Using Lift embedded in Jetty 9.4.9

[Dan Gravell]

I noticed I needed to do something similar to https://shadowfiend.posthaven.com/notes-on-deploying-lift-apps-to-glassfish to get continuations working in Jetty 9.4.9.

My resulting web.xml is:

<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">

<filter>

  <filter-name>LiftFilter</filter-name>

  <filter-class>net.liftweb.http.LiftFilter</filter-class>

  <async-supported>true</async-supported>

</filter>

 

<filter-mapping>

  <filter-name>LiftFilter</filter-name>

  <url-pattern>/*</url-pattern>

</filter-mapping>

</web-app>

I still see a lot of old-school web.xmls around on the web. Am I being *too* cool for school here?

Dan

[Donald McLean]

That's nearly identical to mine (last modified November 2010).

I'm missing the <async-supported> - should I have that?

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[Dan Gravell]

I found that when Jetty starts it instantiates a FilterHolder which holds the Lift filter. This has an attribute _asyncSupported. For me, I noticed StandardDescriptorProcessor.visitFilter was setting this to false. I think this means no continuations.

Dan

[Antonio Salazar Cardozo]

You definitely want asyncSupported, otherwise most servlet 3.0 containers will tie up

a thread for each of your comet long-poll requests. That usually leads to a situation where

new page loads are blocked after a certain point because comet requests are tying up

threads that can't be used to serve regular pages.

Async turns on continuations as Dan mentions, which means the comet long-polls don't

take up any threads unless they're actively sending something back to the client.

Thanks,

Anotnio

[Tim Nelson]

According to this: https://stackoverflow.com/a/20644532, async-supported was added in Jetty8, but the default was `true`. WIth Jetty 9 they changed the default to `false`. 

I don't use a web.xml at all, I configure everything in Scala. I'm trying to figure out how to add it that way and if our site is even using continuations right now. I guess it pays to read those release notes.

Tim

[Matt Farmer]

This may explain some performance surprises I had on a small application/ server recently. Heh.

[Matt Farmer]

I just checked - our giter8 templates have async-supported set to true, so anyone who has been using those has the correct settings. And my app that I was having a problem with does not :facepalm:

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[Tim Nelson]

In case anyone else doesn't use a web.xml and only uses code, it seems to default to being enabled.

I have code like this:

val context = new WebAppContext(webappPath, "/")

context.addFilter(

  classOf[LiftFilter],

  "/*",

  EnumSet.allOf(classOf[DispatcherType])

)

If you capture the return value of the `addFilter` function:

val holder = context.addFilter(

  classOf[LiftFilter],

  "/*",

  EnumSet.allOf(classOf[DispatcherType])

)

logger.info("async: " + holder.isAsyncSupported)

You can see that `isAsyncSupported` returns `true`.

This is with Jetty 9.4.8.v20171121 and 9.4.9.v20180320

Tim