Need help with californium?
Click the “chat” button below for chat support from the developer who created it, or find similar developers for support.

About the developer

573 Stars 327 Forks Other 2.9K Commits 19 Opened issues


CoAP/DTLS Java Implementation

Services available


Need anything else?

Contributors list

Californium logo

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


The build-process in branch

is tested for jdk 7, jdk 8, jdk 11, jdk 15 and jdk 16. 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

$ mvn clean install -DcreateJavadoc=true

Build earlier release

!!! Since 29. October 2021 !!!

The hostname "" is now existing and all builds of version and tags before that date will fail.

To (re-)build versions before that date the unit tests must therefore be skipped.

$ mvn clean install -DskipTests

Earlier versions (3.0.0-Mx, 2.6.5 and before) may also fail to build with newer JDKs, especially, if java 16 is used! That is cause by the unit test dependency to a deprecated version of "mockito". If such a (re-)build is required, the unit tests must be skipped (which is in the meantime anyway required caused by the "").

In combination with the "" now existing, the build with unit test only works for the current heads of the branches


Build jdk7 compliant

Californium 2.x and newer 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


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 (

is not required).
$ mvn clean install -DuseToolchainJavadoc=true

Build with jdk11 and EdDSA support

To support EdDSA, either java 15, java 16, or java 11 with ed25519-java is required at runtime. Using java 15 to build Californium, leaves out

, using java 11 for building, includes
by default. If
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

, if the eddsa-0.3.0.jar is provided to the classpath separately.

Run unit tests using Bouncy Castle as alternative JCE provider

With 3.0 a first, experimental support for using Bouncy Castle (1.69, bcprov-jdk15on, bcpkix-jdk15on, and, for tls, bctls-jdk15on) is implemented.

To demonstrate the basic functions, run the unit-tests using the profile

$ mvn clean install -Pbc-tests

Supporting Bouncy Castle for the unit test uncovers a couple of differences, which required to adapt the implementation. It is assumed, that more will be found and more adaption will be required. If you find some, don't hesitate to report issues, perhaps research and analysis, and fixes. On the other hand, the project Californium will for now not be able to provide support for Bouncy Castle questions with or without relation to Californium. You may create issues, but it may be not possible for us to answer them.

On issue seems to be the

generator, which shows in some environments strange CPU/time consumption.

With that, it gets very time consuming to test all combinations. Therefore, if you need a specific one, please test it on your own. If you consider, that some adaption is required, let us know by creating an issue or PR.

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

(without the dots):
Current Builds

You can also be bold and try out the most recent build from

. 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
      Californium Repository

You can then simply depend on



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

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://

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

JVM parameter to a suitable regex, for example:

java -DCOAP_NETWORK_INTERFACES='.*wpan0' -jar target/cf-helloworld-server-3.0.0.jar MulticastTestServer


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


Please check out our contribution guidelines

We use cookies. If you continue to browse the site, you agree to the use of cookies. For more information on our use of cookies please see our Privacy Policy.