File Extension JAR
File: filename.JAR
If you cannot open file extension JAR, you may have a file association error or need to install the appropriate application. We recommend you run the free scan below to identity Windows registry errors.Mime Type:
application/java-archive
Related Information:
File extension JAR identifies a Java Archive File used to aggregate a collection of files into a single file. This file extension is also used to distribute java classes and any other associated metadata. JAR files are normally created based on the ZIP file format and can thus, be extracted and created using a JAR command, which is normally used to accompany JDK files. The file can also be extracted and created using most ZIP tools. JAR files also have an optional manifest file that is normally located on the META-INF/MANIFEST.MF path.
The manifest file contains entries that enable it determine the manner in which a JAR file extension is to be used. JAR files that are designed to be implemented as standalone programs have one class identified as the main class. This file format also includes a Classpath entry, which identifies other files that are required to be loaded with the JAR file. The Classpath entry holds a list of relative and absolute paths to more JAR files.
JAR files can be signed digitally. This information, which is referred to as signature information, is then added to the manifest file. If the JAR file is not digitally signed, then each file in the records is listed jointly with a checksum. File extension JAR file may be signed by multiple entities and this may alter the JAR file with every signing though the signed file remains valid.
Whenever the Java Runtime Environment indicates a signed file extension JAR, the signatures may be validated and thus, the class files that fail to match the signature may not be loaded. This can also be used to offer support to sealed packages, where the Classloader only allows java classes to load into one package. However, this is only possible if they have been signed by the same entity. This process is important as it stops malicious code from penetrating into an existing package and gaining access to package-scoped data and classes.
It is possible to conceal a JAR file so that users do not access extra information regarding the file code or to reduce the file size. This is especially important when it comes to mobile phone applications. For users using Microsoft Windows platform and would prefer to use Windows EXE files, they can make use of tools like Launch4J, JSmooth, NSIS-Java Launcher and WinRun4J to wrap file extension JAR and make them executable. Compilers like Eclipse make use of small EXE launchers to display splash screens and launch applications from startup.jar.
The manifest file contains entries that enable it determine the manner in which a JAR file extension is to be used. JAR files that are designed to be implemented as standalone programs have one class identified as the main class. This file format also includes a Classpath entry, which identifies other files that are required to be loaded with the JAR file. The Classpath entry holds a list of relative and absolute paths to more JAR files.
Whenever the Java Runtime Environment indicates a signed file extension JAR, the signatures may be validated and thus, the class files that fail to match the signature may not be loaded. This can also be used to offer support to sealed packages, where the Classloader only allows java classes to load into one package. However, this is only possible if they have been signed by the same entity. This process is important as it stops malicious code from penetrating into an existing package and gaining access to package-scoped data and classes.