#2 First draft for DomainObject validation

src/main/java/de/novatec/ddd/domainprimitives/object/Aggregate.java

@@ -1,4 +1,9 @@
 package de.novatec.ddd.domainprimitives.object;
 
+import de.novatec.ddd.domainprimitives.validation.ObjectValidation;
+
 public abstract class Aggregate extends DomainObject {
+	protected Aggregate(ObjectValidation checkList) {
+		super(checkList);
+	}
 }

src/main/java/de/novatec/ddd/domainprimitives/object/ComposedValueObject.java

@@ -1,4 +1,9 @@
 package de.novatec.ddd.domainprimitives.object;
 
+import de.novatec.ddd.domainprimitives.validation.ObjectValidation;
+
 public abstract class ComposedValueObject extends DomainObject {
+	protected ComposedValueObject(ObjectValidation checkList) {
+		super(checkList);
+	}
 }

src/main/java/de/novatec/ddd/domainprimitives/object/DomainObject.java

@@ -1,66 +1,15 @@
 package de.novatec.ddd.domainprimitives.object;
 
-import de.novatec.ddd.domainprimitives.validation.InvariantException;
-
-import java.util.ArrayList;
-import java.util.List;
-
-import static java.lang.String.format;
+import de.novatec.ddd.domainprimitives.validation.ObjectValidation;
 
 public abstract class DomainObject {
 
-    private final List<String> violations = new ArrayList<>();
-
-    protected DomainObject() {}
-
-    /**
-     * Providing a starting point this stub could be used check on invariant violations.
-     */
-    protected abstract void validate();
-
-    /**
-     * Helping validation method to ensure the field is not null
-     *
-     * @param field The object with should be null-checked
-     * @param label The lable or a description of the field
-     */
-    protected void validateNotNull(Object field, String label) {
-        if (field == null) {
-            violations.add(format("%s should not be null", label));
-        }
-    }
-
-    /**
-     * If you have more complex validations than only null-checks,
-     * the violation could be added to the final {@link InvariantException InvariantException}.
-     *
-     * @param violation Info about the violation.
-     *                  Maybe which constraints are violated.
-     */
-    protected void addInvariantViolation(String violation) {
-        this.violations.add(violation);
-    }
-
-    /**
-     * Evaluate all invariants.
-     *
-     * @param name The Name of the class the invariants are defined.
-     *             If not provided the default is the simple class name, see {@link #evaluateValidations() evaluateValidations} method.
-     * @throws InvariantException containing all invariant violations.
-     */
-    protected void evaluateValidations(String name) throws InvariantException {
-        if (!violations.isEmpty()) {
-            throw new InvariantException(name, violations);
-        }
+    protected DomainObject(ObjectValidation checkList) {
+        validate(checkList);
     }
 
-    /**
-     * Evaluate all invariants.
-     * The label describing the object, the invariants are checked on, is the simple class name.
-     *
-     * @throws InvariantException containing all invariant violations.
-     */
-    protected void evaluateValidations() throws InvariantException {
-        this.evaluateValidations(this.getClass().getSimpleName());
+    private void validate(ObjectValidation checkList) {
+        checkList.forObject(this.getClass().getSimpleName());
+        checkList.validate();
     }
 }

src/main/java/de/novatec/ddd/domainprimitives/object/Entity.java

@@ -1,4 +1,9 @@
 package de.novatec.ddd.domainprimitives.object;
 
+import de.novatec.ddd.domainprimitives.validation.ObjectValidation;
+
 public abstract class Entity extends DomainObject {
+	protected Entity(ObjectValidation checkList) {
+		super(checkList);
+	}
 }

src/main/java/de/novatec/ddd/domainprimitives/validation/Constraints.java

@@ -3,6 +3,7 @@
 import java.time.*;
 import java.time.temporal.Temporal;
 import java.util.function.Consumer;
+import java.util.function.Supplier;
 
 import static java.lang.String.format;
 
@@ -21,6 +22,9 @@ public class Constraints {
     private Constraints() {
     }
 
+    public static Consumer<Validation<Supplier<Boolean>>> conformsCheck(Supplier<String> descriptionSupplier) {
+        return val -> val.constraint(!val.value().get(), descriptionSupplier);
+    }
     // String
 
     public static Consumer<Validation<String>> isNotNull() {
@@ -265,4 +269,8 @@ private static boolean isInFuture(Temporal temporal) {
             throw new DateTimeException("Unsupported Temporal class: " + temporal.getClass());
         }
     }
+
+    public static Consumer<Validation<Object>> isNotNullObject() {
+        return val -> val.constraint(isNotNull(val.value()), () -> format(NULL_ERROR_MESSAGE_TEMPLATE, getValueFormatted(val)));
+    }
 }

src/main/java/de/novatec/ddd/domainprimitives/validation/InvariantException.java

@@ -1,36 +1,12 @@
 package de.novatec.ddd.domainprimitives.validation;
 
-import java.util.List;
-
-import static java.lang.String.format;
-import static java.lang.String.join;
-
 /**
  * InvariantException should be thrown during the validation of an object.
  * It is an unchecked exceptions, its superclass is {@link RuntimeException RuntimeException}.
  */
 public class InvariantException extends RuntimeException {
 
-    private static final String ERROR_MESSAGE_PATTERN = "%s of %s is not valid: %s.";
-
-    /**
-     * Constructs a new invariant exception (a runtime exception) with the following pattern: {@value #ERROR_MESSAGE_PATTERN},
-     * e.g. "Value Name is not valid: Too long."
-     * @param label The name of the object, which is not valid.
-     * @param message The message describing the invalidity.
-     */
-    public InvariantException(String label, String message) {
-        super(format(ERROR_MESSAGE_PATTERN, "Value", label, message));
-    }
-
-    /**
-     * Constructs a new invariant exception (a runtime exception) for a list of invalidities for one lable.
-     * The message will have the following pattern: {@value #ERROR_MESSAGE_PATTERN},
-     * e.g. "Value(s) Name is not valid: Too long. No special characters allowed."
-     * @param label The name of the object, which is not valid.
-     * @param problems All messages describing each invalidity.
-     */
-    public InvariantException(String label, List<String> problems) {
-        super(format(ERROR_MESSAGE_PATTERN, "Value(s)", label, join(". ", problems)));
-    }
+	public InvariantException(String message) {
+		super(message);
+	}
 }

src/main/java/de/novatec/ddd/domainprimitives/validation/ObjectInvariantException.java

@@ -0,0 +1,15 @@
+package de.novatec.ddd.domainprimitives.validation;
+
+import java.util.List;
+
+import static java.lang.String.format;
+import static java.lang.String.join;
+
+public class ObjectInvariantException extends InvariantException {
+
+	private static final String ERROR_MESSAGE_PATTERN = "Value(s) of %s is not valid:\r\n  %s";
+
+	public ObjectInvariantException(String label, List<String> problems) {
+		super(format(ERROR_MESSAGE_PATTERN, label, join("\r\n  ", problems)));
+	}
+}

src/main/java/de/novatec/ddd/domainprimitives/validation/ObjectValidation.java

@@ -0,0 +1,51 @@
+package de.novatec.ddd.domainprimitives.validation;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Consumer;
+
+public final class ObjectValidation {
+
+	private final List<Consumer<Void>> toValidate = new ArrayList<>();
+	private final List<String> problems = new ArrayList<>();
+	private String objectName;
+
+	public ObjectValidation(Consumer<Void>[] validations) {
+		toValidate.addAll(List.of(validations));
+	}
+
+	@SafeVarargs
+	public static <T> ObjectValidation checks(Consumer<Void>... validations) {
+		return new ObjectValidation(validations);
+	}
+
+	public static <T> Consumer<Void> check(T value, String label, Consumer<Validation<T>> constraint) {
+		return var -> Validation.validate(value, label, constraint);
+	}
+
+	public void validate() {
+		if (toValidate.isEmpty()) {
+			//TODO Logger
+			System.out.println("No Validations found for Object: " + objectName);
+		}
+		else {
+			toValidate.forEach(check -> {
+				try {
+					check.accept(null);
+				}
+				catch (InvariantException e) {
+					problems.add(e.getMessage());
+				}
+			});
+			evaluateValidations();
+		}
+	}
+
+	private void evaluateValidations() throws InvariantException {
+		if (!problems.isEmpty()) throw new ObjectInvariantException(objectName, problems);
+	}
+
+	public void forObject(String objectName) {
+		this.objectName = objectName;
+	}
+}

src/main/java/de/novatec/ddd/domainprimitives/validation/Validation.java

@@ -31,7 +31,7 @@ public void addViolation(String problem) {
     }
 
     private void validate() throws InvariantException {
-        if (!problems.isEmpty()) throw new InvariantException(label, problems);
+        if (!problems.isEmpty()) throw new ValueInvariantException(label, problems);
     }
 
     public void constraint(Boolean value, Supplier<String> descriptionSupplier) {

src/main/java/de/novatec/ddd/domainprimitives/validation/ValueInvariantException.java

@@ -0,0 +1,32 @@
+package de.novatec.ddd.domainprimitives.validation;
+
+import java.util.List;
+
+import static java.lang.String.format;
+import static java.lang.String.join;
+
+public class ValueInvariantException extends InvariantException {
+
+	private static final String ERROR_MESSAGE_PATTERN = "%s of %s is not valid: %s.";
+
+	/**
+	 * Constructs a new invariant exception (a runtime exception) with the following pattern: {@value #ERROR_MESSAGE_PATTERN},
+	 * e.g. "Value Name is not valid: Too long."
+	 * @param label The name of the object, which is not valid.
+	 * @param message The message describing the invalidity.
+	 */
+	public ValueInvariantException(String label, String message) {
+		super(format(ERROR_MESSAGE_PATTERN, "Value", label, message));
+	}
+
+	/**
+	 * Constructs a new invariant exception (a runtime exception) for a list of invalidities for one lable.
+	 * The message will have the following pattern: {@value #ERROR_MESSAGE_PATTERN},
+	 * e.g. "Value(s) Name is not valid: Too long. No special characters allowed."
+	 * @param label The name of the object, which is not valid.
+	 * @param problems All messages describing each invalidity.
+	 */
+	public ValueInvariantException(String label, List<String> problems) {
+		super(format(ERROR_MESSAGE_PATTERN, "Value(s)", label, join(". ", problems)));
+	}
+}

src/test/java/de/novatec/ddd/domainprimitives/object/DomainObjectTest.java

@@ -26,7 +26,8 @@ void should_throw_invariant_exception_if_field_is_null() {
         Name name = new Name("Peter");
         InvariantException exception = assertThrows(InvariantException.class, () -> new Person(null, name));
 
-        assertEquals("Value(s) of Person is not valid: Person ID should not be null.", exception.getMessage());
+        assertEquals("Value(s) of Person is not valid:\r\n"
+                + "  Value(s) of Person ID is not valid: Person ID (null) should not be null.", exception.getMessage());
     }
 
     @Test
@@ -35,13 +36,16 @@ void should_throw_invariant_exception_if_custom_violation() {
         Name name = new Name("Peter");
         InvariantException exception = assertThrows(InvariantException.class, () -> new Person(personId,name));
 
-        assertEquals("Value(s) of Person is not valid: This is not allowed.", exception.getMessage());
+        assertEquals("Value(s) of Person is not valid:\r\n"
+                + "  Value(s) of PersonID and Name Constraint is not valid: PersonID and Name Constraint Name Peter with id 12 is not allowed.", exception.getMessage());
     }
 
     @Test
     void should_throw_invariant_exception_if_field_is_null_with_multiple_fields() {
         InvariantException exception = assertThrows(InvariantException.class, () -> new Person(null, null));
 
-        assertEquals("Value(s) of Person is not valid: Person ID should not be null. Name should not be null.", exception.getMessage());
+        assertEquals("Value(s) of Person is not valid:\r\n"
+                + "  Value(s) of Person ID is not valid: Person ID (null) should not be null.\r\n"
+                + "  Value(s) of Name is not valid: Name (null) should not be null.", exception.getMessage());
     }
-}
+}

src/test/java/de/novatec/ddd/domainprimitives/object/testdata/Person.java

@@ -2,32 +2,44 @@
 
 import de.novatec.ddd.domainprimitives.object.Aggregate;
 
-public class Person extends Aggregate {
-
-    private final PersonId personId;
-    private final Name name;
-
-    public Person(PersonId personId, Name name) {
-        this.personId = personId;
-        this.name = name;
-
-        this.validate();
-    }
+import static de.novatec.ddd.domainprimitives.validation.Constraints.conformsCheck;
+import static de.novatec.ddd.domainprimitives.validation.Constraints.isNotNullObject;
+import static de.novatec.ddd.domainprimitives.validation.ObjectValidation.check;
+import static de.novatec.ddd.domainprimitives.validation.ObjectValidation.checks;
 
-    public PersonId getPersonId() {
-        return personId;
-    }
-
-    @Override
-    protected void validate() {
-        validateNotNull(personId, "Person ID");
-        validateNotNull(name, "Name");
-
-        if ((personId != null && personId.getValue().equals(12L)) &&
-                (name != null && "Peter".equals(name.getValue()))) {
-            addInvariantViolation("This is not allowed");
-        }
+public class Person extends Aggregate {
 
-        evaluateValidations();
-    }
+	private final PersonId personId;
+	private final Name name;
+
+
+	/**
+	 * This variant requires an all-args constructor
+	 */
+	public Person(PersonId personId, Name name) {
+		super(checks(
+				check(personId, "Person ID", isNotNullObject()),
+				check(name, "Name", isNotNullObject()),
+				check(() -> (personId != null && personId.getValue().equals(12L)) && (name != null &&"Peter".equals(name.getValue())),
+						"PersonID and Name Constraint", conformsCheck(() -> "Name " +name + " with id "+ personId+ " is not allowed"))
+		));
+		this.personId = personId;
+		this.name = name;
+	}
+
+	public Person(PersonId personId) {
+		this(personId, new Name("defaultName"));
+	}
+
+	public Person(Name name) {
+		this(new PersonId(123L), name);
+	}
+
+	public PersonId getPersonId() {
+		return personId;
+	}
+
+	public Name getName() {
+		return name;
+	}
 }