--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/_posts/2020-11-20-multi-java.md	Fri Nov 20 17:34:39 2020 +0100
@@ -0,0 +1,123 @@
+---
+layout: post
+title:  "Multi java"
+date:   2020-11-20 17:01 +0100
+author: Christoph Kappel
+tags:   tools java jenv macos
+---
+There are many difficulties with Java, specially if you have to use multiple versions on
+your machine like you usual have to. Coming from Debian, this was quite easy with the
+alternative mechanisms, but on macOS?
+
+# Welcome jenv!
+
+[Jenv](https://www.jenv.be/) is a kind of package manager for all your Java versions, which helps you to switch
+between each of them pretty nicely, once you've set it up correctly.
+
+Installation is as easy as open a cold one:
+
+```console
+$ brew install jenv
+```
+
+*Once done, it reminds you to add it to your shell rc, which is probably a good idea.*
+
+Quick side note: Make sure to create the proper directories too, otherwise the commands fail
+in a weird way:
+
+```console
+$ mkdir -p ~/.jenv/version
+````
+
+# One java to go
+
+The easiest way to see your installed Java version sis via the **java_home** command:
+
+```console
+$ /usr/libexec/java_home -V
+Matching Java Virtual Machines (1):
+    1.8.0_201, x86_64:	"Java SE 8"	/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home
+```
+
+So far, nothing much to switch, but we still want to add it to [Jenv](https://www.jenv.be/):
+
+```console
+$ jenv add /Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home
+
+oracle64-1.8.0.201 added
+1.8.0.201 added
+1.8 added
+```
+
+A quick look into **~/.jenv/versions** to check, that it basically created some symlinks to your
+installation.
+
+# Make it two
+
+There is still not much to do, for a Java version manager, when there is only one version. Time
+to install another one, this time [AdoptOpenJdk](https://adoptopenjdk.net/):
+
+```console
+$ brew cask install adoptopenjdk
+$ brew cask install adoptopenjdk11
+```
+
+And another command to add it to [Jenv](https://www.jenv.be/):
+
+```console
+$ jenv add /Library/Java/JavaVirtualMachines/adoptopenjdk-11.jdk/Contents/Home                                                             
+
+openjdk64-11.0.9.1 added
+11.0.9.1 added
+11.0 added
+11 added
+``
+
+# Versions?
+
+Now we have to versions installed, let's check it:
+
+```console
+$ jenv versions                                                                                                                          
+* system (set by /Users/unexist/.jenv/version)
+  openjdk64-11.0.9.1
+  oracle64-1.8.0.201
+```
+
+And what about **java_home**:
+
+````
+$ /usr/libexec/java_home -V
+Matching Java Virtual Machines (2):
+    11.0.9.1, x86_64:	"AdoptOpenJDK 11"	/Library/Java/JavaVirtualMachines/adoptopenjdk-11.jdk/Contents/Home
+    1.8.0_201, x86_64:	"Java SE 8"	/Library/Java/JavaVirtualMachines/jdk1.8.0_201.jdk/Contents/Home
+```
+
+# How to use jenv?
+
+All set up done, we can now do the following:
+
+## Set a java version
+
+This can be done like this:
+
+```console
+$ jenv global openjdk64-11.0.9.1
+```
+
+And verified like:
+
+```console
+$ jenv versions
+  system
+  1.8
+  1.8.0.201
+  11
+  11.0
+  11.0.9.1
+* openjdk64-11.0.9.1 (set by /Users/unexist/.jenv/version)
+  oracle64-1.8.0.201
+```
+
+
+