GWT-RPC Linter that checks that serializable interfaces have implementations and serializable classes have default constructors and serializable fields. Should be invoked from a GWT Generator

GwtRpcLinter.java

public class GwtRpcLinter {
	public static final String PACKAGE_PREFIX = "com.yourcompany"; // only check classes in this package

	private TreeLogger logger;
	private GeneratorContext context;
	private List<String> errorMessages = new ArrayList<>();

	public GwtRpcLinter(TreeLogger logger, GeneratorContext context) {
		this.logger = logger;
		this.context = context;
	}

	public void run() throws UnableToCompleteException {
		TreeLogger lintLogger = logger.branch(TreeLogger.Type.WARN, "GWT-RPC Linter started");

		JClassType type = context.getTypeOracle().findType("com.google.gwt.user.client.rpc.IsSerializable");
		checkSubTypes(type);

		JClassType type2 = context.getTypeOracle().findType("java.io.Serializable");
		checkSubTypes(type2);

		if (errorMessages.isEmpty()) {
			lintLogger.log(TreeLogger.Type.INFO, "GWT-RPC Linter completed without errors");
		} else {
			lintLogger.log(TreeLogger.Type.WARN, "GWT-RPC Linter failed with " + errorMessages.size() + "  errors");
			for (String errorMessage : errorMessages) {
				System.err.println(errorMessage);
				lintLogger.log(TreeLogger.Type.WARN, errorMessage);
			}
			// todo: raise level to ERROR and throw this exception when we are sure it does the right thing.
//			throw new UnableToCompleteException();
		}
	}

	private void checkSubTypes(JClassType type) {
		JClassType[] serializableTypes = type.getSubtypes();
		for (JClassType serializableType : serializableTypes) {
			if (serializableType.getPackage().getName().startsWith(PACKAGE_PREFIX)) {
				if (isSerializableInterfaceWithoutImplementation(serializableType)) {
					errorMessages.add("Serializable/IsSerializable interface " + serializableType + " has no implementation.");
				}

				if (isConcreteClass(serializableType)) {
					if (!hasDefaultConstructor(serializableType)) {
						errorMessages.add("Serializable/IsSerializable class " + serializableType + " has no default constructor.");
					}

					JField[] fields = serializableType.getFields();
					for (JField field : fields) {
						boolean serializableField = isSerializableOrTransientField(field);
						if (!serializableField) {
							errorMessages.add("Serializable/IsSerializable class " + serializableType + " has non-transient field " + field.getName() + " that is not serializable");
						}
					}
				}
			}
		}
	}

	private boolean isSerializableOrTransientField(JField field) {
		boolean serializableField = false;

		JClassType fieldClass = field.getType().isClassOrInterface();
		if (fieldClass != null && !field.isTransient()) {
			JClassType[] interfaces = fieldClass.getImplementedInterfaces();
			for (JClassType anInterface : interfaces) {
				if ("com.google.gwt.user.client.rpc.IsSerializable".equals(anInterface.getName()) ||
				    "java.io.Serializable".equals(anInterface.getName())) {
					serializableField = true;
				}
			}
		} else {
			serializableField = true;
		}

		return serializableField;
	}

	private boolean hasDefaultConstructor(JClassType serializableType) {
		if (serializableType.getConstructors().length == 0) return true;
		try {
			JConstructor defaultConstructor = serializableType.getConstructor(new JType[]{});
			return true;
		} catch (NotFoundException e) {
			return false;
		}
	}

	private boolean isConcreteClass(JClassType serializableType) {
		return !(serializableType.isAbstract() || serializableType.isInterface() == null);
	}

	private boolean isSerializableInterfaceWithoutImplementation(JClassType serializableType) {
		return serializableType.isInterface() != null && serializableType.getSubtypes().length == 0;
	}

}