Fix DtoServer error messages (eclipse-che#5764)

* Fix error message of getting DTO implementation
* Handle non-interface types and types with DTO annotation in parent
Signed-off-by: Dmytro Nochevnov <dnochevnov@codenvy.com>

* Small refactor

Signed-off-by: Dmytro Nochevnov <dnochevnov@codenvy.com>

* Small fixes

Signed-off-by: Dmytro Nochevnov <dnochevnov@codenvy.com>

Author: dmytro-ndp

core/che-core-api-dto/src/main/java/org/eclipse/che/dto/server/DtoFactory.java

@@ -42,6 +42,8 @@
 import java.util.ServiceLoader;
 import java.util.concurrent.ConcurrentHashMap;
 
+import static java.lang.String.format;
+
 /**
  * Provides implementations of DTO interfaces.
  *
@@ -386,11 +388,41 @@ public <T> JsonStringMap<T> createMapDtoFromJson(InputStream json, Class<T> dtoI
     private <T> DtoProvider<T> getDtoProvider(Class<T> dtoInterface) {
         DtoProvider<?> dtoProvider = dtoInterface2Providers.get(dtoInterface);
         if (dtoProvider == null) {
-            throw new IllegalArgumentException("Unknown DTO type " + dtoInterface);
+            if (!dtoInterface.isInterface()) {
+                throw new IllegalArgumentException(format("Only interfaces can be DTO, but %s is not", dtoInterface));
+            }
+
+            if (hasDtoAnnotation(dtoInterface)) {
+                throw new IllegalArgumentException(format("Provider of implementation for DTO type %s isn't found", dtoInterface));
+            } else {
+                throw new IllegalArgumentException(dtoInterface + " is not a DTO type");
+            }
         }
+
         return (DtoProvider<T>)dtoProvider;
     }
 
+    /**
+     * Checks if dtoInterface or its parent have DTO annotation.
+     *
+     * @param dtoInterface
+     *          DTO interface
+     * @return true if only dtoInterface or one of its parent have DTO annotation.
+     */
+    private boolean hasDtoAnnotation(Class dtoInterface) {
+        if (dtoInterface.isAnnotationPresent(DTO.class)) {
+            return true;
+        }
+
+        for (Class parent: dtoInterface.getInterfaces()) {
+            if (hasDtoAnnotation(parent)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     /**
      * Registers DtoProvider for DTO interface.
      *

core/che-core-api-dto/src/test/java/org/eclipse/che/dto/ServerDtoTest.java

@@ -19,11 +19,11 @@
 
 import org.eclipse.che.dto.definitions.ComplicatedDto;
 import org.eclipse.che.dto.definitions.DTOHierarchy;
+import org.eclipse.che.dto.definitions.DTOHierarchy.GrandchildDto;
 import org.eclipse.che.dto.definitions.DtoWithAny;
 import org.eclipse.che.dto.definitions.DtoWithDelegate;
 import org.eclipse.che.dto.definitions.DtoWithFieldNames;
 import org.eclipse.che.dto.definitions.SimpleDto;
-import org.eclipse.che.dto.definitions.DTOHierarchy.GrandchildDto;
 import org.eclipse.che.dto.definitions.model.Model;
 import org.eclipse.che.dto.definitions.model.ModelComponentDto;
 import org.eclipse.che.dto.definitions.model.ModelDto;
@@ -108,7 +108,7 @@ public void testSerializerWithFieldNames() throws Exception {
     }
 
     @Test
-    public void testDeerializerWithFieldNames() throws Exception {
+    public void testDeserializerWithFieldNames() throws Exception {
         final String fooString = "Something";
         final String _default = "test_default_keyword";
 
@@ -380,4 +380,16 @@ public void shouldBeAbleToExtendsNotDTOInterfacesHierarchyWithDTOInterface() {
         assertEquals(childDto.getChildField(), "child-field");
         assertEquals(childDto.getParentField(), "parent-field");
     }
+
+    @Test(expectedExceptions = IllegalArgumentException.class,
+          expectedExceptionsMessageRegExp = "Only interfaces can be DTO, but class java.lang.String is not")
+    public void shouldThrowExceptionWhenThereIsClassType() {
+        DtoFactory.newDto(String.class);
+    }
+
+    @Test(expectedExceptions = IllegalArgumentException.class,
+          expectedExceptionsMessageRegExp = "interface org.eclipse.che.dto.definitions.DTOHierarchy\\$GrandchildWithoutDto is not a DTO type")
+    public void shouldThrowExceptionWhenInterfaceIsNotAnnotatedAsDto() {
+        DtoFactory.newDto(DTOHierarchy.GrandchildWithoutDto.class);
+    }
 }

core/che-core-api-dto/src/test/java/org/eclipse/che/dto/definitions/DTOHierarchy.java

@@ -13,6 +13,8 @@
 
 import org.eclipse.che.dto.shared.DTO;
 
+import java.io.Closeable;
+
 /**
  * Keeps DTO interfaces for hierarchy test
  *
@@ -60,4 +62,10 @@ public interface GrandchildDto extends ChildDto {
         void setShadowedField(GrandchildDto v);
     }
 
+    public interface Child2 extends Parent {
+        String getChild2Field();
+    }
+
+    public interface GrandchildWithoutDto extends Child, Child2 {
+    }
 }