离线安装jdk-8u112-linux-x64

1. 下载jdk-8u112-linux-x64.tar.gz，最好用迅雷下载，速度快

http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html

2. 创建目录

$ mkdir /usr/lib/jvm
$ tar -zxvf jdk-8u112-linux-x64.tar.gz -C /usr/lib/jvm

3. 修改环境变量：

$ vim ~/.bashrc  文件的末尾追加下面内容:
#set oracle jdk environment
export JAVA_HOME=/usr/lib/jvm/jdk1.8.0_112
export JRE_HOME=${JAVA_HOME}/jre  
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib  
export PATH=${JAVA_HOME}/bin:$PATH  

4. 使环境变量马上生效

$ source ~/.bashrc

5. 设置系统默认jdk 版本

$ update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.8.0_112/bin/java 300
$ update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.8.0_112/bin/javac 300
$ update-alternatives --install /usr/bin/jar jar /usr/lib/jvm/jdk1.8.0_112/bin/jar 300
$ update-alternatives --install /usr/bin/javah javah /usr/lib/jvm/jdk1.8.0_112/bin/javah 300
$ update-alternatives --install /usr/bin/javap javap /usr/lib/jvm/jdk1.8.0_112/bin/javap 300
$ update-alternatives --config java

6. 初次安装jdk,会有下面的提示

There is only one alternative in link group java (providing /usr/bin/java):
/usr/lib/jvm/jdk1.7.0_60/bin/java

7. 测试jdk

 $ java -version