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})

src/test/java/org/hostsharing/hsadminng/service/accessfilter/JSonAccessFilterTestFixture.java

@@ -31,7 +31,7 @@ public class JSonAccessFilterTestFixture {
         return dto;
     }
 
-    static class GivenCustomerDto extends FluentBuilder<GivenCustomerDto> {
+    static class GivenCustomerDto implements FluentBuilder<GivenCustomerDto> {
         @SelfId(resolver = GivenService.class)
         @AccessFor(read = ANYBODY)
         Long id;
@@ -44,7 +44,7 @@ public class JSonAccessFilterTestFixture {
     static abstract class GivenCustomerService implements IdToDtoResolver<GivenCustomerDto> {
     }
 
-    static class GivenDto extends FluentBuilder<GivenDto> {
+    static class GivenDto implements FluentBuilder<GivenDto> {
         @SelfId(resolver = GivenService.class)
         @AccessFor(read = ANYBODY)
         Long id;
@@ -109,7 +109,7 @@ public class JSonAccessFilterTestFixture {
     static abstract class GivenChildService implements IdToDtoResolver<GivenChildDto> {
     }
 
-    public static class GivenChildDto extends FluentBuilder<GivenChildDto> {
+    public static class GivenChildDto implements FluentBuilder<GivenChildDto> {
 
         @SelfId(resolver = GivenChildService.class)
         @AccessFor(read = Role.ANY_CUSTOMER_USER)

src/test/java/org/hostsharing/hsadminng/service/accessfilter/JSonDeserializationWithAccessFilterUnitTest.java

@@ -73,18 +73,20 @@ public class JSonDeserializationWithAccessFilterUnitTest {
         given(ctx.getAutowireCapableBeanFactory()).willReturn(autowireCapableBeanFactory);
         given(autowireCapableBeanFactory.createBean(GivenService.class)).willReturn(givenService);
         given(givenService.findOne(1234L)).willReturn(Optional.of(new GivenDto()
-            .with(dto -> dto.id = 1234L)
+            .with( dto -> {
-            .with(dto -> dto.customerId = 888L)
+                dto.id = 1234L;
-            .with(dto -> dto.openIntegerField = 11111)
+                dto.customerId = 888L;
-            .with(dto -> dto.openPrimitiveIntField = 2222)
+                dto.openIntegerField = 11111;
-            .with(dto -> dto.openLongField = 33333333333333L)
+                dto.openPrimitiveIntField = 2222;
-            .with(dto -> dto.openPrimitiveLongField = 44444444L)
+                dto.openLongField = 33333333333333L;
-            .with(dto -> dto.openBooleanField = true)
+                dto.openPrimitiveLongField = 44444444L;
-            .with(dto -> dto.openPrimitiveBooleanField = false)
+                dto.openBooleanField = true;
-            .with(dto -> dto.openBigDecimalField = SOME_BIG_DECIMAL)
+                dto.openPrimitiveBooleanField = false;
-            .with(dto -> dto.openStringField = "3333")
+                dto.openBigDecimalField = SOME_BIG_DECIMAL;
-            .with(dto -> dto.restrictedField = "initial value of restricted field")
+                dto.openStringField = "3333";
-            .with(dto -> dto.restrictedBigDecimalField = SOME_BIG_DECIMAL)
+                dto.restrictedField = "initial value of restricted field";
+                dto.restrictedBigDecimalField = SOME_BIG_DECIMAL;
+            })
         ));
         given(autowireCapableBeanFactory.createBean(GivenCustomerService.class)).willReturn(givenCustomerService);
         given(givenCustomerService.findOne(888L)).willReturn(Optional.of(new GivenCustomerDto()