Implement MUCH simpler SAX-driven XML parser.

guacamole/src/main/java/net/sourceforge/guacamole/net/basic/xml/DocumentHandler.java

@@ -0,0 +1,183 @@
+package net.sourceforge.guacamole.net.basic.xml;
+
+/*
+ *  Guacamole - Clientless Remote Desktop
+ *  Copyright (C) 2010  Michael Jumper
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+import java.util.LinkedList;
+import org.xml.sax.Attributes;
+import org.xml.sax.SAXException;
+import org.xml.sax.helpers.DefaultHandler;
+
+/**
+ * A simple ContentHandler implementation which digests SAX document events and
+ * produces simpler tag-level events, maintaining its own stack for the
+ * convenience of the tag handlers.
+ * 
+ * @author Mike Jumper
+ */
+public class DocumentHandler extends DefaultHandler {
+
+    /**
+     * The name of the root element of the document.
+     */
+    private String rootElementName;
+    
+    /**
+     * The handler which will be used to handle element events for the root
+     * element of the document.
+     */
+    private TagHandler root;
+
+    /**
+     * The stack of all states applicable to the current parser state. Each
+     * element of the stack references the TagHandler for the element being
+     * parsed at that level of the document, where the current element is
+     * last in the stack, and the root element is first.
+     */
+    private LinkedList<DocumentHandlerState> stack =
+            new LinkedList<DocumentHandlerState>();
+
+    /**
+     * Creates a new DocumentHandler which will use the given TagHandler
+     * to handle the root element.
+     * 
+     * @param rootElementName The name of the root element of the document
+     *                        being handled.
+     * @param root The TagHandler to use for the root element.
+     */
+    public DocumentHandler(String rootElementName, TagHandler root) {
+        this.root = root;
+        this.rootElementName = rootElementName;
+    }
+    
+    /**
+     * Returns the current element state. The current element state is the
+     * state of the element the parser is currently within.
+     * 
+     * @return The current element state.
+     */
+    private DocumentHandlerState getCurrentState() {
+        return stack.getLast();
+    }
+    
+    @Override
+    public void startElement(String uri, String localName, String qName,
+        Attributes attributes) throws SAXException {
+
+        // Get current state
+        DocumentHandlerState current = getCurrentState();
+        
+        // Handler for tag just read
+        TagHandler handler;
+
+        // If no stack, use root handler
+        if (current == null) {
+
+            // Validate element name
+            if (!localName.equals(rootElementName))
+                throw new SAXException("Root element must be '" + rootElementName + "'");
+            
+            handler = root;
+        }
+
+        // Otherwise, get handler from parent
+        else {
+            TagHandler parent_handler = current.getTagHandler();
+            handler = parent_handler.childElement(localName, attributes);
+        }
+
+        // Append new element state to stack
+        stack.addLast(new DocumentHandlerState(handler));
+        
+    }
+
+    @Override
+    public void endElement(String uri, String localName, String qName)
+            throws SAXException {
+
+        // Pop last element from stack
+        DocumentHandlerState completed = stack.removeLast();
+
+        // Finish element by sending text content
+        completed.getTagHandler().complete(
+                completed.getTextContent().toString());
+
+    }
+
+    @Override
+    public void characters(char[] ch, int start, int length)
+            throws SAXException {
+
+        // Append received chunk to text content
+        getCurrentState().getTextContent().append(ch, start, length);
+
+    }
+
+    /**
+     * The current state of the DocumentHandler.
+     */
+    private class DocumentHandlerState {
+
+        /**
+         * The current text content of the current element being parsed.
+         */
+        private StringBuilder textContent = new StringBuilder();
+
+        /**
+         * The TagHandler which must handle document events related to the
+         * element currently being parsed.
+         */
+        private TagHandler tagHandler;
+       
+        /**
+         * Creates a new DocumentHandlerState which will maintain the state
+         * of parsing of the current element, as well as contain the TagHandler
+         * which will receive events related to that element.
+         * 
+         * @param tagHandler The TagHandler which should receive any events
+         *                   related to the element being parsed.
+         */
+        public DocumentHandlerState(TagHandler tagHandler) {
+            this.tagHandler = tagHandler;
+        }
+
+        /**
+         * Returns the mutable StringBuilder which contains the current text
+         * content of the element being parsed.
+         * 
+         * @return The mutable StringBuilder which contains the current text
+         *         content of the element being parsed.
+         */
+        public StringBuilder getTextContent() {
+            return textContent;
+        }
+
+        /**
+         * Returns the TagHandler which must handle any events relating to the
+         * element being parsed.
+         * 
+         * @return The TagHandler which must handle any events relating to the
+         *         element being parsed.
+         */
+        public TagHandler getTagHandler() {
+            return tagHandler;
+        }
+        
+    }
+
+}

guacamole/src/main/java/net/sourceforge/guacamole/net/basic/xml/TagHandler.java

@@ -0,0 +1,57 @@
+package net.sourceforge.guacamole.net.basic.xml;
+
+/*
+ *  Guacamole - Clientless Remote Desktop
+ *  Copyright (C) 2010  Michael Jumper
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+import org.xml.sax.Attributes;
+import org.xml.sax.SAXException;
+
+/**
+ * A simple element-level event handler for events triggered by the
+ * SAX-driven DocumentHandler parser.
+ * 
+ * @author Mike Jumper 
+ */
+public interface TagHandler {
+
+    /**
+     * Called when a child element of the current element is parsed.
+     * 
+     * @param localName The local name of the child element seen.
+     * @param attributes The attributes of the child element seen.
+     * @return The TagHandler which should handle all element-level events
+     *         related to the child element.
+     * @throws SAXException If the child element being parsed was not expected,
+     *                      or some other error prevents a proper TagHandler
+     *                      from being constructed for the child element.
+     */
+    public TagHandler childElement(String localName, Attributes attributes)
+            throws SAXException;
+   
+    /**
+     * Called when this element, and all child elements, have been fully parsed,
+     * and the entire text content of this element (if any) is available.
+     * 
+     * @param textContent The full text content of this element, if any.
+     * @throws SAXException If the text content received is not valid for any
+     *                      reason, or the child elements parsed are not
+     *                      correct.
+     */
+    public void complete(String textContent) throws SAXException;
+    
+}