OpenEdge Development:<br />Java Open Clients Microsoft Internet Explorer

Internet Explorer allows you to download and install Java libraries on the user's computer; therefore, the Open Client Runtime can be downloaded and installed once. Internet Explorer also supports versioning on these Java libraries. This allows you to update your users automatically when the Open Client Runtime is updated.

To install the Open Client Runtime from a Web page, you add an OBJECT tag to your Web page as shown in the following code:

<!-- This checks for installation of the Open4GL runtime code, and will install it if it isn't there or is an older version --> <OBJECT CLASSID="CLSID:E79DA910-15D0-11d2-B591-00C04FD4A860" CODEBASE="/cabs/o4glrt.cab#Version=9,1,1115,0">

<!-- This checks for 
installation of the Open4GL runtime code, and will install it if it isn't 
there or is an older version --> <OBJECT 
CLASSID="CLSID:E79DA910-15D0-11d2-B591-00C04FD4A860" 
        CODEBASE="/cabs/o4glrt.cab#Version=9,1,1115,0">

When you do this, you must modify the CODEBASE attribute to the location of the Open Client Runtime packages on the Web server from which the .cab file was distributed. When Internet Explorer encounters this tag, it looks in the user’s Windows registry for an entry with the specified class ID and version. Then, it looks to see if the o4glrt.cab file exists. If either of these above conditions is not met, the .cab file is downloaded.

The Microsoft security classes are not available as a standalone package. You can get these security classes by downloading the latest Microsoft Java SDK from http://www.microsoft.com.

Each Open Client Runtime .cab file has a unique class ID. This allows your application to change the types of network protocols it uses dynamically the next time the Web page is run. The version number, which changes for each release, is supplied by OpenEdge in the o4glrt.cab file's open4glrt??.inf file.

Once the .cab file is downloaded, a dialog box opens, advising the user that this code needs to be trusted and is signed by Progress Software Corporation. If the user selects OK, the .zip file is installed in the Windows/Java/TrustedLib directory, and all required registry keys are added or updated.

If the user selects OK, the .zip file also is added dynamically to the TrustedClassPath. This entry is volatile, and if the user restarts Internet Explorer, the .zip file is no longer included in its CLASSPATH. Therefore, any time you have a Web page that uses the Open Client Runtime, you should include that OBJECT tag. Once the code is installed, there is no further action required by users based on that OBJECT tag, even if they restart Internet Explorer. Since the runtime is installed on the TrustedClassPath, only trusted code can access it. Since you need to be trusted to open a connection to an OpenEdge server, you are required to package your applet and proxies into a signed .cab file. Once you have done this, you can add an applet tag like this:


<applet code=Open4GLDSO.class width=0 height=0 id=datactl MAYSCRIPT=true> <PARAM NAME=cabbase VALUE=/cabs/o4gldso.cab> </applet>

The code attribute specifies your applet's class name that must be contained in the .cab file specified with the cabbase PARAM. The value of the cabbase PARAM should point to the .cab file's path that contains the applet and proxy on the distribution Web server.

Internet Explorer looks for the cabbase, and if it finds it, downloads the specified .cab file. Since this is a signed .cab file, a dialog box opens and displays information from your code signing certificate. Your Java code is saved in Internet Explorer's volatile cache, so if the user restarts the Internet Explorer, your .cab file is downloaded again.