Creating a JAR File

The basic format of the command for creating a JAR file is:

jar cf jar-file input-file(s)

The options and arguments used in this command are:

• The c option indicates that you want to create a JAR file.
• The f option indicates that you want the output to go to a file rather than to stdout.
• jar-file is the name that you want the resulting JAR file to have. You can use any filename for a JAR file. By convention, JAR filenames are given a .jar extension, though this is not required.
• The input-file(s) argument is a space-separated list of one or more files that you want to include in your JAR file. The input-file(s) argument can contain the wildcard * symbol. If any of the "input-files" are directories, the contents of those directories are added to the JAR archive recursively.

The c and f options can appear in either order, but there must not be any space between them.

Viewing the Contents of a JAR File

The basic format of the command for viewing the contents of a JAR file is:

jar tf jar-file

Let's look at the options and argument used in this command:

• The t option indicates that you want to view the table of contents of the JAR file.
• The f option indicates that the JAR file whose contents are to be viewed is specified on the command line.
• The jar-file argument is the path and name of the JAR file whose contents you want to view.

The t and f options can appear in either order, but there must not be any space between them.
This command will display the JAR file's table of contents to stdout.
You can optionally add the verbose option, v, to produce additional information about file sizes and last-modified dates in the output.

Extracting the Contents of a JAR File

The basic command to use for extracting the contents of a JAR file is:

jar xf jar-file [archived-file(s)]

Let's look at the options and arguments in this command:

• The x option indicates that you want to extract files from the JAR archive.
• The f option indicates that the JAR file from which files are to be extracted is specified on the command line, rather than through stdin.
• The jar-file argument is the filename (or path and filename) of the JAR file from which to extract files.
• archived-file(s) is an optional argument consisting of a space-separated list of the files to be extracted from the archive. If this argument is not present, the Jar tool will extract all the files in the archive.

As usual, the order in which the x and f options appear in the command doesn't matter, but there must not be a space between them.

Updating a JAR File

The Jar tool provides a u option that 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.
• 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.
When extracting files, the Jar tool makes copies of the desired files and writes them to the current directory, reproducing the directory structure that the files have in the archive. The original JAR file remains unchanged.