【FAQ】ubuntu：java opensdk 7 如何升級到 8？

因要裝 SonarQube，必須要升級到 8 才行（SONAR_Requirements）。當前 opensdk 版本爲 7：

# java -version
java version "1.7.0_101"
OpenJDK Runtime Environment (IcedTea 2.6.6) (7u101-2.6.6-0ubuntu0.14.04.1)
OpenJDK 64-Bit Server VM (build 24.95-b01, mixed mode)

升級步驟後如下：

1，安裝 opensdk 8：

# add-apt-repository ppa:openjdk-r/ppa
# apt-get update
# apt-get install openjdk-8-jdk

2，爲了避免版本差異，7 暫時保留，故先手工切換默認 opensdk：

# update-java-alternatives -l
java-1.7.0-openjdk-amd64 1071 /usr/lib/jvm/java-1.7.0-openjdk-amd64
java-1.8.0-openjdk-amd64 1069 /usr/lib/jvm/java-1.8.0-openjdk-amd64

# update-alternatives --config java
There are 2 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                            Priority   Status
------------------------------------------------------------
  0            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1071      auto mode
  1            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1071      manual mode
* 2            /usr/lib/jvm/java-8-openjdk-amd64/jre/bin/java   1069      manual mode

Press enter to keep the current choice[*], or type selection number: 2

# java -version
openjdk version "1.8.0_91"
OpenJDK Runtime Environment (build 1.8.0_91-8u91-b14-0ubuntu4~14.04-b14)
OpenJDK 64-Bit Server VM (build 25.91-b14, mixed mode)

大功告成：）