FluentBuilder<D> as interface with default method

src/main/java/org/hostsharing/hsadminng/service/dto/CustomerDTO.java

@@ -14,7 +14,7 @@ import java.util.Objects;
 /**
  * A DTO for the Customer entity.
  */
-public class CustomerDTO extends FluentBuilder<CustomerDTO> implements AccessMappings {
+public class CustomerDTO implements AccessMappings, FluentBuilder<CustomerDTO>  {
 
     @SelfId(resolver = CustomerService.class)
     @AccessFor(read = Role.ANY_CUSTOMER_USER)

src/main/java/org/hostsharing/hsadminng/service/dto/FluentBuilder.java

@@ -2,10 +2,41 @@ package org.hostsharing.hsadminng.service.dto;
 
 import java.util.function.Consumer;
 
-public class FluentBuilder<T> {
+/**
+ * Just 'implement' this interface in your class to get a pseudo fluent builder, no more code needed.
+ *
+ * @param <T> class to be build (same as to which the interface was added)
+ */
+public interface FluentBuilder<T> {
 
+    /**
+     * Allows statements on the target instance possible as expression.
+     *
+     * This allows creating nested object structures, e.g. for test data
+     * in a much more readable way.
+     *
+     * <h3>Example</h3>
+     * {code
+     *      // adding a fluent builder to your class
+     *      class YourClass implements FluentBuilder<YourClass> {
+     *          public int someField;
+     *          public String anotherField;
+     *          // ...
+     *      }
+     *
+     *      // using the fluent builder somewhere else
+     *      someMethod( new YourClass().with( it -> {
+     *          it.someField = 5;
+     *          it.anotherField = "Hello";
+     *      }));
+     * }
+     *
+     * @param builderFunction statements to apply to 'this'
+     *
+     * @return the instance on which 'with(...)' was executed.
+     */
     @SuppressWarnings("unchecked")
-    public T with(
+    default T with(
         Consumer<T> builderFunction) {
         builderFunction.accept((T) this);
         return (T) this;

src/main/java/org/hostsharing/hsadminng/service/dto/MembershipDTO.java

@@ -8,14 +8,13 @@ import org.springframework.context.ApplicationContext;
 
 import javax.validation.constraints.NotNull;
 import javax.validation.constraints.Size;
-import java.io.Serializable;
 import java.time.LocalDate;
 import java.util.Objects;
 
 /**
  * A DTO for the Membership entity.
  */
-public class MembershipDTO extends FluentBuilder<MembershipDTO> implements Serializable, AccessMappings {
+public class MembershipDTO implements AccessMappings, FluentBuilder<MembershipDTO>  {
 
     @SelfId(resolver = MembershipService.class)
     @AccessFor(read = {Role.CONTRACTUAL_CONTACT, Role.FINANCIAL_CONTACT})