获取java安装路径前要判断是否已经安装成功java

执行命令：

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>
    .......

在查看java版本：

java -version

[root@localhost Desktop]# java -version
openjdk version "1.8.0_65"
OpenJDK Runtime Environment (build 1.8.0_65-b17)
OpenJDK 64-Bit Server VM (build 25.65-b01, mixed mode)

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如果以上2步都没问题就可以查询安装路径了

1. 如果在/etc/profile文件中配置了JAVA_HOME则可以直接获取：

echo $JAVA_HOME

[root@localhost local]# echo $JAVA_HOME
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.65-3.b17.el7.x86_64/jre/bin/java

2. 如果以上方法无法查询到，使用如下：

[root@localhost local]# which java
/usr/bin/java

[root@localhost local]# ls -lrt /usr/bin/java
lrwxrwxrwx. 1 root root 22 Mar  7 19:12 /usr/bin/java -> /etc/alternatives/java

[root@localhost local]# ls -lrt /etc/alternatives/java
lrwxrwxrwx. 1 root root 70 Mar  7 19:12 /etc/alternatives/java -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.65-3.b17.el7.x86_64/jre/bin/java

3. 然后编辑/etc/profile文件,在文件末尾添加

vi /etc/profile

export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.65-3.b17.el7.x86_64/jre/bin/java
export PATH=$JAVA_HOME/bin:$PATH
export CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar

4. 保存命令设置

source /etc/profile

5. 在执行查看命令：

[root@localhost local]# echo $JAVA_HOME
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.65-3.b17.el7.x86_64/jre/bin/java