ubuntu vps 安装java

Introduction

Java is a programming technology originally developed by Sun Microsystems and later acquired by Oracle. Oracle Java is a proprietary implementation for Java that is free to download and use for commercial use, but not to redistribute, therefore it is not included in a officially maintained repository.

There are many reasons why you would want to install Oracle Java over OpenJDK. In this tutorial, we will not discuss the differences between the above mentioned implementations.

 

Assumptions

This tutorial assumes that you have an account with DigitalOcean, as well as a Droplet running Debian 7 or Ubuntu 12.04 or above. You will need root privileges (via sudo) to complete the tutorial.

You will need to know whether you are running a 32 bit or a 64 bit OS:

uname -m

• x86_64: 64 bit kernel

• i686: 32 bit kernel

 

Downloading Oracle Java JDK

Using your web browser, go to the Oracle Java SE (Standard Edition) website and decide which version you want to install:

• JDK: Java Development Kit. Includes a complete JRE plus tools for developing, debugging, and monitoring Java applications.

• Server JRE: Java Runtime Environment. For deploying Java applications on servers. Includes tools for JVM monitoring and tools commonly required for server applications.

In this tutorial we will be installing the JDK Java SE Development Kit 8 x64 bits. Accept the license and copy the download link into your clipboard. Remember to choose the right tar.gz (64 or 32 bits). Use wget to download the archive into your server:

    wget --header "Cookie: oraclelicense=accept-securebackup-cookie" http://download.oracle.com/otn-pub/java/jdk/8u5-b13/jdk-8u5-linux-x64.tar.gz

Oracle does not allow downloads without accepting their license, therefore we needed to modify the header of our request. Alternatively, you can just download the compressed file using your browser and manually upload it using a SFTP/FTP client.

Always get the latest version from Oracle's website and modify the commands from this tutorial accordingly to your downloaded file.

 

Installing Oracle JDK

In this section, you will need sudo privileges:

    sudo su

The /opt directory is reserved for all the software and add-on packages that are not part of the default installation. Create a directory for your JDK installation:

    mkdir /opt/jdk

and extract java into the /opt/jdk directory:

    tar -zxf jdk-8u5-linux-x64.tar.gz -C /opt/jdk

Verify that the file has been extracted into the /opt/jdk directory.

    ls /opt/jdk

 

Setting Oracle JDK as the default JVM

In our case, the java executable is located under /opt/jdk/jdk1.8.0_05/bin/java . To set it as the default JVM in your machine run:

    update-alternatives --install /usr/bin/java java /opt/jdk/jdk1.8.0_05/bin/java 100

and

    update-alternatives --install /usr/bin/javac javac /opt/jdk/jdk1.8.0_05/bin/javac 100

 

Verify your installation

Verify that java has been successfully configured by running:

    update-alternatives --display java

and

    update-alternatives --display javac

The output should look like this:

    java - auto mode
    link currently points to /opt/jdk/jdk1.8.0_05/bin/java
    /opt/jdk/jdk1.8.0_05/bin/java - priority 100
    Current 'best' version is '/opt/jdk/jdk1.8.0_05/bin/java'.

    javac - auto mode
    link currently points to /opt/jdk/jdk1.8.0_05/bin/javac
    /opt/jdk/jdk1.8.0_05/bin/javac - priority 100
    Current 'best' version is '/opt/jdk/jdk1.8.0_05/bin/javac'.

Another easy way to check your installation is:

    java -version

The output should look like this:

    java version "1.8.0_05"
    Java(TM) SE Runtime Environment (build 1.8.0_05-b13)
    Java HotSpot(TM) 64-Bit Server VM (build 25.5-b02, mixed mode)