Fix #304 - Better error message if wrong generic type is used

hapi-fhir-base/src/main/java/ca/uhn/fhir/util/ElementUtil.java

@@ -99,7 +99,14 @@ public class ElementUtil {
 			return true;
 		}
 		for (int i = 0; i < theElements.size(); i++) {
-			IBase next = theElements.get(i);
+			IBase next;
+			try {
+				next = theElements.get(i);
+			} catch (ClassCastException e) {
+				List<?> elements = theElements;
+				String s = "Found instance of " + elements.get(i).getClass() + " - Did you set a field value to the incorrect type? Expected " + IBase.class.getName();
+				throw new ClassCastException(s);
+			}
 			if (next != null && !next.isEmpty()) {
 				return false;
 			}

hapi-fhir-structures-dstu2/src/test/java/ca/uhn/fhir/model/dstu2/ModelDstu2Test.java

@@ -1,7 +1,6 @@
 package ca.uhn.fhir.model.dstu2;
 
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.fail;
 
 import java.util.Arrays;
 import java.util.List;
@@ -18,21 +17,17 @@ public class ModelDstu2Test {
 	/**
 	 * See #304
 	 */
-	@SuppressWarnings("rawtypes")
+	@SuppressWarnings({ "rawtypes", "unchecked" })
 	@Test
 	public void testPopulateWrongGenericType() {
 		Patient p = new Patient();
 		List names = Arrays.asList("name");
+		p.setName(names);
 
-		p.setName(null);
-
-		ourCtx.newXmlParser().encodeResourceToString(p);
-		
 		try {
-			p.setName(names);
-			fail();
+			ourCtx.newXmlParser().encodeResourceToString(p);
 		} catch (ClassCastException e) {
-			assertEquals("Failed to set invalid value, found element in list of type String but expected ca.uhn.fhir.model.dstu2.composite.HumanNameDt", e.getMessage());
+			assertEquals("Found instance of class java.lang.String - Did you set a field value to the incorrect type? Expected org.hl7.fhir.instance.model.api.IBase", e.getMessage());
 		}
 	}
 

src/changes/changes.xml

@@ -164,6 +164,12 @@
 				other similar errors are handled. This allows the parser to be more lenient
 				when needed.
 			</action>
+			<action type="add" issue="304">
+				Improve error message if incorrect type is placed in a list field in the data model. Java
+				uses generics to prevent this at compile time, but if someone is in an environment without 
+				generics this helps improve the error message at runtime. Thanks to Hugo Soares for
+				suggesting.
+			</action>
 		</release>
 		<release version="1.4" date="2016-02-04">
 			<action type="add">