Managing multiple JDK installations using xenv - reflecting

On jdon 2020-11-06 01:20:02
managing multiple jdk installations using

jEnv It's a convenient tool , You can manage multiple... Between different projects JDK edition .

As a developer , We often work on different codebases at the same time . Especially in environments with microservices , We may have to switch the code base several times a day .

New... Is released every two years Java In the days of the version , It's usually not a problem , Because most codebases need the same Java edition .

When Java Release rhythm every 6 When it's changed once a month , This will change . today , If we're using multiple codebases , It is possible for each code base to use a different Java edition .

jEnv It's a tool , Can help us manage multiple JDK Install and configure each code base to use specific JDK edition , Without change JAVA_HOME environment variable .


install jEnv

jEnv Support Linux and MacOS operating system . If you are using Windows, You need to install Linux Of Windows Subsystem ( or bash Simulator , Such as GitBash) To use it .

according to jEnv Home page Installation instructions on the installation of jEnv.


install JDK

If you are reading this article , It is possible to set up a new JDK. Let's start with AdoptOpenJDK Website download JDK .

Select the version you want and download . take .tar.gz Unzip the file to any location .

About jEnv Are the benefits of , We don't need to pass brew,yum or apt Package manager to install JDK. We just need to download one JDK And put it in a folder .

You can still use brew,yum or apt To install JDK, You just need to find the package manager and place JDK Folder can be .


take JDK Add to jEnv

To put the new JDK And jEnv Use it together , We need to tell jEnv Where to find it . First , Use jenv versions Command check jEnv What has been supported JDK .

As far as I'm concerned , I have installed JDK 11、13 and 14. Each version has three different names .

Suppose we've downloaded JDK 15 And extract it to the folder ​​ in ~/software/java/jdk-15+36.

Now? , We will have a new JDK Add to jEnv in :

jenv add /home/tom/software/java/jdk-15+36/

If run again jenv versions, Will find : stay JDK 15 Has been added to the name 15 and openjdk64-15.


Local and global JDK

jEnv Support the overall situation JDK And multiple local JDK The concept of .

overall situation JDK Is in java Any place on the computer will use when typing the command line JDK .

Local JDK Is configured for specific folders only JDK. If we java Enter the command line in this folder , It will not use the global JDK, It's local JDK.

We can use it to configure different... For different projects JDK( As long as they're in different folders ).

  • Setting global JDK

First , We look at the whole picture JDK Version of :

jenv global

In my case , Output is :


This means that the system is installed with JDK Will be used as a global JDK. The name system Not very helpful , Because it doesn't say which version it is . Let's take the whole picture JDK Change to a more meaningful one with a version number JDK:

jenv global 11

This command has been used globally JDK Version changed to 11. As far as I'm concerned , This version is the same as before , But if you type jenv global, Which I'm going to see now JDK Version is my global version .

  • Set up local JDK

Remember what we downloaded JDK 15 Do you ? The reason for downloading it may be that we are developing a need to run JDK 15 New projects .

Suppose the project is in a folder ~/shiny-project. Let us cd I'm gonna go into this folder .

If you type in now java -version, The following results will be obtained :

openjdk version "11.0.8" 2020-07-14

This is because JDK 11 It's all about me JDK.

Let's change this project to JDK 15:

jenv local 15

Now type again java -version, The output will be :

openjdk version "15" 2020-09-15

How it works ?

Use this jenv local After the command , You will .java-version Find a file named in the current folder . This file contains local JDK Version number of .

During installation ,jEnv Will cover the java command . Every time we java Now call time ,jEnv Will look for one .java-version file , If you find a file , Then the... Defined in the file will be launched JDK edition . If you can't find it .java-version file , The global configuration will be started JDK.


Use Maven and Gradle

therefore , If we java Call... From the command line , It will immediately select a locally configured JDK. Big !

however , Such as Maven or Gradle Tools like that still use JDK System version of !

Let's see what we can do .

  • To configure jEnv In order to Maven Use it together

send Maven And jEnv Defined local JDK It's easy to use together . We just need to install maven plug-in unit :

jenv enable-plugin maven

If you're in ~/shiny-project Run... In folder mvn -version, You will get the following output :

Maven home: .../apache-maven-3.6.3
Java version: 15, vendor: AdoptOpenJDK, runtime: /home/tom/software/java/jdk-15+36
Default locale: en_AU, platform encoding: UTF-8
OS name: "linux", version: "5.4.0-52-generic", arch: "amd64", family: "unix"

  • To configure jEnv To use the Gradle

As far as I'm concerned ,Gradle Automatically selected jEnv Locally configured JDK!

If you can't use it immediately , It can be similar to the above Maven Install the plug-in like that gradle plug-in unit :

jenv enable-plugin gradle

If you're in ~/shiny-project Run... In folder gradle -version, Installation results will be obtained .



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