THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Adding an Annotation and a Filter to customize Tapestry's page rendering |
Meta-Programming Page Content
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Again, this could be done by having a specific base-class that included a beginRender() method, but I think you'll see that the meta-programming approach is nearly as easy and much more flexible.
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Defining the Annotation
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package com.fnord.annotations;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Marker annotation for pages that should not allow framing.
*/
@Target({ ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
public @interface ForbidFraming {
}
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Defining the Constant
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package com.fnord; import org.apache.tapestry5.http.services.BaseURLSource; import com.fnord.annotations.ForbidFraming; public class FnordSymbols { /** * Meta-data key; when true, MarkupRendererFilter will inject some extra * content into the response to enforce that the content may not be framed * (i.e., "stolen"). * * @see ForbidFraming */ public static final String FORBID_FRAMING = "forbid-framing"; } |
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Next, we'll create a module just for the logic directly related to framing. In the module, we'll define the default value for the meta-data.
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package com.fnord.services.forbidframing; import org.apache.tapestry5.ioccommons.MappedConfiguration; import org.apache.tapestry5.ioc.annotations.Contribute; import org.apache.tapestry5.ioc.services.FactoryDefaults; import org.apache.tapestry5.ioc.services.SymbolProvider; import com.fnord.FnordSymbols; public class ForbidFramingModule { @Contribute(SymbolProvider.class) @FactoryDefaults public static void setupForbidFramingDefault( MappedConfiguration<String, String> configuration) { configuration.add(FnordSymbols.FORBID_FRAMING, "false"); } } |
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Most of the work has already been done for us: we just have to make a contribution to the MetaWorker service, which is already plugged into the component class transformation pipeline. MetaWorker spots the annotations we define and uses a second object, a MetaDataExtractor we provide, to convert the annotation into a meta-data value.
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@Contribute(MetaWorker.class)
public static void mapAnnotationsToMetaDataValue(
MappedConfiguration<Class, MetaDataExtractor> configuration) {
configuration
.add(ForbidFraming.class, new FixedExtractor<ForbidFraming>(
FnordSymbols.FORBID_FRAMING));
}
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If the ForbidFraming annotation has had attributes, we would have provided an implementation of MetaDataExtractor that examined those attributes to set the meta-data value. Since it has no annotationsattributes, the FixedExtractor class can be used. The argument is the meta-data key, and the default value is "true".
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The work we ultimately want to do occurs when rendering a page. Tapestry defines a pipeline for that overall process. The point of a pipeline is that we can add filters to it. We'll add a filter that checks for the meta-data key and adds the response header and JavaScript.
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We contribute into the pipeline; the order is important: since the filter will need to write JavaScript, it must be added after the built-in filter that provides the JavaScriptSupport environmental object.
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@Contribute(MarkupRenderer.class)
public static void addFilter(
OrderedConfiguration<MarkupRendererFilter> configuration) {
configuration.addInstance("ForbidFraming", ForbidFramingFilter.class,
"after:JavascriptSupport");
}
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How do you know what filters are built-in and where to add your own? The right starting point is the JavaDoc for the method of TapestryModule that contributes the base set: contributeMarkupRenderer()
Implementing the Filter
Everything comes together in the filter:
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package com.fnord.services.forbidframing;
import org.apache.tapestry5.MarkupWriter;
import org.apache.tapestry5.ioc.annotations.Inject;
import org.apache.tapestry5.services.MarkupRenderer;
import org.apache.tapestry5.services.MarkupRendererFilter;
import org.apache.tapestry5.services.MetaDataLocator;
import org.apache.tapestry5.services.RequestGlobals;
import org.apache.tapestry5.services.Response;
import org.apache.tapestry5.services.javascript.InitializationPriority;
import org.apache.tapestry5.services.javascript.JavaScriptSupport;
import com.fnord.FnordSymbols;
public class ForbidFramingFilter implements MarkupRendererFilter {
@Inject
private RequestGlobals requestGlobals;
@Inject
private MetaDataLocator metaDataLocator;
@Inject
private Response response;
@Inject
private JavaScriptSupport jsSupport;
public void renderMarkup(MarkupWriter writer, MarkupRenderer renderer) {
String pageName = requestGlobals.getActivePageName();
boolean forbidFraming = metaDataLocator.findMeta(
FnordSymbols.FORBID_FRAMING, pageName, boolean.class);
if (forbidFraming) {
response.setHeader("X-Frame-Options", "DENY");
jsSupport.addScript(InitializationPriority.IMMEDIATE,
"Fnord.popOutOfFrame();");
}
renderer.renderMarkup(writer);
}
}
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There's a bit going on in this short piece of code. The heart of the code is the MetaDataLocator service; given a meta-data key and a page name, it can not only extract the value, but then coerce it to a desired type, all in one go.
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This code makes one assumption: that the fnord application's Layout component added fnord.js to every page. That's necessary for the JavaScript that's added:
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Fnord = {
popOutOfFrame : function() {
if (top != self)
top.location.replace(location);
}
}
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The code in this example was designed for Tapestry version 5.2 . Some names were changed to maintain the anonymity of the client (whose project is still secret at the time of writing)and later. |