sudo update-alternatives --install /usr/bin/java java /tmp/jdk1.8.0/bin/java 300
sudo update-alternatives --install /usr/bin/javac javac /tmp/jdk1.8.0/bin/javac 300
设置：
#set java environment
export JAVA_HOME=/tmp/jdk1.8.0
export JRE_HOME=${JAVA_HOME}/jre
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib
export PATH=${JAVA_HOME}/bin/$PATH