linux使用yum安装jdk

1. 看Linux系统是否有自带的jdk：

1、输入：java -version
2、发现有输入：rpm -qa | grep java 检测jdk的安装包，（注意：rpm命令符没有时记得下载一个输入：apt-get install +命令名称）
3、接着进行一个个删除包，输入：rpm -e –nodeps +包名
4、最后再次：rpm -qa | grep java检查是否删除完即可

2、查询要安装jdk的版本

命令：yum -y list java*

3、安装所需版本

命令：yum install -y java-1.8.0-openjdk.devel.x86_64

注意这里一定要安装devel版本, 否则会出现只安装了jre的情况导致无法使用javac命令

4. 查看是否安装成功

javac, java -version

javac命令报错bash:javac:command not found | yum provide javac

问题分析：自带的jdk默认只安装了运行环境（找到jdk的安装目录下，发现只有jre文件夹，没有bin、lib等文件夹）。

自查方法：

（1）先找到jdk的安装目录

[root@localhost home]# which java
/usr/bin/java
[root@localhost home]# ls -lrt /usr/bin/java
lrwxrwxrwx. 1 root root 22 Apr 18 13:09 /usr/bin/java -> /etc/alternatives/java
[root@localhost home]# ls -lrt /etc/alternatives/java
lrwxrwxrwx. 1 root root 73 Apr 18 13:09 /etc/alternatives/java -> /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64/jre/bin/java12345

这就是jdk安装的文件夹：/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64

（2）打开这个文件夹，检查它的子文件夹。如果只有jre一个文件夹，那就是需要安装devel开发环境。

[root@localhost home]# cd /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64
[root@localhost java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64]# ll
total 0
drwxr-xr-x. 4 root root   28 Apr 18 13:09 jre123

解决方法：使用yum安装开发环境 devel。（注意下载对应的版本。所以最好用yum找到准确的devel版本名字，精准下载）

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0. 检查自己的openjdk版本，发现是1.8.0
（如果没有安装openjdk,则用yum安装openjdk之后，再来安装一次devel即可）
【参考教程linux 上使用yum 安装openjdk1.8】

[root@localhost ~]# java -version
openjdk version "1.8.0_242"
OpenJDK Runtime Environment (build 1.8.0_242-b08)
OpenJDK 64-Bit Server VM (build 25.242-b08, mixed mode)
1234

1. 用yum查找可以安装的jdk：yum search java|grep jdk

[root@localhost java-1.8.0-openjdk-1.8.0.102-4.b14.el7.x86_64]# yum search java|grep jdk
openjdk.x86_64 : OpenJDK Runtime Environment
java-1.8.0-openjdk.i686 : OpenJDK Runtime Environment 8
java-1.8.0-openjdk-accessibility.i686 : OpenJDK accessibility connector
java-1.8.0-openjdk-accessibility.x86_64 : OpenJDK accessibility connector
java-1.8.0-openjdk-accessibility-debug.i686 : OpenJDK 8 accessibility connector
java-1.8.0-openjdk-accessibility-debug.x86_64 : OpenJDK 8 accessibility
java-1.8.0-openjdk-debug.i686 : OpenJDK Runtime Environment 8 with full debug on
java-1.8.0-openjdk-debug.x86_64 : OpenJDK Runtime Environment 8 with full debug
java-1.8.0-openjdk-demo.i686 : OpenJDK Demos 8
java-1.8.0-openjdk-demo.x86_64 : OpenJDK Demos 8
java-1.8.0-openjdk-demo-debug.i686 : OpenJDK Demos 8 with full debug on
java-1.8.0-openjdk-demo-debug.x86_64 : OpenJDK Demos 8 with full debug on
java-1.8.0-openjdk-devel.i686 : OpenJDK Development Environment 8
java-1.8.0-openjdk-devel.x86_64 : OpenJDK Development Environment 8
java-1.8.0-openjdk-devel-debug.i686 : OpenJDK Development Environment 8 with
java-1.8.0-openjdk-devel-debug.x86_64 : OpenJDK Development Environment 8 with
java-1.8.0-openjdk-headless.x86_64 : OpenJDK Runtime Environment1234567891011121314151617

（有很多很多文件，这里删减了一部分）
找到了我需要的版本：java-1.8.0-openjdk-devel.x86_64。

2. 安装java-1.8.0-openjdk-devel.x86_64：
yum install java-1.8.0-openjdk-devel.x86_64

这时候会有提示：Is this ok [y/d/N]:
输入y （y的意思是-下载并安装）。

然后静待下载…complete!

3.检查jdk目录下是否有了bin、lib等文件夹：

[root@localhost home]# cd /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64
[root@localhost java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64]# ll
total 4
drwxr-xr-x. 2 root root 4096 Apr 18 13:09 bin
drwxr-xr-x. 3 root root  132 Apr 18 13:09 include
drwxr-xr-x. 4 root root   28 Apr 18 13:09 jre
drwxr-xr-x. 3 root root  144 Apr 18 13:09 lib
drwxr-xr-x. 2 root root  204 Apr 18 13:09 tapset
12345678

有了！
再次输入javac，没有报错：

[root@localhost jvm]# javac
Usage: javac <options> <source files>
where possible options include:
  -g                         Generate all debugging info
  -g:none                    Generate no debugging info
  -g:{lines,vars,source}     Generate only some debugging info
  -nowarn                    Generate no warnings
  -verbose                   Output messages about what the compiler is doing
  -deprecation               Output source locations where deprecated APIs are used
  -classpath <path>          Specify where to find user class files and annotation processors
  -cp <path>                 Specify where to find user class files and annotation processors
  -sourcepath <path>         Specify where to find input source files
  -bootclasspath <path>      Override location of bootstrap class files
  -extdirs <dirs>            Override location of installed extensions
  -endorseddirs <dirs>       Override location of endorsed standards path
  -proc:{none,only}          Control whether annotation processing and/or compilation is done.
  -processor <class1>[,<class2>,<class3>...] Names of the annotation processors to run; bypasses default discovery process
  -processorpath <path>      Specify where to find annotation processors
  -parameters                Generate metadata for reflection on method parameters
  -d <directory>             Specify where to place generated class files
  -s <directory>             Specify where to place generated source files
  -h <directory>             Specify where to place generated native header files
  -implicit:{none,class}     Specify whether or not to generate class files for implicitly referenced files
  -encoding <encoding>       Specify character encoding used by source files
  -source <release>          Provide source compatibility with specified release
  -target <release>          Generate class files for specific VM version
  -profile <profile>         Check that API used is available in the specified profile
  -version                   Version information
  -help                      Print a synopsis of standard options
  -Akey[=value]              Options to pass to annotation processors
  -X                         Print a synopsis of nonstandard options
  -J<flag>                   Pass <flag> directly to the runtime system
  -Werror                    Terminate compilation if warnings occur
  @<filename>                Read options and filenames from file