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Californium (Cf) - CoAP for Java

Eclipse Californium is a Java implementation of RFC7252 - Constrained Application Protocol for IoT Cloud services. Thus, the focus is on scalability and usability instead of resource-efficiency like for embedded devices. Yet Californium is also suitable for embedded JVMs.

More information can be found at and

Build using Maven

You need to have a working maven installation to build Californium. Then simply run the following from the project's root directory:

$ mvn clean install

Executable JARs of the examples with all dependencies can be found in the demo-apps/run folder.

The build-process is tested for jdk 7, jdk 8 and jdk 11. For jdk 7 the revapi maven-plugin is disabled, it requires at least java 8.

To generate the javadocs, add "-DcreateJavadoc=true" to the command line and set the JAVA_HOME.

$ mvn clean install -DcreateJavadoc=true

Build jdk7 compliant

Californium 2.x can be used with java 7 or newer. If you want to build it with a jdk 7, but use also plugins which are only supported for newer jdks, the toolchain plugin could be used. That requires a toolchains configuration in "toolchains.xml" in your maven ".m2" folder

<?xml version="1.0" encoding="UTF8"?>
	<!-- JDK toolchains -->

To use the jdk7 toolchain, add "-DuseToolchain=true" to the command line.

$ mvn clean install -DuseToolchain=true

To use the jdk7 toolchain and create javadocs, add "-DuseToolchainJavadoc=true" to the command line (JAVA_HOME is not required).

$ mvn clean install -DuseToolchainJavadoc=true

Build with jdk11 and EdDSA support

To support EdDSA, either java 15, or java 11 with ed25519-java is required at runtime. Using java 15 to build Californium, leaves out ed25519-java, using java 11 for building, includes ed25519-java by default. If ed25519-java should NOT be included into the californium's jars, add to maven's arguments.

$ mvn clean install

In that case, it's still possible to use ed25519-java, if the eddsa-0.3.0.jar is provided to the classpath separately.

Using Californium in Maven Projects

We are publishing Californium's artifacts for milestones and releases to Maven Central. To use the latest released version as a library in your projects, add the following dependency to your pom.xml (without the dots):

Current Builds

You can also be bold and try out the most recent build from master. However, we are not publishing those to Maven Central but to Californium's project repository at Eclipse only. You will therefore need to add the Eclipse Repository to your pom.xml first:

      <name>Californium Repository</name>

You can then simply depend on 3.0.0-SNAPSHOT.


The project can be easily imported into a recent version of the Eclipse IDE. Make sure to have the following before importing the Californium (Cf) projects:

Then choose [Import... » Maven » Existing Maven Projects] to import californium into Eclipse.


The project can also be imported to IntelliJ as follows:

In IntelliJ, choose [File.. » Open] then select the location of the cloned repository in your filesystem. IntelliJ will then automatically import all projects and resolve required Maven dependencies.

Interop Server

A test server is running at coap://

(Note: that changed from "" on the 9th. December 2020. All 2.x demo- and plugtest-clients must therefore use the new destination "" explicitly!)

It is an instance of the cf-plugtest-server from the demo-apps. The root resource responds with its current version.

More information can be found at and technical details at

Another interop server with a different implementation can be found at coap:// More information can be found at

Adapter Selection

For some systems (particularly when multicasting), it may be necessary to specify/restrict californium to a particular network interface, or interfaces. This can be achieved by setting the COAP_NETWORK_INTERFACES JVM parameter to a suitable regex, for example:

java -DCOAP_NETWORK_INTERFACES='.*wpan0' -jar target/cf-helloworld-server-2.6.1.jar MulticastTestServer


A bug, an idea, an issue? Join the Mailing list or create an issue here on GitHub.


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