CentOS8.2安裝Java 14.0.2

Java是一種安全，穩定且廣爲人知的通用編程語言和計算技術平臺，具備許多相互關聯的功能。

要運行基於Java的應用程序，必須在服務器上安裝Java。您一般須要Java Runtime Environment（JRE），這是用於在Linux機器上運行Java應用程序的軟件組件的集合。

若是要開發Java的軟件應用程序，則須要安裝Oracle Java開發工具包（JDK），該工具包帶有一個完整的JRE軟件包，其中包含用於開發，調試和監視Java應用程序的工具，它是Oracle支持的Java SE（標準版）版本。

注意：若是您正在尋找開放源代碼和免費的JDK版本，請安裝OpenJDK，它在GPL許可下提供與Oracle JDK相同的功能和性能。

在撰寫本文時，OpenJDK 11是要使用默認存儲庫中的如下命令安裝的Java的當前LTS版本：

[1] 安裝[java-11-openjdk]包，

若是須要編譯器，也要安裝[java-11-openjdk-devel]包。

[root@nfsclient ~]# dnf -y install java-11-openjdk java-11-openjdk-devel
Last metadata expiration check: 0:29:58 ago on Wed 09 Dec 2020 10:25:45 PM CST.
Dependencies resolved.
==============================================================================================================================
 Package                            Architecture     Version                                        Repository           Size
==============================================================================================================================
Installing:
 java-11-openjdk                    x86_64           1:11.0.9.11-0.el8_2                            AppStream           251 k
 java-11-openjdk-devel              x86_64           1:11.0.9.11-0.el8_2                            AppStream           3.4 M
Installing dependencies:
 copy-jdk-configs                   noarch           3.7-1.el8                                      AppStream            27 k
 java-11-openjdk-headless           x86_64           1:11.0.9.11-0.el8_2                            AppStream            40 M
 javapackages-filesystem            noarch           5.3.0-1.module_el8.0.0+11+5b8c10bd             AppStream            30 k
 lksctp-tools                       x86_64           1.0.18-3.el8                                   base                100 k
 ttmkfdir                           x86_64           3.0.9-54.el8                                   AppStream            62 k
 tzdata-java                        noarch           2020d-1.el8                                    AppStream           190 k
 xorg-x11-fonts-Type1               noarch           7.5-19.el8                                     AppStream           522 k
Enabling module streams:
 javapackages-runtime                                201801

Transaction Summary
==============================================================================================================================



[root@nfsclient ~]# java --version
openjdk 11.0.9 2020-10-20 LTS
OpenJDK Runtime Environment 18.9 (build 11.0.9+11-LTS)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.9+11-LTS, mixed mode, sharing)



# verify to create test program
[root@nfsclient ~]# cat >/tmp/java_test.java<<EOF
class java_test {
    public static void main(String[] args) {
        System.out.println("Hello Java World !");
    }
}
EOF

[root@dlp ~]# javac java_test.java
[root@dlp ~]# java java_test
Hello Java World !




若是你從CentOS官方存儲庫中安裝了多個版本的Java，你能夠用其餘的方法來切換它們。


[root@nfsclient ~]# java --version
openjdk 11.0.5 2019-10-15 LTS
OpenJDK Runtime Environment 18.9 (build 11.0.5+10-LTS)
OpenJDK 64-Bit Server VM 18.9 (build 11.0.5+10-LTS, mixed mode, sharing)
[root@dlp ~]# javac --version
javac 11.0.5

[2]安裝 jdk-14.0.2_linux-x64_bin.rpm

[root@nfsclient tmp]# dnf -y install jdk-14.0.2_linux-x64_bin.rpm


[root@nfsclient tmp]# java --version
java 14.0.2 2020-07-14
Java(TM) SE Runtime Environment (build 14.0.2+12-46)
Java HotSpot(TM) 64-Bit Server VM (build 14.0.2+12-46, mixed mode, sharing)


[root@nfsclient tmp]# cat >/etc/profile.d/jdk14.sh <<EOF
export JAVA_HOME=/usr/java/default
export PATH=\$PATH:\$JAVA_HOME/bin
EOF

To use Java Home, source the file.

[root@nfsclient tmp]# source /etc/profile.d/jdk14.sh

測試Java安裝。
爲了測試咱們的Java安裝，讓咱們建立一個簡單的html文件。建立一個test.java文件，其內容以下

[root@nfsclient ~]# cat >/tmp/HelloWorld.java<<EOF
public class HelloWorld {
	public static  void main(String[] args) {
	System.out.println(「Hello, world」);
	}
}
EOF


[root@nfsclient ~]# cat >/tmp/java_test01.java<<EOF
class java_test {
    public static void main(String[] args) {
        System.out.println("Hello Java World !");
    }
}
EOF

[root@nfsclient ~]#javac java_test01.java
[root@nfsclient ~]# java java_test01
Hello Java World !

若是你從CentOS官方存儲庫中安裝了多個版本的Java，你能夠用其餘的方法來切換它們。

[root@nfsclient tmp]# alternatives --config java

There are 2 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
   1           java-11-openjdk.x86_64 (/usr/lib/jvm/java-11-openjdk-11.0.9.11-0.el8_2.x86_64/bin/java)
*+ 2           /usr/java/jdk-14.0.2/bin/java

Enter to keep the current selection[+], or type selection number: 2




[root@nfsclient ~]#alternatives --config javac


[root@nfsclient ~]# alternatives --install /usr/bin/javac javac /usr/java/jdk-14.0.2/bin/javac 100
[root@nfsclient tmp]# alternatives --config javac

There are 2 programs which provide 'javac'.

  Selection    Command
-----------------------------------------------
   1           java-11-openjdk.x86_64 (/usr/lib/jvm/java-11-openjdk-11.0.9.11-0.el8_2.x86_64/bin/javac)
*+ 2           /usr/java/jdk-14.0.2/bin/javac

Enter to keep the current selection[+], or type selection number: