Creating a JAR File
The basic format of the command for creating a JAR file is:
The options and arguments used in this command are:
This command will generate a compressed JAR file and place it in the current directory. The command will also generate a default manifest file for the JAR archive.
Note: The metadata in the JAR file, such as the entry names, comments, and contents of the manifest, must be encoded in UTF8.
You can add any of these additional options to the cf options of the basic command:
Note: When you create a JAR file, the time of creation is stored in the JAR file. Therefore, even if the contents of the JAR file do not change, when you create a JAR file multiple times, the resulting files are not exactly identical. You should be aware of this when you are using JAR files in a build environment. It is recommended that you use versioning information in the manifest file, rather than creation time, to control versions of a JAR file. See the Setting Package Version Information section.
TicTacToe folder Hierarchy
You can obtain all these files from jar/examples directory when you download the entire Tutorial online. To package this demo into a single JAR file namedTicTacToe.jar, you would run this command from inside the TicTacToe directory:
The audio and images arguments represent directories, so the Jar tool will recursively place them and their contents in the JAR file. The generated JAR fileTicTacToe.jar will be placed in the current directory. Because the command used the v option for verbose output, you would see something similar to this output when you run the command:
You can see from this output that the JAR file TicTacToe.jar is compressed. The Jar tool compresses files by default. You can turn off the compression feature by using the 0 (zero) option, so that the command would look like:
You might want to avoid compression, for example, to increase the speed with which a JAR file could be loaded by a browser. Uncompressed JAR files can generally be loaded more quickly than compressed files because the need to decompress the files during loading is eliminated. However, there is a tradeoff in that download time over a network may be longer for larger, uncompressed files.
The Jar tool will accept arguments that use the wildcard * symbol. As long as there weren't any unwanted files in the TicTacToe directory, you could have used this alternative command to construct the JAR file:
Though the verbose output doesn't indicate it, the Jar tool automatically adds a manifest file to the JAR archive with path name META-INF/MANIFEST.MF. See theWorking with Manifest Files: The Basics section for information about manifest files.
In the above example, the files in the archive retained their relative path names and directory structure. The Jar tool provides the -C option that you can use to create a JAR file in which the relative paths of the archived files are not preserved. It's modeled after TAR's -C option.
As an example, suppose you wanted to put audio files and gif images used by the TicTacToe demo into a JAR file, and that you wanted all the files to be on the top level, with no directory hierarchy. You could accomplish that by issuing this command from the parent directory of the images and audio directories:
The -C images part of this command directs the Jar tool to go to the images directory, and the . following -C images directs the Jar tool to archive all the contents of that directory. The -C audio . part of the command then does the same with the audio directory. The resulting JAR file would have this table of contents:
By contrast, suppose that you used a command that did not employ the -C option:
The resulting JAR file would have this table of contents:
jar cf jar-file input-file(s)
- 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.
This command will generate a compressed JAR file and place it in the current directory. The command will also generate a default manifest file for the JAR archive.
Note: The metadata in the JAR file, such as the entry names, comments, and contents of the manifest, must be encoded in UTF8.
| Option | Description |
|---|---|
| v | Produces verbose output on stdout while the JAR file is being built. The verbose output tells you the name of each file as it's added to the JAR file. |
| 0(zero) | Indicates that you don't want the JAR file to be compressed. |
| M | Indicates that the default manifest file should not be produced. |
| m | Used to include manifest information from an existing manifest file. The format for using this option is:jar cmf existing-manifest jar-file input-file(s) Warning: The manifest must end with a new line or carriage return. The last line will not be parsed properly if it does not end with a new line or carriage return. |
| -C | To change directories during execution of the command. See below for an example. |
Note: When you create a JAR file, the time of creation is stored in the JAR file. Therefore, even if the contents of the JAR file do not change, when you create a JAR file multiple times, the resulting files are not exactly identical. You should be aware of this when you are using JAR files in a build environment. It is recommended that you use versioning information in the manifest file, rather than creation time, to control versions of a JAR file. See the Setting Package Version Information section.
An Example
Let us look at an example. A simple TicTacToe applet. You can see the source code of this Applet at TicTacToe.java. This demo contains a bytecode class file, audio files, and images having this structure:You can obtain all these files from jar/examples directory when you download the entire Tutorial online. To package this demo into a single JAR file namedTicTacToe.jar, you would run this command from inside the TicTacToe directory:
jar cvf TicTacToe.jar TicTacToe.class audio images
adding: TicTacToe.class (in=3825) (out=2222) (deflated 41%) adding: audio/ (in=0) (out=0) (stored 0%) adding: audio/beep.au (in=4032) (out=3572) (deflated 11%) adding: audio/ding.au (in=2566) (out=2055) (deflated 19%) adding: audio/return.au (in=6558) (out=4401) (deflated 32%) adding: audio/yahoo1.au (in=7834) (out=6985) (deflated 10%) adding: audio/yahoo2.au (in=7463) (out=4607) (deflated 38%) adding: images/ (in=0) (out=0) (stored 0%) adding: images/cross.gif (in=157) (out=160) (deflated -1%) adding: images/not.gif (in=158) (out=161) (deflated -1%)
jar cvf0 TicTacToe.jar TicTacToe.class audio images
The Jar tool will accept arguments that use the wildcard * symbol. As long as there weren't any unwanted files in the TicTacToe directory, you could have used this alternative command to construct the JAR file:
jar cvf TicTacToe.jar *
In the above example, the files in the archive retained their relative path names and directory structure. The Jar tool provides the -C option that you can use to create a JAR file in which the relative paths of the archived files are not preserved. It's modeled after TAR's -C option.
As an example, suppose you wanted to put audio files and gif images used by the TicTacToe demo into a JAR file, and that you wanted all the files to be on the top level, with no directory hierarchy. You could accomplish that by issuing this command from the parent directory of the images and audio directories:
jar cf ImageAudio.jar -C images . -C audio .
META-INF/MANIFEST.MF cross.gif not.gif beep.au ding.au return.au yahoo1.au yahoo2.au
jar cf ImageAudio.jar images audio
META-INF/MANIFEST.MF images/cross.gif images/not.gif audio/beep.au audio/ding.au audio/return.au audio/yahoo1.au audio/yahoo2.au
Viewing the Contents of a JAR File
The basic format of the command for viewing the contents of a JAR file is:Let's look at the options and argument used in this command:jar tf jar-fileThe 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.
- 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.
An Example
Let's use the Jar tool to list the contents of the TicTacToe.jar file we created in the previous section:This command displays the contents of the JAR file to stdout:jar tf TicTacToe.jarThe JAR file contains the TicTacToe class file and the audio and images directory, as expected. The output also shows that JAR file contains a default manifest file, META-INF/MANIFEST.MF, which was automatically placed in the archive by the JAR tool. For more information, see the Understanding the Default Manifestsection. All pathnames are displayed with forward slashes, regardless of the platform or operating system you're using. Paths in JAR files are always relative; you'll never see a path beginning with C:, for example. The JAR tool will display additional information if you use the v option: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.gifFor example, the verbose output for the TicTacToe JAR file would look similar to this:jar tvf TicTacToe.jar256 Mon Apr 18 10:50:28 PDT 2005 META-INF/MANIFEST.MF 3885 Mon Apr 18 10:49:50 PDT 2005 TicTacToe.class 0 Wed Apr 20 16:39:32 PDT 2005 audio/ 4032 Wed Apr 20 16:39:32 PDT 2005 audio/beep.au 2566 Wed Apr 20 16:39:32 PDT 2005 audio/ding.au 6558 Wed Apr 20 16:39:32 PDT 2005 audio/return.au 7834 Wed Apr 20 16:39:32 PDT 2005 audio/yahoo1.au 7463 Wed Apr 20 16:39:32 PDT 2005 audio/yahoo2.au 0 Wed Apr 20 16:39:44 PDT 2005 images/ 157 Wed Apr 20 16:39:44 PDT 2005 images/cross.gif 158 Wed Apr 20 16:39:44 PDT 2005 images/not.gifExtracting the Contents of a JAR File
The basic command to use for extracting the contents of a JAR file is:Let's look at the options and arguments in this command:jar xf jar-file [archived-file(s)]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. 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.
- The x option indicates that you want to extract files from the JAR archive.
- The f options 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.
Caution: When it extracts files, the Jar tool will overwrite any existing files having the same pathname as the extracted files.An Example
Let's extract some files from the TicTacToe JAR file we've been using in previous sections. Recall that the contents of TicTacToe.jar are:Suppose you want to extract the TicTacToe class file and the cross.gif image file. To do so, you can use this command: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.gifThis command does two things:jar xf TicTacToe.jar TicTacToe.class images/cross.gifThe original TicTacToe JAR file remains unchanged. As many files as desired can be extracted from the JAR file in the same way. When the command doesn't specify which files to extract, the Jar tool extracts all files in the archive. For example, you can extract all the files in the TicTacToe archive by using this command:
- It places a copy of TicTacToe.class in the current directory.
- It creates the directory images, if it doesn't already exist, and places a copy of cross.gif within it.
jar xf TicTacToe.jarUpdating a JAR File
The Jar tool 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:In this command:jar uf jar-file input-file(s)Any files already in the archive having the same pathname as a file being added will be overwritten. When creating a new JAR file, you can optionally use the -C option to indicate a change of directory. For more information, see the Creating a JAR File section.
- 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.
Examples
Recall that TicTacToe.jar has these contents: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 theimages directory: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.gifThe revised JAR file would have this table of contents:jar uf TicTacToe.jar images/new.gifYou can use the -C option to "change directories" during execution of the command. For example: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.gifThis 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 ofnew.gif when it's added to the archive, resulting in a table of contents that looks like this:jar uf TicTacToe.jar -C images new.gifMETA-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.gifRunning JAR-Packaged Software
Now that you've learned how to create JAR files, how do you actually run the code that you've packaged? Consider these three scenarios:This section will cover the first two situations. A separate trail in the tutorial on the extension mechanism covers the use of JAR files as extensions.
- Your JAR file contains an applet that is to be run inside a browser.
- Your JAR file contains an application that is to be invoked from the command line.
- Your JAR file contains code that you want to use as an extension.
Applets Packaged in JAR Files
To invoke any applet from an HTML file for running inside a browser, you need to use the APPLET tag. For more information, see the Java Applets lesson. If the applet is bundled as a JAR file, the only thing you need to do differently is to use the ARCHIVE parameter to specify the relative path to the JAR file. As an example, let's use (again!) the TicTacToe demo applet that ships with the Java™ Development Kit. The APPLET tag in the HTML file that calls the demo looks like this:If the TicTacToe demo were packaged in a JAR file named TicTacToe.jar, you could modify the APPLET tag with the simple addition of an ARCHIVE parameter:<applet code=TicTacToe.class width=120 height=120> </applet>The ARCHIVE parameter specifies the relative path to the JAR file that contains TicTacToe.class. This example assumes that the JAR file and the HTML file are in the same directory. If they're not, you would need to include the JAR file's relative path in the ARCHIVE parameter's value. For example, if the JAR file was one directory below the HTML file in a directory called applets, the APPLET tag would look like this:<applet code=TicTacToe.class archive="TicTacToe.jar" width=120 height=120> </applet><applet code=TicTacToe.class archive="applets/TicTacToe.jar" width=120 height=120> </applet>JAR Files as Applications
You can run JAR-packaged applications with the Java interpreter. The basic command is:The -jar flag tells the interpreter that the application is packaged in the JAR file format. You can only specify one JAR file, which must contain all the application-specific code. Before you execute this command make sure the runtime environment has an information of which class within the JAR file is the application's entry point. To indicate which class is the application's entry point, you must add a Main-Class header to the JAR file's manifest. The header takes the form:java -jar jar-fileThe header's value, classname, is the name of the class that's the application's entry point. For more information, see the Setting an Application's Entry Point section. When the Main-Class is set in the manifest file, you can run the application from the command line:Main-Class: classnameTo run the application from jar file that is in other directory, we need to specify the path of that directory as below:java -jar app.jarjava -jar path/app.jarwherepathis the directory path at which thisapp.jarresides.
No comments:
Post a Comment