Add comprehensive Javadoc to XmlNodeBuilder (#11925)

Document the multi-document stream reading behavior, whitespace
trimming semantics, empty vs self-closing element handling, and
child-vs-text-value semantics. Also document all public build()
overloads and the InputLocationBuilder interface.

Closes #11526

Author: utafrali

impl/maven-xml/src/main/java/org/apache/maven/internal/xml/XmlNodeBuilder.java

@@ -32,53 +32,141 @@
 import org.codehaus.plexus.util.xml.pull.XmlPullParserException;
 
 /**
- * All methods in this class attempt to fully parse the XML.
- * The caller is responsible for closing {@code InputStream} and {@code Reader} arguments.
+ * Builds an {@link XmlNodeImpl} DOM tree from XML input using an {@link XmlPullParser}.
+ *
+ * <p>All {@code build} methods in this class parse a single XML document element (including
+ * its children) from the input and return it as an {@link XmlNodeImpl}. The caller is
+ * responsible for closing any {@link InputStream} or {@link Reader} passed to these methods.</p>
+ *
+ * <h2>Multi-document stream reading</h2>
+ *
+ * <p>When the underlying {@link Reader} or {@link InputStream} contains multiple concatenated
+ * XML documents, each call to {@code build} consumes exactly one root element and its children.
+ * The stream position is left immediately after the closing tag of that element, so a subsequent
+ * call to {@code build} with a new parser wrapping the same reader will parse the next document.
+ * For example, given a reader over the concatenation of two identical documents:</p>
+ *
+ * <pre>
+ *   String doc = "&lt;?xml version='1.0'?&gt;&lt;doc&gt;&lt;child&gt;foo&lt;/child&gt;&lt;/doc&gt;";
+ *   Reader r = new StringReader(doc + doc);
+ *   XmlNode first  = XmlService.read(r);   // reads the first &lt;doc&gt;
+ *   XmlNode second = XmlService.read(r);   // reads the second &lt;doc&gt;
+ *   // first.equals(second) is true
+ * </pre>
+ *
+ * <h2>Whitespace trimming</h2>
+ *
+ * <p>By default, text content is trimmed of leading and trailing whitespace. This can be
+ * disabled by passing {@code trim = false}, or on a per-element basis by setting the
+ * {@code xml:space="preserve"} attribute on an element.</p>
+ *
+ * <h2>Empty vs. self-closing elements</h2>
+ *
+ * <p>Self-closing tags (e.g. {@code <item/>}) produce a node whose value is {@code null}.
+ * An element with an explicit open and close tag but no content (e.g. {@code <item></item>})
+ * produces a node whose value is the empty string {@code ""}.</p>
+ *
+ * <h2>Child elements vs. text content</h2>
+ *
+ * <p>If an element contains child elements, the resulting node carries the children and its
+ * text value is {@code null}, even if there is interleaved text content. If an element
+ * contains only text (no child elements), the node carries the text value and has no
+ * children.</p>
+ *
+ * @deprecated Use {@link org.apache.maven.api.xml.XmlService} instead.
  */
 @Deprecated
 public class XmlNodeBuilder {
     private static final boolean DEFAULT_TRIM = true;
 
+    /**
+     * Builds an XML node tree from the given reader, trimming whitespace by default and
+     * without tracking input locations.
+     *
+     * @param reader the reader to parse XML from
+     * @return the parsed XML node tree
+     * @throws XmlPullParserException if the XML is not well-formed
+     * @throws IOException if an I/O error occurs while reading
+     */
     public static XmlNodeImpl build(Reader reader) throws XmlPullParserException, IOException {
         return build(reader, (InputLocationBuilder) null);
     }
 
     /**
-     * @param reader the reader
-     * @param locationBuilder the builder
+     * Builds an XML node tree from the given reader, trimming whitespace by default.
+     *
+     * @param reader the reader to parse XML from
+     * @param locationBuilder optional builder for recording input locations of parsed elements,
+     *                        or {@code null} to skip location tracking
+     * @return the parsed XML node tree
+     * @throws XmlPullParserException if the XML is not well-formed
+     * @throws IOException if an I/O error occurs while reading
      * @since 3.2.0
-     * @return DOM
-     * @throws XmlPullParserException XML well-formedness error
-     * @throws IOException I/O error reading file or stream
      */
     public static XmlNodeImpl build(Reader reader, InputLocationBuilder locationBuilder)
             throws XmlPullParserException, IOException {
         return build(reader, DEFAULT_TRIM, locationBuilder);
     }
 
+    /**
+     * Builds an XML node tree from the given input stream, trimming whitespace by default.
+     *
+     * @param is the input stream to parse XML from
+     * @param encoding the character encoding of the stream (e.g. {@code "UTF-8"}),
+     *                 or {@code null} to let the parser detect it
+     * @return the parsed XML node tree
+     * @throws XmlPullParserException if the XML is not well-formed
+     * @throws IOException if an I/O error occurs while reading
+     */
     public static XmlNodeImpl build(InputStream is, String encoding) throws XmlPullParserException, IOException {
         return build(is, encoding, DEFAULT_TRIM);
     }
 
+    /**
+     * Builds an XML node tree from the given input stream.
+     *
+     * @param is the input stream to parse XML from
+     * @param encoding the character encoding of the stream (e.g. {@code "UTF-8"}),
+     *                 or {@code null} to let the parser detect it
+     * @param trim if {@code true}, leading and trailing whitespace is removed from text
+     *             content unless the element has {@code xml:space="preserve"}
+     * @return the parsed XML node tree
+     * @throws XmlPullParserException if the XML is not well-formed
+     * @throws IOException if an I/O error occurs while reading
+     */
     public static XmlNodeImpl build(InputStream is, String encoding, boolean trim)
             throws XmlPullParserException, IOException {
         XmlPullParser parser = new MXParser();
         parser.setInput(is, encoding);
         return build(parser, trim);
     }
 
+    /**
+     * Builds an XML node tree from the given reader without location tracking.
+     *
+     * @param reader the reader to parse XML from
+     * @param trim if {@code true}, leading and trailing whitespace is removed from text
+     *             content unless the element has {@code xml:space="preserve"}
+     * @return the parsed XML node tree
+     * @throws XmlPullParserException if the XML is not well-formed
+     * @throws IOException if an I/O error occurs while reading
+     */
     public static XmlNodeImpl build(Reader reader, boolean trim) throws XmlPullParserException, IOException {
         return build(reader, trim, null);
     }
 
     /**
-     * @param reader the reader
-     * @param trim to trim
-     * @param locationBuilder the builder
+     * Builds an XML node tree from the given reader.
+     *
+     * @param reader the reader to parse XML from
+     * @param trim if {@code true}, leading and trailing whitespace is removed from text
+     *             content unless the element has {@code xml:space="preserve"}
+     * @param locationBuilder optional builder for recording input locations of parsed elements,
+     *                        or {@code null} to skip location tracking
+     * @return the parsed XML node tree
+     * @throws XmlPullParserException if the XML is not well-formed
+     * @throws IOException if an I/O error occurs while reading
      * @since 3.2.0
-     * @return DOM
-     * @throws XmlPullParserException XML well-formedness error
-     * @throws IOException I/O error reading file or stream
      */
     public static XmlNodeImpl build(Reader reader, boolean trim, InputLocationBuilder locationBuilder)
             throws XmlPullParserException, IOException {
@@ -87,22 +175,57 @@ public static XmlNodeImpl build(Reader reader, boolean trim, InputLocationBuilde
         return build(parser, trim, locationBuilder);
     }
 
+    /**
+     * Builds an XML node tree from the given pull parser, trimming whitespace by default and
+     * without tracking input locations.
+     *
+     * @param parser the pull parser positioned at or before the root element's start tag
+     * @return the parsed XML node tree
+     * @throws XmlPullParserException if the XML is not well-formed
+     * @throws IOException if an I/O error occurs while reading
+     */
     public static XmlNodeImpl build(XmlPullParser parser) throws XmlPullParserException, IOException {
         return build(parser, DEFAULT_TRIM);
     }
 
+    /**
+     * Builds an XML node tree from the given pull parser without location tracking.
+     *
+     * @param parser the pull parser positioned at or before the root element's start tag
+     * @param trim if {@code true}, leading and trailing whitespace is removed from text
+     *             content unless the element has {@code xml:space="preserve"}
+     * @return the parsed XML node tree
+     * @throws XmlPullParserException if the XML is not well-formed
+     * @throws IOException if an I/O error occurs while reading
+     */
     public static XmlNodeImpl build(XmlPullParser parser, boolean trim) throws XmlPullParserException, IOException {
         return build(parser, trim, null);
     }
 
     /**
+     * Core parsing method. Builds an XML node tree from the given pull parser.
+     *
+     * <p>Parsing begins at the parser's current event and consumes tokens through the
+     * matching end tag of the first start tag encountered. When this method returns, the
+     * parser is positioned immediately after that end tag, so the caller (or a subsequent
+     * {@code build} call) can continue reading the same stream.</p>
+     *
+     * <p>Child elements are parsed recursively. If the element contains only text content
+     * (no child elements), the text is stored as the node's value. If child elements are
+     * present, the text value is {@code null} and children are accessible via
+     * {@link XmlNodeImpl#getChildren()}.</p>
+     *
+     * @param parser the pull parser positioned at or before the root element's start tag
+     * @param trim if {@code true}, leading and trailing whitespace is removed from text
+     *             content unless the element has {@code xml:space="preserve"}
+     * @param locationBuilder optional builder for recording input locations of parsed elements,
+     *                        or {@code null} to skip location tracking
+     * @return the parsed XML node tree
+     * @throws XmlPullParserException if the XML is not well-formed
+     * @throws IOException if an I/O error occurs while reading
+     * @throws IllegalStateException if the end of the document is reached before the root
+     *                               element's end tag is found
      * @since 3.2.0
-     * @param locationBuilder builder
-     * @param parser the parser
-     * @param trim do trim
-     * @return DOM
-     * @throws XmlPullParserException XML well-formedness error
-     * @throws IOException I/O error reading file or stream
      */
     public static XmlNodeImpl build(XmlPullParser parser, boolean trim, InputLocationBuilder locationBuilder)
             throws XmlPullParserException, IOException {
@@ -157,11 +280,22 @@ public static XmlNodeImpl build(XmlPullParser parser, boolean trim, InputLocatio
     }
 
     /**
-     * Input location builder interface, to be implemented to choose how to store data.
+     * Callback interface for creating input location objects during parsing.
+     *
+     * <p>Implementations determine how source location information (line number, column, etc.)
+     * is captured and stored for each parsed element. The returned object is attached to the
+     * resulting {@link XmlNodeImpl} as its location.</p>
      *
      * @since 3.2.0
      */
     public interface InputLocationBuilder {
+        /**
+         * Creates an input location object from the parser's current position.
+         *
+         * @param parser the pull parser, positioned at the start tag of the element being built
+         * @return an object representing the source location, or {@code null} if location
+         *         tracking is not needed for this element
+         */
         Object toInputLocation(XmlPullParser parser);
     }
 }