Asynchronous web programming using Java

[ShayanJ]

I want to learn web programming with Java. I'm using eclipse neon with tomcat 8.5.13. My question is do these tools support asynchronous programming and server push technologies or should I use other tools?
Thanks

 

[jedishrfu]

NodeJS is a popular alternative to Tomcat and Java. Everything client and server side is done in javascript. Its asynchronous and scalable. Many sites rely on NodeJS too.

 

[ShayanJ]

I know about NodeJS but I want to learn Java web programming. I'm sure there is an implementation of asynchronous web programming for Java too, isn't there?

 

[jedishrfu]

Ahh okay.

So when you say server push, you really mean the client sends a request and once the server responds the client immediately sends another request for update. This allows the server to respond whenever and it has a port to do it.

https://en.wikipedia.org/wiki/Push_technology

 

[DrZoidberg]

There is a simple async API built into Java in the form of AsynchronousSocketChannel and AsynchronousServerSocketChannel. Those are already sufficient to implement server push. But there are also more full featured libraries like e.g. Netty.

 

[ShayanJ]

There is a simple async API built into Java in the form of AsynchronousSocketChannel and AsynchronousServerSocketChannel. Those are already sufficient to implement server push. But there are also more full featured libraries like e.g. Netty.

I downloaded Netty and tried to run an example. So I created a project with the code below(got it from here):

//package io.netty.example.discard;

import io.netty.buffer.ByteBuf;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

/**
* Handles a server-side channel.
*/
public class DiscardServerHandler extends ChannelInboundHandlerAdapter { // (1)

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) { // (2)
        // Discard the received data silently.
        ((ByteBuf) msg).release(); // (3)
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { // (4)
        // Close the connection when an exception is raised.
        cause.printStackTrace();
        ctx.close();
    }
}

But when I run it with tomcat, I get:

HTTP Status 404 – Not Found
Type Status Report

Description The origin server did not find a current representation for the target resource or is not willing to disclose that one exists.

Apache Tomcat/8.5.13

P.S.
I commented package io.netty.example.discard; because it gives the error:

The declared package "io.netty.example.discard" does not match the expected package ""

 

[DrZoidberg]

I don't have a tomcat installation. But I did run the example code on http://netty.io/wiki/user-guide-for-4.x.html directly with

java -cp .;"E:\netty-4.1.9.Final\jar\all-in-one\netty-all-4.1.9.Final.jar" io.netty.example.discard.DiscardServer

and it worked fine. There must be some error in your tomcat configuration.
Btw. There are many libraries you could use. It doesn't have to be netty. A quick google search for "netty alternatives" will give you several other options. You could even just use the built in classes if your task is relatively simple.