java.net.MalformedURLException:使用xsd架构验证xml字符串时没有协议

import javax.xml.XMLConstants;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;
import org.xml.sax.SAXException;
import java.io.StringReader;
import java.net.URL;

public class XMLValidator {
    public static void main(String[] args) {
        String xmlString = "<xml>...</xml>";
        String xsdUrl = "http://example.com/schema.xsd";

        try {
            URL schemaUrl = new URL(xsdUrl);
            SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
            Schema schema = factory.newSchema(schemaUrl);
            Validator validator = schema.newValidator();
            validator.validate(new StreamSource(new StringReader(xmlString)));
            System.out.println("XML is valid.");
        } catch (MalformedURLException e) {
            System.out.println("Invalid XSD URL: " + e.getMessage());
        } catch (SAXException e) {
            System.out.println("Invalid XML: " + e.getMessage());
        } catch (Exception e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}