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Docker

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Mounting files — config, ontologies, stylesheets — into the default Docker setup covers many cases; for local runs, mount them with docker-compose.override.yml as shown in Compose overrides. But you may also want to build a dedicated Docker image for your app using LinkedDataHub as the base. Usually this is done to COPY files inside the image or RUN additional commands.

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The recommended approach is a multi-stage Docker build: the first stage uses Maven to compile your WAR overlay, and the second stage copies it into the LinkedDataHub base image alongside any static files:

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FROM maven:3.9-eclipse-temurin-21 AS maven\n\nWORKDIR /usr/src/myapp\n\nCOPY src /usr/src/myapp/src\nCOPY pom.xml /usr/src/myapp/pom.xml\n\nRUN mvn clean install\n\n# =================\n\nFROM atomgraph/linkeddatahub:6.0.0\n\nWORKDIR $CATALINA_HOME\n\nENV SERVLET_NAME=com.example.myapp.Application\n\nCOPY --from=maven /usr/src/myapp/target/ROOT webapps/ROOT\n\nCOPY files/layout.xsl /usr/local/tomcat/webapps/ROOT/static/com/example/myapp/xsl/layout.xsl\nCOPY files/client.xsl /usr/local/tomcat/webapps/ROOT/static/com/example/myapp/xsl/client.xsl\nCOPY files/style.css  /usr/local/tomcat/webapps/ROOT/static/com/example/myapp/css/style.css

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Replace 6.0.0 with the LinkedDataHub release you are running.

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SERVLET_NAME must be set to the fully-qualified name of your JAX-RS application class (see the Java section below).

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Java

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The Java layer of LinkedDataHub is a Maven project with a webapp layout. It uses JAX-RS — specifically Jersey 3 — as the HTTP/REST framework, and Apache Jena 6 for RDF I/O.

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If you want to extend the Java codebase, for example to add a custom REST endpoint, create a new Maven project (Java 21, packaged as WAR named ROOT) with LinkedDataHub as a WAR overlay dependency:

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<dependencies>\n    <dependency>\n        <groupId>com.atomgraph</groupId>\n        <artifactId>linkeddatahub</artifactId>\n        <version>6.0.0</version>\n        <classifier>classes</classifier>\n    </dependency>\n    <dependency>\n        <groupId>com.atomgraph</groupId>\n        <artifactId>linkeddatahub</artifactId>\n        <version>6.0.0</version>\n        <type>war</type>\n    </dependency>\n</dependencies>\n<build>\n    <plugins>\n        <plugin>\n            <groupId>org.apache.maven.plugins</groupId>\n            <artifactId>maven-compiler-plugin</artifactId>\n            <configuration>\n                <release>21</release>\n            </configuration>\n        </plugin>\n        <plugin>\n            <groupId>org.apache.maven.plugins</groupId>\n            <artifactId>maven-war-plugin</artifactId>\n            <configuration>\n                <warName>ROOT</warName>\n                <webappDirectory>target/ROOT</webappDirectory>\n                <attachClasses>true</attachClasses>\n                <overlays>\n                    <overlay>\n                        <groupId>com.atomgraph</groupId>\n                        <artifactId>linkeddatahub</artifactId>\n                    </overlay>\n                </overlays>\n            </configuration>\n        </plugin>\n    </plugins>\n</build>

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After adding a new endpoint, extend LinkedDataHub's JAX-RS application class (com.atomgraph.linkeddatahub.Application) and register your class there. Set the SERVLET_NAME Docker environment variable to the fully-qualified name of your subclass so LinkedDataHub loads it instead of the default application.

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By convention, static files (e.g. stylesheets, images) are placed in the src/main/webapp/static/ folder in the codebase, which then becomes /usr/local/tomcat/webapps/ROOT/static/ within the webapp deployed in the Docker container, and is served at static/ under the dataspace's base URI.

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This means that if you want to deploy static files as part of your LinkedDataHub app, you will have to either mount them into the /usr/local/tomcat/webapps/ROOT/static/ folder in the container, or copy them into a custom Docker image to the same effect.

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You can allow Java debugger access using configuration properties.

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XSLT

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LinkedDataHub uses XSLT 3.0 for UI rendering both on the server- and on the client-side.

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You can specify a custom server-side XSLT 3.0 stylesheet in the dataspace configuration.

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You can reuse LinkedDataHub's stylesheets by importing them as explained in the Change layout guide.

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Server-side

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The default server-side stylesheet layout.xsl and its imports can be found in the src/main/webapp/static/com/atomgraph/linkeddatahub/xsl folder.

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Client-side

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Client-side stylesheets render the layout in the browser and implement the interactive parts of the UI (event handling, AJAX calls etc.) using the IXSL extension\n provided by the Saxon-JS 3 library. After the server renders the initial page, the client-side stylesheet injects the left sidebar, navigation, document and tab panes, content blocks, forms and modal dialogs into the DOM, and re-renders in place as the user navigates. This makes the frontend almost entirely declarative: it requires virtually no hand-written JavaScript, apart from third-party libraries such as Google Charts and OpenLayers.

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Client-side stylesheets share common document-, resource-, and property-level templates with the server-side stylesheets. The client-side stylesheet may not contain any XML entity declarations (limitation of\n Saxon-JS) and must be compiled into a SEF file before it can be run by the Saxon-JS runtime.\n The URL of the client-side SEF stylesheet is passed as the $client-stylesheet parameter of the document-level server-side xhtml:Script template.

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