THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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How to create a library of your custom components |
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This page has not yet been fully updated for Tapestry 5.4. Things are different and simpler in 5.4 than in previous releases. |
Creating Component Libraries
Nearly every Tapestry application includes a least a couple of custom components, specific to the application. What's exciting about Tapestry is how easy it is to package components for reuse across many applications ... and the fact that applications using a component library need no special configuration.
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A Tapestry component library consists of components (and optionally mixins, pages and component base classes). In addition, a component library will have a module that can define new services (needed by the components) or configure other services present in Tapestry. Finally, components can be packaged with assets: resources such as images, stylesheets and JavaScript libraries that need to be provided to the client web browser.
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Tapestry doesn't mandate that you use any build system, but we'll assume for the moment that you are using Maven 2. In that case, you'll have a pom.xml file something like the following:
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<project> <modelVersion>4.0.0</modelVersion> <groupId>org.example</groupId> <artifactId>happylib</artifactId> <version>1.0-SNAPSHOT</version> <packaging>jar</packaging> <name>happylib Tapestry 5 Library</name> <dependencies> <dependency> <groupId>org.apache.tapestry</groupId> <artifactId>tapestry-core</artifactId> <version>${tapestry-release-version}</version> </dependency> <dependency> <groupId>org.testng</groupId> <artifactId>testng</artifactId> <version>5.1</version> <classifier>jdk15</classifier> <scope>test</scope> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>1.5</source> <target>1.5</target> <optimize>true</optimize> </configuration> </plugin> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> <configuration> <archive> <manifestEntries> <Tapestry-Module-Classes>org.example.happylib.services.HappyModule</Tapestry-Module-Classes> </manifestEntries> </archive> </configuration> </plugin> </plugins> </build> <repositories> <repository> <id>codehaus.snapshots</id> <url>http://snapshots.repository.codehaus.org</url> </repository> <repository> <id>OpenQA_Release</id> <name>OpenQA Release Repository</name> <url>http://archiva.openqa.org/repository/releases/</url> </repository> </repositories> <properties> <tapestry-release-version>5.4-beta-28</tapestry-release-version> </properties> </project> |
You will need to modify the Tapestry release version number ("5.2.0" in the listing above) to reflect the current version of Tapestry when you create your component library.
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Our component is very simple:
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package org.example.happylib.components; import org.apache.tapestry5.Asset; import org.apache.tapestry5.MarkupWriter; import org.apache.tapestry5.annotations.Path; import org.apache.tapestry5.ioc.annotations.Inject; public class HappyIcon { @Inject @Path("happy.jpg") private Asset happyIcon; boolean beginRender(MarkupWriter writer) { writer.element("img", "src", happyIcon); writer.end(); return false; } } |
HappyIcon appears inside the components sub-package. The happyIcon field is injected with the the Asset for the file happy.jpg. The path specified with the @Path annotation is relative to the HappyIcon.class file; it should be stored in the project under src/main/resources/org/example/happylib/components.
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The above naming is somewhat clumsy, and can be improved by introducing an additional namespace into the template:
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<html xmlns:t="http://tapestry.apache.org/schema/tapestry_5_1_0.xsd" xmlns:h="tapestry-library:happy"> ... <h:icon/> ... </html> |
The special namespace mapping for sets up namespace prefix "h:" to mean the same as "happy/". It then becomes possible to reference components within the happy virtual folder directly.
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At application startup, Tapestry will read the library module along with all other modules and configure the ComponentClassResolver service using information in the module:
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package org.example.happylib.services; import org.apache.tapestry5.ioc.Configuration; import org.apache.tapestry5.services.LibraryMapping; public class HappyModule { public static void contributeComponentClassResolver(Configuration<LibraryMapping> configuration) { configuration.add(new LibraryMapping("happy", "org.example.happylib")); } } |
The ComponentClassResolver service is responsible for mapping libraries to packages; it takes as a contribution a collection of these LibraryMapping objects. Every module may make its own contribution to the ComponentClassResolver service, mapping its own package ("org.example.happylib") to its own folder ("happy").
This module class is also where you would define new services that can be accessed by your components (or other parts of the application).
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It is possible to add a mapping for "core", the core library for Tapestry components; all the built-in Tapestry components (TextField, BeanEditForm, Grid, etc.) are actually in the core library. When Tapestry doesn't find a component in your application, it next searches inside the "core" library. Contributing an additional package as "core" simply extends the number of packages searched for core components (it doesn't replace Tapestry's default package, org.apache.tapestry5.corelib). Adding to "core" is sometimes reasonable, if you ensure that there is virtually no chance of a naming conflict (via different modules contributing packages to core with conflicting class names). |
Step 5: Configure the module to autoload
For Tapestry to load your module at application startup, it is necessary to put an entry in the JAR manifest. This is taken care of in the pom.xml above:
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<plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> <configuration> <archive> <manifestEntries> <Tapestry-Module-Classes>org.example.happylib.services.HappyModule</Tapestry-Module-Classes> </manifestEntries> </archive> </configuration> </plugin> |
Step 6: Extending Client Access
As of Tapestry 5.2, a new step is needed: extending access for the assets. This is accomplished in your library's module class, HappyModule:
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public static void contributeRegexAuthorizer(Configuration<String> configuration) { configuration.add("^org/example/happylib/.*\\.jpg$"); } |
This contribution uses a regular expression to identify that any resource on the classpath under the org/example/happylib folder with a jpg extension is allowed. If you had a mix of different image types, you could replace jpg with (jpg|gif|png).
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To handle this problem in Tapestry 5.1 and earlier, you should map your library assets to a versioned folder. This can be accomplished using another contribution from the HappyModule, this time to the ClasspathAssetAliasManager service whose configuration maps a virtual folder underneath /assets to a package:
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public static void contributeClasspathAssetAliasManager(MappedConfiguration<String, String> configuration) { configuration.add("happylib/1.0", "org/example/happylib"); } |
With this in place, and the library and applications rebuilt and redeployed, the URL for happy.jpg becomes /happyapp/assets/happylib/1.0/components/happy.jpg. This is shorter, but also incorporates a version number ("1.0") that can be changed in a later release.
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