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alternatives java 多版本切换

用yum安装了openjdk，然后又想用oracle jdk。原来的openjdk，又不想丢，怎么办呢？

1，已有openjdk

[root@localhost ~]# alternatives --config java

共有 1 个提供“java”的程序。

  选项    命令
-----------------------------------------------
*+ 1           java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/jre/bin/java)

按 Enter 保留当前选项[+]，或者键入选项编号：

[root@localhost jvm]# env |grep -i java
OLDPWD=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64
JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64
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/lib/dt.jar:/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/lib/tools.jar

2，安装oracle jdk1.8

下载：https://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html

jdk-8u231-linux-x64.tar.gz，这是二进制包，下来了就能用

# tar zxvf jdk-8u231-linux-x64.tar.gz
# mv jdk1.8.0_231 /usr/local/

3，用alternatives将java加入多版本

# alternatives --install /usr/bin/java java /usr/local/jdk1.8.0_231/bin/java 2

# alternatives --config java

共有 2 个提供“java”的程序。

  选项    命令
-----------------------------------------------
*+ 1           java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/jre/bin/java)
   2           /usr/local/jdk1.8.0_231/bin/java

按 Enter 保留当前选项[+]，或者键入选项编号：2  //选择2

修改环境变量：

# export JAVA_HOME=/usr/local/jdk1.8.0_231
# export CLASSPATH=$JAVA_HOME/lib:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
[root@localhost ~]# java -version
java version "1.8.0_231"
Java(TM) SE Runtime Environment (build 1.8.0_231-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.231-b11, mixed mode)

4，恢复到openjdk1.8

[root@localhost ~]# alternatives --config java

共有 2 个提供“java”的程序。

  选项    命令
-----------------------------------------------
*  1           java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64/jre/bin/java)
 + 2           /usr/local/jdk1.8.0_231/bin/java

按 Enter 保留当前选项[+]，或者键入选项编号：1

# export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.201.b09-2.el7_6.x86_64
# export CLASSPATH=$JAVA_HOME/lib:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar
[root@localhost ~]# 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)

原文 http://blog.51yip.com/android/2278.html

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