1.创建目录
mkdir /usr/java
cd /usr/java
2.下载jdk,网址 http://www.oracle.com/technetwork/java/javase/downloads/java-archive-downloads-javase7-521261.html ，然后解压到指定目录
tar -xvf jdk-7u79-linux-x64.tar.gz -C /usr/java
3.设置环境变量
[root@master ~]# vi /etc/profile
在profile中添加如下内容:
JAVA_HOME=/usr/java/jdk1.7.0_79
JRE_HOME=/usr/java/jdk1.7.0_79/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@master ~]# source /etc/profile
4.验证JDK有效性
[root@localhost java]# java -version
java version "1.6.0_22"
OpenJDK Runtime Environment (IcedTea6 1.10.4) (rhel-1.41.1.10.4.el6-x86_64)
OpenJDK 64-Bit Server VM (build 20.0-b11, mixed mode)
发现版本还是1.6.0_22
由于系统中可能会有默认的其他版本JDK，所以，为了将我们安装的JDK设置为默认JDK版本，还要进行如下操作：
update-alternatives --install /usr/bin/java java /usr/java/jdk1.7.0_79/bin/java 300
update-alternatives --install /usr/bin/javac javac /usr/java/jdk1.7.0_79/bin/javac 300
update-alternatives --install /usr/bin/jar jar /usr/java/jdk1.7.0_79/bin/jar 300
update-alternatives --install /usr/bin/javah javah /usr/java/jdk1.7.0_79/bin/javah 300
update-alternatives --install /usr/bin/javap javap /usr/java/jdk1.7.0_79/bin/javap 300
执行下面命令，设置默认版本，此命令执行后，系统会列出当前存在的各种JDK版本，会提示你选择
[root@master jdk1.7.0_79]# update-alternatives --config java
There are 2 programs which provide 'java'.
Selection Command
-----------------------------------------------
*+ 1 /usr/lib/jvm/jre-1.6.0-openjdk.x86_64/bin/java
2 /usr/java/jdk1.7.0_79/bin/java
Enter to keep the current selection[+], or type selection number: 2
最终验证：
[root@master jdk1.7.0_79]# java -version
java version "1.7.0_79"
Java(TM) SE Runtime Environment (build 1.7.0_79-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.79-b02, mixed mode)
结论：成功更新到1.7.0_79