Jar:

JAR(Java Archive) [1] is a platform-independent file format, which allows many record group files to be compressed into one file. JAR files created for J2EE applications are EAR files (enterprise JAR files). JAR file format is based on the popular ZIP file format. Different from ZIP files, JAR files are not only used for compression and publishing, but also for deploying and encapsulating libraries, components and plug-ins, which can be directly used by compilers, JVMs and other tools. JAR contains some special files, such as manifest and deployment descriptor, which are used to instruct tools how to deal with a specific JAR.

JAR files can be signed using the jarsigner tool or directly through the java.securityAPI The signed JAR file is exactly the same as the original JAR file, except that its list has been updated and two files, a signature file and a signature block file, have been added to the META-INF directory. JAR files are signed by certificates stored in the keystore database. The certificate stored in the keystore is protected by a password, and the password must be provided to the jarsigner tool to sign the JAR file.