ubuntu 16.04虚拟机 安装 openjdk 1.7

sudo add-apt-repository ppa:openjdk-r/ppa

sudo apt-get update

发现更新失败，是因为ubuntu部分源在大陆无法访问。

编辑/etc/apt/sources.list文件, 在文件最前面添加以下条目(操作前请做好相应备份)：

deb http://mirrors.ustc.edu.cn/ubuntu/ xenial main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-security main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-proposed main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-security main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-updates main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-proposed main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ xenial-backports main restricted universe multiverse

之后再输入：

sudo apt-get update

更新源。

安装openjdk 1.7

sudo apt-get install openjdk-7-jdk

$ sudo 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-8-openjdk-amd64/jre/bin/java   1081      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   1081      manual mode
Press to keep the current choice[*], or type selection number:

$ sudo update-alternatives --config javac
There are 2 choices for the alternative javac (providing /usr/bin/javac).
  Selection    Path                                         Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-8-openjdk-amd64/bin/javac   1081      auto mode
  1            /usr/lib/jvm/java-7-openjdk-amd64/bin/javac   1071      manual mode
  2            /usr/lib/jvm/java-8-openjdk-amd64/bin/javac   1081      manual mode
Press to keep the current choice[*], or type selection number: 

都选1，$ java -version
java version "1.7.0_95"
OpenJDK Runtime Environment (IcedTea 2.6.4) (7u95-2.6.4-3)
OpenJDK 64-Bit Server VM (build 24.95-b01, mixed mode)
$ javac -version
javac 1.7.0_95