Converting java lambda to pre java 1.8 function

Question

I am using Babbler to write an XMPP soft client for doing load testing.

In the API documentation Babbler documentation , it mentions adding listeners to intercept incoming messages. However, the example code is written in lambda form.

// Listen for messages
xmppClient.addInboundMessageListener(e -> {
    Message message = e.getMessage();
    // Handle inbound message.
});

I need help converting this to Java 1.7 function since our load generation tool (nGrinder) does not support lambda syntax.

Answer 1

Such a lambda is a just a shorthand for an anonymous implementation of a [functional] interface. You can always implement it yourself "the long way":

// Listen for messages
xmppClient.addInboundMessageListener(new Consumer<MessageEvent>() {
    @Override
    public void accept(MessageEvent e) {
        Message message = e.getMessage();
        // Handle inbound message.
    }
});

Answer 2

// Listen for messages
xmppClient.addInboundMessageListener(new Consumer<MessageEvent>() {

    public void accept(MessageEvent e) { 
        Message message = e.getMessage();
        // Handle inbound message.
    }
});

You can also avoid creating a new Consumer instance every time you invoke a certain lambda function by storing it in an instance variable.

private Consumer<MessageEvent> inboundMessageListener;

//should be called during startup only
public void initialize() {
    inboundMessageListener = new Consumer<MessageEvent>() {

        public void accept(MessageEvent e) { 
            Message message = e.getMessage();
            // Handle inbound message.
        }
    };
}

//can be reused for more than one XMPP client, assuming there's no difference in handling different clients
public void addInboundMessageListener() {

    xmppClient.addInboundMessageListener(inboundMessageListener);
}