Java - (Jar|Java ARchive) File
Table of Contents
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.
Articles Related
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.
Management
Create
With the jar command-line utility.
jar cf myPackage.jar *.class
where:
- 'c': create new archive.
- 'f': create a file.
Verify / Sign
Verification
jar tf build/libs/building-java-libraries.jar
META-INF/
META-INF/MANIFEST.MF
Library.class
You should see the required manifest file —MANIFEST.MF— and the compiled class.
Search class
Windows
for /R %G in (*.jar) do @jar -tvf "%G" | find "ClassName" > NUL && echo %G
where:
- <wrap box>for /R %G in (*.jar) do</note> loop over all JAR files in the directory tree, store the file name in %G. See Dos - For Statement
- <wrap box>@jar -tvf %G |</note> - 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.
- <wrap box>find “ClassName” > NUL</note> - 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.
- <wrap box>&& echo %G</note> - if ERRORLEVEL is non-zero, write the Java archive file name to standard output (the console). See the AND control opertaor (&&)
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