An alternative approach

`GenericEndpoint` now uses `CompletionException` as a wrapper instead of
`RuntimeException`, and wraps the cause of an
`InvocationTargetException` rather than the exception itself.

org.eclipse.lsp4j.jsonrpc/src/main/java/org/eclipse/lsp4j/jsonrpc/services/GenericEndpoint.java

@@ -21,6 +21,7 @@
 import java.util.List;
 import java.util.Set;
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionException;
 import java.util.function.Function;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -64,13 +65,9 @@ protected void recursiveFindRpcMethods(Object current, Set<Class<?>> visited, Se
 					Object[] arguments = this.getArguments(method, arg);
 					return (CompletableFuture<Object>) method.invoke(current, arguments);
 				} catch (InvocationTargetException e) {
-					if (e.getTargetException() instanceof ResponseErrorException) {
-						ResponseErrorException ree = (ResponseErrorException) e.getTargetException();
-						throw ree;
-					}
-					throw new RuntimeException(e);
-				} catch ( IllegalAccessException e) {
-					throw new RuntimeException(e);
+					throw new CompletionException(e.getCause());
+				} catch (IllegalAccessException e) {
+					throw new CompletionException(e);
 				}
 			};
 			if (methodHandlers.put(methodInfo.name, handler) != null) {
@@ -86,13 +83,9 @@ protected void recursiveFindRpcMethods(Object current, Set<Class<?>> visited, Se
 					LOG.fine("A delegate object is null, jsonrpc methods of '" + method + "' are ignored");
 				}
 			} catch (InvocationTargetException e) {
-				if (e.getTargetException() instanceof ResponseErrorException) {
-					ResponseErrorException ree = (ResponseErrorException) e.getTargetException();
-					throw ree;
-				}
-				throw new RuntimeException(e);
-			} catch ( IllegalAccessException e) {
-				throw new RuntimeException(e);
+				throw new CompletionException(e.getCause());
+			} catch (IllegalAccessException e) {
+				throw new CompletionException(e);
 			}
 		});
 	}