Java PlugIn & PolicyTool
(Applet writes to a local file)

• Click here to download the file involved in this example.
• JavaScript w/Applet writes to a local file via using Java Plug-In and a policy file.
  Currently works with IE only.
  Java Security Example- Writing Files
  Example of JavaScript interfacing to an Applet that will read & write to the users local file system.  A policy needs to be created by the user that allows the applet to write/read to that directory.
  Steps
  • When you run this example, I will want to download the Java Plug-in 1.3.0_01 from Sun's site.
    Note:  It looks like you must have this version.  Not an earlier or later version.  I'm not sure why Sun (or whoever) has designed it this way.
  • At the DOS prompt, execute the program:  policytool.exe
    • When you installed the Java Plug-in (includes JRE) this program was installed also.  If you get a bad command, you may want to specify the full pathname.
      Ex:  C:\Program Files\JavaSoft\JRE\1.3.0_01\bin\policytool.exe
  • Policy Tool Steps: Create a policy file, if one does not exist.
    • The first time you run policytool.exe you may get an error: Could not find policy file: <file name>.  That's OK.  Make sure you right down the full pathname of the file name it is looking for.  
      Ex:  c:\winnt\Profiles\<your user id>\.java.policy
      • If you did not have a policy file, the click on File, Save.
      • Next type in the policy file name as it appeared in the error.
      • Now you have a policy file in the default location.
  • Policy Tool Steps:  Create appropriate policies.
    • Click on "Add Policy Entry"
      • CodeBase = file:/c:/test
      • Signed By: <leave blank>
    • Click on "Add Permission" to add the following permissions.
      • File Permission to Read & Write.
        • FilePermission
        • Target Name: c:/test/MyAppletWriteFile.txt 
        • read, write
        • Click on "OK"
      • (Optional) Property Premissions - If you plan to use the link that runs  getDebugProperties(), you will need to add the following permissions:
        • PropertyPermission, user.home, read
        • PropertyPermission, java.home, read
    • Click on "Done"
    • File, Save.
  • Now in your Windows Explorer, launch the web page:  MyAppletWriteFile.html in the c:\test directory.
    Warning:  While testing, if you make any changes to the policy file you must exit all browser windows, then reopen the browser and then the web page.
    • On this new web page, click on the first 3 links under "Using JavaScript with Java Plug-in: (works w/IE)"
    • The 4th link will give Security Errors unless you create the PropertyPermissions listed above.
  • Once you are successful with the above steps, you may try to setup the policy tool to allow my web page to write to your c:\test directory.
    Click Here to launch the same web page from my site.
    Hint:  Set up the same permissions above.  You will need to add another policy entry and use the following CodeBase:
    http://www.michael-thomas.com/java/javaadvanced/security/javaplugin