[LINUX] [Java] How to switch between multiple versions of Java


There is also a method using multiple versions of Java by switching Java, such as method using jenv, but here the method using orthodox alternatives I'd like to introduce_______

For example, I think it will be useful in the following scenes, so it may be useful to remember just the command name alternatives.

What is the alternatives command?

alternatives are commands that come standard with CentOS.

If you look up alternatives with the man command, it says "maintain symbolic links determining default commands". It's hard to understand in English, but it's an excellent command that says, "You can use symbolic links to switch between software with similar functions and software with different versions."

In other words, it can be applied not only to Java but also to various commands **.

testing environment

[[email protected] ~]# java -version
java version "12.0.1" 2019-04-16
Java(TM) SE Runtime Environment (build 12.0.1+12)
Java HotSpot(TM) 64-Bit Server VM (build 12.0.1+12, mixed mode, sharing)

Advance preparation

Installation of new Java (OpenJDK)

  1. Download Java12 tar.gz from OpenJDK Site.
  2. Place and extract tar.gz under an appropriate directory (* here / usr / local) to complete the installation.
[[email protected] ~]# cd /usr/local/
[[email protected] local]# tar zxvf openjdk-12.0.1_linux-x64_bin.tar.gz 
[[email protected] local]# ls | grep jdk

Switching Java with the alternatives command

Check the current status

[[email protected] local]# alternatives --config java

There is one program'java'To provide.

Select command
*+ 1           /usr/java/jdk-12.0.1/bin/java

Press Enter to select the current[+]Or enter the selection number:

Command registration-Switching the JVM to use

[[email protected] local]# alternatives --install /usr/bin/java java /usr/local/jdk-12.0.1/bin/java 2
[[email protected] local]# alternatives --config java

There are 2 programs'java'To provide.

Select command
*+ 1           /usr/java/jdk-12.0.1/bin/java
   2           /usr/local/jdk-12.0.1/bin/java

Press Enter to select the current[+]Or enter the selection number:2

Check the status after setting

[[email protected] local]# alternatives --config java

There are 2 programs'java'To provide.

Select command
*  1           /usr/java/jdk-12.0.1/bin/java
 + 2           /usr/local/jdk-12.0.1/bin/java

Press Enter to select the current[+]Or enter the selection number:
[[email protected] local]# java -version
openjdk version "12.0.1" 2019-04-16
OpenJDK Runtime Environment (build 12.0.1+12)
OpenJDK 64-Bit Server VM (build 12.0.1+12, mixed mode, sharing)


Reference URL

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