一、查看是否已经安装了JDK
#查看本机是否已经安装了jdk $ sudo yum list installed | grep java java-1.8.0-openjdk.x86_64 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-accessibility.x86_64 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-accessibility-debug.x86_64 java-1.8.0-openjdk-debug.x86_64 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-demo.x86_64 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-demo-debug.x86_64 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-devel.x86_64 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-devel-debug.x86_64 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-headless.x86_64 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-headless-debug.x86_64 java-1.8.0-openjdk-javadoc.noarch 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-javadoc-debug.noarch 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-javadoc-zip.noarch 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-javadoc-zip-debug.noarch java-1.8.0-openjdk-src.x86_64 1:1.8.0.201.b09-2.el7_6 @updates java-1.8.0-openjdk-src-debug.x86_64 1:1.8.0.201.b09-2.el7_6 @updates java-atk-wrapper.x86_64 0.30.4-5.el7 @base javapackages-tools.noarch 3.4.1-11.el7 @base python-javapackages.noarch 3.4.1-11.el7 @base tzdata-java.noarch 2018i-1.el7 @updates
二、卸载原有jdk
# *表示卸载所有以java-1.8.0-openjdk开头的,-y 表示自动回复yes $ sudo yum -y remove java-1.8.0-openjdk* javapackages-tools.noarch python-javapackages.noarch tzdata-java.noarch
三、查看JDk软件包列表
$ sudo yum list java* 已加载插件：fastestmirror Loading mirror speeds from cached hostfile * base: mirrors.163.com * extras: mirrors.163.com * updates: mirrors.163.com 可安装的软件包 java-1.6.0-openjdk.x86_64 1:1.6.0.41-1.13.13.1.el7_3 base # jdk6 java-1.6.0-openjdk-demo.x86_64 1:1.6.0.41-1.13.13.1.el7_3 base java-1.6.0-openjdk-devel.x86_64 1:1.6.0.41-1.13.13.1.el7_3 base java-1.6.0-openjdk-javadoc.x86_64 1:1.6.0.41-1.13.13.1.el7_3 base java-1.6.0-openjdk-src.x86_64 1:1.6.0.41-1.13.13.1.el7_3 base java-1.7.0-openjdk.x86_64 1:1.7.0.211-2.6.17.1.el7_6 updates # jdk7 java-1.7.0-openjdk-accessibility.x86_64 1:1.7.0.211-2.6.17.1.el7_6 updates java-1.7.0-openjdk-demo.x86_64 1:1.7.0.211-2.6.17.1.el7_6 updates java-1.7.0-openjdk-devel.x86_64 1:1.7.0.211-2.6.17.1.el7_6 updates java-1.7.0-openjdk-headless.x86_64 1:1.7.0.211-2.6.17.1.el7_6 updates java-1.7.0-openjdk-javadoc.noarch 1:1.7.0.211-2.6.17.1.el7_6 updates java-1.7.0-openjdk-src.x86_64 1:1.7.0.211-2.6.17.1.el7_6 updates java-1.8.0-openjdk.i686 1:1.8.0.191.b12-1.el7_6 updates # jdk8 java-1.8.0-openjdk.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-accessibility.i686 1:1.8.0.191.b12-1.el7_6 updates java-1.8.0-openjdk-accessibility.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-accessibility-debug.i686 1:1.8.0.191.b12-1.el7_6 updates java-1.8.0-openjdk-accessibility-debug.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-debug.i686 1:1.8.0.191.b12-1.el7_6 updates java-1.8.0-openjdk-debug.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-demo.i686 1:1.8.0.191.b12-1.el7_6 updates java-1.8.0-openjdk-demo.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-demo-debug.i686 1:1.8.0.191.b12-1.el7_6 updates java-1.8.0-openjdk-demo-debug.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-devel.i686 1:1.8.0.191.b12-1.el7_6 updates java-1.8.0-openjdk-devel.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-devel-debug.i686 1:1.8.0.191.b12-1.el7_6 updates java-1.8.0-openjdk-devel-debug.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-headless.i686 1:1.8.0.191.b12-1.el7_6 updates java-1.8.0-openjdk-headless.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-headless-debug.i686 1:1.8.0.191.b12-1.el7_6 updates java-1.8.0-openjdk-headless-debug.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-javadoc.noarch 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-javadoc-debug.noarch 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-javadoc-zip.noarch 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-javadoc-zip-debug.noarch 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-src.i686 1:1.8.0.191.b12-1.el7_6 updates java-1.8.0-openjdk-src.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-1.8.0-openjdk-src-debug.i686 1:1.8.0.191.b12-1.el7_6 updates java-1.8.0-openjdk-src-debug.x86_64 1:1.8.0.201.b09-2.el7_6 updates java-11-openjdk.i686 1:11.0.2.7-0.el7_6 updates #jdk11 java-11-openjdk.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-debug.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-debug.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-demo.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-demo.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-demo-debug.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-demo-debug.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-devel.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-devel.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-devel-debug.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-devel-debug.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-headless.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-headless.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-headless-debug.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-headless-debug.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-javadoc.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-javadoc.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-javadoc-debug.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-javadoc-debug.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-javadoc-zip.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-javadoc-zip.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-javadoc-zip-debug.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-javadoc-zip-debug.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-jmods.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-jmods.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-jmods-debug.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-jmods-debug.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-src.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-src.x86_64 1:11.0.2.7-0.el7_6 updates java-11-openjdk-src-debug.i686 1:11.0.2.7-0.el7_6 updates java-11-openjdk-src-debug.x86_64 1:11.0.2.7-0.el7_6 updates java-atk-wrapper.i686 0.30.4-5.el7 base java-atk-wrapper.x86_64 0.30.4-5.el7 base java_cup.noarch 1:0.11a-16.el7 base java_cup-javadoc.noarch 1:0.11a-16.el7 base java_cup-manual.noarch 1:0.11a-16.el7 base javacc.noarch 5.0-10.el7 base javacc-demo.noarch 5.0-10.el7 base javacc-javadoc.noarch 5.0-10.el7 base javacc-manual.noarch 5.0-10.el7 base javacc-maven-plugin.noarch 2.6-17.el7 base javacc-maven-plugin-javadoc.noarch 2.6-17.el7 base javamail.noarch 1.4.6-8.el7 base javamail-javadoc.noarch 1.4.6-8.el7 base javapackages-tools.noarch 3.4.1-11.el7 base javassist.noarch 3.16.1-10.el7 base javassist-javadoc.noarch 3.16.1-10.el7 base
四、安装JDK
#安装java-1.8.0-openjdk开头的所有程序，-y表示自动回复yes。直到控制台返回Complete或者完毕，表示安装成功。 $ sudo yum install -y java-1.8.0-openjdk*
查看版本信息
$ sudo java -version openjdk version "1.8.0_201" OpenJDK Runtime Environment (build 1.8.0_201-b09) OpenJDK 64-Bit Server VM (build 25.201-b09, mixed mode) $ sudo javac -version javac 1.8.0_201
五、查看JDK安装路径
已经通过yum安装好了jdk，那么安装到哪里去了呢？
查看方式一：
此时，如果使用javac，java都是可以的。我们还没有设置环境变量，为什么直接可使用了呢？
这就体现出了在线安装的好处了，它会自动配置环境变量。我们可以通过echo $PATH命令查看
#:为Linux系统中环境变量分隔符 $ sudo echo $PATH /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
如何查看jdk的安装路径，JAVA_HOME呢？
$ sudo whereis javac # 很明显，/usr/bin/javac默认加入了PATH路径（/usr/bin）中 javac: /usr/bin/javac /usr/share/man/man1/javac.1.gz # 可以使用ll命令(或ls -l)查看它链接的地址 $ sudo ll /usr/bin/javac # 可以看到/usr/bin/javac指向的地址是/etc/alternatives/javac lrwxrwxrwx. 1 root root 22 3月 25 07:28 /usr/bin/javac -> /etc/alternatives/javac # 继续查看是否有链接 $ sudo ll /etc/alternatives/javac # 可以看到/etc/alternatives/javac 指向/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/bin/javac lrwxrwxrwx. 1 root root 73 3月 25 07:28 /etc/alternatives/javac -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/bin/javac # 继续查看是否有链接 $ sudo ll /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/bin/javac
# 可以看到/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/bin/javac为一个真实的地址，而非一个软链接
-rwxr-xr-x. 1 root root 7376 3月 5 06:55 /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/bin/javac
所以JAVA_HOME就是/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64
查看方式二：
其实yum命令默认安装路径为/usr/lib/jvm，那么完整的安装路径是什么呢？
$ sudo ll /usr/lib/jvm 总用量 0 lrwxrwxrwx. 1 root root 26 3月 25 07:28 java -> /etc/alternatives/java_sdk lrwxrwxrwx. 1 root root 32 3月 25 07:28 java-1.8.0 -> /etc/alternatives/java_sdk_1.8.0 lrwxrwxrwx. 1 root root 40 3月 25 07:28 java-1.8.0-openjdk -> /etc/alternatives/java_sdk_1.8.0_openjdk drwxr-xr-x. 9 root root 109 3月 25 07:28 java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64 #其他都是软链接，只有这个和下面一个是真实地址。下面那个是debug，当然这个就是jdk的安装路径了，也就是JAVA_HOME地址。 drwxr-xr-x. 9 root root 109 3月 25 07:28 java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64-debug lrwxrwxrwx. 1 root root 34 3月 25 07:28 java-openjdk -> /etc/alternatives/java_sdk_openjdk lrwxrwxrwx. 1 root root 21 3月 25 07:28 jre -> /etc/alternatives/jre lrwxrwxrwx. 1 root root 27 3月 25 07:28 jre-1.8.0 -> /etc/alternatives/jre_1.8.0 lrwxrwxrwx. 1 root root 35 3月 25 07:28 jre-1.8.0-openjdk -> /etc/alternatives/jre_1.8.0_openjdk lrwxrwxrwx. 1 root root 51 3月 25 07:28 jre-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64 -> java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/jre lrwxrwxrwx. 1 root root 57 3月 25 07:28 jre-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64-debug -> java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64-debug/jre lrwxrwxrwx. 1 root root 29 3月 25 07:28 jre-openjdk -> /etc/alternatives/jre_openjdk
六、设置环境变量
#设置JAVA_HOME指向jdk的安装路径 $ sudo vi /etc/profile #在文件最后加入如下内容： # add java environment export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64 export JRE_HOME=${JAVA_HOME}/jre export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib export PATH=${JAVA_HOME}/bin:${JRE_HOME}:${CLASSPATH}:$PATH #修改/etc/profile之后让其生效 $ sudo source /etc/profile #查看JAVA_HOME路径 $ sudo echo $JAVA_HOME /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64 #查看JRE_HOME路径 $ sudo echo $JRE_HOME /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/jre #查看CLASSPATH路径 $ sudo echo $CLASSPATH .:/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/lib:/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/jre/lib #查看完整PATH路径 $ sudo echo $PATH /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/bin:/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/jre:.:/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/lib:/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/jre/lib:/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin