Immutable Value objects and JPA

Is there way to map immutable Value objects like email address using JPA?

@Immutable
@Embeddable
public final class EmailAddress {
    private final String value;

    public EmailAddress(String value) {
        this.value = value;
    }

    public String getValue() {
        return value;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        EmailAddress that = (EmailAddress) o;
        return value.equals(that.value);
    }

    @Override
    public int hashCode() {
        return value.hashCode();
    }
}

Now I get exception on entity save

org.hibernate.InstantiationException: No default constructor for entity: com.domain.EmailAddress
    org.hibernate.tuple.PojoInstantiator.instantiate(PojoInstantiator.java:107)
    org.hibernate.tuple.component.AbstractComponentTuplizer.instantiate(AbstractComponentTuplizer.java:102)
    org.hibernate.type.ComponentType.instantiate(ComponentType.java:515)
    org.hibernate.type.ComponentType.deepCopy(ComponentType.java:434)
    org.hibernate.type.TypeHelper.deepCopy(TypeHelper.java:68)
    org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:302)
    org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:203)
    org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:129)
    org.hibernate.ejb.event.EJB3PersistEventListener.saveWithGeneratedId(EJB3PersistEventListener.java:69)
    org.hibernate.event.def.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:179)
    org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:135)
    org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:61)
    org.hibernate.impl.SessionImpl.firePersist(SessionImpl.java:808)
    org.hibernate.impl.SessionImpl.persist(SessionImpl.java:782)
    org.hibernate.impl.SessionImpl.persist(SessionImpl.java:786)
    org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:672)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    java.lang.reflect.Method.invoke(Method.java:597)
    org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:240)
    $Proxy25.persist(Unknown Source)
    org.springframework.data.jpa.repository.support.SimpleJpaRepository.save(SimpleJpaRepository.java:360)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    java.lang.reflect.Method.invoke(Method.java:597)
    org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.executeMethodOn(RepositoryFactorySupport.java:368)
    org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:349)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationI开发者_如何学Cnterceptor.java:155)
    org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
    $Proxy26.save(Unknown Source)
    com.controller.UserController.create(UserController.java:64)

I want use final fields and hibernate as JPA implementation.

You won't be able to do that using standard JPA annotations and an embeddable object, because the object will have to be created using a default constructor, and the value set via reflection.

You could however use a Hibernate custom type. Read this part of the Hibernate reference documentation, where there is an example Money type, which is instantiated using a constructor with arguments, and could thus be immutable.

Probably the easiest solution which works with a little older versions like 3.5 of Hibernate is to implement org.hibernate.usertype.UserType. There is quite a few methods in it but for immutable types you can extract most of them to common superclass:

package com.acme;

import java.io.Serializable;

import org.hibernate.usertype.UserType;

public abstract class AbstractImmutableType
  implements UserType {

 public AbstractImmutableType() {
  super();
 }

 public boolean isMutable() {
  return false;
 }

 public Serializable disassemble(Object value) {
  return (Serializable) value;
 }

 public Object assemble(Serializable cached, Object owner) {
  return cached;
 }

 public Object deepCopy(Object value) {
  return value;
 }

 public Object replace(Object original, Object target,
   Object owner) {
  return original;
 }

 public boolean equals(Object x, Object y) {
  if (x != null && y != null) {
   return x.equals(y);
  }
  // Two nulls are equal as well
  return x == null && y == null;
 }

 public int hashCode(Object x) {
  if (x != null) {
   return x.hashCode();
  }
  return 0;
 }
}

And you can use it like this:

package com.acme;

import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Types;

public class CurrencyType extends AbstractImmutableType {

 public static final String TYPE = "com.acme.CurrencyType";

 private static final int[] SQL_TYPES = {
    Types.VARCHAR
 };

 public CurrencyType() {
  super();
 }

 public Object nullSafeGet(ResultSet rs, String[] names,
    Object owner) throws SQLException {
  String value = rs.getString(names[0]);
  if (rs.wasNull()) {
   return null;
  }
  return Currency.valueOf(value);
 }

 public void nullSafeSet(PreparedStatement st, Object value,
    int index) throws SQLException {
  if (value != null) {
   st.setString(index, ((Currency)value).getCode());
  } else {
   st.setNull(index, SQL_TYPES[0]);
  }
 }

 public Class<?> returnedClass() {
  return Currency.class;
 }

 public int[] sqlTypes() {
  return SQL_TYPES;
 }
}

Longer explanation for this code you can find here

For JPA to be able to create objects via reflection, you have to have a default constructor, but it doesn't have to be public. I also like to keep my fields final, but this might be too restrictive for reflection -- you'll have to try.

I'd suggest dropping the final field modifier and adding a private default constructor with a short comment (so you still know why that no-op constructor is there next week):

public final class EmailAddress {
    private String value; // no final modifier

    private EmailAddress() {
        // for JPA
    }

    public EmailAddress(String value) {
        this.value = value;
    }
...
}