安装Oracle JDK

在官网下载：http://www.oracle.com/technetwork/java/javase/downloads/index.html
解压后放到 /opt目录下

update-alternatives --install /usr/bin/java java /opt/jdk1.8.0_40/bin/java 1
update-alternatives --install /usr/bin/javac javac /opt/jdk1.8.0_40/bin/javac 1
update-alternatives --install /usr/lib/mozilla/plugins/libjavaplugin.so mozilla-javaplugin.so /opt/jdk1.8.0_40/jre/lib/amd64/libnpjp2.so 1
update-alternatives --set java /opt/jdk1.8.0_40/bin/java
update-alternatives --set javac /opt/jdk1.8.0_40/bin/javac
update-alternatives --set mozilla-javaplugin.so /opt/jdk1.8.0_40/jre/lib/amd64/libnpjp2.so

确认是否成java -version