From Erlang / Elixir to Java and back. Adventure for 20 minutes

Hi all!

When you have to communicate from the Erlang / Elixir world with Java and back, there are not too many options. All abandoned jinterface and the new library encon , the basic example of the use of which is presented under the cat.

Add dependencies

Add Encon dependency to JVM application:

Maven :

 <dependencies> ... <dependency> <groupId>io.appulse.encon</groupId> <artifactId>encon</artifactId> <version>1.6.4</version> </dependency> ... </dependencies> 

Gradle :

 dependencies { compile 'io.appulse.encon:encon:1.6.4' } 

NOTE: if there is such a need (for example, a project on Ant ), then dependencies in the form of jar files can be found on GitHub, in the releases section.

Run Erlang node

 import io.appulse.encon.Node; import io.appulse.encon.Nodes; import io.appulse.encon.config.NodeConfig; //   . //   - .  encon-config NodeConfig config = NodeConfig.builder() // true -   , // false ( ) -   .shortName(true) .cookie("secret") .build(); // ,   EPMD     Erlang  Node node = Nodes.singleNode("echo-node", config); 

NOTE: for the above example to work, you must either start the EPMD daemon or its Java implementation .

Create Mailbox

Mailbox, it is a process in Erlang terminology:

 import io.appulse.encon.mailbox.Mailbox; Mailbox mailbox = node.mailbox() .name("popa") //  .build(); 

Connection to nodes

NOTE: You can initiate a connection from Erlang / Elixir or Java by automatically sending a message using the {, } or PID format (if any).

You can start communication between the nodes by sending a ping message from the Erlang side via net_adm:ping/1 :

 (erlang@localhost)1> net_adm:ping('java@localhost'). pong (erlang@localhost)2> 

It is also possible to send a message to {Name, Node} , where Node is an atom of the form 'java@localhost' , and Name is the PID or registered mailbox name that exists on the Java side.

 (erlang@localhost)1> {my_process, 'java@localhost'} ! hello. hello (erlang@localhost)2> 

If the mailbox exists on the Java side, then it will receive a message.

We send the message from Java

There is a whole family of send methods for Mailbox , which deliver:

• send ( ErlangPid , ErlangTerm ) - sends a message to a remote or local PID ;
• send ( String , ErlangTerm ) - sends the term to the local mailbox by its name of the same node;
• send ( String , String , ErlangTerm ) - sends a message to a remote / local node and mailbox by its name.

Let's try, open the Erlang-shell and register it with the name ... 'shell' :

 (erlang@localhost)1> erlang:register(shell, self()). true (erlang@localhost)2> 

Now, we can send a message from Java (the connection with the node will be established automatically):

 import static io.appulse.encon.terms.Erlang.atom; mailbox.send("erlang@localhost", "shell", atom("hello")); 

We return to Erlang and read the received message:

 (erlang@localhost) 1> flush(). Shell got hello ok (erlang@localhost) 2> 

Receiving messages in java

To receive an incoming message, you must use one of the Mailbox methods: receive() or receive(timeout, timeUnit) , which can wait indefinitely for a new message or a fixed amount of time.

 import io.appulse.encon.Node; import io.appulse.encon.Nodes; import io.appulse.encon.config.NodeConfig; import io.appulse.encon.connection.regular.Message; import io.appulse.encon.mailbox.Mailbox; public class Main { public static void main (String[] args) { NodeConfig config = NodeConfig.builder() .shortName(true) .build(); Node node = Nodes.singleNode("java@localhost", config); Mailbox mailbox = node.mailbox() .name("my_process") .build(); Message message = mailbox.receive(); System.out.println("Incoming message: " + message.getBody().asText()); } } 

Start the Erlang node and send a message:

 $> erl -sname erlang@localhost ... (erlang@localhost)1> {my_process, 'java@localhost'} ! hello. 

Conclusion

These and many other examples can be viewed on the project website and / or on the GitHub page .