Idea for dynamic domain model in Java

gistfile1.java

public interface Struct {
    <T> T get(FieldType<T> type);
    <T> void set(FieldType<T> type, T value);
}

///////////////////////////////////////

public interface FieldType<T> {
    String getFieldName();
    Class<T> getType();
    T get(Object value);
    T validate(T value);
}

///////////////////////////////////////

public abstract class BasicType {

    private final String name;
    
    protected BasicType(String name) {
        this.name = name;
    }
    
    public String getFieldName() {
        return name;
    }
}

///////////////////////////////////////

public class StringType extends BasicType implements FieldType<String> {

    public StringType(String name) {
        super(name);
    }

    public Class<String> getType() {
        return String.class;
    }

    public String get(Object value) {
        return value == null ? null : value.toString();
    }

    public String validate(String value) {
        return value;
    }
}

///////////////////////////////////////

public class IntType extends BasicType implements FieldType<Integer> {

    public IntType(String name) {
        super(name);
    }

    public Class<Integer> getType() {
        return Integer.class;
    }

    public Integer get(Object value) {
        if (value == null) return null;
        if (value instanceof Integer) return (Integer) value;
        return Integer.parseInt(value.toString());
    }

    public Integer validate(Integer value) {
        return value;
    }
}

///////////////////////////////////////

public class PositiveType extends IntType {

    public PositiveType(String name) {
        super(name);
    }

    public Integer validate(Integer value) {
        if (value == null || value < 1) {
            throw new IllegalArgumentException("Value must be positive");
        }
        return value;
    }
}

///////////////////////////////////////

public class StructType extends BasicType implements FieldType<Struct> {

    protected StructType(String name) {
        super(name);
    }

    public Class<Struct> getType() {
        return Struct.class;
    }

    public Struct get(Object value) {
        if (value == null) return null;
        if (value instanceof Struct) return (Struct) value;
        throw new IllegalArgumentException("Could not convert");
    }

    public Struct validate(Struct value) {
        return value;
    }
}

///////////////////////////////////////

public class MapStruct implements Struct {

    private Map<String, Object> values = new HashMap<String, Object>();
    
    public <T> T get(FieldType<T> type) {
        return type.get(values.get(type.getFieldName()));
    }

    public <T> void set(FieldType<T> type, T value) {
        values.put(type.getFieldName(), type.validate(value));
    }
}

///////////////////////////////////////

public class Address {
    public static final FieldType<String> email = new StringType("email");
}

///////////////////////////////////////

public class User {
    public static final FieldType<String> firstName = new StringType("firstName");
    public static final FieldType<String> lastName = new StringType("lastName");
    public static final FieldType<Integer> age = new PositiveType("age");
    public static final FieldType<Struct> address = new StructType("address");
}

///////////////////////////////////////

import static User.*;
import static Address.*;

public class UserTest {

    @Test
    public void test() {
        Struct user = new MapStruct();
     // User user = new User();
        user.set(firstName, "John");
     // user.setFirstName("John");
        user.set(lastName, "Bloggs");
     // user.setLastName("Bloggs");
        user.set(age, 40);
     // user.setAge(40);
     
        user.set(address, new MapStruct());
     // user.setAddress(new Address());
        user.get(address).set(email, "john.bloggs@test.com");
     // user.getAddress().setEmail("john.bloggs@test.com");
        
        System.out.println(user.get(firstName) 
                + " " + user.get(lastName) 
                + " " + user.get(address).get(email));
        
     // System.out.println(user.getFirstName() 
     //         + " " + user.getLastName();
     //         + " " + user.getAddress().getEmail();
        
    }
}