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the use of java in web browsers has had mixed results. applications that run in browsers rather than locally find a host of different hurdles. theyre more restricted, run slower at times and take a long time to load, thus making complex applications more difficult. advances in security and virtual machine technology have addressed the first two items. the third item remains somewhat challenging. faster modems, increased bandwidth and compressed file formats alleviate the problem somewhat but their impact varies. when fourth-generation browsers appeared, they included some new technology with features that allowed developers to have their applets and supporting classes installed permanently.
this article is focused on distributing java classes that are permanently installed on a users machine (see figure 1). the next time a user visits the page, the classes are loaded locally instead of from the network. ill start with a short explanation of some concepts and tools used in this process, and apply this knowledge to a working example for internet explorer and netscape communicator. well then look at some problems that can occur and some links to additional information.
the examples in this article use a test certificate, not a production certificate from a certificate authority. for purposes of this article, i thought a test certificate - also referred to as a self-signed certificate - was best since not everyone has a certificate. it also teaches you how to generate a certificate for testing. regardless, the procedures described here apply exactly the same when youre using a real certificate. when you have a real one, you can just skip the parts about generating a test certificate.
the software used in this article was: ie4.0 40bit ns communicator 4.51 with smartupdate ms personal web server (create a virtual directory called "sample" to run samples) ms windows nt 4.0 sp4 in a typical scenario visitors to a web page download any elements into their browser cache. this could include the page itself, and some images as well as applets. depending on browser settings, the next time users visit the page all of these elements may be reloaded from the web site. this is certainly feasible for elements such as html and images, but can be time-consuming and frustrating for users of your applets. internet explorer and netscape have different approaches to the actual implementation of downloading and installing, but they also share some common ideas.
digital certificate and signatures
the use of digital signatures and certificates to verify the authenticity of s... 下一页