The Java TM Tutorial

| Start of Tutorial > Start of Trail > Start of Lesson | Search

Trail: Security in JDK 1.2
Lesson: Quick Tour of Controlling Applets

## See the Policy File Effects

> Now that you have created the `mypolicy` policy file, you should be able to successfully execute the `WriteFile` applet to create and to write the file `writetest`, as shown in the following figure.

> Whenever you run an applet, or an application with a security manager, the policy files that are loaded and used by default are the ones specified in the "security properties file", which is located at one of the following:

>       Windows:
>         java.home\lib\security\java.security
>       UNIX:
>         java.home/lib/security/java.security

> Note that java.home indicates the directory into which the JRE was installed.

> The policy file locations are specified as the values of properties whose names are of the form

> >     policy.url.n

> Here `n` indicates a number. You specify each such property value in a line of the following form:

> >     policy.url.n=URL

> Here URL is a URL specification. For example, the default policy files, sometimes referred to as the system and user policy files, respectively, are defined in the security properties file as

> >     policy.url.1=file:${java.home}/lib/security/java.policy
> >     policy.url.2=file:${user.home}/.java.policy

> > Note: Use of the notation `${propName}` in the security properties file is a way of specifying the value of a property. Thus `${java.home}` will be replaced at runtime by the actual value of the `"java.home"` property, which indicates the directory into which the JRE was installed, and `${user.home}` will be replaced by the value of the `"user.home"` property, for example, `C:\Windows`.

> In the previous step you did not modify one of these policy files. You created a policy file named `mypolicy`. There are two possible ways you can have the `mypolicy` file be considered as part of the overall policy, in addition to the policy files specified in the security properties file. You can either specify the additional policy file in a property passed to the runtime system, as described in Approach 1, or add a line in the security properties file specifying the additional policy file, as discussed in Approach 2.

> > Note: On a UNIX system, you must have DNS configured in order for the `WriteFile` program to be downloaded from the public web site as in the command executions shown below. You need to have `dns` in the list of lookup services for hosts in your `/etc/nsswitch.conf` file, as in

> >         hosts:    dns files nis

> > You also need a `/etc/resolv.conf` file with a list of nameservers. Consult your system administrator for more information.

### Approach 1

> You can use an `appletviewer` command-line argument, `-J-Djava.security.policy`, to specify a policy file that should be used in addition to the ones specified in the security properties file. To run the `WriteFile` applet with the `mypolicy` policy file included, type the following in the directory in which `mypolicy` is stored:

> >     appletviewer -J-Djava.security.policy=mypolicy
> >      http://java.sun.com/docs/books/tutorial/security1.2/tour1/
> >      example-1dot2/WriteFile.html

> > Notes:
> > - This must be typed as a single line, with a space between `mypolicy` and the URL and no spaces in the URL. Multiple lines are used in the example just for legibility purposes.

> > - If this command line is longer than the maximum number of characters you are allowed to type on a single line, do the following. Create a text file containing the full command, and name the file with a `.bat` extension, for example, `wf.bat`. Then in your command window simply type the name of the `.bat` file instead of the command. This results in execution of the full command.

> If the applet still reports an error, something is wrong in the policy file. Use the Policy Tool to open the `mypolicy` file (using File > Open) and check the policy entries you just created in the previous step, Set Up a Policy File to Grant the Required Permissions. Change any typos or other errors.

> To view or edit an existing policy entry, select the line for that entry in the main Policy Tool window, then choose the Edit Policy Entry button. Alternatively you can simply double-click the line for that entry.

> This brings up the same type of Policy Entry dialog box as appears when you are adding a new policy entry after choosing the Add Policy Entry button, except in this case the dialog box is filled in with the existing policy entry information. To change the information, simply retype it (for the CodeBase and SignedBy values) or add, remove, or modify permissions.

### Approach 2

> You can specify a number of URLs (including ones of the form "http://") in `policy.url.n` properties in the security properties file, and all the designated policy files will get loaded.

> So one way to have our `mypolicy` file's policy entry considered by the `appletviewer` is to add an entry specifying that policy file in the security properties file.

> > Important: If you are running your own copy of the JDK, you can easily edit your security properties file. If you are running a version shared with others, you may only be able to modify the system-wide security properties file if you have write access to it or if you ask your system administrator to modify the file when appropriate. However, it's probably not appropriate for you to make modifications to a system-wide policy file for this tutorial test. We suggest that you just read the following to see how it's done or that you install your own private version of the JDK to use for the tutorial lessons.

> To modify the security properties file, open it in an editor suitable for editing an ASCII text file. Then add the following line after the line starting with `policy.url.2`:

>       Windows:
>         policy.url.3=file:/C:/Test/mypolicy
>       UNIX:
>         policy.url.3=file:${user.home}/test/mypolicy

> On a UNIX system you can alternatively explicitly specify your home directory, as in

> >     policy.url.3=file:/home/susanj/test/mypolicy

> Now you should be able to successfully run the following:

> >     appletviewer http://java.sun.com/docs/books/tutorial/
> >     security1.2/tour1/example-1dot2/WriteFile.html

> Type this command on one line, without spaces in the URL.

> As with approach 1, if you still get a security exception, something is wrong in the policy file. Use the Policy Tool to check the policy entry you just created in the previous step, Set Up a Policy File to Grant the Required Permissions. Change any typos or other errors.

> > Important: The `mypolicy` policy file is also used in the Quick Tour of Controlling Applications lesson. If you will not be doing that lesson, you may want to delete the line you just added in the security properties file (or comment it out), since you probably do not want the `mypolicy` file included when you are not running the tutorial lessons.

| Start of Tutorial > Start of Trail > Start of Lesson | Search