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    <p>In general <strong>Value Objects</strong> should be Immutable. Like <em>Integer</em> or <em>String</em> objects in Java. We can use them for transferring data between software layers. If the software layers or services running in different remote nodes like in a microservices environment or in a legacy Java Enterprise App. We must make almost exact copies of two classes. This is the where we met DTOs.</p> <pre><code>|-----------| |--------------| | SERVICE 1 |--&gt; Credentials DTO &gt;--------&gt; Credentials DTO &gt;-- | AUTH SERVICE | |-----------| |--------------| </code></pre> <p>In legacy Java Enterprise Systems DTOs can have various EJB stuff in it.</p> <p>I do not know this is a best practice or not but I personally use <strong>Value Objects</strong> in my Spring MVC/Boot Projects like this:</p> <pre><code> |------------| |------------------| |------------| -&gt; Form | | -&gt; Form | | -&gt; Entity | | | Controller | | Service / Facade | | Repository | &lt;- View | | &lt;- View | | &lt;- Entity / Projection View | | |------------| |------------------| |------------| </code></pre> <p><strong>Controller</strong> layer doesn't know what are the entities are. It communicates with <strong>Form</strong> and <strong>View Value Objects</strong>. Form Objects has JSR 303 Validation annotations (for instance @NotNull) and <strong>View Value Objects</strong> have Jackson Annotations for custom serialization. (for instance @JsonIgnore)</p> <p>Service layer communicates with repository layer via using Entity Objects. Entity objects have JPA/Hibernate/Spring Data annotations on it. Every layer communicates with only the lower layer. The inter-layer communication is prohibited because of circular/cyclic dependency.</p> <pre><code>User Service ----&gt; XX CANNOT CALL XX ----&gt; Order Service </code></pre> <p>Some <strong>ORM</strong> Frameworks have the ability of projection via using additional interfaces or classes. So repositories can return View objects directly. There for you do not need an additional transformation.</p> <p>For instance this is our User entity:</p> <pre class="lang-java prettyprint-override"><code>@Entity public final class User { private String id; private String firstname; private String lastname; private String phone; private String fax; private String address; // Accessors ... } </code></pre> <p>But you should return a Paginated list of users that just include id, firstname, lastname. Then you can create a View Value Object for ORM projection.</p> <pre class="lang-java prettyprint-override"><code>public final class UserListItemView { private String id; private String firstname; private String lastname; // Accessors ... } </code></pre> <p>You can easily get the paginated result from repository layer. Thanks to spring you can also use just interfaces for projections.</p> <pre class="lang-java prettyprint-override"><code>List&lt;UserListItemView&gt; find(Pageable pageable); </code></pre> <p>Don't worry for other conversion operations <code>BeanUtils.copy</code> method works just fine.</p>
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