如何在Linux服务器中找到正在运行的应用程序的JRE版本

Question

I am getting below result, Does it mean I am having JDK 1.7.0_45 and JRE is 1.42 ? Please advise.

$ javac -version
Eclipse Java Compiler v_677_R32x, 3.2.1 release, Copyright IBM Corp 2000, 2006. All rights reserved.
$ java -version
java version "1.7.0_45"
Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)
$ alternatives --config java
There is 1 program that provides 'java'.

  Selection    Command
-----------------------------------------------
*+ 1           **/usr/lib/jvm/jre-1.4.2-gcj/bin/java**

Enter to keep the current selection[+], or type selection number:

Answer 1

It would appear that you have two versions of Java installed:

• The Java on your PATH is Java 1.7.0. I think it is an Oracle build rather than a build from your Linux system's package repository.

• The Java configured using alternatives looks like a GCJ Java that is compatible with Java 1.4.2. It was probably installed from your package repository. IMO, it is inadvisable to use this from a technical standpoint. In fact, I would recommend uninstalling it.

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Actually I am getting "Unsupported major.minor version 51.0" error after uploading a external jar file to Informatica powercenter Java transformation.

That implies that Informatica is using the Java 1.4.2 installation.

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Now, the version of Java that an application uses will depend on what version of Java the application's launcher / launch script is using. That could depend on a number of things:

• If the launcher uses an absolute path for the java command, then that is what will use.
• If the launcher uses a simple name (eg java ) then the version used will depend on the launcher's $PATH . This is probably what is happening ... and the $PATH used is different from your shell's $PATH .

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So what is the solution?

• You could add the Oracle Java install to the alternatives system. See man alternatives or Google for instructions using "java oracle alternatives install"

• You could tweak the $PATH used by the application's launcher.

• Depending on your Linux distro, you could install an OpenJDK 1.7.0 JDK or JRE from the package repos. That will (should) add the new installed Java to the alternatives database, so that you can select it instead of the old GCJ 1.4.2 installation.