source: josm/src/org/openstreetmap/josm/tools/XmlObjectParser.java@ 215

package org.openstreetmap.josm.tools;

import java.io.Reader;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Stack;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;

import uk.co.wilson.xml.MinML2;

/**
 * An helper class that reads from a XML stream into specific objects.
 *
 * @author Imi
 */
public class XmlObjectParser implements Iterable<Object> {

        public static class Uniform<T> implements Iterable<T>{
                private Iterator<Object> iterator;
                /**
                 * @param klass This has to be specified since generics are ereased from
                 * class files so the JVM cannot deduce T itself.
                 */
                public Uniform(Reader input, String tagname, Class<T> klass) {
                        XmlObjectParser parser = new XmlObjectParser();
                        parser.map(tagname, klass);
                        parser.start(input);
                        iterator = parser.iterator();
                }
                public Iterator<T> iterator() {
                        return new Iterator<T>(){
                                public boolean hasNext() {return iterator.hasNext();}
                                @SuppressWarnings("unchecked") public T next() {return (T)iterator.next();}
                                public void remove() {iterator.remove();}
                        };
                }
        }

        private class Parser extends MinML2 {
                Stack<Object> current = new Stack<Object>();
                String characters = "";
                @Override public void startElement(String ns, String lname, String qname, Attributes a) throws SAXException {
                        if (mapping.containsKey(qname)) {
                                Class<?> klass = mapping.get(qname).klass;
                                try {
                                        current.push(klass.newInstance());
                                } catch (Exception e) {
                                        throw new SAXException(e);
                                }
                                for (int i = 0; i < a.getLength(); ++i)
                                        setValue(a.getQName(i), a.getValue(i));
                                if (mapping.get(qname).onStart)
                                        report();
                        }
                }
                @Override public void endElement(String ns, String lname, String qname) throws SAXException {
                        if (mapping.containsKey(qname) && !mapping.get(qname).onStart)
                                report();
                        else if (characters != null && !current.isEmpty())
                                setValue(qname, characters);
                }
                @Override public void characters(char[] ch, int start, int length) {
                        String s = new String(ch, start, length);
                        characters += s;
                }

                private void report() {
                        try {
                                queue.put(current.pop());
                        } catch (InterruptedException e) {
                        }
                        characters = "";
                }

                private Object getValueForClass(Class<?> klass, String value) {
                        if (klass == Boolean.TYPE)
                                return parseBoolean(value);
                        else if (klass == Integer.TYPE || klass == Long.TYPE)
                                return Long.parseLong(value);
                        else if (klass == Float.TYPE || klass == Double.TYPE)
                                return Double.parseDouble(value);
                        return value;
                }
                
                private void setValue(String fieldName, String value) throws SAXException {
                        if (fieldName.equals("class") || fieldName.equals("default") || fieldName.equals("throw") || fieldName.equals("new") || fieldName.equals("null"))
                                fieldName += "_";
                        try {
                                Object c = current.peek();
                                Field f = null;
                                try {
                        f = c.getClass().getField(fieldName);
                } catch (NoSuchFieldException e) {
                }
                                if (f != null && Modifier.isPublic(f.getModifiers()))
                                        f.set(c, getValueForClass(f.getType(), value));
                                else {
                                        fieldName = "set" + fieldName.substring(0,1).toUpperCase() + fieldName.substring(1);
                                        Method[] methods = c.getClass().getDeclaredMethods();
                                        for (Method m : methods) {
                                                if (m.getName().equals(fieldName) && m.getParameterTypes().length == 1) {
                                                        m.invoke(c, new Object[]{getValueForClass(m.getParameterTypes()[0], value)});
                                                        return;
                                                }
                                        }
                                }
                        } catch (Exception e) {
                                e.printStackTrace(); // SAXException does not dump inner exceptions.
                                throw new SAXException(e);
                        }
                }
                private boolean parseBoolean(String s) {
                        return s != null && 
                                !s.equals("0") && 
                                !s.startsWith("off") && 
                                !s.startsWith("false") &&
                                !s.startsWith("no");
                }
        }

        private static class Entry {
                Class<?> klass;
                boolean onStart;
                public Entry(Class<?> klass, boolean onStart) {
                        super();
                        this.klass = klass;
                        this.onStart = onStart;
                }
        }

        private Map<String, Entry> mapping = new HashMap<String, Entry>();
        private Parser parser;
        
        /**
         * The queue of already parsed items from the parsing thread.
         */
        private BlockingQueue<Object> queue = new ArrayBlockingQueue<Object>(10);

        /**
         * This stores one item retrieved from the queue to give hasNext a chance.
         * So this is also the object that will be returned on the next call to next().
         */
        private Object lookAhead = null;
        
        /**
         * This object represent the end of the stream (null is not allowed as
         * member in class Queue).
         */
        private Object EOS = new Object();

        public XmlObjectParser() {
                parser = new Parser();
        }

        public Iterable<Object> start(final Reader in) {
                new Thread(){
                        @Override public void run() {
                                try {
                                        parser.parse(in);
                                } catch (Exception e) {
                                        try {
                                                queue.put(e);
                                        } catch (InterruptedException e1) {
                                        }
                                }
                                parser = null;
                                try {
                                        queue.put(EOS);
                                } catch (InterruptedException e) {
                                }
                        }
                }.start();
                return this;
        }

        public void map(String tagName, Class<?> klass) {
                mapping.put(tagName, new Entry(klass,false));
        }

        public void mapOnStart(String tagName, Class<?> klass) {
                mapping.put(tagName, new Entry(klass,true));
        }

        /**
         * @return The next object from the xml stream or <code>null</code>,
         * if no more objects.
         */
        public Object next() throws SAXException {
                fillLookAhead();
                if (lookAhead == EOS)
                        throw new NoSuchElementException();
                Object o = lookAhead;
                lookAhead = null;
                return o;
        }

        private void fillLookAhead() throws SAXException {
                if (lookAhead != null)
                        return;
            try {
                        lookAhead = queue.take();
                        if (lookAhead instanceof SAXException)
                                throw (SAXException)lookAhead;
                        else if (lookAhead instanceof RuntimeException)
                                throw (RuntimeException)lookAhead;
                        else if (lookAhead instanceof Exception)
                                throw new SAXException((Exception)lookAhead);
                } catch (InterruptedException e) {
                throw new RuntimeException("XmlObjectParser must not be interrupted.", e);
                }
    }

        public boolean hasNext() throws SAXException {
                fillLookAhead();
        return lookAhead != EOS;
        }

        public Iterator<Object> iterator() {
                return new Iterator<Object>(){
                        public boolean hasNext() {
                                try {
                                        return XmlObjectParser.this.hasNext();
                                } catch (SAXException e) {
                                        e.printStackTrace();
                                        throw new RuntimeException(e);
                                }
                        }
                        public Object next() {
                                try {
                                        return XmlObjectParser.this.next();
                                } catch (SAXException e) {
                                        e.printStackTrace();
                                        throw new RuntimeException(e);
                                }
                        }
                        public void remove() {
                                throw new UnsupportedOperationException();
                        }
                };
        }
}