| Excerpt |
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Adding an Annotation and a Filter to customize Tapestry's page rendering |
Meta-Programming Page Content
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Defining the Annotation
| Code Block |
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| language | java |
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| title | ForbidFraming.java |
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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
| Code Block |
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| language | java |
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| title | FnordSymbols.java |
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package com.fnord;
import org.apache.tapestry5.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.
| Code Block |
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| language | java |
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| title | ForbidFramingModule.class |
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package com.fnord.services.forbidframing;
import org.apache.tapestry5.ioc.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.
| Code Block |
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| language | java |
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| title | ForbidFramingModule.java (partial) |
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| lang | java |
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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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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.
| Code Block |
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| language | java |
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| title | ForbidFramingModule.java (partial) |
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| lang | java |
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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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...
Everything comes together in the filter:
| Code Block |
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| language | java |
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| title | ForbidFramingFilter.java |
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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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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:
| Code Block |
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| language | js |
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| title | fnord.js (partial) |
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| lang | javascript |
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Fnord = {
popOutOfFrame : function() {
if (top != self)
top.location.replace(location);
}
}
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...