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# 一、基于 CentOS7 系统安装配置 JDK8

（1）下载jdk安装包
打开 [jdk下载地址](https://www.oracle.com/java/technologies/javase/javase-jdk8-downloads.html)，找到linux下64位的安装包，点击下载（注意此步骤需要注册Oracle账号并登录

（2）、将安装包上传至服务器，然后解压
```bash
tar -zxvf jdk-8u331-linux-x64.tar.gz
```
（3）将解压文件夹移动至 /usr/local/目录下
```bash
mv jdk1.8.0_331 /usr/local/
```
（4）、配置环境变量
```bash
vi /etc/profile
```
在文件末尾增加以下内容
```bash
export JAVA_HOME=/usr/local/jdk1.8.0_331 
export PATH=$JAVA_HOME/bin:$PATH
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib
```

（5）、使环境变量生效
```bash
source /etc/profile
```
（6）查看java版本号
```bash
[root@iZbp1flzt6x7pxmxfhmxeeZ pkg]# java -version
java version "1.8.0_331"
Java(TM) SE Runtime Environment (build 1.8.0_331-b09)
Java HotSpot(TM) 64-Bit Server VM (build 25.331-b09, mixed mode)
[root@iZbp1flzt6x7pxmxfhmxeeZ pkg]#
```

（7）执行javac，如下表示环境配置已经配置OK
```bash
[root@iZbp1flzt6x7pxmxfhmxeeZ pkg]# 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

[root@iZbp1flzt6x7pxmxfhmxeeZ pkg]#
```

# 二、基于CentOS7 安装 openjdk 17
（1） 下载openjdk 17的安装包
```bash
wget https://download.java.net/java/GA/jdk17/0d483333a00540d886896bac774ff48b/35/GPL/openjdk-17_linux-x64_bin.tar.gz
```

（2）解压文件并移动到 /usr/local/ 目录下
```bash
tar -zxvf openjdk-17_linux-x64_bin.tar.gz
mv jdk-17 /usr/local/
```
（3）vi /etc/profile 文件，在末尾增加如下内容：
```bash
export JAVA_HOME=/usr/local/jdk-17/
export PATH=$JAVA_HOME/bin:$PATH
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib
```
（4）查看java的版本，如下所示表示安装配置成功
```bash
[root@redrose2100 opt]# java -version
openjdk version "17" 2021-09-14
OpenJDK Runtime Environment (build 17+35-2724)
OpenJDK 64-Bit Server VM (build 17+35-2724, mixed mode, sharing)
```

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