Jar File
This article needs additional citations for. Unsourced material may be challenged and removed.Find sources: – ( June 2008) Java Archive.jarapplication/java-archivecom.sun.java-archive50 4b 03 04 ASCII:PKx03x04Developed by,Type of format,Extended fromA JAR ( Java ARchive) is a typically used to aggregate many and associated and resources (text, images, etc.) into one file for distribution. It is used to store classes of java created by the user in order to help the runnable and inference concepts embedded within the language.JAR files are that include a Java-specific.
They are built on the and typically have a.jar. Contents.Design A JAR file allows Java runtimes to efficiently an entire application, including its classes and their associated resources, in a single request. JAR file elements may be compressed, shortening download times.A JAR file may contain a manifest file, that is located at META-INF/MANIFEST.MF. The entries in the manifest file describe how to use the JAR file. For instance, a entry can be used to specify other JAR files to load with the JAR.Extraction The contents of a JAR file may be extracted using any standard decompression software, or the jar command line utility: ' jar -xf foo.jar'.Security Developers can JAR files. In that case, the signature information becomes part of the embedded manifest file. The JAR itself is not signed, but instead every file inside the archive is listed along with its checksum; it is these checksums that are signed.
Multiple entities may sign the JAR file, changing the JAR file itself with each signing, although the signed files themselves remain valid. Download software kidzwin cd version ( win-xp-pro-sp3). When the Java runtime loads signed JAR files, it can validate the signatures and refuse to load classes that do not match the signature. It can also support 'sealed' packages, in which the will only permit Java classes to be loaded into the same package if they are all signed by the same entities. This prevents malicious code from being inserted into an existing package, and so gaining access to package-scoped classes and data.The content of JAR files may be to make more difficult.Executable JAR files An executable Java program can be packaged in a JAR file, along with any libraries the program uses. Executable JAR files have the manifest specifying the class with Main-Class: myPrograms.MyClass and an explicit Class-Path (and the -cp argument is ignored). Some operating systems can run these directly when clicked. The typical invocation is java -jar foo.jar from a command line.Native launchers can be created on most platforms.
For instance, users who prefer having Windows files can use tools such as, Launch4J, WinRun4J or to wrap single JAR files into executables.Manifest A manifest file is a file contained within a JAR. It defines extension and package-related data.
It contains organized in sections. If a JAR file is intended to be used as an executable file, the manifest file specifies the main class of the application. The manifest file is named MANIFEST.MF. The manifest directory has to be the first entry of the compressed archive.Specifications The manifest appears at the location META-INF/MANIFEST.MF. There can be only one manifest file in an archive and it must be at that location.The content of the manifest file in a JAR file created with version 1.0 of the is the following.Manifest-Version: 1.0The name is separated from its value by a colon.
Jar Files Crashing
The default manifest shows that it conforms to version 1.0 of the manifest specification.The manifest can contain information about the other files that are packaged in the archive. Manifest contents depend on the intended use for the JAR file. The default manifest file makes no assumptions about what information it should record about other files, so its single line contains data only about itself.Special-Purpose Manifest Headers JAR files created only for the purpose of archiving do not use the MANIFEST.MF file.Most uses of JAR files go beyond simple archiving and compression and require special information in the manifest file.Applications If an application is contained in a JAR file, the needs to know the application's entry point. An entry point is any class with a public static void main(String args) method.
Java Runtime Environment
This information is provided in the Main-Class header, which has the general form:Main-Class: com.example.MyClassNameIn this example com.example.MyClassName.main executes at application launch.Package Sealing Optionally, a package within a JAR file can be sealed, which means that all classes defined in that package are archived in the same JAR file. A package might be sealed to ensure version consistency among the classes in the software or as a security measure.To seal a package, a Name entry needs to appear, followed by a Sealed header, such as. Name: myCompany/myPackage/ Sealed: trueThe Name header's value is the package's relative pathname. Note that it ends with a '/' to distinguish it from a filename. Any headers following a Name header, without any intervening blank lines, apply to the file or package specified in the Name header. In the above example, because the Sealed header occurs after the Name: myCompany/myPackage header with no intervening blank lines, the Sealed header applies (only) to the package myCompany/myPackage.Package Versioning Several manifest headers hold versioning information. One set of headers can be assigned to each package.
The versioning headers appear directly beneath the Name header for the package. This example shows all the versioning headers.
Pkg1.jar path/to/pkg2.jar Apache Ant Zip/JAR support The build tool has its own package to read and write Zip and JAR archives, including support for extensions.
Opening the Jar File wizardThe Jar File wizard can be used to export the content of a project into a jar file. To bring up the Jar File wizard −.In the Package Explorer select the items that you want to export. If you want to export all the classes and resources in the project just select the project.Click on the File menu and select Export.In the filter text box of the first page of the export wizard type in JAR.Under the Java category select JAR file.Click on Next.Using the Jar File wizardIn the JAR File Specification page −.Enter the JAR file name and folder.The default is to export only the classes. To export the source code also, click on the Export Java source files and resources check box.Click on Next to change the JAR packaging options.Click on Next to change the JAR Manifest specification.Click on Finish.