Groovy DOMBuilder update

I finally got around to submitting my NSDOMBuilder code to the Groovy dev list. I got the "why didn't you just fix the existing class instead of creating a new one" response that I sort of expected, which made me go back and figure out what that didn't work when I tried it. Someone in that thread did point out StreamingDOMBuilder, which would probably work for the situations I need, except default namespace handling is currently broken in the releases, but now fixed in svn. It's not documented anywhere that I could find, but it's not too hard to figure out.

Very un-groovy

I really like Groovy as a language, but it does have its flaws. My colleague and I came across some very strange syntax and weird behavior surrounding GPathResult. GPathResult is fine and dandy for a read-only view of an object graph, but it does support some write operations. The documentation says you should only use it for read operations and then gives examples of how to write.

Unfortunately, those write operations are a bit broken. You can add nodes but the changes won't be reflected by the iterators or size() method. There is not method to remove a node, but you can effectively do so by replacing it with an empty closure. Unfortunately there are some downsides that as well because in some cases the nodes act like a linked list and if you replace one in the middle, you lose all the nodes after it.

Probably the worst thing about GPathResult is the overridden plus operator. I have never seen the plus operator overridden to perform a mutation on the object, but that's what GPathResult does. Take this from a mock Grails plugin for example:

class AGrailsPlugin {
    def doWithWebDescriptor = { xml ->
        def mappingElement = xml.'servlet'
        mappingElement[mappingElement.size() - 1] + {
            'servlet' {
                'servlet-name'('a')
                'servlet-class'('com.discorp.web.AServlet')
            }
        }
    }
}

That actually adds a new servlet node right after the last servlet node in the tree. That has to be to most un-groovy syntax I have seen in Groovy. It's not at all obvious what going on and it's very hackish. Unfortunately I don't think there is any other way to perform that function in Grails, though I have a ticket open for it.

Google I/O thoughts

I attended the Google I/O conference a couple weeks ago. Here are some thoughts I had from that.

Google has resource constraints, makes mistakes and misses deadlines too. They work in small, focused teams. 40% of Google’s new products in the last year have come out of 20-percent time projects. They do a lot of split A/B testing where they test different versions of the site on small groups and use metrics to determine what’s best. Google’s view is that anything that expands the web is good for Google, so they’re providing all these cool APIs for free.

It will be hard for a small company to keep up with the technology, especially if it is spread thin. Disruptive innovation will always happen before implementation and deployment of a current technology can be completed on a large project.

The web as an application platform is getting much better. It still sucks in many ways, like Javascript as a language, tool support, desktop integration, etc., but there initiatives to address those problems. Gears is a big step forward. SSBs (e.g. Prism and Fluid) and platforms like Adobe Air solve some of these problems. Web applications will never keep up with desktop applications in terms of user interface, performance, and integration.

Javascript still sucks. GWT does solve a lot of the suckiness, but what's the long term viability of it? GWT is pretty cool and is not an all-or-nothing venture, so it would be good to investigate. Javascript 2 is still a long ways off and may not even address the enough of the suckiness. This is a downside of going to a mostly web-based platform.

There seems to be a trend for moving more application logic to the client side Javascript layer of the application. This is necessary if offline support is to be achieved. This does open up security issues unless constraints are also enforced on the server side, creating duplication and therefore maintenance issues.

The web is moving away from RDBMSes as a back end data store. They just don't scale. An emphasis is being placed on what information is "current enough" instead of always the most up to date. In what contexts can this method be used vs. strict transactional, relational data? To what capacity does a project need to scale? That will be the biggest factor in determining whether or not to move to a data store like HBase.

Android is a cool platform, but will still be limited by the wireless companies that use it. No accessory (e.g. printer or signature capture pad) support in the near future and it's unlikely to be able to hack it in because you can't install native apps. It’s an open platform, but can and most likely will be locked down by the wireless companies. Android will have Gears support though.

Targeting WebKit will likely be the best way to get apps to the iPhone and Android phones for the next few years. It may be the only way to target both platforms without significant development overlap. It may be possible to provide specific hooks to the native platforms via browser plugins (currently impossible) or apps that embed the browser (will be possible on Android and iPhone 2.0, though limited).

The best way to develop apps for the web may be to determine if it is possible to deliver 80-90% of the requested features with just the browser and then make up the next 5-10% with optional native hooks. For example, one could deliver a web-based contact manager. If the user has installed Gears, the user can get offline lookup of some subset of contacts and perform some, but not all, actions on those contacts. Providing offline support will require architectural overhead, which may be minor or very significant – I can’t really say at this point.

Wisdom: the forgotten context

In high school and college I was really big on seeking wisdom. I figured the facts and stuff would follow. Somewhere along the line, I forgot all that and became content with whatever wisdom I already had. I also forgot the source of the wisdom that had served me so well in the past.

I was reading through Proverbs last week and came across what was a favorite verse of mine. Proverbs 24:3-4 says,

By wisdom a house is built,
And by understanding it is established;
And by knowledge the rooms are filled
With all precious and pleasant riches.

Ya, I learned a lot of facts over the years, but without the context of wisdom those facts are not put to good use. Here's to a renewed goal of seeking wisdom, the context for knowledge.

Faith for the little things

I've been going through a pretty rough time the past couple weeks with some stressful situations. The biggest struggle was really with my faith. It wasn't so much a crisis of faith in that I questioned what I believe; it was more an issue of putting into practice what I do believe, particularly that God is in control and I need to trust Him to take care of me.

One of the reasons this problem came up is that I had not been trusting God in the little things. We can get by with a lot on this earth without God. Billions of unbelievers do it every day. Doing things that way seems to work out while circumstances are good. It doesn't lead to a life of joy or peace, but it's not really agony either. But what happens when something comes along that is more than we can handle without God?

If we don't trust Him for the little things, the every day things, if we're not trusting in Him when times are good, how can we expect to trust Him when times are bad?

No wonder the church isn't effective

I heard Michael Zimmerman on a radio program last night talking about the compatibility of Christianity and science. Zimmerman is a scientist who founded the
Clergy Letter Project, a statement that basically reduces the Bible to a book of "moral truths" in an effort to reconcile Christianity and science. Now I think that Christianity and science are 100% compatible, but I don't think you need to throw out the Bible to get there. I think it's a mistake for the Christian community to deny that species change over time -- it just makes us look stupid. But I think it's also a mistake to think that current scientific theory trumps God's word. Zimmerman did have one excellent point: science cannot prove or disprove the existence of God. I would add to that that science will never be able to prove or disprove the Genesis creation story because you cannot evaluate the supernatural with natural methods.

Anyway, back to the title point: it's no wonder the church isn't as effective as it should be when you have thousands of Christian leaders willing to throw the idea of the Bible as the authoritative word of God out the window.

Groovy DOMBuilder namespace

I'm building some XML in Groovy and it's pretty rad. However, I had the hardest time figuring out how to make namespaces work the way I thought they should. The examples didn't seem to cover the case I needed. I eventually got it, so in case anyone else is trying to do this, here it is:

Update: this didn't actually work. It looks right when serialized, but the in-memory DOM doesn't have the correct Element implementation. I ended up writing a new NSDOMBuilder class.

import groovy.xml.DOMBuilder
import groovy.xml.QName
import javax.xml.XMLConstants

import org.w3c.dom.Element
import org.joda.time.format.DateTimeFormatter
import org.joda.time.format.ISODateTimeFormat

DateTimeFormatter dateTimeFormatter = ISODateTimeFormat.dateTimeNoMillis()
def builder = DOMBuilder.newInstance()
def now = new DateTime()
        
Element el = builder.'ebiz:GetInventoryConsumption'(releaseID:'9.0',
        xmlns:[(new QName(XMLConstants.XMLNS_ATTRIBUTE_NS_URI, 'xmlns')):'http://www.openapplications.org/oagis/9',
               (new QName(XMLConstants.XMLNS_ATTRIBUTE_NS_URI, 'xmlns:ebiz')):'http://www.dis-corp.com/xml/ebusiness/2.0']) {
    ApplicationArea() {
        Sender(InetAddress.getLocalHost().getHostName())
        CreationDateTime(dateTimeFormatter.print(now))
        BODID(UUID.randomUUID())
    }
    DataArea() {
        Get() {
            Expression()
        }
        InventoryConsumption() {
            'ebiz:InventoryConsumptionHeader'() {
                // stuff goes here
            }
        }
    }
}

Update 2. Here's the actual code:
HashMapStack.java

package groovy.xml;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.ListIterator;
import java.util.Map;
import java.util.Set;

public class HashMapStack
    implements Map
{
    private LinkedList stack = new LinkedList();

    public HashMapStack()
    {
        stack.add(new HashMap());
    }

    /**
     * Clears the whole structure.
     */
    public void clear()
    {
        stack.clear();
        stack.add(new HashMap());
    }

    public boolean containsKey(Object key)
    {
        for (ListIterator iter = stack.listIterator(stack.size()); iter.hasPrevious();)
        {
            Map map = (Map) iter.previous();
            if (map.containsKey(key))
            {
                return true;
            }
        }
        return false;
    }

    public boolean containsValue(Object value)
    {
        for (ListIterator iter = stack.listIterator(stack.size()); iter.hasPrevious();)
        {
            Map map = (Map) iter.previous();
            if (map.containsValue(value))
            {
                return true;
            }
        }
        return false;
    }

    public Set entrySet()
    {
        throw new UnsupportedOperationException();
    }

    public Object get(Object key)
    {
        for (ListIterator iter = stack.listIterator(stack.size()); iter.hasPrevious();)
        {
            Map map = (Map) iter.previous();
            if (map.containsKey(key))
            {
                return map.get(key);
            }
        }
        return null;
    }

    public boolean isEmpty()
    {
        return false;
    }

    public Set keySet()
    {
        HashSet set = new HashSet();
        for (Iterator iter = stack.iterator(); iter.hasNext();)
        {
            Map map = (Map) iter.next();
            set.addAll(map.keySet());
        }
        return set;
    }

    /**
     * Only returns the value of the item replaced in the current frame, not in any lower frames.
     */
    public Object put(Object key, Object value)
    {
        return ((Map) stack.getLast()).put(key, value);
    }

    public void putAll(Map t)
    {
        ((Map) stack.getLast()).putAll(t);
    }

    /**
     * Only removes the key from the current frame.
     */
    public Object remove(Object key)
    {
        return ((Map) stack.getLast()).remove(key);
    }

    public int size()
    {
        return keySet().size();
    }

    public Collection values()
    {
        throw new UnsupportedOperationException();
    }

    public void push()
    {
        stack.add(new HashMap());
    }

    public void pop()
    {
        if (stack.size() > 1)
        {
            stack.removeLast();
        }
        else
        {
            throw new IndexOutOfBoundsException();
        }
    }
}

NSDOMBuilder.groovy

package groovy.xml

import javax.xml.namespace.QName
import groovy.xml.FactorySupport

import javax.xml.namespace.QName
import javax.xml.parsers.DocumentBuilder
import javax.xml.parsers.DocumentBuilderFactory
import javax.xml.parsers.ParserConfigurationException

import org.w3c.dom.Document
import org.w3c.dom.Element
import org.w3c.dom.Node
import org.xml.sax.InputSource
import org.xml.sax.SAXException

class NSDOMBuilder extends BuilderSupport {
    
    private boolean namespaceAware
    private HashMapStack nsMap = new HashMapStack()
    private Document document
    private DocumentBuilder documentBuilder

    static NSDOMBuilder newInstance() throws ParserConfigurationException {
        return newInstance(false, true)
    }

    static NSDOMBuilder newInstance(boolean validating, boolean namespaceAware) throws ParserConfigurationException {
        DocumentBuilderFactory factory = FactorySupport.createDocumentBuilderFactory()
        factory.setNamespaceAware(namespaceAware)
        factory.setValidating(validating)
        return new NSDOMBuilder(factory.newDocumentBuilder())
    }

    static Document parse(Reader reader) throws SAXException, IOException, ParserConfigurationException {
        return parse(reader, false, true)
    }

    static Document parse(Reader reader, boolean validating, boolean namespaceAware)
            throws SAXException, IOException, ParserConfigurationException {
        DocumentBuilderFactory factory = FactorySupport.createDocumentBuilderFactory()
        factory.setNamespaceAware(namespaceAware)
        factory.setValidating(validating)
        DocumentBuilder documentBuilder = factory.newDocumentBuilder()
        return documentBuilder.parse(new InputSource(reader))
    }

    NSDOMBuilder(Document document) {
        this(document, true)
    }

    NSDOMBuilder(Document document, boolean namespaceAware) {
        this.document = document
        this.namespaceAware = namespaceAware
    }

    NSDOMBuilder(DocumentBuilder documentBuilder) {
        this.documentBuilder = documentBuilder
        this.namespaceAware = documentBuilder.namespaceAware
    }

    protected void setParent(Object parent, Object child) {
        Node current = (Node) parent
        Node node = (Node) child

        current.appendChild(node)
    }

    protected Object createNode(Object name) {
        return createNode(name, [:])
    }

    protected Document createDocument() {
        if (documentBuilder == null) {
            throw new IllegalArgumentException("No Document or DOMImplementation available so cannot create Document")
        } else {
            return documentBuilder.newDocument()
        }
    }

    protected Object createNode(Object name, Object value) {
        Element element = (Element) createNode(name, [:])
        element.appendChild(document.createTextNode(value.toString()))
        return element
    }

    protected Object createNode(Object name, Map attributes, Object value) {
        Element element = (Element) createNode(name, attributes)
        element.appendChild(document.createTextNode(value.toString()))
        return element
    }

    protected Object createNode(Object name, Map attributes) {
        if (namespaceAware) {
         nsMap.push()
         
         for (Iterator iter = attributes.entrySet().iterator(); iter.hasNext();) {
             def entry = iter.next()
             String attrName = entry.key.toString()
             if ("xmlns".equals(attrName) || attrName.startsWith("xmlns:")) {
                 String prefix = ''
                 if (attrName.startsWith("xmlns:")) {
                     prefix = attrName.substring(6)
                 }
                 nsMap.put(prefix, entry.value)
                 iter.remove()
             }
         }
        }

        if (document == null) {
            document = createDocument()
        }
        
        Element element
        
        if (namespaceAware) {
      def qname = parseQName(name)
         element = document.createElementNS(qname.namespaceURI, name)
        } else {
         element = document.createElement(name)
        }

        attributes.each { k, value ->
            String valueText = (value != null) ? value.toString() : ""
            element.setAttribute(k.toString(), valueText)
        }
        
        return element
    }
    
    protected void nodeCompleted(Object parent, Object node) {
        if (namespaceAware) {
         nsMap.pop()
        }
    }
    
    protected QName parseQName(String name) {
        String prefix = ''
        String localPart = name
        int i = name.indexOf(':')
        if (i > -1) {
            prefix = name.substring(0, i)
            localPart = name.substring(i + 1)
        }
        String namespaceURI = nsMap.get(prefix)
        return new QName(namespaceURI, localPart, prefix)
    }
}

Update 3: here's an example of how to actually use it.

    Element createGetSupplierPartyMaster(Dealer dealer, Customer customer = null)
    {
     assert dealer != null
     assert dealer.dealerId != null
     
        def builder = NSDOMBuilder.newInstance()
        
        def el = builder.'ebiz:GetSupplierPartyMaster'(releaseID:'9.0',
                                                       xmlns:'http://www.openapplications.org/oagis/9',
                                                       'xmlns:ebiz':'http://www.dis-corp.com/xml/ebusiness/2.0') {
            ApplicationArea() {
                Sender(InetAddress.localHost.hostName)
                CreationDateTime(dateTimeFormatter.print(new DateTime()))
                BODID(UUID.randomUUID())
            }
            DataArea() {
                Get() {
                    Expression()
                }
                SupplierPartyMaster() {
                    PartyIDs() {
                        ID(schemeURI:BODHelper.DEALER_SCHEME_URI, dealer.dealerId)
                        if (customer?.store)
                        {
                            ID(schemeURI:BODHelper.STORE_SCHEME_URI, customer.store.storeCode)
                        }
                    }
                    if (customer)
                    {
                     AccountIDs() {
                         ID(customer.customerNumber)
                     }
                    }
                }
            }
        }

        el.ownerDocument.appendChild(el)
        return el
    }