CS 209 Spring, 2006 Lab 12: JAR Files Instructor: J.G. Neal

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1 CS 209 Spring, 2006 Lab 12: JAR Files Instructor: J.G. Neal Objectives: To gain experience with the creation and use of JAR files, particularly for an applet. Notes: 1. This lab exercise corresponds to Chapter 14 of the textbook. 2. For this exercise, do not use NetBeans to create the required JAR file. For this exercise, we will use the Java Development Kit (JDK) jar tool. The JDK toolset is used by the majority of the Java IDEs including NetBeans and JBuilder, for example. 3. Applets and applications are deployed in Java ARchive (JAR) files. 4. The purpose of using a JAR file is to: a. Enable a Java applet and all its requisite components (e.g., class files, images, sound files, etc.) to be downloaded to a browser in a single HTTP transaction, instead of opening a new connection for each item. b. Enable a Java standalone application and all its requisite components to be combined into a single JAR file to facilitate delivery and installation. c. Provide compression of the files in the JAR file, achieving smaller file size to further improve download speed for applets. JAR files use the ZIP compression technology. 5. In particular, an applet is deployed in a JAR file on a web server for remote or local access via network connectivity. The network could be the Internet, another Wide Area Network (WAN) such as a company s private network, or a Local Area Network (LAN). 6. A JAR file should hold all the files required for the applet or application. This improves performance by reducing the number of client-server communications over the network. 7. You should not put source code files in a JAR file. Your source code is the intellectual property of you or your company and should be protected as such. Lab Instructions: 1. Use your Lab 9 applet program; if it s not working, use instructor-provided program files. a. For this lab exercise, you will use the applet program that you completed for Lab Exercise 9. b. If you did not get the program for Lab Exercise 9 to work properly, then you may use the applet program provided by your instructor as an alternative. If you use the instructorprovided program files, you will first need to create a project for the program in NetBeans, compile and run the program, and edit the HTML file so that it works with your version of the program. 2. Create a new folder for this assignment. a. Using your computer s operating system (OS), create a new folder named Lab12 for this assignment (e.g., for the Windows OS, use Windows Explorer to create the folder). b. Within the Lab12 folder, create two subfolders, one named Lab12-Work and the second named Lab12-Test. c. From your NetBeans project for Lab Exercise 9, copy the package folder that is contained within the /build/classes folder. Copy this package folder into your Lab12 subfolder named Lab12-Work. d. The package folder should contain only the compiled.class file(s) from your Lab 9 Java project program, and it should not contain any source code files. If any of your program s classes contain inner classes, when compiled, each of the inner classes will generate a separate compiled.class file in addition to the compiled.class file for the containing class. All of these.class files should be in the package folder and need to be included in the jar file when it is created. Page 1 of 12

2 e. Copy the HTML file from your Lab Exercise 9 project into your Lab12-Work folder. Be sure that the HTML file is the one from your top level Lab Exercise 9 project folder, which used relative paths. f. Make sure that the Lab12 folder and its subfolders contain no Java source code files. That is, they should contain no files with extension.java. 3. Create the JAR file for your applet program. a. The command line to create the JAR file should be as follows: C:\Program Files\Java\jdk1.5.0_06\bin\jar cfv Lab12.jar lab09 b. In the command line shown above in Step a, the first item in quotes is the path to the executable jar tool. You need to make sure that this path to the executable jar tool is correct on your computer. c. "Lab12.jar" is the name of the JAR file to be created, and "lab09" specifies the name of the package folder containing the compiled.class files that should be added to the JAR file. d. You should execute the above command in the Lab12-Work folder. You can do this using a batch file or by opening a Command Prompt window and entering the command at the command prompt. e. For your convenience, you should create a batch file containing this command line. Add the pause command as the second line of the batch file, as you have done in the batch files for all your previous exercises. f. Based on the official Java documentation available at the main Java website hosted at the Sun Microsystems website, the options include those listed below. Of these options, note that our example command above uses c, f, and v. i. c - Create a new archive ii. t - List the table of contents iii. x - Extract all or named files iv. f - Specifies the JAR file v. v - Verbose vi. m - Manifest file name to include vii. o - Store only, without compression viii. M - Do not create manifest file ix. u - Update JAR file x. i - Generate index information xi. -c - Temporarily change directory xii. -Joption - Pass option to the Java virtual machine g. For more information on the jar tool, see the JDK Jar Tool documentation attached to this Lab Exercise, which is from the Sun Microsystems website. 4. Use a batch file to create the JAR file for the program. a. For convenience, use a batch file to create the JAR file for your program. Create a batch file with a name such as MakeJar.bat. The batch file should consist of two lines similar to the following: C:\Program Files\Java\jdk1.5.0_04\bin\jar cfv Lab12.jar <package> pause b. Edit the path to the jar tool executable so that it is correct for your computer. c. Make sure that the quote characters are simple ASCII text characters, and not the smart quotes use by Microsoft Word. d. The <package> should be replaced by the name of your package folder. Remember that this package is named in the package statement within your program files. e. To execute the batch file, do either of the following: Page 2 of 12

3 o Enter the name of the batch file at the command prompt of a Command Prompt window or o Double-click on the file icon for the batch file in the operating system window (e.g., Windows Explorer). 5. Example JAR creation. a. The example in this step uses a completed version of the Lab 9 applet program. b. The command line consists of: C:\Program Files\Java\jdk1.5.0_06\bin\jar cfv Lab12.jar layoutexs where layoutexs is the name of the package. You used a different package name, of course. c. The window capture below shows the results of executing the command line to create the jar file. Since the main program class contains two inner classes, when compiled, each of these inner classes generates a separate compiled.class file. All are in the package-folder, and are added to the newly created jar file. 6. Make sure that the HTML file uses only relative paths; this should have already been done as part of Lab Exercise 9. a. You must use only relative paths both in the code of the Java JApplet itself and in the Applet tag within the HTML file. b. The use of relative paths is necessary so that your JAR file can be placed in any folder on any web server on any computer. Remember that recipients of your JAR file cannot recompile your program. They do not, and should not, have the source code. They will simply deploy it on their web server. c. Bring up your HTML file in an editor such as WordPad. d. Edit the codebase attribute of the Applet tag. The codebase value should be a relative path as shown here. The dot represents the current directory (folder), which also holds the HTML file itself. codebase = "." This tells the runtime engine that the current folder contains the folder/file specified by the code attribute representing the compiled code for the applet. The code attribute specifies the name of the applet file and where the applet code is located, namely in the package folder. For example, the code attribute would be similar to the following: code="lab09/employeeapplet.class" or Page 3 of 12

4 code="layoutexs/employeearyappletparsdone.class" 7. Modify the HTML file so that the archive attribute is specified. a. Add an archive attribute such as the following to the Applet tag of your HTML file: archive = Lab12.jar b. The archive attribute could actually list multiple JAR files, if needed, such as: archive = Lab12.jar, ExceptionHandling.jar, Sounds.jar 8. Test your new JAR file. a. Within your Lab12 folder, create a second folder named Lab12-Test that is separate from the Lab12-Work folder used to create the JAR file. b. Copy only two files from the Lab12-Work folder into the new Lab12-Test folder: (1) the new JAR file named Lab12.jar, and (2) the HTML file. c. The Lab12-Test folder should only contain the JAR file and the HTML file. Nothing else. d. The HTML file used in this example is shown below. Page 4 of 12

5 e. To test your program and JAR file, you should be able to double-click on the HTML file to bring up the HTML page in your browser, and the HTML page should include and display your working applet. The program should work just as it did for Lab 9, as shown in the figure below. Page 5 of 12

6 9. Run, test, and debug your program. a. Make sure that your program works correctly for all inputs. b. Be sure that when the Test folder is copied to any location on any computer (with the correct version of Java installed), the program still runs correctly when a person double-clicks on the HTML file (or when served up by a web server). 10. Create ReadMe file. a. Using Microsoft Word, create a file named ReadMe. b. In this document, insert your name at the top, along with the assignment number. c. Then enter any comments regarding the assignment and your program. d. Then insert your window captures that demonstrate that the program works correctly. e. Be sure the ReadMe document file is in your top level NetBeans project folder. 11. Zip the project folder and all its contents and submit for credit. a. Create a zip file containing your Lab12 folder. Your Lab12 folder must contain your Lab12- Work folder and Lab12-Test folder and all their sub-folders and files. b. Your Lab12 folder must contain your ReadMe file, as for previous project assignments. c. Change the name the zip file so that its name consists of your name along with the assignment number, as follows: JohnJones-12.zip. Do not use spaces in the name of the file, use hyphens instead. d. Submit the Zip file for credit. Submit to instructor s dropbox for this assignment. 12. Deployment by instructor. a. Your instructor will place your submitted Lab12-Test folder on a college web server for testing and demonstration purposes. You should be able to see that your deployed program works via remote access over the Internet. b. Your instructor will announce the URL for accessing the submitted Lab 12 projects. c. Using a web browser, you should then be able to enter the URL for your HTML page in the Address field of your web browser, hit the Enter key in the Address field or click the Go button. Your HTML page should be displayed in the browser and your applet should be displayed on the page. The applet should work correctly, just as it did for Lab 9. TO RECEIVE CREDIT FOR YOUR ASSIGNMENT: Submit the following for credit to the Angel Drop Box for Exercise 12: a. The zip file must contain your Lab12 folder containing your two folders for this assignment. The two subfolders should be named Lab12-Work and Lab12-Test. b. Your Lab12 folder must contain a ReadMe file. The ReadMe file must include your name at the top, the lab number, any comments regarding the assignment, and window captures to show the program execution. The ReadMe file must be in the top level Lab12 folder. c. Your Lab12-Test folder must contain only your HTML page and your JAR file. To test your program, a person should be able to double-click on the HTML file and view the HTML page containing your applet. The user should be able to interact with and use your applet that is embedded within the HTML page. d. You must submit your zip file to the Lab12 Drop Box for this CS 209 course in Angel ( DUE DATE: Tuesday, May 2. Page 6 of 12

7 DOCUMENTATION ON THE JAVA ARCHIVE TOOL from the Sun Microsystems website documentation available at : A copy is included below for your reference. jar-the Java Archive Tool Combines multiple files into a single JAR archive file. Synopsis Description Options Command Line Argument Files Examples See Also SYNOPSIS Create jar file jar c[v0m]f jarfile [-C dir] inputfiles [-Joption] jar c[v0]mf manifest jarfile [-C dir] inputfiles [-Joption] jar c[v0m] [-C dir] inputfiles [-Joption] jar c[v0]m manifest [-C dir] inputfiles [-Joption] Update jar file jar u[v0m]f jarfile [-C dir] inputfiles [-Joption] jar u[v0]mf manifest jarfile [-C dir] inputfiles [-Joption] jar u[v0m] [-C dir] inputfiles [-Joption] jar u[v0]m manifest [-C dir] inputfiles [-Joption] Extract jar file jar x[v]f jarfile [inputfiles] [-Joption] jar x[v] [inputfiles] [-Joption] List table of contents of jar file jar t[v]f jarfile [inputfiles] [-Joption] jar t[v] [inputfiles] [-Joption] Add index to jar file jar i jarfile [-Joption] where: cuxtiv0mmf Options that control the jar command. jarfile Jar file to be created (c), updated (u), extracted (x), or have its table of contents viewed (t). The f option and filename jarfile are a pair -- if either is present, they must both appear. Note that omitting f and jarfile accepts a "jar file" from standard input (for x and t) or sends the "jar file" to standard output (for c and u). inputfiles Page 7 of 12

8 Files or directories, separated by spaces, to be combined into jarfile (for c and u), or to be extracted (for x) or listed (for t) from jarfile. All directories are processed recursively. The files are compressed unless option O (zero) is used. manifest Pre-existing manifest file whose name: value pairs are to be included in MANIFEST.MF in the jar file. The m option and filename manifest are a pair -- if either is present, they must both appear. The letters m and f must appear in the same order that manifest and jarfile appear. -C dir Temporarily changes directories to dir while processing the following inputfiles argument. Multiple -C dir inputfiles sets are allowed. -Joption Option to be passed into the Java runtime environment. (There must be no space between -J and option). DESCRIPTION The jar tool combines multiple files into a single JAR archive file. jar is a general-purpose archiving and compression tool, based on ZIP and the ZLIB compression format. However, jar was designed mainly to facilitate the packaging of java applets or applications into a single archive. When the components of an applet or application (.class files, images and sounds) are combined into a single archive, they may be downloaded by a java agent (like a browser) in a single HTTP transaction, rather than requiring a new connection for each piece. This dramatically improves download times. jar also compresses files and so further improves download time. In addition, it allows individual entries in a file to be signed by the applet author so that their origin can be authenticated. The syntax for the jar tool is almost identical to the syntax for the tar command. A jar archive can be used as a class path entry, whether it is compressed or not. Typical usage to combine files into a jar file is: C:\Java> jar cf myfile.jar *.class In this example, all the class files in the current directory are placed into the file named "myfile.jar". A manifest file entry named META-INF/MANIFEST.MF is automatically generated by the jar tool and is always the first entry in the jar file. The manifest file is the place where any meta-information about the archive is stored as name: value pairs. Refer to the JAR file specification for details about how meta-information is stored in the manifest file. If you have a pre-existing manifest file whose name: value pairs you want the jar tool to include for the new jar archive, you can specify it using the m option: C:\Java> jar cmf mymanifestfile myfile.jar *.class Be sure that any pre-existing manifest file that you use ends with a new line. The last line of a manifest file will not be parsed if it doesn't end with a new line character. Note that when you specify "cfm" instead of "cmf" (i.e., you invert the order of the "m" and "f" options), you need to specify the name of the jar archive first, followed by the name of the manifest file: C:\Java> jar cfm myfile.jar mymanifestfile *.class The manifest is in a text format inspired by RFC822 ASCII format, so it is easy to view and process manifest-file contents. To extract the files from a jar file, use x, as in: C:\Java> jar xf myfile.jar To extract only certain files from a jar file, supply their filenames: Page 8 of 12

9 C:\Java> jar xf myfile.jar foo bar Beginning with version 1.3 of the Java 2 SDK, the jar utility supports JarIndex, which allows application class loaders to load classes more efficiently from jar files. If an application or applet is bundled into multiple jar files, only the necessary jar files will be downloaded and opened to load classes. This performance optimization is enabled by running jar with the i option. It will generate package location information for the specified main jar file and all the jar files it depends on, which need to be specified in the Class-Path attribute of the main jar file's manifest. C:\Java> jar i main.jar In this example, an INDEX.LIST file is inserted into the META-INF directory of main.jar. The application class loader will use the information stored in this file for efficient class loading. Refer to the JarIndex specification for details about how location information is stored in the index file. A standard way to copy directories is to first compress files in dir1 to standard out, then extract from standard in to dir2 (omitting f from both jar commands): C:\Java> (cd dir1; jar c.) (cd dir2; jar x) Examples of using the jar tool to operate on jar files and jar file manifests are provided below and in the Jar trail of the Java Tutorial. OPTIONS c u x t i f Creates a new archive file named jarfile (if f is specified) or to standard output (if f and jarfile are omitted). Add to it the files and directories specified by inputfiles. Updates an existing file jarfile (when f is specified) by adding to it files and directories specified by inputfiles. For example: jar uf foo.jar foo.class would add the file foo.class to the existing jar file foo.jar. The u option can also update the manifest entry, as given by this example: jar umf manifest foo.jar updates the foo.jar manifest with the name: value pairs in manifest. Extracts files and directories from jarfile (if f is specified) or standard input (if f and jarfile are omitted). If inputfiles is specified, only those specified files and directories are extracted. Otherwise, all files and directories are extracted. Lists the table of contents from jarfile (if f is specified) or standard input (if f and jarfile are omitted). If inputfiles is specified, only those specified files and directories are listed. Otherwise, all files and directories are listed. Generate index information for the specified jarfile and its dependent jar files. For example: jar i foo.jar would generate an INDEX.LIST file in foo.jar which contains location information for each package in foo.jar and all the jar files specified in the Class-Path attribute of foo.jar. See the index example. Page 9 of 12

10 v 0 M m Specifies the file jarfile to be created (c), updated (u), extracted (x), indexed (i), or viewed (t). The f option and filename jarfile are a pair -- if present, they must both appear. Omitting f and jarfile accepts a "jar file" from standard input (for x and t) or sends the "jar file" to standard output (for c and u). Generates verbose output to standard output. Examples shown below. (zero) Store without using ZIP compression. Do not create a manifest file entry (for c and u), or delete a manifest file entry if one exists (for u). Includes name: value attribute pairs from the specified manifest file manifest in the file at META-INF/MANIFEST.MF. A name: value pair is added unless one already exists with the same name, in which case its value is updated. On the command line, the letters m and f must appear in the same order that manifest and jarfile appear. Example use: jar cmf mymanifestfile myfile.jar *.class You can add special-purpose name: value attribute pairs to the manifest that aren't contained in the default manifest. Examples of such attributes would be those for vendor information, version information, package sealing, and to make JAR-bundled applications executable. See the JAR Files trail in the Java Tutorial and the Notes for Developers page for examples of using the m option. -C dir Temporarily changes directories (cd dir) during execution of the jar command while processing the following inputfiles argument. Its operation is intended to be similar to the -C option of the UNIX tar utility. For example: jar uf foo.jar -C classes bar.class would change to the classes directory and add the bar.class from that directory to foo.jar. The following command, jar uf foo.jar -C classes. -C bin xyz.class would change to the classes directory and add to foo.jar all files within the classes directory (without creating a classes directory in the jar file), then change back to the original directory before changing to the bin directory to add xyz.class to foo.jar. If classes holds files bar1 and bar2, then here's what the jar file would contain using jar tf foo.jar: META-INF/ META-INF/MANIFEST.MF bar1 bar2 xyz.class -Joption Pass option to the Java runtime environment, where option is one of the options described on the reference page for the java application launcher. For example, -J-Xmx48M sets the maximum memory to 48 megabytes. It is a common convention for -J to pass options to the underlying runtime environment. COMMAND LINE ARGUMENT FILES Page 10 of 12

11 To shorten or simplify the jar command line, you can specify one or more files that themselves contain arguments to the jar command (except -J options). This enables you to create jar commands of any length, overcoming command line limits imposed by the operating system. An argument file can include options and filenames. The arguments within a file can be spaceseparated or newline-separated. Filenames within an argument file are relative to the current directory, not the location of the argument file. Wildcards (*) that might otherwise be expanded by the operating system shell are not expanded. Use of the '@' character to recursively interpret files is not supported. The -J options are not supported because they are passed to the launcher, which does not support argument files. When executing jar, pass in the path and name of each argument file with the '@' leading character. When jar encounters an argument beginning with the character `@', it expands the contents of that file into the argument list. For example, you could use a single argument file named "classes.list" to hold the names of the files: C:\Java> dir /b *.class > classes.list Then execute the jar command passing in the argfile: C:\Java> jar cf An argument file can be passed in with a path, but any filenames inside the argument file that have relative paths are relative to the current working directory, not the path passed in. Here's such an example: C:\Java> EXAMPLES To add all the files in a particular directory to an archive (overwriting contents if the archive already exists). Enumerating verbosely (with the "v" option) will tell you more information about the files in the archive, such as their size and last modified date. C:\Java> dir 12/09/96 12:20a <DIR>. 12/09/96 12:17a <DIR>.. 12/09/96 12:18a au 12/09/96 12:18a 1,039 2.au 12/09/96 12:18a au 12/09/96 12:19a 48,072 spacemusic.au 12/09/96 12:19a 527 at_work.gif 12/09/96 12:19a 12,818 monkey.jpg 12/09/96 12:19a 16,242 Animator.class 12/09/96 12:20a 3,368 Wave.class 10 File(s) 91,118 bytes C:\Java> jar cvf bundle.jar * adding manifest adding: 1.au adding: 2.au adding: 3.au adding: Animator.class adding: Wave.class adding: at_work.gif adding: monkey.jpg adding: spacemusic.au Page 11 of 12

12 If you already have separate subdirectories for images, audio files and classes, you can combine them into a single jar file: C:\Java> dir 12/09/96 12:11a <DIR>. 12/09/96 12:17a <DIR>.. 12/03/96 06:54p <DIR> audio 12/06/96 02:02p <DIR> images 12/09/96 12:10a <DIR> classes 5 File(s) 207,360 bytes C:\Java> jar cvf bundle.jar audio classes images adding: audio/1.au adding: audio/2.au adding: audio/3.au adding: audio/spacemusic.au adding: classes/animator.class adding: classes/wave.class adding: images/monkey.jpg adding: images/at_work.gif C:\Java> dir 12/09/96 12:11a <DIR>. 12/09/96 12:17a <DIR>.. 12/09/96 12:11a 207,360 bundle.jar 12/03/96 06:54p <DIR> audio 12/06/96 02:02p <DIR> images 12/09/96 12:10a <DIR> classes 6 File(s) 207,360 bytes To see the entry names in the jarfile, use the "t" option: C:\Java> jar tf bundle.jar META-INF/ META-INF/MANIFEST.MF audio/1.au audio/2.au audio/3.au audio/spacemusic.au classes/animator.class classes/wave.class images/monkey.jpg images/at_work.gif To add an index file to the jar file for speeding up class loading, use the "i" option. Let's say you split the inter-dependent classes for a stock trade application, into three jar files: main.jar, buy.jar, and sell.jar. If you specify the Class-path attribute in the main.jar manifest as: Class-Path: buy.jar sell.jar then you can use the i option to speed up your application's class loading time: C:\Java> jar i main.jar An INDEX.LIST file is inserted to the META-INF directory which will enable the application class loader to download the specified jar files when it is searching for classes or resources. Page 12 of 12