Home Accessibility Courses Twitter The Mouth Facebook Resources Site Map About Us Contact
 
Python and Tcl - public course schedule [here]
Private courses on your site - see [here]
Please ask about maintenance training for Perl, PHP, Lua, etc
 
Running straight from the jar, but not from a tar

tar v jar files - format comparison Why can you run applications in Java straight from the jar, but you'll never find mainstream applications extracting their code from a tar file? It all comes down to the different indexing structure.

A tar file was originally designed as a "tape archive". So it's a sequential file that contains file name, file length, file data for the first file, then the same thing for the second file, for the third file, and so on. It means that when a tape is written, you have a high data integrity even on a device that doesn't have random access facilities, as there's no need to store statistics about a file once it's been added, nor to look them up right at the start or end of writing the file which may - on a multiuser system - have changed. But it does mean that if you want to read back something from a "tar" file you have to look at each header block in turn until you find what you need.

By contrast, a jar file [same format as zip] contains all the data at the start of the jar, then an index of where each object starts and ends at the end of the file. Which means you can very quickly read the list of contents ("Manifest") and jump to what you need even in a huge file - but it does require random access.

You may ask why the list of contents for a jar is at the end. That's so that a jar file can be updated / have things added to it without having to rewrite the whole file - adding a new file is as simple as reading the old manifest, adding the new file's data starting where the manifest used to start, and then writing an updated manifest.

(written 2009-05-26)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
A101 - Web Application Deployment - Linux -An Introduction For Users
  [3819] Packing a tar, jar or war file - best practise - (2012-07-26)
  [3791] The Kernel, Shells and Daemons. Greek Gods in computing - (2012-07-01)
  [3256] Displaying a directory or file system tree - Linux - (2011-04-22)
  [3179] Oops - I typed ci not vi, and have lost my file ... - (2011-02-21)
  [2831] Recording (a macro) in vi - (2010-06-27)
  [2636] Linux - useful tips including history and file name completion - (2010-02-15)
  [2494] Making Linux Politically correct - (2009-11-06)
  [2479] Accidentally typed ci rather than vi? - (2009-10-27)
  [2300] What does x on a linux directory mean? - (2009-07-21)
  [2299] How much space does my directory take - Linux - (2009-07-20)
  [2203] Always use su with minus. And where do programs come from? - (2009-05-27)
  [1904] Ruby, Perl, Linux, MySQL - some training notes - (2008-11-23)
  [1902] sstrwxrwxrwx - Unix and Linux file permissions - (2008-11-23)
  [1897] Keeping on an even keel - (2008-11-21)
  [1893] Some Linux and Unix tips - (2008-11-18)
  [1803] FTP passive mode - a sometimes cure for upload hangs - (2008-09-20)
  [1764] Yank and Push - copy and move in vi - (2008-08-21)
  [1651] ls command - favourite options - (2008-05-23)
  [1527] Selecting file names in a shell - one word or another - (2008-02-02)
  [1438] Copy and paste / cut and paste and other vi techniques - (2007-11-20)
  [1408] Wireless hotel tips - FTP and Skype connections failing - (2007-10-26)
  [1366] awk - a powerful data extraction and manipulation tool - (2007-09-25)
  [1288] Linux run states, shell special commands, and directory structures - (2007-08-03)
  [1287] Work and play at Well House Manor - Football and Shell Shortcuts - (2007-08-02)
  [1259] Where am I and how did I get here? - (2007-07-05)
  [1068] ls -l report, Linux / Unix - types and permssions - (2007-02-06)
  [1013] Copy multiple files - confusing error message from cp - (2006-12-30)
  [1012] Moving files between Windows / DOS and Linux / Unix - (2006-12-30)
  [984] Cardinal numbers and magic numbers - (2006-12-14)
  [749] Cottage industry or production line data handling methods - (2006-06-07)
  [711] THE home directory or MY home directory - (2006-05-06)
  [710] Linux training Glasgow, Python programming course Dundee - (2006-05-05)
  [703] Copying files and preserving ownership - (2006-04-28)
  [679] More or less on the edge of the page - (2006-04-11)
  [659] Web Application Components - (2006-03-28)
  [593] Finding where the disc space has gone - (2006-02-06)
  [431] File permissions of Linux and Unix systems - (2005-08-31)
  [430] Linux commands - some basics - (2005-08-31)
  [249] An easy way out - (2005-03-17)
  [152] Aladdin, or careful what you wish. - (2004-12-15)
  [74] pushd and popd - (2004-10-05)
  [73] vi - full circle - (2004-10-04)

A165 - Web Application Deployment - Installing Software
  [4259] Upgrading our training systems to all the current stable versions - (2014-04-07)
  [3053] Make - automating the commands for building and installing - (2010-11-16)
  [2139] OS Commerce install made simple - (2009-04-24)
  [1700] FTP server on Fedora Linux - (2008-07-06)
  [809] What to do during a Linux build - (2006-07-20)


Back to
England, Scotland, Northern Ireland
Previous and next
or
Horse's mouth home
Forward to
Bright Colours
Some other Articles
An evening walk in Carrickfergus
Images in a database? How big is a database? (MySQL)
Bright Colours
Running straight from the jar, but not from a tar
England, Scotland, Northern Ireland
Improving the structure of your early PHP programs
On the road, at a Service area thats a cut above the others
New Example - cacheing results in PHP for faster loading
A two day gap - first time in five years?
4759 posts, page by page
Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96 at 50 posts per page


This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

Link to Ezine home page (for reading).
Link to Blogging home page (to add comments).

You can Add a comment or ranking to this page

© WELL HOUSE CONSULTANTS LTD., 2019: 404 The Spa • Melksham, Wiltshire • United Kingdom • SN12 6QL
PH: 01225 708225 • EMAIL: info@wellho.net • WEB: http://www.wellho.net • SKYPE: wellho

PAGE: http://www.wellho.net/mouth/2201_Run ... a-tar.html • PAGE BUILT: Sat May 27 16:49:10 2017 • BUILD SYSTEM: WomanWithCat