Java - (Jar|Java ARchive) File

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1 - About

JAR stands for Java ARchive and is file format born in 1996 as a simple extension of the popular ZIP archive format with class and others required resource files:

  • signature files
  • images, sounds

The primary motivation for its development was so that Java applets and their requisite components (files, images and sounds) can be downloaded to a browser in a single HTTP transaction, rather than opening a new connection for each piece.

With the advent of the Main-Class manifest header, entire applications can be delivered.

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3 - Hell

Jar hell is a term similar to describe all the various ways in which the class loading process can end up not working.

To avoid a Jar hell, the shading technique can be used.

4 - Management

4.1 - Create

With the jar command-line utility.

jar cf myPackage.jar *.class

where:

  • 'c': create new archive.
  • 'f': create a file.

4.2 - Verify / Sign

  • jarsigner: You use the jarsigner tool to sign and verify Java Archive (JAR) files.

4.3 - Search class

4.3.1 - Windows

for /R %G in (*.jar) do @jar -tvf "%G" | find "ClassName" > NUL && echo %G

where:

  • for /R %G in (*.jar) do loop over all JAR files in the directory tree, store the file name in %G. See Dos - For Statement
  • @jar -tvf %G | - run the Java Archive command to list all file names within the given archive, and write the results to standard output; the @ symbol suppresses the echoing of the command to standard output.
  • find “ClassName” > NUL - search standard input, piped from the output of the jar command, for the given class name. It will set ERRORLEVEL to 1 if there's a match (otherwise 0). See DOS - Find Command.
  • && echo %G - if ERRORLEVEL is non-zero, write the Java archive file name to standard output (the console). See the AND control opertaor (&&)
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4.3.2 - Linux

  • below a certain location
find path/to/jars -name "*.jar" -exec grep -Hsli ClassName  {} \;
  • anywhere
for i in $(locate "*.jar");
  do echo $i; jar -tvf $i | grep -Hsi ClassName;
done

5 - Documentation / Reference

lang/java/jar.txt · Last modified: 2019/09/11 11:36 by gerardnico