Skip to main content

Applet Jar download without browser restart

We use an applet in our website for uploading multiple files/folder tree to the server. Recently we ran into an issue where our code signing certificate was expired and we had to sign the jars again and publish new jars. We use CACHE_VERSION to give each jar a version that way on each browser restart the applet doesn't go to server for checking if a new version is available on the server or not. Refer for more details on CACHE_VERSION.

We ran into an issue where even after uploading the new jars to the server and giving them each a different CACHE_VERSION customers were still complaining about the expired certificate dialog. Doing some googling found that its a common problem in Java plugins in most browsers and a restart of browser would fix it. The browsers will check the cache version in an open browser only once and then even if you render the applet tag again it wont check the cache version. Wow so many people hadn't restarted a browser in 2-3 days, as this can happen again where we can push a server change that's incompatible with the old jars, we need to find a solution.

The solution to the problem was simple, every time the jar on server is changed generate a unique name for the jar. This was done by appending the changelist number of the file in svn to jar name in JSP. The jar name can be generated as upload.V13456.jar. At server we can write an apache rewrite rule that would strip of this .V13456 and serve the jar file. We are already doing this for our images. We use a _@version_@ tag in JSP files that gets replaced during build time using python with svn changelist no of that file. Using the same logic here solved the issue.


  1. That's a clever solution. I've just recently started working with java and applets, and your tutorials have been very helpful.


Post a Comment

Popular posts from this blog

RabbitMQ java clients for beginners

Here is a sample of a consumer and producer example for RabbitMQ. The steps are
Download ErlangDownload Rabbit MQ ServerDownload Rabbit MQ Java client jarsCompile and run the below two class and you are done.
This sample create a Durable Exchange, Queue and a Message. You will have to start the consumer first before you start the for the first time.

For more information on AMQP, Exchanges, Queues, read this excellent tutorial
import com.rabbitmq.client.Connection; import com.rabbitmq.client.Channel; import com.rabbitmq.client.*; public class RabbitMQProducer { public static void main(String []args) throws Exception { ConnectionFactory factory = new ConnectionFactory(); factory.setUsername("guest"); factory.setPassword("guest"); factory.setVirtualHost("/"); factory.setHost(""); factory.setPort(5672); Conne…

Spring query timeout or transaction timeout

If you are using spring to manage transactions then you can specify default transaction timeout using

    <bean id="transactionManager"
        <property name="dataSource" ref="dataSource" />
        <property name="defaultTimeout" value="30" /> <!--30 sec--->             

or you can override the timeout in the annotation

    @Transactional(readOnly = false, timeout=30)

or if you are doing it programatic transactions then you can do

DataSourceTransactionManager transactionManager = new DataSourceTransactionManager(dataSource);

 or you can override the timeout for one particular transaction

TransactionTemplate transactionTemplate = new TransactionTemplate();

Python adding pid file

I have a thumbnail generator that launches multiple processes and the correct way to shut it down is to send kill -HUP to the parent process. To automate I had to write a pid file from python, it was a piece of cake
def writePidFile(): pid = str(os.getpid()) f = open('', 'w') f.write(pid) f.close()