Refactoring handling of XmlPrologDirective handling (#850)

Author: cowtowncoder

src/main/java/tools/jackson/dataformat/xml/ser/ToXmlGenerator.java

@@ -100,11 +100,11 @@ public class ToXmlGenerator
      */
 
     /**
-     * Document Type Declaration to write, if any; {@code null} if none.
+     * XML directives (DTD, Comments, PIs) to write, if any.
      *
      * @since 3.2
      */
-    protected DTD _dtd;
+    protected List<XmlPrologDirective> _prologDirectives;
 
     /*
     /**********************************************************************
@@ -260,8 +260,10 @@ public void initGenerator() throws JacksonException
             }
 
             // 19-Apr-2026, tatu: [dataformat-xml#150] Allow outputting DTD
-            if (_dtd != null) {
-                _dtd.write(this, _xmlWriter);
+            if (_prologDirectives != null) {
+                for (XmlPrologDirective d : _prologDirectives) {
+                    d.write(this, _xmlWriter);
+                }
             }
 
         } catch (XMLStreamException e) {
@@ -275,12 +277,12 @@ public void initGenerator() throws JacksonException
      *
      * @since 3.2
      */
-    public void initConfig(DTD dtd)
+    public void initProlog(List<XmlPrologDirective> directives)
     {
         if (_initialized) { // sanity check
             _reportError("Internal error: cannot call `initConfig()` after generator already initialized");
         }
-        _dtd = dtd;
+        _prologDirectives = directives;
     }
 
     /*

src/main/java/tools/jackson/dataformat/xml/ser/XmlGeneratorInitializer.java

@@ -1,7 +1,12 @@
 package tools.jackson.dataformat.xml.ser;
 
+import java.util.ArrayList;
+import java.util.List;
+
 import tools.jackson.core.JacksonException;
 import tools.jackson.core.JsonGenerator;
+import tools.jackson.core.exc.StreamWriteException;
+
 import tools.jackson.databind.*;
 import tools.jackson.databind.cfg.GeneratorInitializer;
 
@@ -22,12 +27,14 @@
 public class XmlGeneratorInitializer
     implements GeneratorInitializer
 {
-    protected DTD _dtd;
+    protected List<XmlPrologDirective> _directives;
+
+    protected boolean _hasDTD;
 
     @Override
     public void initialize(SerializationConfig config, JsonGenerator g) throws JacksonException {
         if (g instanceof ToXmlGenerator xg) {
-            xg.initConfig(_dtd);
+            xg.initProlog(_directives);
         }
     }
 
@@ -60,7 +67,18 @@ public XmlGeneratorInitializer addDTD(String rootName,
      * @return This initializer for call chaining
      */
     public XmlGeneratorInitializer addDTD(DTD dtd) {
-        _dtd = dtd;
+        if (_hasDTD) {
+            throw new StreamWriteException(null, "Cannot add another `DTD`, initializer already has one");
+        }
+        _hasDTD = true;
+        return _add(dtd);
+    }
+
+    protected XmlGeneratorInitializer _add(XmlPrologDirective d) {
+        if (_directives == null) {
+            _directives = new ArrayList<>();
+        }
+        _directives.add(d);
         return this;
     }
 }

src/main/java/tools/jackson/dataformat/xml/ser/XmlPrologDirective.java

@@ -13,7 +13,13 @@
 public interface XmlPrologDirective
 {
     /**
-     * Method to call to actually write out the directive.
+     * Method to call to actually write out the directive using given
+     * {@link XMLStreamWriter2}. {@link ToXmlGenerator} is only passed
+     * in case access to configuration was needed.
+     *
+     * @param xmlGen Generator that called this method: MUST NOT call
+     *   its output methods, only to be used for configuration access
+     *   @param sw Writer to use for actual output of XML event
      */
     public void write(ToXmlGenerator xmlGen, XMLStreamWriter2 sw)
         throws XMLStreamException;