参考：https://blog.csdn.net/m0_37202351/article/details/90233146

yum java安装

0.查看yum源中是否有相关套件

  1. yum -y update
  3. yum -y list java-1.6*
  4. yum -y list java-1.7*
  5. yum -y list java-1.8*
  6. yum -y list java-11*
  8. #举例结果：
  9. java-1.6.0-openjdk.x86_64
  10. java-1.7.0-openjdk.x86_64
  11. java-1.8.0-openjdk.x86_64
  13. # 另外一种方式查看
  14. yum list  | grep java | grep devel
  16. java-1.6.0-openjdk-devel.x86_64
  17. java-1.7.0-openjdk-devel.x86_64
  18. java-1.8.0-openjdk-devel.x86_64
  19. java-11-openjdk-devel.x86_64
  21. #安装java8
  22. yum -y install java-1.8.0-openjdk-devel.x86_64
  24. # 查看已经安装的软件
  25. yum list installed
  26. yum list java
  27. yum remove tomcat

环境变量配置

0.查询路径3种方式

  2. which java
  4. ls -lrt /usr/bin/java
  6. ls -lrt /etc/alternatives/java

1.编辑环境变量的配置文件

  1. vim /etc/profile

2.在文件底部加入以下配置

  1. export JAVA_HOME=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64
  2. export JRE_HOME=$JAVA_HOME/jre
  3. export CLASSPATH=$JAVA_HOME/lib:$JRE_HOME/lib:$CLASSPATH
  4. export PATH=$JAVA_HOME/bin:$JRE_HOME/bin:$PATH

3.刷新配置，使其生效

  1. source /etc/profile
  2. source /etc/bashrc

4.测试配置结果

  1. echo $JAVA_HOME

5.jdk1.8.0.212偶数版本发现的问题，可能存在启动慢，警告

Creation of SecureRandom instance for session ID generation using [SHA1PRNG] took [104,492] milliseconds.

  1. # 解决
  2. vim $JAVA_HOME/jre/lib/security/java.security
  3. securerandom.source=file:/dev/random
  4. 替换成
  5. securerandom.source=file:/dev/urandom