一、CentOS7一般会自带Open JDK，先卸载它
- 卸载系统自带的OpenJDK以及相关的java文件
- 在命令行窗口输入：java -version
[root@localhost yum.repos.d]# java -version openjdk version "1.8.0_131" OpenJDK Runtime Environment (build 1.8.0_131-b12) OpenJDK 64-Bit Server VM (build 25.131-b12, mixed mode)
可以看到系统自带的OpenJDK版本信息,在命令窗口键入： rpm -qa | grep java
命令说明：
rpm 管理套件
-qa 使用询问模式，查询所有套件
grep 查找文件里符合条件的字符串
java 查找包含java字符串的文件
[dr@localhost ~]$ rpm -qa | grep java tzdata-java-2017b-1.el7.noarch java-1.8.0-openjdk-1.8.0.131-11.b12.el7.x86_64 java-1.7.0-openjdk-1.7.0.141-2.6.10.5.el7.x86_64 python-javapackages-3.4.1-11.el7.noarch javapackages-tools-3.4.1-11.el7.noarch java-1.7.0-openjdk-headless-1.7.0.141-2.6.10.5.el7.x86_64 java-1.8.0-openjdk-headless-1.8.0.131-11.b12.el7.x86_64
以上文件中,下面这几个可以删除
java-1.8.0-openjdk-1.8.0.131-11.b12.el7.x86_64
java-1.7.0-openjdk-1.7.0.141-2.6.10.5.el7.x86_64
java-1.7.0-openjdk-headless-1.7.0.141-2.6.10.5.el7.x86_64
java-1.8.0-openjdk-headless-1.8.0.131-11.b12.el7.x86_64
# 此命令跟上述命令功能一样 sudo yum remove java-1.*
在root用户下，在命令窗口输入
rpm -e --nodeps java-1.7.0-openjdk-1.7.0.141-2.6.10.5.el7.x86_64 rpm -e --nodeps java-1.8.0-openjdk-1.8.0.131-11.b12.el7.x86_64 rpm -e --nodeps java-1.7.0-openjdk-headless-1.7.0.141-2.6.10.5.el7.x86_64 rpm -e --nodeps java-1.8.0-openjdk-headless-1.8.0.131-11.b12.el7.x86_64
命令介绍：
rpm 管理套件
-e 删除指定的套件
–nodeps 不验证套件档的相互关联性
检查是否已经删除成功在命令窗口键入：java -version
[root@localhost dr]# java -version bash: java: command not found...
到这里CentOS自带的Open JDK已经完全删除了！！！
二、安装jdk1.8
一、本地文件安装
首先去 官网把 jdk1.8 下载 到本地，保存到自己习惯的地方
首先创建java存放目录，这里我在 /usr/local/ 目录下创建了一个 java文件夹
[root@localhost Datafile]# sudo mkdir /usr/local/java
把下载的文件先解压，解压文件会在当前目录下
[root@localhost Datafile]# tar -zxvf jdk-8u171-linux-x64.tar.gz jdk1.8.0_171/ jdk1.8.0_171/javafx-src.zip jdk1.8.0_171/bin/ jdk1.8.0_171/bin/jmc jdk1.8.0_171/bin/serialver jdk1.8.0_171/bin/jmc.ini jdk1.8.0_171/bin/jstack jdk1.8.0_171/bin/rmiregistry jdk1.8.0_171/bin/unpack200 ...
查看解压文件
[root@localhost Datafile]# ll total 186420 drwxr-xr-x. 8 10 143 255 Mar 28 2018 jdk1.8.0_171 -rw-rw-r--. 1 dr dr 190890122 Mar 28 04:41 jdk-8u171-linux-x64.tar.gz
将解压后的文件，启动到新建的目录下
[root@localhost Datafile]# mv jdk1.8.0_171/ /usr/local/java/ # 然后配置环境变量 vi /etc/profile # 按 i 进入编辑模式，去文件最后加上下面两行， path 是存放jdk的路径 /usr/local/java/jdk1.8.0_171 export JAVA_HOME=/path export PATH=$PATH:$JAVA_HOME/bin # 先按Esc键 再按 :wq! 退出保存
最后让配置文件生效
source /etc/profile
测试是否安装成功
[root@localhost Datafile]# java -version java version "1.8.0_171" Java(TM) SE Runtime Environment (build 1.8.0_171-b11) Java HotSpot(TM) 64-Bit Server VM (build 25.171-b11, mixed mode) [root@localhost Datafile]# java Usage: java [-options] class [args...] (to execute a class) or java [-options] -jar jarfile [args...] (to execute a jar file) where options include: -d32 use a 32-bit data model if available -d64 use a 64-bit data model if available -server to select the "server" VM The default VM is server, because you are running on a server-class machine. -cp <class search path of directories and zip/jar files> -classpath <class search path of directories and zip/jar files> A : separated list of directories, JAR archives, and ZIP archives to search for class files. -D<name>=<value> ... [root@localhost Datafile]# javac Usage: javac <options> <source files> where possible options include: -g Generate all debugging info -g:none Generate no debugging info -g:{lines,vars,source} Generate only some debugging info -nowarn Generate no warnings -verbose Output messages about what the compiler is doing -deprecation Output source locations where deprecated APIs are used -classpath <path> Specify where to find user class files and annotation processors -cp <path> Specify where to find user class files and annotation processors -sourcepath <path> Specify where to find input source files -bootclasspath <path> Override location of bootstrap class files -extdirs <dirs> Override location of installed extensions -endorseddirs <dirs> Override location of endorsed standards path -proc:{none,only} Control whether annotation processing and/or compilation is done. ...
