This chapter includes the following topics:
The following information predates the introduction of the
Deployment Toolkit script in the Java SE 6 update 10 release.
See Java Rich Internet
Applications Deployment Advice for information about using the
Deployment Toolkit script.
In order for an application to be launched from a web page via
JNLP, the page must include a link to the JNLP file. E.g., to be
able to launch application app.jnlp on a web site
http://www.MySite.com, the page needs to include the
following link:
<a href=http://www.MySite.com/app.jnlp>Launch the application</a>
It may be the case, however, that Java Web Start is not installed on the user's computer. Thus the page needs to include logic (scripts) to take account of this. In fact, the page should include logic for the following:
Detect if Java Web Start is installed
If so, launch the application.
If not, detect if user is running IE on Window.
If so, provide link to a page that can auto-install the JRE for Windows
If not, provide a link to the general download page for the JDK/JRE.
The scripts, and the HTML for the auto-install page, are discussed below.
Here is the first script that should be run on a web page for launching an application via JNLP:
<SCRIPT LANGUAGE="JavaScript">
var javawsInstalled = 0;
var javaws142Installed=0;
var javaws150Installed=0;
var javaws160Installed = 0;
isIE = "false";
if (navigator.mimeTypes && navigator.mimeTypes.length) {
x = navigator.mimeTypes['application/x-java-jnlp-file'];
if (x) {
javawsInstalled = 1;
javaws142Installed=1;
javaws150Installed=1;
javaws160Installed = 1;
}
}
else {
isIE = "true";
}
</SCRIPT>
This script looks at the navigator.mimeTypes object
and the navigator.mimeTypes.length var to decide if
the browser is Netscape or IE. If length is 0, it is
assumed the browser is IE, as with IE the
navigator.mimeTypes array is defined but always empty.
If length is non-zero, then the browser is assumed to be Netscape
and the JNLP MIME type is checked to see if it exists on Netscape.
If so, javawsInstalled,
javaws142Installed, javaws150Installed
and javaws160Installed are all set to 1. With Netscape
it is not possible to determine which particular version of Java
Web Start is installed, so all four variables are set to 1.
The above JavaScript should be followed by a VBScript that sets variables related to Internet Explorer browers:
<SCRIPT LANGUAGE="VBScript">
on error resume next
If isIE = "true" Then
If Not(IsObject(CreateObject("JavaWebStart.isInstalled"))) Then
javawsInstalled = 0
Else
javawsInstalled = 1
End If
If Not(IsObject(CreateObject("JavaWebStart.isInstalled.1.4.2.0"))) Then
javaws142Installed = 0
Else
javaws142Installed = 1
End If
If Not(IsObject(CreateObject("JavaWebStart.isInstalled.1.5.0.0"))) Then
javaws150Installed = 0
Else
javaws150Installed = 1
End If
If Not(IsObject(CreateObject("JavaWebStart.isInstalled.1.6.0.0"))) Then
javaws160Installed = 0
Else
javaws160Installed = 1
End If
End If
</SCRIPT>
This VBScript is executed if the variable isIE from the
preceeding JavaScript is "true"; i.e., if the
end-user's browser is Internet Explorer. This script instantiates
the isInstalled COM object in
JavaWebStart.dll, and this object determines four
things:
whether the client machine has any version of Java Web Start installed;
whether the client machine has version 1.2 of Java Web Start installed;
whether the client machine has versions 1.4.2 of Java Web Start installed;
whether the client machine has versions 1.5.0 of Java Web Start installed.
whether the client machine has versions 1.6.0 of Java Web Start installed.
After the above two scripts have been executed, the variables
javawsInstalled, javaws142Installed,
javawsInstalled150 and javawsInstalled160
will be set to either 1 or 0, as follows:
|
Browser |
|
|
|
|
|---|---|---|---|---|
|
Internet Explorer |
1 if any version of Java Web Start is installed; 0 otherwise. |
1 if Java Web Start 1.4.2 is installed; 0 otherwise. |
1 if Java Web Start 1.5.0 is installed; 0 otherwise. |
1 if Java Web Start 1.6.0 is installed; 0 otherwise. |
|
Netscape Navigator |
1 if any version of Java Web Start is installed; 0 otherwise. |
1 if any version of Java Web Start is installed; 0 otherwise. |
1 if any version of Java Web Start is installed; 0 otherwise. |
1 if any version of Java Web Start is installed; 0 otherwise. |
An additional JavaScript can be used to decide whether to:
provide a link to the application's jnlp file (i.e., Java Web Start is installed);
initiate auto-download of JRE 6.0, which includes Java Web Start (i.e., Java Web Start is not installed and the user is running IE on Windows);
or provide a link to the general download page for the 6.0 JDK/JRE (i.e., Java Web Start is not installed and the user is not running IE on Windows).
The following JavaScript handles these scenarios:
<script language="JavaScript">
/* Note that the logic below always launches the JNLP application
*if the browser is Gecko based. This is because it is not possible
*to detect MIME type application/x-java-jnlp-file on Gecko-based browsers.
*/
if (javawsInstalled || (navigator.userAgent.indexOf("Gecko") !=-1)) {
document.write("<a href=http://www.MySite.com/app.jnlp>Launch
the application</a>");
} else {
document.write("Click ");
document.write("<a href=http://java.sun.com/PluginBrowserCheck?
pass=http://www.MySite.com/download.html&
fail=http://java.sun.com/javase/downloads/ea.jsp>here</a> ");
document.write("to download and install JRE 5.0 and
the application.");
}
</SCRIPT>
Notes:
The script only uses
javawsInstalled—not
javaws142Installed or javaws150Installed
or javaws160Installed.
The line breaks following '?' and
'&' are for readability purposes only; in an
actual script there should be no breaks in the href
string.
If javawsInstalled is 1, indicating that Java Web Start
is already available on the client, then the script provides a link
to the application's jnlp file. If Java Web Start is
not installed on the client, the script instead provides a link to
the PluginBrowserCheck program on the
java.sun.com web site. PluginBrowserCheck
checks whether the client uses Internet Explorer on a Microsoft
Windows platform. If so, PluginBrowserCheck sends the
user to the auto-install page
http://www.MySite.com/download.html. (See the next
section, Creating an auto-install page, for
how to create an auto-install page for IE running on Windows.) If
PluginBrowserCheck determines the user is not using
Internet Explorer on Microsoft Windows, the user is redirected to
the 6.0 JRE general download page on java.sun.com.
The download.html file should be staged on the server side. It contains special OBJECT and PARAM tags that will download to the client an auto-installer for JRE 6.0 . Along with Java Web Start, an ActiveX control will be downloaded to the client. The ActiveX control will launch the application using the newly installed Java Web Start. Here is a sample download.html file:
<HTML> <BODY> <OBJECT codebase="http://java.sun.com/update/1.6.0/jinstall-6-windows-i586.cab#Version=6,0,0,0" classid="clsid:5852F5ED-8BF4-11D4-A245-0080C6F74284" height=0 width=0> <PARAM name="app" value="http://www.MySite.com/app.jnlp"> <PARAM name="back" value="true"> <!-- Alternate HTML for browsers which cannot instantiate the object --> <A href="http://java.sun.com/javase/downloads/ea.jsp"> Download Java Web Start</A> </OBJECT> </BODY> </HTML>
The OBJECT tag fetches a .cab file that
contains an auto-installer for JRE 6.0.
The URL:
http://java.sun.com/update/1.6.0/jinstall-6-windows-i586.cab
will return the latest update release available for the Java SE 6 release.
The string: Version=6,0,0,0 will be used to compare with the wsdetect.dll version, which is registered with the CLSID above. If the local machine has the dll installed and the version is greater than or equal to the Version specified, we will just load the dll in the local machine. Otherwise it will download and install Java from the codebase specified.
The PARAM tags specify the location of the
application's jnlp file so that it may be
automatically launched after the JRE is installed on the
client.
app: Once the Java Web Start Active-X control is
installed/loaded, it will invoke Java Web Start to launch the
application specified by this URL.
back: This controls the behavior of the browser
after launching the application. It can remain on the current page
(download.html in this case) or navigate back to the previous
page.
For issues relating to application development see the next chapter, Application Development Considerations.
