2020-04-02更新： 之前的安装方法已经废弃了，可通过以下方式安装
brew tap AdoptOpenJDK/openjdk
brew cask install <version>
这里有全部的version列表 例如可以这么安装
brew cask install adoptopenjdk8
之前用brew安装了java9。但我有些软件不兼容，只能降级到java8。这里简单记录下步骤。
卸载
brew cask uninstall java
安装指定版本
brew tap caskroom/versions
foam@foamdeMBP: sens » brew cask search java [15:13:54]
==> Exact Match
java
==> Partial Matches
charles-applejava eclipse-javascript java6 netbeans-java-ee yourkit-java-profiler
eclipse-java java-jdk-javadoc java8 netbeans-java-se
估计我没更新brew的缘故，上面只列出java6和java8。java7呢，有点懵逼。 键入下面命令，然后就会自动下载安装了。可能会有点慢。
foam@foamdeMBP: sens » brew cask install java8
Updating Homebrew...
^CWarning: Unexpected method 'license' called during caveats on Cask java8.
Follow the instructions here:
https://github.com/caskroom/homebrew-cask#reporting-bugs
==> Caveats
This Cask makes minor modifications to the JRE to prevent issues with
packaged applications, as discussed here:
https://bugs.eclipse.org/bugs/show_bug.cgi?id=411361
If your Java application still asks for JRE installation, you might need
to reboot or logout/login.
==> Satisfying dependencies
==> Downloading http://download.oracle.com/otn-pub/java/jdk/8u172-b11/a58eab1ec242421181065cdc37240b08/jdk-8u172-macosx-x64.dmg
######################################################################## 100.0%
==> Verifying checksum for Cask java8
==> Installing Cask java8
==> Running installer for java8; your password may be necessary.
==> Package installers may write to any location; options such as --appdir are ignored.
Password:
==> installer: Package name is JDK 8 Update 172
==> installer: Installing at base path /
==> installer: The install was successful.
🍺 java8 was successfully installed!
确认下，ok了。
foam@foamdeMBP: sens » java -version [15:46:05]
java version "1.8.0_172"
Java(TM) SE Runtime Environment (build 1.8.0_172-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.172-b11, mixed mode)