Linux下安装JDK 1.8

前言

JDK是 JAVA 的软件开发工具包，如果要使用JAVA来进行开发，或者部署基于其开发的应用，那么就需要安装JDK。本次将在Linux下安装JDK及配置环境。

本人环境：CentOS 7.3 64位

下载JDK

在安装之前，检查是否存在Linux下自带的OpenJDK，命令：rpm -qa | grep java。若存在，则需要进行卸载，命令：rpm -e --nodeps 卸载的软件名。

JDK历史版本链接：https://www.oracle.com/technetwork/java/javase/archive-139210.html

接着，我们可以通过 wget 命令下载JDK安装包，或者下载后传到Linux。我这里下载的安装包版本是 jdk-8u131-linux-x64.tar.gz 。

解压安装包

创建一个文件夹，用于存放JDK安装包，然后解压到该目录下。

创建文件夹：mkdir /root/JDK
进入文件夹：cd /root/JDK
解压：tar -zxvf /root/JDK/jdk-8u131-linux-x64.tar.gz

可以看到，本次解压到了当前目录 /root/JDK/jdk1.8.0_131下。

配置环境

解压完成之后，我们要配置下环境变量，通过 vim 命令修改配置文件 /etc/profile 来设置环境变量。

vim /etc/profile

在文件最后一行，输入 i 进入编辑模式，添加以下内容，然后按 Esc 退出编辑模式，再输入 :wq 保存并退出。

export JAVA_HOME=/root/JDK/jdk1.8.0_131  
export JRE_HOME=${JAVA_HOME}/jre  
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib  
export PATH=${JAVA_HOME}/bin:$PATH

设置完之后，如果要使环境变量立即生效，需要通过命令：source /etc/profile，重新加载配置文件。

验证是否安装成功

所有都配置好了，我们需要验证下是否安装成功。

依次输入 java -version、java、javac，不会出现报错并且显示出 jdk版本号及 java/javac相关命令参数说明界面。

[root@wintest JDK]# java -version
-bash: java: command not found
[root@wintest JDK]# source /etc/profile
[root@wintest JDK]# java -version
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)
[root@wintest JDK]# 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.

    -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>
                  set a system property
    -verbose:[class|gc|jni]
                  enable verbose output
    -version      print product version and exit
    -version:<value>
                  Warning: this feature is deprecated and will be removed
                  in a future release.
                  require the specified version to run
    -showversion  print product version and continue
    -jre-restrict-search | -no-jre-restrict-search
                  Warning: this feature is deprecated and will be removed
                  in a future release.
                  include/exclude user private JREs in the version search
    -? -help      print this help message
    -X            print help on non-standard options
    -ea[:<packagename>...|:<classname>]
    -enableassertions[:<packagename>...|:<classname>]
                  enable assertions with specified granularity
    -da[:<packagename>...|:<classname>]
    -disableassertions[:<packagename>...|:<classname>]
                  disable assertions with specified granularity
    -esa | -enablesystemassertions
                  enable system assertions
    -dsa | -disablesystemassertions
                  disable system assertions
    -agentlib:<libname>[=<options>]
                  load native agent library <libname>, e.g. -agentlib:hprof
                  see also, -agentlib:jdwp=help and -agentlib:hprof=help
    -agentpath:<pathname>[=<options>]
                  load native agent library by full pathname
    -javaagent:<jarpath>[=<options>]
                  load Java programming language agent, see java.lang.instrument
    -splash:<imagepath>
                  show splash screen with specified image
See http://www.oracle.com/technetwork/java/javase/documentation/index.html for more details.
[root@wintest JDK]# 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@wintest JDK]#