Use XML Transformer for xml serialization to fix missing default namespace when serializing xml

Author: magott

src/main/java/com/fasterxml/jackson/databind/ext/DOMSerializer.java

@@ -1,6 +1,7 @@
 package com.fasterxml.jackson.databind.ext;
 
 import java.io.IOException;
+import java.io.StringWriter;
 
 import org.w3c.dom.Node;
 import  org.w3c.dom.bootstrap.DOMImplementationRegistry;
@@ -15,29 +16,41 @@
 import com.fasterxml.jackson.databind.jsonFormatVisitors.JsonFormatVisitorWrapper;
 import com.fasterxml.jackson.databind.ser.std.StdSerializer;
 
+import javax.xml.transform.*;
+import javax.xml.transform.dom.DOMSource;
+import javax.xml.transform.stream.StreamResult;
 @SuppressWarnings("serial")
 public class DOMSerializer extends StdSerializer<Node>
 {
-    protected final DOMImplementationLS _domImpl;
+
+    private final TransformerFactory transformerFactory;
 
     public DOMSerializer() {
         super(Node.class);
-        DOMImplementationRegistry registry;
         try {
-            registry = DOMImplementationRegistry.newInstance();
+            transformerFactory = TransformerFactory.newInstance();
         } catch (Exception e) {
-            throw new IllegalStateException("Could not instantiate DOMImplementationRegistry: "+e.getMessage(), e);
+            throw new IllegalStateException("Could not instantiate TransformerFactory: "+e.getMessage(), e);
         }
-        _domImpl = (DOMImplementationLS)registry.getDOMImplementation("LS");
     }
 
     @Override
     public void serialize(Node value, JsonGenerator jgen, SerializerProvider provider)
         throws IOException
     {
-        if (_domImpl == null) throw new IllegalStateException("Could not find DOM LS");    	
-        LSSerializer writer = _domImpl.createLSSerializer();
-        jgen.writeString(writer.writeToString(value));
+        try {
+            Transformer transformer = transformerFactory.newTransformer();
+            transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
+            transformer.setOutputProperty(OutputKeys.INDENT, "no");
+            StreamResult result = new StreamResult(new StringWriter());
+            DOMSource source = new DOMSource(value);
+            transformer.transform(source, result);
+            jgen.writeString(result.getWriter().toString());
+        } catch (TransformerConfigurationException e) {
+            throw new IllegalStateException("Could not create XML Transformer: "+e.getMessage(), e);
+        } catch (TransformerException e) {
+            provider.reportMappingProblem(e,"XML Transformation failed: %s", e.getMessage());
+        }
     }
 
 	@Override

src/test/java/com/fasterxml/jackson/databind/ext/DOMTypeReadWriteTest.java

@@ -14,6 +14,8 @@ public class DOMTypeReadWriteTest extends com.fasterxml.jackson.databind.BaseMap
         "<root attr='3'><leaf>Rock &amp; Roll!</leaf><?proc instr?></root>";
     final static String SIMPLE_XML_NS =
         "<root ns:attr='abc' xmlns:ns='http://foo' />";
+    final static String SIMPLE_XML_DEFAULT_NS =
+            "<root xmlns='http://foo'/>";
 
     private final ObjectMapper MAPPER = new ObjectMapper();
 
@@ -33,6 +35,22 @@ public void testSerializeSimpleNonNS() throws Exception
         assertEquals(SIMPLE_XML, normalizeOutput(output));
     }
 
+    public void testSerializeSimpleDefaultNS() throws Exception
+    {
+        // Let's just parse first, easiest
+        Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse
+                (new InputSource(new StringReader(SIMPLE_XML_DEFAULT_NS)));
+        assertNotNull(doc);
+        // need to strip xml declaration, if any
+        String outputRaw = MAPPER.writeValueAsString(doc);
+        // And re-parse as String, since JSON has quotes...
+        String output = MAPPER.readValue(outputRaw, String.class);
+        /* ... and finally, normalize to (close to) canonical XML
+         * output (single vs double quotes, xml declaration etc)
+         */
+        assertEquals(SIMPLE_XML_DEFAULT_NS, normalizeOutput(output));
+    }
+
     public void testDeserializeNonNS() throws Exception
     {
         for (int i = 0; i < 2; ++i) {