// 1 - encapsulate xml marshalling in a class
byte[] asXml(Invoice invoice) {
    ByteArrayOutputStream outStream = new ByteArrayOutputStream();
    JaxbMarshaller jaxbMarshaller = new JaxbMarshaller(Invoice.class);
    jaxbMarshaller.marshallObject(invoice, outStream);
    byte[] resultXml = outStream.toByteArray();
    IOUtils.closeQuietly(outStream);
    return resultXml;
}



// 2 - refactor to iliminate all null checks and branching
class AmazonS3File {

    private final String path;
    private Metadata metadata;

    void setMetadata(@Nullable Metadata metadata) {
        this.metadata = metadata;
    }

    @Nullable
    Metadata getMetadata() {…}
}

class AmazonS3Bucket {
    void upload(AmazonS3File file) {
        … upload ...
        if (file.getMetadata() != null) {
            uploadMetadata(file.getMetadata());
        }
    }
}



// 3 - refactor to conform to command-query separation
class Registration {

    private final RegistrationForm form;

    Optional<ValidationErrors> complete() {
        if (!form.isNotValid()) {
             … complete registration ...
        } else {
            return form.validationErrors();
        }
    }
}



// 4 - does the method violate the principle of least astonishment? why?
Ban ban(User user) {
    Ban ban = new Ban(user.ipAddress(), Period.ofDays(3));
    user.banned();
    return ban;
}