Render Tapestry5 Block to a string from code

Recently I integrated Select2 component to my tapestry5 application.

Select2 can load data from server using ajax when user scrolls through drop down.

There could be any data formats in ajax response provided that developer implements javascript results() function that parses the response into the format expected by select2.

Select2 provides two more callback functions that developers usually implement to post-process returned data:

• id() function that retrieves id from the choice object;
• formatResult() function that builds HTML markup which is used to display choice object in drop down.

I used Tynamo's tapestry-resteasy to build REST service that returns data to select2, and my REST service returned everything needed to implement id() and formatResult() functions.

I could just implement formatResult() to build HTML markup for select2, but I already had similar tapestry5 component that builds the same markup and I wanted to increase code reuse.

To do that I built tapestry5 service that does just this – EventResponseRenderer (see code below).

To use it:

1. Declare a block you want to render, as you usually do. In my example I created separate page –internal/CompanyBlocks.tml – and there is my addressBlock;
2. Declare event handler method that handles "Render" event and returns the block you want to render (note that you may also use tapestry5 AjaxResponseRenderer.addRender());
1. In my example this is:
• public Block onRenderFromCompanyAddress(Company company)
2. Note that you must specify id of tapestry5 component in event handler method name. This is the limitation of my EventResponseRenderer implementation and only required to conform tapestry5 API. This could be id of any component from the page;
3. You will probably want to declare some parameters that you will use to initialize page properties required for block renderer. You don't have to implement type coercers for them, because you will pass values for these parameters from code;
3. @Inject instance of EventResponseRenderer and call its render() method passing instance of RenderEvent to it. RenderEvent constructor accepts pageName where event handler method declared, componentId that was used in event handler method name (see previous step), and eventArgs – list of objects that will be passed as parameters to the event handler method. See method CompanyResourceImpl.createMatch()
4. Thats it.

Usage Example

	import x.y.z.entities.Company;
	import org.apache.tapestry5.Block;
	import org.apache.tapestry5.annotations.Property;
	import org.apache.tapestry5.ioc.annotations.Inject;
	public class CompanyBlocks
	{
	@Property private Company company;
	@Inject private Block addressBlock;
	public Block onRenderFromCompanyAddress(Company company)
	{
	// Setup properties used by this block
	this.company = company;
	// // You may also wrap your block to a zone and pass it to the render queue.
	// // In this case you don't need to return anything from this method.
	// ajaxResponseRenderer.addRender(addressBlockZone);
	return addressBlock;
	}
	}

view raw CompanyBlocks.java hosted with ❤ by GitHub

	<div
	xmlns:t="http://tapestry.apache.org/schema/tapestry_5_3.xsd"
	xmlns:p="tapestry:parameter">
	<t:block id="addressBlock">
	<t:company.address t:id="companyAddress" company="company" />
	</t:block>
	</div>

view raw CompanyBlocks.tml hosted with ❤ by GitHub

	import java.util.ArrayList;
	import java.util.List;
	import x.y.z.entities.Company;
	import x.y.z.rest.CompanyResource;
	import x.y.z.services.search.SearchService;
	import x.y.z.services.tapestry5.EventResponseRenderer;
	import x.y.z.services.tapestry5.RenderEvent;
	import org.apache.tapestry5.ioc.annotations.Inject;
	import org.apache.tapestry5.json.JSONObject;
	public class CompanyResourceImpl implements CompanyResource
	{
	private static final Logger logger = LoggerFactory.getLogger(CompanyResourceImpl.class);
	@Inject private SearchService searchService;
	@Inject private EventResponseRenderer renderer;
	@Override
	public Matches search(String term, int page, int pageLimit)
	{
	logger.info("Searching for term='{}', page={}, pageLimit={}",
	new Object[] { term, page, pageLimit });
	Matches result = new Matches();
	// ...
	int offset = page > 1 ? (page - 1) * pageLimit : 0;
	List<Company> matches = searchService.findMatches(term, offset, pageLimit + 1);
	result.hasMore = matches.size() > pageLimit;
	for (int i = 0; i < pageLimit && i < matches.size(); i++)
	{
	Company company = matches.get(i);
	result.add(createMatch(company));
	}
	return result;
	}
	protected Match createMatch(final Company company)
	{
	String rawAddress = renderer.render(new RenderEvent(
	"internal/companyblocks", "companyAddress", company));
	String htmlAddress = new JSONObject(rawAddress).getString("content");
	return new Match(
	company.getId(),
	company.getName(),
	htmlAddress);
	}
	}

view raw CompanyResourceImpl.java hosted with ❤ by GitHub

EventResponseRenderer Implementation

	public interface EventResponseRenderer
	{
	String render(RenderEvent renderEvent);
	}

view raw EventResponseRenderer.java hosted with ❤ by GitHub

	import java.io.ByteArrayOutputStream;
	import java.io.IOException;
	import java.io.PrintWriter;
	import org.apache.tapestry5.SymbolConstants;
	import org.apache.tapestry5.internal.EmptyEventContext;
	import org.apache.tapestry5.internal.services.RequestImpl;
	import org.apache.tapestry5.internal.services.ResponseImpl;
	import org.apache.tapestry5.internal.services.TapestrySessionFactory;
	import org.apache.tapestry5.ioc.annotations.Inject;
	import org.apache.tapestry5.ioc.annotations.Symbol;
	import org.apache.tapestry5.services.Ajax;
	import org.apache.tapestry5.services.ComponentEventRequestHandler;
	import org.apache.tapestry5.services.ComponentEventRequestParameters;
	import org.apache.tapestry5.services.RequestGlobals;
	public class EventResponseRendererImpl implements EventResponseRenderer
	{
	@Ajax
	@Inject private ComponentEventRequestHandler ajaxHandler;
	@Inject private RequestGlobals requestGlobals;
	@Symbol(SymbolConstants.CHARSET)
	@Inject private String applicationCharset;
	@Inject private TapestrySessionFactory sessionFactory;
	@Override
	public String render(RenderEvent renderEvent)
	{
	ByteArrayOutputStream out = new ByteArrayOutputStream();
	final PrintWriter printWriter = new PrintWriter(out);
	requestGlobals.storeRequestResponse(
	new RequestImpl(requestGlobals.getHTTPServletRequest(), applicationCharset, sessionFactory),
	new ResponseImpl(requestGlobals.getHTTPServletRequest(),
	requestGlobals.getHTTPServletResponse())
	{
	@Override
	public PrintWriter getPrintWriter(String contentType)
	throws IOException
	{
	return printWriter;
	}
	});
	try
	{
	ComponentEventRequestParameters parameters = new ComponentEventRequestParameters(
	renderEvent.getPageName(),
	renderEvent.getPageName(),
	renderEvent.getNestedComponentId(),
	RenderEvent.RENDER_EVENT_TYPE,
	new EmptyEventContext(),
	new RenderEventContext(renderEvent.getEventArgs()));
	ajaxHandler.handle(parameters);
	return new String(out.toByteArray(), applicationCharset);
	}
	catch (IOException e)
	{
	throw new RuntimeException(e);
	}
	}
	}

view raw EventResponseRendererImpl.java hosted with ❤ by GitHub

	public class RenderEvent
	{
	public static final String RENDER_EVENT_TYPE = "Render";
	private String pageName;
	private String nestedComponentId;
	private Object[] eventArgs;
	public RenderEvent(String pageName, String nestedComponentId, Object... eventArgs)
	{
	this.pageName = pageName;
	this.nestedComponentId = nestedComponentId;
	this.eventArgs = eventArgs;
	}
	public String getPageName()
	{
	return pageName;
	}
	public String getNestedComponentId()
	{
	return nestedComponentId;
	}
	public Object[] getEventArgs()
	{
	return eventArgs;
	}
	}

view raw RenderEvent.java hosted with ❤ by GitHub

	import org.apache.tapestry5.EventContext;
	public class RenderEventContext implements EventContext
	{
	private Object[] args;
	public RenderEventContext(Object... args)
	{
	this.args = args != null ? args : new Object[0];
	}
	@Override
	public int getCount()
	{
	return args.length;
	}
	@SuppressWarnings("unchecked")
	@Override
	public <T> T get(Class<T> desiredType, int index)
	{
	if (!desiredType.isAssignableFrom(args[index].getClass()))
	{
	throw new IllegalArgumentException("Argument at index "
	+ index + " expected to be of class "
	+ desiredType.getName() + ", but was "
	+ args[index].getClass());
	}
	return (T) args[index];
	}
	@Override
	public String[] toStrings()
	{
	// Not used
	return null;
	}
	}

view raw RenderEventContext.java hosted with ❤ by GitHub