检测当前的应用版本

Question

When I was working with XCode and iOS, there was a simple way to check the application's current version by reading the plist.

Is there a similar way to do this in Java?

Answer 1

XCode stores that version value in a resource file that is distributed with your application. In Java the equivalent would be your Manifest file, which is packed inside your JAR/WAR/EAR archive.

A Manifest file is just a metadata text file named MANIFEST.MF that stores some standard key/value pairs which are recognized by many tools and that is packaged inside a special folder named META-INF inside your java archive.

To get the Manifest file for your own JAR this question would give you some clues. Once you have your own Manifest instance then use either one of the next options to get that version value.

This way to get the Specification Version:

Manifest mf = .... // get the manifest file
String specVersion = mf.getAttribute("Specification-Version");

This way to get the Implementation Version:

Manifest mf = .... // get the manifest file
String specVersion = mf.getAttribute("Implementation-Version");

More info regarding the JAR manifests can be found here .

EDIT:

If you are getting null values for any of those properties that means that they haven't been configured in your MANIGEST.MF file. That's easy to check: unzip your JAR file (JAR files are just ZIP files with a different extension name) and go the META-INF folder to find the MANIFEST.MF file, since it's a text file you can print its contents to the console, if there is a Specification-Version or Implementation-Version attribute defined there and you are still getting null values then you might be loading a manifest file from a different JAR.

FOR THE RECORD:

To get that attributes in your Manifest file you would need to configure your build tool to do so. Maven would do it automatically (you can customize it though), with Ant you will need to use a specific Ant Task , with Eclipse you will need go through its docs (same with any other IDE).

Answer 2

As Alonso says, in Java, your code isn't automatically assigned a build version by the compiler. Java leaves that up to the build tool that your compiler is run by, eg ant or maven. If your app isn't using the manifest file, which is often the case, but using instead a version number suffix, eg my_app_1.2.3.jar then you could do this to get the jar name:

Class.getProtectionDomain().getCodeSource().getLocation()

Answer 3

If it has a GUI and the main purpose ¹ is 'update' use Java Web Start to deploy it.

For displaying the version to the user I would store the version number in the manifest of each Jar of the app., and show the Implementation-Version s in a JTable at run-time.

1. As an aside, to get better answers, put aside what you are trying to 'do' and instead name the 'feature' you are trying to achieve. The latter can be expressed as the application feature you would like to offer the user. It might be something like 'Can be expanded with plug-ins', 'Has free auto-upgrade for 24 months', 'Whiter, brighter, more suds'..