Java Reference

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This document describes specific Java build and deploy configurations.

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Function and handler

import io.nuclio.Context;
import io.nuclio.Event;
import io.nuclio.EventHandler;
import io.nuclio.Response;

public class EmptyHandler implements EventHandler {

    @Override
    public Response handleEvent(Context context, Event event) {
       return new Response().setBody("");
    }
}

The handler field must simply contain the class name. In the example above, the handler is EmptyHandler.

Build

When instructed to build the user’s handler (to create a user handler JAR), the Java runtime will generate a Gradle build script from the following template:

plugins {
  id 'com.github.johnrengelman.shadow' version '2.0.2'
  id 'java'
}

repositories {
    {{ range .Repositories }}
    {{ . }}
    {{ end }}
}

dependencies {
    {{ range .Dependencies }}
    compile group: '{{.Group}}', name: '{{.Name}}', version: '{{.Version}}'
    {{ end }}

    compile files('./nuclio-sdk-1.0-SNAPSHOT.jar')
}

shadowJar {
   baseName = 'user-handler'
   classifier = null  // Don't append "all" to jar name
}

task userHandler(dependsOn: shadowJar)

The shim layer JAR is contained within the onbuild image, and an uber JAR is created from the user’s JAR and the shim layer JAR. All dependencies (for example, com.github.johnrengelman.shadow) are contained within the build cache, so no internet access is required by the basic build process.

Dependencies

The Java runtime will format spec.build.dependencies into the Gradle build script. For example, the following function.yaml section

spec:
  build:
    dependencies:
    - "group: com.fasterxml.jackson.core, name: jackson-databind, version: 2.9.0"
    - "group: com.fasterxml.jackson.core, name: jackson-core, version: 2.9.0"
    - "group: com.fasterxml.jackson.core, name: jackson-annotations, version: 2.9.0"

will populate the Gradle build script as follows:

dependencies {
    compile group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: '2.9.0'
    compile group: 'com.fasterxml.jackson.core', name: 'jackson-core', version: '2.9.0'
    compile group: 'com.fasterxml.jackson.core', name: 'jackson-annotations', version: '2.9.0'
}

Runtime attributes

By providing the repositories runtime attribute, you can override the repositories section in the build.gradle. When this field is empty, mavenCentral() is used. For example, the following function.yaml section

spec:
  build:
    runtimeAttributes:
      repositories:
      - mavenCentral()
      - jcenter()

will populate the Gradle build script as follows:

repositories {
    mavenCentral()
    jcenter()
}

Custom Gradle script

Providing a build.gradle file inside the function directory or archive overrides the script generation.

Dockerfile

See Deploying Functions from a Dockerfile.

ARG NUCLIO_LABEL=0.5.6
ARG NUCLIO_ARCH=amd64
ARG NUCLIO_BASE_IMAGE=openjdk:9-jre-slim
ARG NUCLIO_ONBUILD_IMAGE=nuclio/handler-builder-java-onbuild:${NUCLIO_LABEL}-${NUCLIO_ARCH}

# Supplies processor, handler.jar
FROM ${NUCLIO_ONBUILD_IMAGE} as builder

# Supplies uhttpc, used for healthcheck
FROM nuclio/uhttpc:0.0.1-amd64 as uhttpc

# From the base image
FROM ${NUCLIO_BASE_IMAGE}

# Copy required objects from the suppliers
COPY --from=builder /home/gradle/bin/processor /usr/local/bin/processor
COPY --from=builder /home/gradle/src/wrapper/build/libs/nuclio-java-wrapper.jar /opt/nuclio/nuclio-java-wrapper.jar
COPY --from=uhttpc /home/nuclio/bin/uhttpc /usr/local/bin/uhttpc

# Readiness probe
HEALTHCHECK --interval=1s --timeout=3s CMD /usr/local/bin/uhttpc --url http://127.0.0.1:8082/ready || exit 1

# Run processor with configuration and platform configuration
CMD [ "processor", "--config", "/etc/nuclio/config/processor/processor.yaml", "--platform-config", "/etc/nuclio/config/platform/platform.yaml" ]