Please help. I can not deal with generics. I have:
Generic interface repository:
#NoRepositoryBean
public interface PageBaseRepository<T extends PageBase> extends CrudRepository<T, Long> {
List<T> findAllByUserId(UUID userId);
}
#Repository
public interface StandardPageRepository extends PageBaseRepository<StandardPageEntity> {
}
#Repository
public interface BlockPageRepository extends PageBaseRepository<BlockPageEntity> {
}
#MappedSuperclass
#Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class PageBaseEntity {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#NotNull
private UUID userId;
private String content;
#Entity
public class StandardPageEntity extends PageBaseEntity {
private String extraField;
}
#Entity
public class BlockPageEntity extends PageBaseEntity {
private String blockPosition;
}
#Component
#RequiredArgsConstructor
public class PageRepositoryFactory {
private final StandardPageRepository standardPageRepository;
private final BlockPageRepository blockPageRepository;
public <R extends PageBaseRepository<E>, E extends PageBaseEntity> R getRepository(final E entity) {
if (entity instanceof StandardPageEntity) {
return standardPageRepository;
}
if (entity instanceof BlockPageEntity) {
return blockPageRepository;
}
throw new IllegalArgumentException("Not recognised pension object " + pensionEntity.getClass());
}
}
I am getting hint in intelij:
Incompatible types. Required: R Found:StandardPageRepository
and error in console:
PageRepositoryFactory.java:15: error: incompatible types:
StandardPageRepository cannot be converted to R
return standardPageRepository;
^ where R,E are type-variables:
R extends PageBaseRepository declared in method getRepository(E)
E extends PageBaseEntity declared in method getRepository(E)
One thing I found out is that I can do casting, but this is ugly, compilator says it is Unchecked cast. And I do not wanna this warning.
I want to get rid of the following code duplication within the MyFacadeBean. Consider the following situation:
public class FacadeBean implements Facade {
#EJB
private CrudService crudService;
#Inject
private FirstAssembler firstAssembler;
#Inject
private SecondAssembler secondAssembler;
#Inject
private ThirdAssembler thridAssembler;
#Inject
private FourthAssembler fourthAssembler;
#Override
public void save(FirstValue value) {
FirstEntity entity = this.firstAssembler.transformToEntity(value);
this.crudService.persist(entity);
}
#Override
public void save(SecondValue value) {
SecondEntity entity = this.secondAssembler.transformToEntity(value);
this.crudService.persist(entity);
}
#Override
public void save(ThirdValue value) {
ThirdEntity entity = this.thirdAssembler.transformToEntity(value);
this.crudService.persist(entity);
}
#Override
public void save(FourthValue value) {
FourthEntity entity = this.fourthAssembler.transformToEntity(value);
this.crudService.persist(entity);
}
}
public interface MyFacade {
void save(FirstValue value);
void save(SecondValue value);
}
With the CrudService:
public interface CrudService {
void persist(Object entity);
}
#Stateless
#Local(CrudService.class)
#TransactionAttribute(TransactionAttributeType.MANDATORY)
public class CrudServiceBean implements CrudService {
public static final String PERSISTENCE_UNIT_NAME = "my_persistence_unit";
private EntityManager entityManager;
#PersistenceContext(unitName = PERSISTENCE_UNIT_NAME)
public void setEntityManager(EntityManager entityManager) {
this.entityManager = entityManager;
}
#Override
public void persist(Object entity) {
this.entityManager.persist(entity);
}
}
With the following assemblers:
public class FirstAssembler extends AbstractAssembler<FirstEntity> {
public FirstEntity transformToEntity(FirstValue value) {
if (value == null)
return null;
FirstEntity entity = new FirstEntity();
transformAbstractValueToAbstractObject(value, entity);
entity.setFixedRate(value.getFixedRate());
entity.setStartDate(value.getStartDate());
return entity;
}
}
public class SecondAssembler extends AbstractAssembler<SecondEntity> {
public SecondEntity transformToEntity(SecondValue value) {
if (value == null)
return null;
SecondEntity entity = new SecondEntity();
transformAbstractValueToAbstractObject(value, entity);
entity.setTransactionType(value.getTransactionType());
entity.setValueDate(value.getValueDate());
return entity;
}
}
public abstract class AbstractAssembler<T extends AbstractEntity> {
protected void transformAbstractValueToAbstractObject(AbstractValue value, T object) {
object.setUniqueId(value.getUniqueId());
object.setNominalAmountValue(value.getNominalAmountValue());
}
}
With the following entities:
#Entity
public class FirstEntity extends AbstractEntity {
private static final long serialVersionUID = 1L;
#Id
#Column(name = "ID")
private Long id;
#Column(name = "START_DATE")
#Temporal(TemporalType.DATE)
private Date startDate;
#Column(name = "FIXED_RATE")
#Digits(integer = 1, fraction = 10)
private BigDecimal fixedRate;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public Date getStartDate() {
return startDate;
}
public void setStartDate(Date startDate) {
this.startDate = startDate;
}
public BigDecimal getFixedRate() {
return fixedRate;
}
public void setFixedRate(BigDecimal fixedRate) {
this.fixedRate = fixedRate;
}
}
#Entity
public class SecondEntity extends AbstractEntity {
private static final long serialVersionUID = 1L;
#Id
#Column(name = "ID")
private Long id;
#Column(name = "VALUE_DATE")
#Temporal(TemporalType.DATE)
private Date valueDate;
#Column(name = "TRANSACTION_TYPE")
#Enumerated(EnumType.STRING)
private TransactionType transactionType;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public Date getValueDate() {
return valueDate;
}
public void setValueDate(Date valueDate) {
this.valueDate = valueDate;
}
public TransactionType getTransactionType() {
return transactionType;
}
public void setTransactionType(TransactionType transactionType) {
this.transactionType = transactionType;
}
}
#MappedSuperclass
public abstract class AbstractEntity implements Serializable {
private static final long serialVersionUID = 1L;
#Column(name = "TRANSACTION_NOM_AMOUNT_VALUE")
#Digits(integer = 18, fraction = 5)
#Min(0)
private BigDecimal nominalAmountValue;
public BigDecimal getNominalAmountValue() {
return nominalAmountValue;
}
public void setNominalAmountValue(BigDecimal nominalAmountValue) {
this.nominalAmountValue = nominalAmountValue;
}
}
I tried the following approach:
public class FacadeBean implements Facade {
#Inject
private Assembler assembler;
#Inject
private AssemblerFactory assemblerFactory;
#Override
public <T extends AbstractValue> void save(T value) {
Assembler assembler = assemblerFactory.createAssembler(value);
AbstractEntity entity = assembler.transformToEntity(value);
this.crudService.persist(entity);
}
}
Problems are the AssemblerFactoryImpl and the AssemblerImpl in which I have to do instanceOf checks and castings...
Another idea would be to let the value know which transformer to use (or how to transform). But I want the value to be "dumb".
#Glenn Lane
public AbstractValue save(AbstractValue value) {
AbstractAssembler<AbstractValue, AbstractEntity> assembler = new FirstAssembler();
AbstractEntity entity = assembler.transformToEntity(value);
AbstractValue result = assembler.transformToValue(entity);
return result;
}
does not work, because of
Type mismatch: cannot convert from FirstAssembler to AbstractAssembler
I'm posting this as a separate answer, since I don't really think there's anything wrong with having a save method for every AbstractValue type.
First we'll establish your base value class for this example. I'm using an interface just so we don't muddy the waters. Your AbstractValue interface:
public interface AbstractValue
{
int getUniqueId();
double getNominalValue();
<T> T accept(AbstractValueVisitor<T> visitor);
}
And the "visitor interface":
public interface AbstractValueVisitor<T>
{
T visit(FirstValue value);
T visit(SecondValue value);
T visit(ThirdValue value);
T visit(FourthValue value);
}
I know you don't want intelligence baked into AbstractValue, but we are going to add one specification... that all concrete implementations of AbstractValue (all four) implement the accept method exactly this way:
#Override
public <T> T accept(AbstractValueVisitor<T> visitor)
{
return visitor.visit(this);
}
So that method is implemented four times: in all four value classes, exactly the same way. Because the visitor interface is aware of all concrete implementations, the appropriate method will be called for each particular value type. All three of these parts put together is the "visitor pattern".
Now we'll make an entity factory. Its job is to create the appropriate AbstractEntity when provided an AbstractValue:
public class AbstractEntityFactory
implements AbstractValueVisitor<AbstractEntity>
{
private static final AbstractEntityFactory INSTANCE;
static
{
INSTANCE = new AbstractEntityFactory();
}
// Singleton pattern
private AbstractEntityFactory()
{
}
public static AbstractEntity create(AbstractValue value)
{
if (value == null)
{
return null;
}
AbstractEntity e = value.accept(INSTANCE);
e.setNominalValue(value.getNominalValue());
e.setUniqueId(value.getUniqueId());
return e;
}
#Override
public AbstractEntity visit(FirstValue value)
{
FirstEntity entity = new FirstEntity();
// Set all properties specific to FirstEntity
entity.setFixedRate(value.getFixedRate());
entity.setStartDate(value.getStartDate());
return entity;
}
#Override
public AbstractEntity visit(SecondValue value)
{
SecondEntity entity = new SecondEntity();
// Set all properties specific to SecondEntity
entity.setTransactionType(value.getTransactionType());
entity.setValueDate(value.getValueDate());
return entity;
}
#Override
public AbstractEntity visit(ThirdValue value)
{
ThirdEntity entity = new ThirdEntity();
// Set all properties specific to ThirdEntity
return entity;
}
#Override
public AbstractEntity visit(FourthValue value)
{
FourthEntity entity = new FourthEntity();
// Set all properties specific to FourthEntity
return entity;
}
}
Now your facade implementation takes an AbstractValue, and you got that one save method you're looking for:
public class FacadeBean implements Facade
{
#EJB
private CrudService crudService;
#Override
public void save(AbstractValue value)
{
AbstractEntity entity = AbstractEntityFactory.create(value);
crudService.persist(entity);
}
}
Because your AbstractValue now follows the visitor pattern, you can do all sorts of polymorphic behavior. Such as:
public class AbstractValuePrinter implements AbstractValueVisitor<Void>
{
private final Appendable out;
public AbstractValuePrinter(Appendable out)
{
this.out = out;
}
private void print(String s)
{
try
{
out.append(s);
out.append('\n');
}
catch (IOException e)
{
throw new IllegalStateException(e);
}
}
#Override
public Void visit(FirstValue value)
{
print("I'm a FirstValue!");
print("Being a FirstValue is groovy!");
return null;
}
#Override
public Void visit(SecondValue value)
{
print("I'm a SecondValue!");
print("Being a SecondValue is awesome!");
return null;
}
#Override
public Void visit(ThirdValue value)
{
print("I'm a ThirdValue!");
print("Meh.");
return null;
}
#Override
public Void visit(FourthValue value)
{
print("I'm a ThirdValue!");
print("Derp.");
return null;
}
}
In this example, this visitor isn't returning anything... it's "doing" something, so we'll just set the return value as Void, since it's non-instantiatable. Then you print the value simply:
// (value must not be null)
value.accept(new AbstractValuePrinter(System.out));
Finally, the coolest part of the visitor pattern (in my opinion): you add FifthValue. You add the new method to your visitor interface:
T visit(FifthValue value);
And suddenly, you can't compile. You must address the lack of this handling in two places: AbstractEntityFactory and AbstractValuePrinter. Which is great, because you should consider it in those places. Doing class comparisons (with either instanceof or rinde's solution of a class-to-factory map) is likely to "miss" the new value type, and now you have runtime bugs... especially if you're doing 100 different things with these value types.
Anyhoo, I didn't want to get into this, but there you go :)
Use a generic method with a bound type parameter in order to spare yourself the repetition:
public <T extends AbstractValue> T save(T value) {...}
Within the method body, you'll be able to reference the argument value with all methods pertaining to AbstractValue.
Notes
Since your save methods seem to be overrides in this example, you might need to change the design of the parent class or interface too.
You could also use a generic class to start with (instead of a generic method in a non-necessarily generic class), depending on your use case.
I think a problem in your code is that the generic type of AbstractAssembler is that of the output of the transform method, not the input. If you change it as follows:
public abstract class AbstractAssembler<T extends AbstractValue> {
protected void transformAbstractValueToAbstractObject(AbstractEntity entity, T value) {
entity.setUniqueId(value.getUniqueId());
entity.setNominalAmountValue(value.getNominalAmountValue());
}
public abstract AbstractEntity transformToEntity(T value);
}
Then you can change the FacadeBean to the following.
public class FacadeBean {
#EJB
private CrudService crudService;
final Map<Class<?>, AbstractAssembler<?>> knownAssemblers;
FacadeBean() {
knownAssemblers = new LinkedHashMap<>();
knownAssemblers.put(FirstValue.class, new FirstAssembler());
knownAssemblers.put(SecondValue.class, new SecondAssembler());
// add more assemblers here
}
public <T extends AbstractValue> void save(T value, Class<T> type) {
#SuppressWarnings("unchecked") // safe cast
final AbstractAssembler<T> assembler =
(AbstractAssembler<T>) knownAssemblers.get(type);
final AbstractEntity entity = assembler.transformToEntity(value);
this.crudService.persist(entity);
}
}
Notice that I changed the signature of the save(..) method such that we have the type of the object that needs to be saved. With this type we can simply lookup the right assembler that should be used. And because the assembler is now generic on its input type, we can do a safe cast (be careful to keep your map consistent).
This implementation avoids duplication of code as you only need one save method. The use of the instanceof operator is prevented by changing the generic type of AbstractAssembler and storing all assemblers in a map.
The assemblers can look like this:
public class FirstAssembler extends AbstractAssembler<FirstValue> {
#Override
public FirstEntity transformToEntity(FirstValue value) {
final FirstEntity entity = new FirstEntity();
// do transformational stuff
super.transformAbstractValueToAbstractObject(entity, value);
entity.setFixedRate(value.getFixedRate());
entity.setStartDate(value.getStartDate());
return entity;
}
}
public class SecondAssembler extends AbstractAssembler<SecondValue> {
#Override
public SecondEntity transformToEntity(SecondValue value) {
final SecondEntity entity = new SecondEntity();
// do transformational stuff
super.transformAbstractValueToAbstractObject(entity, value);
return entity;
}
}
Note: I'm not familiar with Java beans so you probably have to adapt the code a little if you want to use the #Injected assemblers instead of calling the constructors directly.
You're getting close to gold-plating here, but there is a bit of reduction you can do, specifically the null-check and calling the common field-setting method from each extension.
public abstract class AbstractAssembler<V extends AbstractValue, E extends AbstractEntity>
{
public final E transformToEntity(V value)
{
if (value == null)
{
return null;
}
E entity = createEntity(value);
entity.setUniqueId(value.getUniqueId());
entity.setNominalAmountValue(value.getNominalAmountValue());
return entity;
}
/**
* #return
* Appropriate entity object, with the fields not common to all AbstractEntity
* already set
*/
protected abstract E createEntity(V value);
}
And then the extended assembler:
public class FirstAssembler extends AbstractAssembler<FirstValue, FirstEntity>
{
#Override
protected FirstEntity createEntity(FirstValue value)
{
FirstEntity entity = new FirstEntity();
entity.setFixedRate(value.getFixedRate());
entity.setStartDate(value.getStartDate());
return entity;
}
}
If you really want a single factory class to handle all your values/entities, I would look into the visitor pattern, enhanced with a generic type parameter on the visitor interface (and the entity/value accept methods return a type based on the visiting interface). I won't show an example here simply because I don't think it's warranted in your case.
You can have one save method from the point of view of the classes that save those values, but you still have to implement three individual save methods.
Implement a class with all three save methods. For example:
public class ValuePersister {
#Inject
private Assembler1 assembler1;
#Inject
private Assembler2 assembler2;
#Inject
private Assembler3 assembler3;
public Value1 save(Value1 value1, CrudService crudService) {
Entity1 entity1 = assembler1.transformToObject(value1);
crudService.persist(entity1);
return assembler1.transformToValue(entity1);
}
public Value2 save(Value2 value2, CrudService crudService) {
Entity2 entity2 = assembler2.transformToObject(value2);
crudService.persist(entity2);
return assembler2.transformToValue(entity2);
}
public Value3 save(Value3 value3, CrudService crudService) {
Entity3 entity3 = assembler3.transformToObject(value3);
crudService.persist(entity3);
return assembler3.transformToValue(entity3);
}
}
Add an abstract method to AbstractValue:
public abstract AbstractValue save(ValuePersister valuePersister, CrudService crudService);
Implement that method in each class that extends AbstractValue:
#Override
public AbstractValue save(ValuePersister valuePersister, CrudService crudService) {
return valuePersister.save(this, crudService);
}
Inject ValuePersister and implement your original generic save method:
#Inject
private ValuePersister valuePersister;
#Override
public AbstractValue save(AbstractValue value) {
return value.save(valuePersister, crudService)
}
I have a bean ArtistEntityBean extending GenericEntityBean:
public class ArtistEntityBean extends GenericEntityBean<Artist> {
public ArtistEntityBean() {
item = new Artist();
}
}
-
public abstract class GenericEntityBean<T extends IntEntity> implements Serializable {
protected T item;
public void init(Integer id){
item.setId(id);
}
}
-
public class Artist extends ArtistBaseEntity implements Comparable<Artist> {
...
}
-
public abstract class ArtistBaseEntity implements IntEntity {
...
}
-
public interface IntEntity {
Integer getId();
void setId(Integer id);
}
-
I'm trying to put as much code as possible in the GenericEntityBean class, which is why I thought of using an interface in order to be able to set the id of the item.
This does not work tough, as I get a NoSuchFieldError in the constructor of ArtistEntityBean and I don't know why?
If item is public, protected or default you have to use
super.item = new Artist();
in the constructor of ArtistEntityBean.
If it is private you have to provide a setter method in the abstract class.
Edit: If you did not specify item in the abstract class then do the following
public abstract class GenericEntityBean<T extends IntEntity> implements Serializable {
protected T item;
public void init(Integer id){
item.setId(id);
}
}
Simple class Person.class
class Person {
#NotNull(groups = {PartlyCheck.class})
private String name;
#NotNull(groups = {FullCheck.class})
private String adress;
private boolean isFullCheck;
}
Check interfaces
public interface PartlyCheck{}
public interface FullCheck extends PartlyCheck{}
I use two approach:
if(person.isFullCheck) {
validator.validate(person, FullCheck.class);
else {
validator.validate(person, PartlyCheck.class);
}
1.
If isFullCheck=true used both checks (FullCheck.class and PartlyCheck.class)
If isFullCheck=false used only PartlyCheck.class.
It is an understandable behavior.
#GroupSequenceProvider(PersonGroupSequenceProvider.class)
#Override
public List<Class<?>> getValidationGroups(Person person) {
List<Class<?>> defaultGroupSequence = new ArrayList<>();
defaultGroupSequence.add(Person.class);
if (person.isFullCheck) {
defaultGroupSequence.add(FullCheck.class);
} else {
defaultGroupSequence.add(PartlyCheck.class);
}
return defaultGroupSequence;
}
In the second case, I added #GroupSequenceProvider(PersonGroupSequenceProvider.class).
If isFullCheck=true used only FullCheck.class.
Why extends is not considered for this case?
If isFullCheck=false used only PartlyCheck.class.
I'm having some trouble understanding the following scenario.
I have a "generified" interface that is implemented by an abstract class and a concrete class that extends the abstract class.
The problem is that all the methods in the abstract class returning parametrized lists have lost their type so I'm getting a compilation error telling me that it cannot convert from object to the original List type.
Could anyone provide some insight?.
In the end what I would like is to have the a getId and setId method on the abstract class having a return type of java.lang.object or <T extends Object> and the concrete classes implementing their return type to whatever they want.
Here is the code for my different objects :
A generic interface
public interface MyInterface<T>{
public T getId();
public void setId(T id);
}
An abstract class implementing the interface
public abstract class MyAbstractClass<T> implements MyInterface<T>{
private List<String> texts;
private List<Integer> notes;
public List<String> getTexts(){
return texts;
}
public List<Integer> getNotes(){
return notes;
}
}
A Concrete class implementing the abstract class
public class MyConcreteClass implements MyAbstractClass<Integer>{
private Integer id;
public Integer getId(){
return this.id;
}
public void setId(Integer id){
this.id = id;
}
}
Some other class :
public class SomeOtherClass{
public void process(List<T extends MyAbstractClass> myClassList){
// Compilation error ->
// Type mismatch: cannot convert from element type Object to String
for(MyAbstractClass myObj : myClassList){
System.out.println("object Id : " + myObj.getId());
// Compilation error ->
// Type mismatch: cannot convert from element type Object to String
for(String txt : myObj.getTexts()){
}
}
}
}
When you use generic type MyAbstractClass<T> as raw type (MyAbstractClass), all generic-related stuff in declarations of its members is disabled (i.e. List<String> turns into List).
Therefore you need to declare an argument of your method as parameterized type. If you don't care about actual type parameter, use wildcard:
public void process(MyAbstractClass<?> myClass) { ... }
I think you need another interface. See here with MyAbstractClass implementing two interfaces MyInterface<T>, MyOtherInterface.
public static interface MyInterface<T> {
public T getId();
public void setId(T id);
}
public static interface MyOtherInterface {
public List<String> getTexts();
public List<Integer> getNotes();
}
public abstract class MyAbstractClass<T> implements MyInterface<T>, MyOtherInterface {
private List<String> texts;
private List<Integer> notes;
public List<String> getTexts() {
return texts;
}
public List<Integer> getNotes() {
return notes;
}
}
public static class MyConcreteClass extends MyAbstractClass<Integer> {
private Integer id;
public Integer getId() {
return this.id;
}
public void setId(Integer id) {
this.id = id;
}
}
public class SomeOtherClass {
public void process(MyOtherInterface myClass) {
// NO Compilation error
for (String str : myClass.getTexts()) {
// some processing
}
}
}