Speeding up your load time for your Java applets and webstart applications | MyThinkPond

Today we are going to look at a new feature available in Java 5 and above that can speed up your load time of your jar’s within your applets and web start (provided you have a web server that’s hosting the jar that’s HTTP/1.1 compatible server).

Let’s first take a look at what happens on the back-end:

In a typical applet (same applies to a web-start application), you have a src/source tag that points to a JAR file like this:

[sourcecode language=“jscript”]


Here your browser requests a JAR containing the needed class files under “/archive/”.  If the web server finds the JAR, it sends it back to the requesting code.

Well in Java 5 and above, they have a new compression scheme called “Pack200” - see (java.util.jar.Pack200) that allows you to send an alternative file that has it’s content compressed further using Pack200 format. The file’s can usually be reduced by 1/8th the original deflated jar file.

So when the browser requests the server for that JAR file, in the request header it will send all the formats that it can accept, namely -

Accept-Encoding=pack200-gzip, gzip

This tells the server that if you have a pack200-gzip then send that but in the case you do not, then send me the gzip-ed version of the JAR file.

So the next step in making this magic trick work is to modify the ARCHIVE tag to a servlet instead of a resource request. So now your ARCHIVE tag looks like this:

ARCHIVE = "/archive/MyJARServlet.do?file=MyAppletArchive.jar"

And in your MyJARServlet, you can scan on the file-system first for a”MyAppletArchive.pack.jar.gz” file and send it and in the case that the request does not have a Accept_Encoding of “pack200-gzip” then your code can default to sending in the plain-old “gzip” JAR file.

To see a sample of how this work, see the following URL: http://java.sun.com/j2se/1.5.0/docs/guide/deployment/deployment-guide/pack200.html

Now the next question one would ask is “How do I pack it using Pack200 format?”

Simple, within the JRE/bin or JDK/bin directory of Java 5 or later, you will find a utility called “pack200.exe” (windows). You can take an existing JAR file and pack it into that format by using the following command:

JRE/bin>pack200 myjarfile.jar

By using this strategy, you can decrease the time it takes to send that file. Smaller file = less time to send and less bandwidth that’s used.  If you plan on implementing this, bear in mind that there is a little bit of overhead to unpacking a Pack200 or compressed-gzip file as opposed to a JAR-ed non-compressed file. So you decide which approach makes sense.


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Venkatt Guhesan avatar
About Venkatt Guhesan
Enterprise Software Architect currently working at DataDirect Networks developing a highly scalable monitoring solution called DDN Insight. My passions include all things Open Source including Linux (CentOS, Red Hat, Gentoo, Open Stack, Docker & Ubuntu), embedded ARM processors and microcontrollers (Arduino, UDOO, Cubieboard, BeagleBoard, OnionIO, TI's Zigbee). Coming from an Electrical and Computer Engineering background, working in developing and designing enterprise - distributed, highly scalable software requires a unique set of software skills with a good understanding of the hardware. This makes his work challenging and interesting. In his free time, he spends his time with his family and two children. He also enjoys researching on topics including - world ancient history and yoga. Visit the 'About' section for more details.
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