How to use the command jenv (with examples)

The jenv command-line tool is used to manage the “JAVA_HOME” environment variable. It allows you to add, display, and set different Java versions for your system. This is especially useful if you work on multiple projects that require different Java versions.

Use Case 1: Add a Java version to jEnv

Code:

jenv add path/to/jdk_home

Motivation: Adding a Java version to jEnv is necessary if you want to manage multiple Java versions on your system. By adding a Java version, you make it available for use with jEnv and can easily switch between different versions.

Explanation:

• jenv add: This is the command to add a Java version to jEnv.
• path/to/jdk_home: This is the path to the JDK installation directory. Replace it with the actual path on your system.

Example Output:

$ jenv add /usr/lib/jvm/java-11-openjdk-amd64
Adding java version 11.0.12 to the database...
Shell script detected (bash)
Adding java.sh shim...
Adding javac.sh shim...
Adding jshell.sh shim...
Adding jdi.sh shim...
Adding keytool.sh shim...
Adding orbd.sh shim...
Adding pack200.sh shim...
Adding policytool.sh shim...
Adding rmid.sh shim...
Adding rmiregistry.sh shim...
Adding servertool.sh shim...
Adding tnameserv.sh shim...
Adding jexec shims...
Adding man/appletviewer.sh shim...
Adding man/extcheck.sh shim...
Adding man/idlj.sh shim...
Adding man/jar.sh shim...
Adding man/javafxpackager.sh shim...
Adding man/javah.sh shim...
Adding man/javap.sh shim...
Adding man/javaw.sh shim...
Adding man/jcmd.sh shim...
Adding man/jconsole.sh shim...
Adding man/jdb.sh shim...
Adding man/jdeps.sh shim...
Adding man/jhat.sh shim...
Adding man/jinfo.sh shim...
Adding man/jjs.sh shim...
Adding man/jmap.sh shim...
Adding man/jps.sh shim...
Adding man/jrunscript.sh shim...
Adding man/jstack.sh shim...
Adding man/jstat.sh shim...
Adding man/jstatd.sh shim...
Adding man/keytool.sh shim...
Adding man/native2ascii.sh shim...
Adding man/orbd.sh shim...
Adding man/pack200.sh shim...
Adding man/policytool.sh shim...
Adding man/rmid.sh shim...
Adding man/rmiregistry.sh shim...
Adding man/schemagen.sh shim...
Adding man/servertool.sh shim...
Adding man/serialver.sh shim...
Adding man/tnameserv.sh shim...
Adding man/unpack200.sh shim...
Adding visualvm shims...
Adding jup.sh shim...
Calling shim: "/usr/lib/jvm/java-11-openjdk-amd64/jre/../bin/jdwp-listen"
Detected JDK_HOME: /usr/lib/jvm/java-11-openjdk-amd64
JDK detected at /usr/lib/jvm/java-11-openjdk-amd64

Use Case 2: Display the current JDK version used

Code:

jenv version

Motivation: Sometimes, it’s necessary to verify which Java version is currently being used as the default. Using jenv version allows you to quickly check the current JDK version.

Explanation:

• jenv version: This command displays the current JDK version used.

Example Output:

$ jenv version
11.0.12 (set by /home/user/.jenv/version)

Use Case 3: Display all managed JDKs

Code:

jenv versions

Motivation: When using jEnv, you can manage multiple JDK versions. The jenv versions command shows you all the JDK versions currently managed by jEnv, making it easy to see which versions are available for use.

Explanation:

• jenv versions: This command displays all managed JDK versions.

Example Output:

$ jenv versions
* system (set by /usr/local/Cellar/jenv/.version)
  11.0
  11.0.12
  oracle64-1.8.0.181

Use Case 4: Set the global JDK version

Code:

jenv global java_version

Motivation: By setting the global JDK version, you define the default Java version to be used by your system. This is particularly useful when you want to ensure a consistent Java version across all projects.

Explanation:

• jenv global: This command sets the global JDK version.
• java_version: The JDK version you want to set as the global default.

Example Output:

$ jenv global 11.0.12

Use Case 5: Set the JDK version for the current shell session

Code:

jenv shell java_version

Motivation: Sometimes, you may want to set a specific JDK version for a particular shell session without affecting the global settings. This allows you to temporarily switch to a different Java version for a specific task.

Explanation:

• jenv shell: This command sets the JDK version for the current shell session.
• java_version: The JDK version you want to set for the current shell session.

Example Output:

$ jenv shell 11.0.12

Use Case 6: Enable a jEnv plugin

Code:

jenv enable-plugin plugin_name

Motivation: jEnv provides various plugins that can extend its functionality. By enabling a specific plugin, you gain access to additional features that can enhance your Java development workflow.

Explanation:

• jenv enable-plugin: This command enables a jEnv plugin.
• plugin_name: The name of the plugin you want to enable.

Example Output:

$ jenv enable-plugin export

Conclusion:

The jenv command-line tool is a powerful utility for managing Java versions on your system. With its various commands, you can add, display, and set different JDK versions effortlessly. This gives you the flexibility to work on projects with specific Java requirements and ensures consistency across your development environment.