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Trail: JAR Files
Lesson: Using JAR Files: The Basics

## Updating a JAR File

> The Jar tool in version 1.2 of the JavaTM Development Kit provides a `u` option which you can use to update the contents of an existing JAR file by modifying its manifest or by adding files.

> The basic command for adding files has this format:

> >     jar uf jar-file input-file(s)

> In this command:

> - The `u` option indicates that you want to update an existing JAR file.
> - The `f` option indicates that the JAR file to update is specified on the command line. If the `f` option is not present, the Jar tool will expect a JAR filename on stdin.
> - `jar-file` is the existing JAR file that's to be updated.
> - `input-file(s)` is a space-deliminated list of one or more files that you want to add to the Jar file.

> Any files already in the archive having the same pathname as a file being added will be overwritten.

> As when creating a new JAR file, you can optionally use the `-C` option to indicate a change of directory.

> You can combine the `u` option with the `m` option to update an existing JAR file's manifest:

> >     jar umf manifest jar-file

> In this command:

> - The `m` option indicates that you want to update the JAR file's manifest.
> - `manifest` is the manifest whose contents you want to merge into the manifest of the existing JAR file.

### Examples

> Recall that `TicTacToe.jar` has these contents:

> >     META-INF/MANIFEST.MF
> >     TicTacToe.class
> >     audio/
> >     audio/beep.au
> >     audio/ding.au
> >     audio/return.au
> >     audio/yahoo1.au
> >     audio/yahoo2.au
> >     images/
> >     images/cross.gif
> >     images/not.gif

> Suppose that you want to add the file `images/new.gif` to the JAR file. You could accomplish that by issuing this command from the parent directory of the `images` directory:

> >     jar uf TicTacToe.jar images/new.gif

> The revised JAR file would have this table of contents:

> >     META-INF/MANIFEST.MF
> >     TicTacToe.class
> >     audio/
> >     audio/beep.au
> >     audio/ding.au
> >     audio/return.au
> >     audio/yahoo1.au
> >     audio/yahoo2.au
> >     images/
> >     images/cross.gif
> >     images/not.gif
> >     images/new.gif

> You can use the `-C` option to "change directories" during execution of the command. For example:

> >     jar uf TicTacToe.jar -C images new.gif

> This command would change to the `images` directory before adding `new.gif` to the JAR file. The `images` directory would not be included in the pathname of `new.gif` when it's added to the archive, resulting in a table of contents that looks like this:

> >     META-INF/MANIFEST.MF
> >     TicTacToe.class
> >     audio/
> >     audio/beep.au
> >     audio/ding.au
> >     audio/return.au
> >     audio/yahoo1.au
> >     audio/yahoo2.au
> >     images/
> >     images/cross.gif
> >     images/not.gif
> >     new.gif

> As a final example, suppose you want to modify the default manifest of `TicTacToe.jar` by adding some version and vendor information. (Version and vendor information is contained in special headers that you can add to a JAR file's manifest. See the section on Understanding the Manifest for information about special headers.) You would first prepare a text file containing the headers that you wish to add to the default manifest. Your text file might consist of this information, for example:

> >     Name: TicTacToe.class
> >     Implementation-Title: "TicTacToe demo"
> >     Implementation-Version: "build57"
> >     Implementation-Vendor: "Sun Microsystems, Inc."

> If the file containing this information was called `versionInfo`, you would add the information to the manifest in `TicTacToe.jar` by using this command:

> >     jar umf versionInfo TicTacToe.jar

> After running this command, `TicTacToe.jar`'s manifest would contain the information from your `versionInfo` file.

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