Refactor: surface static-init failures as ExceptionInInitializerError

src/main/java/org/apache/commons/xml/FallbackIgnoreLSResourceResolver.java

@@ -37,13 +37,13 @@
 final class FallbackIgnoreLSResourceResolver implements LSResourceResolver {
 
     /** DOM Level 3 Load/Save implementation used to build the empty input for unresolved lookups. */
-    private static final DOMImplementationLS DOM_LS = domImplementationLS();
+    private static final DOMImplementationLS DOM_LS;
 
-    private static DOMImplementationLS domImplementationLS() {
+    static {
         try {
-            return (DOMImplementationLS) DOMImplementationRegistry.newInstance().getDOMImplementation("LS");
-        } catch (final ClassNotFoundException | InstantiationException | IllegalAccessException e) {
-            throw new HardeningException("No DOM Level 3 Load/Save implementation available to build the empty schema input", e);
+            DOM_LS = (DOMImplementationLS) DOMImplementationRegistry.newInstance().getDOMImplementation("LS");
+        } catch (final ReflectiveOperationException e) {
+            throw new ExceptionInInitializerError(e);
         }
     }
 

src/main/java/org/apache/commons/xml/FallbackIgnoreURIResolver.java

@@ -20,7 +20,6 @@
 import java.util.function.Supplier;
 
 import javax.xml.parsers.DocumentBuilderFactory;
-import javax.xml.parsers.FactoryConfigurationError;
 import javax.xml.parsers.ParserConfigurationException;
 import javax.xml.transform.Source;
 import javax.xml.transform.TransformerException;
@@ -53,11 +52,10 @@
      * Backing for the default ignore outcome. Consumers parse the resolved {@link Source}, and an empty character stream is not a well-formed XML document
      * (XSLTC rejects it for {@code document()} and for an ignored {@code xsl:include}/{@code xsl:import}), so the default supplier answers with a well-formed
      * empty document that evaluates to no content. It is never mutated, so one instance serves every resolution.
-     *
-     * @see #newEmptyDocument()
      */
-    private static final Document EMPTY_DOCUMENT = newEmptyDocument();
+    private static final Document EMPTY_DOCUMENT;
 
+    static {
     /**
      * Creates a new empty document.
      *
@@ -66,11 +64,12 @@
      * @throws FactoryConfigurationError Thrown from a factory in case of a {@link java.util.ServiceConfigurationError service
      *                                   configuration error} or if the implementation is not available or cannot be instantiated.
      */
     private static Document newEmptyDocument() {
         try {
-            return DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
+            EMPTY_DOCUMENT = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
         } catch (final ParserConfigurationException e) {
-            throw new HardeningException("A DocumentBuilder cannot be created which satisfies the configuration requested.", e);
+            // Checked exceptions cannot escape static initialization; a FactoryConfigurationError from newInstance() already can and propagates as-is.
+            throw new ExceptionInInitializerError(e);
         }
     }