Issue #10066 - Allow customization of `SAXParserFactory` and `SAXParser` in `XmlParser` (#10067)

* Allow customization of SAXParserFactory / SAXParser in XmlParser
* Introduce method `.getSAXParser()`
---------

Signed-off-by: Joakim Erdfelt <joakim.erdfelt@gmail.com>
Co-authored-by: Greg Wilkins <gregw@webtide.com>

jetty-xml/src/main/java/org/eclipse/jetty/xml/XmlParser.java

@@ -66,7 +66,7 @@ public class XmlParser
      */
     public XmlParser()
     {
-        SAXParserFactory factory = SAXParserFactory.newInstance();
+        SAXParserFactory factory = newSAXParserFactory();
         boolean validatingDefault = factory.getClass().toString().contains("org.apache.xerces.");
         String validatingProp = System.getProperty("org.eclipse.jetty.xml.XmlParser.Validating", validatingDefault ? "true" : "false");
         boolean validating = Boolean.valueOf(validatingProp).booleanValue();
@@ -83,11 +83,16 @@ public class XmlParser
         return _lock.lock();
     }
 
+    protected SAXParserFactory newSAXParserFactory()
+    {
+        return SAXParserFactory.newInstance();
+    }
+
     public void setValidating(boolean validating)
     {
         try
         {
-            SAXParserFactory factory = SAXParserFactory.newInstance();
+            SAXParserFactory factory = newSAXParserFactory();
             factory.setValidating(validating);
             _parser = factory.newSAXParser();
 
@@ -129,6 +134,11 @@ public class XmlParser
         return _parser.isValidating();
     }
 
+    public SAXParser getSAXParser()
+    {
+        return _parser;
+    }
+
     public void redirectEntity(String name, URL entity)
     {
         if (entity != null)

jetty-xml/src/test/java/org/eclipse/jetty/xml/XmlParserTest.java

@@ -14,10 +14,17 @@
 package org.eclipse.jetty.xml;
 
 import java.net.URL;
+import javax.xml.parsers.SAXParser;
+import javax.xml.parsers.SAXParserFactory;
 
 import org.junit.jupiter.api.Test;
+import org.xml.sax.SAXException;
+import org.xml.sax.XMLReader;
 
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assumptions.assumeTrue;
 
 public class XmlParserTest
 {
@@ -38,4 +45,32 @@ public class XmlParserTest
         assertTrue(testDocStr.startsWith("<Configure"));
         assertTrue(testDocStr.endsWith("</Configure>"));
     }
+
+    /**
+     * Customize SAXParserFactory behavior.
+     */
+    @Test
+    public void testNewSAXParserFactory() throws SAXException
+    {
+        XmlParser xmlParser = new XmlParser()
+        {
+            @Override
+            protected SAXParserFactory newSAXParserFactory()
+            {
+                SAXParserFactory saxParserFactory = super.newSAXParserFactory();
+                // Configure at factory level
+                saxParserFactory.setXIncludeAware(false);
+                return saxParserFactory;
+            }
+        };
+
+        SAXParser saxParser = xmlParser.getSAXParser();
+        assertNotNull(saxParser);
+
+        XMLReader xmlReader = saxParser.getXMLReader();
+        // Only run testcase if Xerces is being used.
+        assumeTrue(xmlReader.getClass().getName().contains("org.apache.xerces."));
+        // look to see it was set at XMLReader level
+        assertFalse(xmlReader.getFeature("http://apache.org/xml/features/xinclude"));
+    }
 }