Ubuntu 18.04 安装java8
<p>OpenJDK和Oracle Java有两个主要的实现，几乎没有区别，只是Oracle Java有一些额外的商业功能。</p><p>现在Oracle Java开始收费了。。。官网下载需要登录。</p>
<p><strong>安装OpenJDK</strong></p>
<p>OpenJDK 10，Java平台的开源实现是Ubuntu 18.04中的默认Java开发和运行时。 一旦OpenJDK 11达到GA，它将成为Ubuntu 18.04的默认版本。</p>
<p>安装OpenJDK非常简单直接。</p>
<p><strong>安装OpenJDK 10 JDK</strong></p>
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<pre><span style="color: rgba(0, 0, 255, 1)">sudo</span> apt <span style="color: rgba(0, 0, 255, 1)">install</span> default-jdk</pre>
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<p><strong>安装OpenJDK 8 JDK</strong></p>
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<pre><span style="color: rgba(0, 0, 255, 1)">sudo</span> apt <span style="color: rgba(0, 0, 255, 1)">install</span> openjdk-<span style="color: rgba(128, 0, 128, 1)">8</span>-jdk</pre>
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<p><strong>安装Oracle Java</strong></p>
<p>在本节中，我们将完成从WebUpd8存储库安装Oracle Java的步骤。 WebUpd8软件包会自动为我们下载并安装Oracle JDK。</p>
<p>为了能够使用add-apt-repository命令添加新的存储库，首先我们需要安装software-properties-common软件包。</p>
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<pre><span style="color: rgba(0, 0, 255, 1)">sudo</span> apt <span style="color: rgba(0, 0, 255, 1)">install</span> software-properties-common dirmngr</pre>
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<p>现在我们可以添加WebUpd8存储库并安装Oracle Java：</p>
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<pre><span style="color: rgba(0, 0, 255, 1)">sudo</span> add-apt-repository ppa:webupd8team/<span style="color: rgba(0, 0, 0, 1)">java
</span><span style="color: rgba(0, 0, 255, 1)">sudo</span> apt update</pre>
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<p><strong>安装Oracle Java 8（去年Oracle停止维护java8 所以现在无法通过该方法安装）</strong></p>
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<pre><span style="text-decoration: line-through">sudo apt-get <span style="color: rgba(0, 0, 255, 1); text-decoration: line-through">instal</span></span><span style="text-decoration: line-through"><span style="color: rgba(0, 0, 255, 1); text-decoration: line-through">l</span> oracle-java8-installer</span></pre>
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<p>安装程序会要求您接受Oracle许可条款。 要安装软件包，您需要接受这些条件。</p>
<p><strong>所以这种方式还是推荐安装Oracle Java 11、12</strong></p>
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<pre><span style="color: rgba(0, 0, 255, 1)">sudo</span> add-apt-repository ppa:linuxuprising/<span style="color: rgba(0, 0, 0, 1)">java
</span><span style="color: rgba(0, 0, 255, 1)">sudo</span> apt-<span style="color: rgba(0, 0, 0, 1)">get update
</span><span style="color: rgba(0, 0, 255, 1)">sudo</span> apt-get <span style="color: rgba(0, 0, 255, 1)">install</span> oracle-java11-<span style="color: rgba(0, 0, 0, 1)">installer
</span><span style="color: rgba(0, 0, 255, 1)">sudo</span> apt-get <span style="color: rgba(0, 0, 255, 1)">install</span> oracle-java12-installer</pre>
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<p> </p>
<p><strong>非要安装Oracle Java 8的话</strong></p>
<p>手动下载压缩包安装oracle Java JDK<br>1、前往oracle Java官网下载JDK（http://www.oracle.com/technetwork/java/javase/downloads/index.html）现在Oracle Java开始收费了。。。官网下载需要登录。所以（https://github.com/frekele/oracle-java/releases）你懂的</p>
<p>解压缩到指定目录（以jdk-8u221-linux-x64.tar.gz为例）</p>
<p>创建目录:</p>
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<pre><span style="color: rgba(0, 0, 255, 1)">sudo</span> <span style="color: rgba(0, 0, 255, 1)">mkdir</span> /usr/lib/java</pre>
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<p>解压缩到该目录:</p>
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<pre><span style="color: rgba(0, 0, 255, 1)">sudo</span> <span style="color: rgba(0, 0, 255, 1)">tar</span> -zxvf jdk-8u212-linux-x64.tar.gz -C /usr/lib/java</pre>
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<p>修改环境变量: </p>
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<pre><span style="color: rgba(0, 0, 255, 1)">sudo</span> <span style="color: rgba(0, 0, 255, 1)">gedit</span> ~/.bashrc</pre>
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<p>在文件末尾追加下面内容：</p>
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<pre><span style="color: rgba(0, 0, 0, 1)">#set oracle jdk environment
export JAVA_HOME</span>=/usr/lib/java/jdk1.<span style="color: rgba(128, 0, 128, 1)">8</span><span style="color: rgba(0, 0, 0, 1)">.0_212## 这里要注意目录要换成自己解压的jdk 目录
export JRE_HOME</span>=${JAVA_HOME}/<span style="color: rgba(0, 0, 0, 1)">jre
export CLASSPATH</span>=.:${JAVA_HOME}/lib:${JRE_HOME}/<span style="color: rgba(0, 0, 0, 1)">lib
export PATH</span>=${JAVA_HOME}/bin:$PATH</pre>
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<p>使环境变量马上生效：</p>
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<pre>source ~/.bashrc</pre>
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<p>系统注册此jdk（300为优先级）</p>
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<pre><span style="color: rgba(128, 0, 128, 1)">sudo update-alternatives --install /usr/bin/java java /usr/lib/java/jdk1.8.0_212/bin/java 300<br></span></pre>
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<p><strong>设置默认版本</strong></p>
<p>我们可以检查我们的默认Java版本：</p>
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<pre>java -version</pre>
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<p>输出：</p>
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<pre>openjdk version <span style="color: rgba(128, 0, 0, 1)">"</span><span style="color: rgba(128, 0, 0, 1)">10.0.1</span><span style="color: rgba(128, 0, 0, 1)">"</span> <span style="color: rgba(128, 0, 128, 1)">2019</span>-<span style="color: rgba(128, 0, 128, 1)">08</span>-<span style="color: rgba(128, 0, 128, 1)">24</span><span style="color: rgba(0, 0, 0, 1)">
OpenJDK Runtime Environment (build </span><span style="color: rgba(128, 0, 128, 1)">10.0</span>.<span style="color: rgba(128, 0, 128, 1)">1</span>+<span style="color: rgba(128, 0, 128, 1)">10</span>-Ubuntu-<span style="color: rgba(0, 0, 0, 1)">3ubuntu1)
OpenJDK </span><span style="color: rgba(128, 0, 128, 1)">64</span>-Bit Server VM (build <span style="color: rgba(128, 0, 128, 1)">10.0</span>.<span style="color: rgba(128, 0, 128, 1)">1</span>+<span style="color: rgba(128, 0, 128, 1)">10</span>-Ubuntu-3ubuntu1, mixed mode)</pre>
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<p> </p>
<p>如果我们在服务器上安装了多个Java版本，我们可以使用update-alternatives系统更改默认版本：</p>
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<pre><span style="color: rgba(0, 0, 255, 1)">sudo</span> update-alternatives --config java</pre>
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<p>输出：</p>
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<pre>有 <span style="color: rgba(128, 0, 128, 1)">3</span> 个候选项可用于替换 java (提供 /usr/bin/<span style="color: rgba(0, 0, 0, 1)">java)。
选择 路径 优先级状态
</span>------------------------------------------------------------
* <span style="color: rgba(128, 0, 128, 1)">0</span> /usr/lib/jvm/java-<span style="color: rgba(128, 0, 128, 1)">11</span>-openjdk-amd64/bin/java <span style="color: rgba(128, 0, 128, 1)">1101</span><span style="color: rgba(0, 0, 0, 1)"> 自动模式
</span><span style="color: rgba(128, 0, 128, 1)">1</span> /usr/lib/jvm/java-<span style="color: rgba(128, 0, 128, 1)">11</span>-openjdk-amd64/bin/java <span style="color: rgba(128, 0, 128, 1)">1101</span><span style="color: rgba(0, 0, 0, 1)"> 手动模式
</span><span style="color: rgba(128, 0, 128, 1)">2</span> /usr/lib/jvm/java-<span style="color: rgba(128, 0, 128, 1)">8</span>-openjdk-amd64/jre/bin/java<span style="color: rgba(128, 0, 128, 1)">1081</span><span style="color: rgba(0, 0, 0, 1)"> 手动模式
</span><span style="color: rgba(128, 0, 128, 1)">3</span> /usr/lib/jvm/java-<span style="color: rgba(128, 0, 128, 1)">9</span>-openjdk-amd64/bin/java <span style="color: rgba(128, 0, 128, 1)">1091</span><span style="color: rgba(0, 0, 0, 1)"> 手动模式
要维持当前值[</span>*]请按<回车键><span style="color: rgba(0, 0, 0, 1)">，或者键入选择的编号：
在出现提示时输入号码并按Enter键。</span></pre>
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<p> </p><br><br>
来源：https://www.cnblogs.com/zzy1024/p/11406269.html
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