首先查看yum库中有哪些jdk版本

root@localhost ~]#yumsearch java|grep jdk

ldapjdk-javadoc.x86_64 : Javadocfor ldapjdk

java-1.6.0-openjdk.x86_64 : OpenJDK Runtime Environment

java-1.6.0-openjdk-demo.x86_64 : OpenJDK Demos

java-1.6.0-openjdk-devel.x86_64 : OpenJDK Development Environment

java-1.6.0-openjdk-javadoc.x86_64 : OpenJDK API Documentation

java-1.6.0-openjdk-src.x86_64 : OpenJDK Source Bundle

java-1.7.0-openjdk.x86_64 : OpenJDK Runtime Environment

java-1.7.0-openjdk-demo.x86_64 : OpenJDK Demos

java-1.7.0-openjdk-devel.x86_64 : OpenJDK Development Environment

java-1.7.0-openjdk-javadoc.noarch : OpenJDK API Documentation

java-1.7.0-openjdk-src.x86_64 : OpenJDK Source Bundle

java-1.8.0-openjdk.x86_64 : OpenJDK Runtime Environment

java-1.8.0-openjdk-demo.x86_64 : OpenJDK Demos

java-1.8.0-openjdk-devel.x86_64 : OpenJDK Development Environment

java-1.8.0-openjdk-headless.x86_64 : OpenJDK Runtime Environment

java-1.8.0-openjdk-javadoc.noarch : OpenJDK API Documentation

java-1.8.0-openjdk-src.x86_64 : OpenJDK Source Bundle

ldapjdk.x86_64 : The Mozilla LDAP Java SDK

安装1.7版本

/选择1.7版本进行安装[root@localhost ~]#yuminstalljava-1.7.0-openjdk

//安装完之后，默认的安装目录是在: /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.75.x86_64

设置环境变量，打开配置文件

[root@localhost ~]#vi/etc/profile

添加以下配置代码(尤其注意你的jdk是否叫这个名字，不能直接复制我的，否则会出错)

#set java environment

JAVA_HOME=/usr/lib/jvm/java-1.7.0-openjdk-1.7.0.75.x86_64

JRE_HOME=$JAVA_HOME/jre

CLASS_PATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar:$JRE_HOME/lib

PATH=$PATH:$JAVA_HOME/bin:$JRE_HOME/bin

export JAVA_HOME JRE_HOME CLASS_PATH PATH

让修改生效

[root@localhost java]# source /etc/profile

验证输入命令：java -version

[root@localhost ]# java -version

java version "1.7.0_171"

OpenJDK Runtime Environment (rhel-2.6.13.0.el7_4-x86_64 u171-b01)

OpenJDK 64-Bit Server VM (build 24.171-b01, mixed mode)