Ubuntu18.04 安装 JDK7

直接下载jdk压缩包方式安装

1.官网下载JDK　　　

     地址: http://www.oracle.com/technetwork/articles/javase/index-jsp-138363.html

　　选择相应的 .gz包下载

2. 解压缩,放到指定目录(以jdk-7u60-linux-x64.gz为例)

　　创建目录:

sudo mkdir /usr/lib/jvm

　加压缩到该目录:

 sudo tar -zxvf jdk-7u60-linux-x64.gz -C /usr/lib/jvm

3.修改环境变量:　　

sudo vim ~/.bashrc

　文件的末尾追加下面内容:

#set oracle jdk environment
export JAVA_HOME=/usr/lib/jvm/jdk1.7.0_60  ## 这里要注意目录要换成自己解压的jdk 目录
export JRE_HOME=${JAVA_HOME}/jre
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib
export PATH=${JAVA_HOME}/bin:$PATH  

　使环境变量马上生效

 source ~/.bashrc

4.设置系统默认jdk 版本

sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.7.0_60/bin/java 300
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.7.0_60/bin/javac 300
sudo update-alternatives --install /usr/bin/jar jar /usr/lib/jvm/jdk1.7.0_60/bin/jar 300
sudo update-alternatives --install /usr/bin/javah javah /usr/lib/jvm/jdk1.7.0_60/bin/javah 300
sudo update-alternatives --install /usr/bin/javap javap /usr/lib/jvm/jdk1.7.0_60/bin/javap 300   

　然后执行:

sudo update-alternatives --config java

若是初次安装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

　否者,选择合适的jdk

5.测试jdk

java -version

java version "1.7.0_60"

  Java(TM) SE Runtime Environment (build 1.7.0_60-b19)
  Java HotSpot(TM) 64-Bit Server VM (build 24.60-b09, mixed mode)

jdk 安装成功