计算机基础教程

# jdk

Jdk vs Openjdk

https://www.oracle.com/technetwork/java/javase/downloads/index.html archive https://www.oracle.com/technetwork/java/javase/downloads/java-archive-javase8-2177648.html

Runtime source: rt.jar /java/jre18XXX/lib

No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK? https://stackoverflow.com/questions/19655184/no-compiler-is-provided-in-this-environment-perhaps-you-are-running-on-a-jre-ra

https://docs.oracle.com/javase/8/docs/

openjdk source: https://github.com/openjdk/jdk/tree/jdk8-b25

openjdk release(注意，有些低版本的updates比高版本还要新): https://openjdk.org/projects/jdk/ https://github.com/adoptium/temurin8-binaries/releases/

# jdk install

推荐安装方式：

直接解压到比如
/opt/java-1.8
ln -s java-1.8 java
然后添加PATH :/opt/java
这样方便升级java以及测试各种版本

difference between JAVA_HOME and update-alternatives

https://unix.stackexchange.com/questions/123412/what-is-the-difference-between-java-home-and-update-alternatives

update-java-alternatives vs update-alternatives --config java

https://askubuntu.com/questions/315646/update-java-alternatives-vs-update-alternatives-config-java

-----------------------------------------
--- java home:
-----------------------------------------
vim ~/.bash_profile

export JAVA_HOME=/opt/jdk1.8.0_221
PATH=$PATH:$HOME/.local/bin:$HOME/bin:$JAVA_HOME/bin
export PATH

source ~/.bash_profile


yum list java*devel*
sudo yum install java-<version>-openjdk-devel.x86_64

# $JAVA_HOME

$JAVA_HOME is where software can be told to look through the use of an environment variable. Adding it to the $PATH simply adds the executables present in $JAVA_HOME/bin to your $PATH. This is sometimes necessary for certain applications.

The 2 mechanisms are related but can be used together or independent of each other, it really depends on the Java application which mechanism is preferable.

# Alternatives

Alternatives is a tool that will manage the locations of the installed software using links under the control of the alternatives tool.

These links are ultimately managed under /etc/alternatives with intermediate links created under a directory in $PATH, typically /usr/bin.

查看系统安装的所有java版本
update-alternatives --config java


$ update-alternatives --config java

There are 2 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
   1           java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.232.b09-0.el7_7.x86_64-debug/jre/bin/java)
*+ 2           java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.232.b09-0.el7_7.x86_64/jre/bin/java)

Enter to keep the current selection[+], or type selection number:
failed to create /var/lib/alternatives/java.new: Permission denied
$ which java
/usr/bin/java
$ ll /usr/bin/java
lrwxrwxrwx 1 root root 22 Nov 25  2019 /usr/bin/java -> /etc/alternatives/java
$ ll /etc/alternatives/java
lrwxrwxrwx 1 root root 73 Nov 25  2019 /etc/alternatives/java -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.232.b09-0.el7_7.x86_64/jre/bin/java

# 系统安装

-----------------------------------------
--- UBUNTU:
-----------------------------------------
sudo add-apt-repository ppa:openjdk-r/ppa
sudo apt-get update
sudo apt-get install openjdk-8-jdk
apt-cache search jdk
export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64/
export PATH=$PATH:$JAVA_HOME/bin
java -version
-----------------------------------------
--- centos:
-----------------------------------------
yum install

yum list installed|grep java

yum remove java-1.8.0-openjdk-headless

#rpm -qa|grep jre
  jre1.8-1.8.0_221-fcs.x86_64

rpm -e jre1.8-1.8.0_221-fcs

# jdk troubleshooting

# security

Diagnosing TLS, SSL, and HTTPS (opens new window)

更多内容参考另一篇文章

# 验证码无法显示

，需要输出完整的错误日志

使用的是log4j2

logger.error("exception: {} " , e.getMessage());
改为
logger.error("exception: {} " , e);

config加上 %ex{full}：
PatternLayout:
  pattern: "%-d{yyyy-MM-dd HH:mm:ss.SSS}-[%l]-[%p] ${PID:-} %m%n - %ex{full}"

- java.lang.NullPointerException
        at sun.awt.FontConfiguration.getVersion(FontConfiguration.java:1264)
        at sun.awt.FontConfiguration.readFontConfigFile(FontConfiguration.java:219)
        at sun.awt.FontConfiguration.init(FontConfiguration.java:107)
        at sun.awt.X11FontManager.createFontConfiguration(X11FontManager.java:776)
        at sun.font.SunFontManager$2.run(SunFontManager.java:431)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.font.SunFontManager.<init>(SunFontManager.java:376)
        at sun.awt.X11FontManager.<init>(X11FontManager.java:57)

搜索openjdk sun.awt.FontConfiguration.getVersion nullpointer基本都是：

yum install fontconfig
fc-cache --force

去到openjdk官网

https://github.com/openjdk/jdk/search?q=FontConfiguration

没有人反应有问题，说明还是系统的问题

从

https://stackoverflow.com/questions/30626136/cannot-load-font-in-jre-8/50802170

得到启发

Also one might need to install at least one font (dejavu, liberation, etc).

应该是找不到系统上任何字体

对比了一个正常的环境，发现有

[vm2-devclr-v08@SG/home/clear]$ll /usr/share/fonts/
total 4
drwxr-xr-x 2 root root 4096 Nov 25  2019 dejavu

但是另外还有一个可以工作的正常环境，里面并没有上述任何字体，

然后又看到

https://docs.oracle.com/javase/9/intl/font-configuration-files.htm

https://docs.oracle.com/javase/8/docs/technotes/guides/intl/fontconfig.html

[vm2-devclr-v05@SG/root]#find / -name "fontconfig*"
/var/cache/fontconfig
/usr/lib64/girepository-1.0/fontconfig-2.0.typelib
/usr/share/doc/fontconfig-2.10.95
/usr/share/doc/fontconfig-2.10.95/fontconfig-user.html
/usr/share/doc/fontconfig-2.10.95/fontconfig-user.txt
/usr/share/fontconfig
/usr/share/xml/fontconfig
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.RedHat.5.bfc
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.RedHat.5.properties.src
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.RedHat.6.bfc
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.RedHat.6.properties.src
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.SuSE.10.bfc
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.SuSE.10.properties.src
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.SuSE.11.bfc
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.SuSE.11.properties.src
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.Turbo.bfc
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.Turbo.properties.src
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.bfc
/usr/java/jre1.8.0_221-amd64/lib/fontconfig.properties.src

]#update-alternatives --config java

There are 3 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
   1           /usr/java/jre1.8.0_221-amd64/bin/java
   2           java-11-openjdk.x86_64 (/usr/lib/jvm/java-11-openjdk-11.0.5.10-0.el7_7.x86_64/bin/java)
*+ 3           java-1.8.0-openjdk.x86_64 (/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.232.b09-0.el7_7.x86_64/jre/bin/java)

#echo $JAVA_HOME
/apps/dependency/java-se-8u40-ri
#echo $PATH
/apps/dependency/java-se-8u40-ri/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
#which java
/apps/dependency/java-se-8u40-ri/bin/java
#java -version
openjdk version "1.8.0_40"
OpenJDK Runtime Environment (build 1.8.0_40-b25)
OpenJDK 64-Bit Server VM (build 25.40-b25, mixed mode)

find / -name "java-1.8.0-openjdk*"

但是也不对，这个jre版本明显跟我们设置的JAVA_HOME版本不一样

最终找到如何在redhat配置fonts

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/desktop_migration_and_administration_guide/configure-fonts

#fc-list : file
/usr/share/X11/fonts/Type1/c0649bt_.pfb:
/usr/share/X11/fonts/Type1/UTRG____.pfa:
/usr/share/X11/fonts/Type1/c0611bt_.pfb:
/usr/share/X11/fonts/Type1/c0419bt_.pfb:
/usr/share/X11/fonts/Type1/UTI_____.pfa:
/usr/share/X11/fonts/Type1/cursor.pfa:
/usr/share/X11/fonts/Type1/c0633bt_.pfb:
/usr/share/X11/fonts/Type1/UTB_____.pfa:
/usr/share/X11/fonts/Type1/c0648bt_.pfb:
/usr/share/X11/fonts/Type1/c0583bt_.pfb:
/usr/share/X11/fonts/Type1/UTBI____.pfa:
/usr/share/X11/fonts/Type1/c0632bt_.pfb:
/usr/share/X11/fonts/Type1/c0582bt_.pfb:

上面是在可以工作的机器上看到的结果，有问题的机器上输出是空，所以查了下redhat linux 7 install X11 fonts，发现这个字体叫做

xorg-x11-fonts ，继而搜索 linux install xorg-x11-fonts，得到

$ yum install xorg-x11-fonts-Type1
$ fc-cache --force