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);
}