message () default "name is required if 'nameRequiredFlag' is true";
Class<? extends Payload>[] payload () default {};
}
public class MyEntityValidator implements Validator<ValidEntity, MyEntity> {
#Override
public boolean isValid ( MyEntity entity, ConstraintValidatorContext context ) {
if ( !entity.nameRequiredFlag ) return true;
return !StringUtils.isBlank( entity.getName() );
}
}
This is laughably cumbersome and doesn't solve my problem. Isn't there any way I can do this with the framework validation?
Edit: This is for a JSON API, and the consumer really needs to be able to associate the error message to a best guess at which field has an issue. It is not helpful to send the consumer an error message for the whole object, or a computed property.

Solution given by #EvicKhaosKat is one way of doing it. However, when there are too many fields dependent on each other in a complicated way, your class becomes full of annotations and I personally struggle a lot relating them.
A simpler approach is to create a method(s) in your pojo which does the cross field validations and returns a boolean. On the top of this method annotate it with #AssertTrue(message = "your message"). It will solve your problem in a cleaner fashion.
public class SampleClass {
private String duration;
private String week;
private String month;
#AssertTrue(message = "Duration and time attributes are not properly populated")
public boolean isDurationCorrect() {
if (this.duration.equalsIgnoreCase("month")) {
if (Arrays.asList("jan", "feb", "mar").contains(month))
return true;
}
if (this.duration.equalsIgnoreCase("week")) {
if (Arrays.asList("1-7", "8-15", "16-24", "25-31").contains(week))
return true;
}
return false;
}
}
Note: I have not tested this code but have used this approach in multiple places and it works.

Possible reason is that name validation operates on not-yet-fully constructed object, so nameRequiredFlag is not filled yet.
As an option there is a #GroupSequence annotation, which allows to group and perform validations in an order you specify.
For example it is possible to add to MyEntity annotations:
#ValidEntity(groups = DependentValidations.class)
#GroupSequence({MyEntity.class, DependentValidations.class})
So all the other validation annotations on MyEntity class gonna be performed first, and after that DependentValidations group, which consists of ValidEntity.
Thus ValidEntity will be called on fully created object, and the last in order.
(DependentValidations.class - just an empty interface created somewhere nearby, like any other marker interface)
https://www.baeldung.com/javax-validation-groups will possibly describe that in much more details.
p.s. answer provided by #Innovationchef will possibly suit the case more :)

Lombok's `#Builder` annotation stubbornly stays package - private

I have the following #Builder - annotated class:
#Data
#Builder(access = AccessLevel.PUBLIC)
#Entity
public class LiteProduct
{
// Minimal information required by our application.
#Id
private Long id; // Unique
private String name;
private Long costInCents;
private String type;
// Model the product types as a Hash Set in case we end up with several
// and need fast retrieval.
public final static Set<String> PRODUCT_TYPES = new HashSet<>
(Arrays.asList("flower", "topical", "vaporizer", "edible", "pet"));
// Have to allow creation of products without args for Entities.
public LiteProduct()
{
}
public LiteProduct(#NonNull final Long id, #NonNull final String name,
#NonNull final String type, #NonNull final Long costInCents)
{
if(!PRODUCT_TYPES.contains(type))
{
throw new InvalidProductTypeException(type);
}
this.name = name;
this.id = id;
this.costInCents = costInCents;
}
Whenever I want to use the builder class that Lombok is purported to give me, despite the fact that the IDE seems to detect it just fine:
I get a compile-time error about its visibility:
I have looked at some workarounds such as this or this, and they all seem to imply that my problem ought to already be solved automatically and that Lombok by default produces public Builder classes. This does not seem to be implied from my output, and does not happen even after I put the parameter access=AccessLevel.PUBLIC in my #Builder annotation in LiteProduct. Any ideas? Is there something wrong with the fact that this class is also an #Entity? Something else I'm not detecting?
// Edit: I determined that when I move the class in the same package as the one I am calling the builder pattern from, it works just fine. This is not an #Entity issue, but a package visibility issue which based on what I'm reading should not be there.

The problem was that I was using the following line of code to create an instance of LiteProduct:
return new LiteProduct.builder().build();
instead of:
return LiteProduct.builder().build();
which is what the #Builder annotation allows you to do. Clearly builder() is like a factory method for Builders that already calls new for you.

Mapstruct Invoking implicitly other mapper with multiple parameter

Given the following classes and a mapper that takes mulitple source arguments
(I use lombok to keep source as short as possible.)
#Getter
#Setter
public class MySourceOne {
private String src1;
}
#Getter
#Setter
public class MySourceTwo {
private String src2;
}
#Getter
#Setter
public class MyTargetObject {
private String prop1;
private String prop2;
}
#Mapper
public interface MyTargetObjectMapper {
#Mapping(target="prop1", source="a")
#Mapping(target="prop2", source="b")
public MyTargetObject mapMyObject(String a, String b);
}
#Getter
#Setter
public class MyComplexTargetObject {
private MyTargetObject myTargetObject;
}
I am trying to create a mapper for MyComplexTargetObject that will invoke implicitly the MyTargetObjectMapper .
But the "source" won't allow to map multiple parameter like this
#Mapper(uses= {MyTargetObjectMapper.class})
public interface MyComplexTargetObjectMapper {
#Mapping(target="myTargetObject", source="one.src1, two.src2")
public MyComplexTargetObject convert(MySourceOne one, MySourceTwo two);
}
So I am trying to use an expression="..." instead of source, but nothing works so far.
Any thoughts a clean way to do this without calling the MyTargetObjectMapper in a concrete method?

MapStruct does not support selection of methods with multiple sources.
However: you can do target nesting to do this.
#Mapper
public interface MyComplexTargetObjectMapper {
#Mapping(target="myTargetObject.prop1", source="one.src1" )
#Mapping(target="myTargetObject.prop2", source="two.src2")
public MyComplexTargetObject convert(MySourceOne one, MySourceTwo two);
}
And let MapStruct take care of generating the mapper. Note: you can still use a MyComplexTargetObjectMapper to do single source to target to achieve this.

Javax #NotNull annotation usage

I have a simple method to get a list of documents for a given companyId. Here is the method:
#Override
public List<Documents> getDocumentList(#NotNull Integer companyId) {
Company company = new Company(companyId);
return this.documentRepository.findByCompany(company);
}
I wanted to use Javax validation constraints to ensure that the companyId being passed in, is not null. But it seems to not have any effect, as I'm able to pass in a null value, and it flows down to the findByCompany call on the repository. I also added #Valid before #NotNull to force validation, but that too didn't do anything.
I could always write a couple of lines to check for a null value, but wanted to use javax.validation annotations to make the code more readable and concise. Is there a way to make the annotations work on method params?

To activate parameter validation, simply annotate the class with #Validated
import org.springframework.validation.annotation.Validated;

From The Java EE 6 Tutorial:
The Bean Validation model is supported by constraints in the form of
annotations placed on a field, method, or class of a JavaBeans
component, such as a managed bean.
You should place your validation of a field related to a declared bean, something like this:
#Entity
#Table(name="users")
public class BackgammonUser {
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private Long userId;
#Column(name="username")
#NotBlank
private String userName;
#NotBlank
private String password;
#NotNull
private Boolean enabled;
}
The BackgammonUser is considered to be a bean.

If you #Inject a class with your method, its working as expected.
#Stateless
public class MyBean{
#Inject
TestClass test;
}
and
public class TestClass {
public List<Documents> getDocumentList(#NotNull Integer companyId)
{
//...
}
}
ConstraintViolationException when you call your method with null parameter:
WFLYEJB0034: EJB Invocation failed on component MyBean for method ...:
javax.ejb.EJBException: javax.validation.ConstraintViolationException:
1 constraint violation(s) occurred during method validation.

#NotNull Annotation,
A method should not return null.
A variable (like fields, local variables, and parameters) cannot hold null value.

Assign custom identifier to an #id property

I'm migrating a legacy system over to use Hibernate 3. It currently generates its own identifiers. To keep with what the system currently does before I try and move it over to something a little better, how would I go about specifying (using annotations) my own class that will return the custom generated identifiers when an insert occurs?
Something like:
#Id
#CustomIdGenerator(Foo.class) // obviously this is not a real annotation
public String getId() { ... }
Where the Foo class has one method that generates the identifier.
Currently I'm just calling the setId(String id) method manually but was hoping for a better way to deal with this situation.

I don't think there is out-of-box support for generating custom Ids using custom annotations using pure JPA-2 API. But if you want to use provider specific API, then the job is pretty simple. Sample Example
To be provider independent try any of following tricks....
IdGeneratorHolder
public abstract class IdGeneratorHolder {
/* PersistentEntity is a marker interface */
public static IdGenerator getIdGenerator(Class<? extends PersistentEntity> entityType) {
/* sample impelementation */
if(Product.class.isAssignableFrom(entityType)) {
return new ProductIdGenerator();
}
return null;
}
}
General IdGenerator interface
public interface IdGenerator {
String generate();
}
Specific IdGenerator - Product Id Generator
public class ProductIdGenerator implements IdGenerator {
public String generate() {
/* some complicated logic goes here */
return ${generatedId};
}
}
Now set the generated id either in no-arg constructor OR in #PrePersist method.
Product.java
public class Product implements PersistentEntity {
private String id;
public Product() {
id = IdGeneratorHolder.getIdGenerator(getClass()).generate();
}
#PrePersist
public void generateId() {
id = IdGeneratorHolder.getIdGenerator(getClass()).generate();
}
}
In above example all the ids are of the same type i.e. java.lang.String. If the persistent entities have ids of different types.....
IdGenerator.java
public interface IdGenerator {
CustomId generate();
}
CustomId.java
public class CustomId {
private Object id;
public CustomId(Object id) {
this.id = id;
}
public String toString() {
return id.toString();
}
public Long toLong() {
return Long.valueOf(id.toString());
}
}
Item.java
#PrePersist
public void generateId() {
id = IdGeneratorHolder.getIdGenerator(getClass()).generate().toLong();
}
You can also use your custom annotation...
CustomIdGenerator.java
public #interface CustomIdGenerator {
IdStrategy strategy();
}
IdStrategy.java
enum IdStrategy {
uuid, humanReadable,
}
IdGeneratorHolder.java
public abstract class IdGeneratorHolder {
public static IdGenerator getIdGenerator(Class<? extends PersistentEntity> entityType) {
try { // again sample implementation
Method method = entityType.getMethod("idMethod");
CustomIdGenerator gen = method.getAnnotation(CustomIdGenerator.class);
IdStrategy strategy = gen.strategy();
return new ProductIdGenerator(strategy);
}
One more thing.... If we set id in #PrePersist method, the equals() method cannot rely on id field (i.e. surrogate key), we have to use business/natural key to implement equals() method. But if we set id field to some unique value (uuid or "app-uid" unique within application) in no-arg constructor, it helps us to implement the equals() method.
public boolean equals(Object obj) {
if(obj instanceof Product) {
Product that = (Product) obj;
return this.id ==that.id;
}
return false;
}
If we or someone else call (intentionally or by mistake) the #PrePersist annotated method more than one times, the "unique id will be changed!!!" So setting id in no-arg constructor is preferable. OR to address this issue put a not null check...
#PrePersist
public void generateId() {
if(id != null)
id = IdGeneratorHolder.getIdGenerator(getClass()).generate();
}
}
UPDATE
If we put the id generation in a
no-arg constructor, wouldn't that
cause a problem when loading entities
from the database? because hibernate
will call the no-arg constructor
causing existing ids to be
re-generated
Yeah you are right, I missed that part. :( Actually, I wanted to tell you that:- in my application every Entity object is associated with an Organization Entity; so I've created an abstract super class with two constructors, and every Entity (except Organization) extends this class.
protected PersistentEntityImpl() {
}
protected PersistentEntityImpl(Organization organization) {
String entityId = UUIDGenerator.generate();
String organizationId = organization.getEntityId();
identifier = new EntityIdentifier(entityId, organizationId);
}
The no-arg constructor is for JPA provider, we never invoke no-arg constructor, but the other organization based constructor. As you can see. id is assigned in Organization based constructor. (I really missed this point while writing the answer, sorry for that).
See if you can implement this or similar strategy in your application.
The second option was using the
#PrePersist annotation. I put that in
and the method never got hit and gave
me an exception stating that I needed
to set the id manually. Is there
something else I should be doing?
Ideally, JPA provider should invoke #PrePersist methods (one declared in class and also all the other methods that are declared in super-classes) before persisting the entity object. Can't tell you what is wrong, unless you show some code and console.

You can.
First, implement org.hibernate.id.IdentifierGenerator
Then you'd have to map it in a mapping xml file. I couldn't find a way to do this with annotations:
<!--
<identifier-generator.../> allows customized short-naming
of IdentifierGenerator implementations.
-->
<!ELEMENT identifier-generator EMPTY>
<!ATTLIST identifier-generator name CDATA #REQUIRED>
<!ATTLIST identifier-generator class CDATA #REQUIRED>
Finally, use #GeneratedValue(generator="identifier-name")
Note that this is hibernate-specific (not JPA)
Update: I took a look at the sources of Hibernate, and it seems at one place, after failing to resolve the short name, hibernates attempts to call Class.forName(..). The parameter there is called strategy. So Here's what you try:
try setting the class fully-qualified name as string in the generator attribute
try setting the class fqn as string in the #GenericGenerator strategy attribute (with some arbitrary name)
Let me know which (if any) worked