Linux CentOS7 安装JDK1.8

1. 下载JDK安装包，我是从官网下载的，官网地址
   https://www.oracle.com/java/technologies/javase/javase-jdk8-downloads.html 如下图找到对应的系统版本，这里下载.tar.gz包
   

点击链接后会提示你同意协议，然后需要登录Oracle. 登录比较慢多试几次。

2. 把下载好的源码包上传到linux服务器(我尝试在linux直接用wget下载，提示没有权限)

3. 解压缩, 复制目录到/usr/local/java

tar -zxvf jdk-8u251-linux-x64.tar.gz
mv jdk1.8.0_251/ /usr/local/java

4. 配置环境变量 /etc/profile

vim /etc/profile   //如果提示vim找不到可以yum install -y vim 安装

在末尾添加以边代码

export JAVA_HOME=/usr/local/java/
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
export PATH=$PATH:$JAVA_HOME/bin

wq保存；然后在命令行输入 source /etc/profile 使配置生效

5. 验证java是否安装成功

[root@VM_0_3_centos java]# java -version
java version "1.8.0_251"
Java(TM) SE Runtime Environment (build 1.8.0_251-b08)
Java HotSpot(TM) 64-Bit Server VM (build 25.251-b08, mixed mode)

[root@VM_0_3_centos java]# 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.
  -processor <class1>[,<class2>,<class3>...] Names of the annotation processors to run; bypasses default discovery process
  -processorpath <path>      Specify where to find annotation processors
  -parameters                Generate metadata for reflection on method parameters
  -d <directory>             Specify where to place generated class files
  -s <directory>             Specify where to place generated source files
  -h <directory>             Specify where to place generated native header files
  -implicit:{none,class}     Specify whether or not to generate class files for implicitly referenced files
  -encoding <encoding>       Specify character encoding used by source files
  -source <release>          Provide source compatibility with specified release
  -target <release>          Generate class files for specific VM version
  -profile <profile>         Check that API used is available in the specified profile
  -version                   Version information
  -help                      Print a synopsis of standard options
  -Akey[=value]              Options to pass to annotation processors
  -X                         Print a synopsis of nonstandard options
  -J<flag>                   Pass <flag> directly to the runtime system
  -Werror                    Terminate compilation if warnings occur
  @<filename>                Read options and filenames from file