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tar, jar, war, ear, sar files

Have you ever wondered why that are so many file extensions ending in "a r"? It's because the "ar" stands for archive, and it's such a reasonable way of naming file that the original tar which stands for tape archive was picked up by Sun and the Java community and transmuted into other file formats.

tar - tape archive
jar - java archive
war - web application archive
ear - enterprise archive
sar - service archive

The original tar or tape archive files are / were used for software distribution and backups. The format they use is that the file is written as a series of units:
• file name
• file length
• file data
which means that the whole archive file has potentially to be scanned when an element is to be extracted. Furthermore, a tar file in its native form is NOT compressed in any way. This means that a tar file can be both big and inconvenient.

Jar or Java Archive files may also be used for software distribution and backups, and although the jat utility that's used to create and (usually) to unpack them is written in Java and most people use them to contain Java - related information, they can actually contain any file and directory structure. There IS a header (an index or MANIFEST) at the top of a jar file saying what's in the file and where it is, so things can be accessed quickly on a random access systems such as a disc drive, and the data is usually stored compressed (turn compression off with the 0 option when you create a jar). This means that a .jar file is an appropriate medium for extracting information on the fly within a live application, even one that's quite heavily used.

Other file types that I mentioned at the start, such as war and ear are also jar files, created with the jar utility. In fact, they're a subtype of jar files with the data they contain being in a specific file and directory stucture. In other words, the arrangment of files within a war is such that the file and its contents are suitable for deployment as a webapp under a container such as Apache Tomcat, and the arrangement of files within a ear is such that it's an Enterprise Archive such as you would use under JBoss, etc.
(written 2006-06-10, updated 2006-06-13)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
A162 - Web Application Deployment - Backups and File System Management
  [4481] Extracting data from backups to restore selected rows from MySQL tables - (2015-05-01)
  [4405] Backup procedures - via backup server - (2015-01-24)
  [4400] Commenting out an echo killed my bash backup script - (2015-01-19)
  [4390] Checking MySQL database backups have worked (not failed) - (2015-01-10)
  [4115] More or less back - what happened to our server the other day - (2013-06-14)
  [4063] Backups by crossover between network centres - setting up automatic scp transfers - (2013-04-13)
  [4056] An overpractical test of our backup strategy! - (2013-03-30)
  [2299] How much space does my directory take - Linux - (2009-07-20)
  [1893] Some Linux and Unix tips - (2008-11-18)
  [1801] Will your backups work if you have to restore them? - (2008-09-18)
  [1765] Dialects of English and Unix - (2008-08-21)
  [1648] The tourists guide to Linux - (2008-05-20)
  [1439] Linux / Unix - layout of operating system files - (2007-11-20)
  [1288] Linux run states, shell special commands, and directory structures - (2007-08-03)
  [1023] Finding public writeable things on your linux file system - (2007-01-06)
  [1013] Copy multiple files - confusing error message from cp - (2006-12-30)
  [735] Boys will be boys, saved by Ubuntu - (2006-05-27)
  [703] Copying files and preserving ownership - (2006-04-28)
  [593] Finding where the disc space has gone - (2006-02-06)
  [554] What backup is adequate? - (2006-01-04)
  [334] Symbolic links and hard links - (2005-06-02)
  [153] Linux - where to put swap space - (2004-12-16)

A502 - Web Application Deployment - Java - Basic Tools
  [4412] Java -making sure you have the right versions - (2015-02-02)
  [3819] Packing a tar, jar or war file - best practise - (2012-07-26)
  [3151] Disassembling Python and Java - previously compiled code - (2011-01-29)
  [2859] Using java, javac, jar, and CLASSPATH - a simple example - (2010-07-07)
  [2422] Looking inside Java classes - javap and javadoc - (2009-09-25)
  [2153] Class Loading and Variable Conversion in Java - (2009-05-02)
  [1909] javax.servlet cannot be resolved - how to solve - (2008-11-26)
  [1771] More HowTo diagrams - MySQL, Tomcat and Java - (2008-08-24)
  [1562] Java Compiler - needs all classes, compiles them all too - (2008-03-03)
  [1192] What are WEB-INF and META-INF directories? - (2007-05-18)
  [1082] Straight from the .jar - (2007-02-16)

A653 - Web Application Deployment - Tomcat - Configuring Web Applications
  [3996] Tips on Tomcat - moving applications around - (2013-02-05)
  [3044] Changing a Servlet - more that just editing and compiling - (2010-11-12)
  [2088] Changing the 404 - file not found - page in Tomcat - (2009-03-18)
  [1564] Default file (MiMe types) for Apache httpd and Apache Tomcat - (2008-03-04)
  [1552] Extra public classes in deploying Apache httpd and Tomcat - (2008-02-24)
  [1074] Java beans and classes, .war and .jar files - (2007-02-10)
  [1006] Apache httpd and Apache Tomcat together tips - (2006-12-24)
  [479] New servlet from old - (2005-10-28)
  [465] Changing Tomcat's web.xml and reloading a web application - (2005-10-15)

A802 - Web Application Deployment - The JBoss application server
J708 - Java - Packages
  [2865] Relationships between Java classes - inheritance, packaging and others - (2010-07-10)
  [2419] Where is my Java class? - (2009-09-24)
  [2114] Which Version of Java am I running? - (2009-04-02)

J951 - Java - Tomcat - Configuring Web Applications

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