how to migrate from opensaml 2.6 to 3.1.1

I have to migrate a class from opensaml 2.6 to opensaml 3.1.1 Compiling I obtain some errors

1)

Element plaintextElement = getElementAssertion(inputBean);
String xml = XMLHelper.prettyPrintXML(plaintextElement);

I can't find the class XMLHelper in the new version.

2)

DefaultBootstrap.bootstrap();
builderFactory = Configuration.getBuilderFactory();
Configuration.getMarshallerFactory().getMarshaller(assertion).marshall(assertion);

I can'f find class DefaultBootstrap and I can't find a class Configuration with the methods getBuilderFactory(), getMarshallerFactory()

3)

BasicCredential credential = new BasicCredential();

Now the contructor new BasicCredential() is not visible.

I haven't found documentation with deprecation indication. What must I do to port this class to the opensaml 3.1.1 version?