CentOS下配置Java开发环境---安装OpenJDK
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<h1 class="postTitle">CentOS下配置Java开发环境---安装OpenJDK</h1>
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<p style="text-align: left">0. 前言 </p>
<p style="text-align: left"> 公司项目运行在centos下，很多底层细节已由前人配置优化，虽然使用无忧，但还是希望了解一下其中的细节，既为以后系统配置升级做准备，也进一步自己丰富知识面的细节。临近年终项目宽松，打算自己搭建一个开发环境，深入学习一下。本文记录一次centos下安装jdk的过程。配置如下：</p>
<p style="text-align: left"> 系统版本：CentOS7.6</p>
<p style="text-align: left"> 安装版本：java-1.8.0-openjdk</p>
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<p style="text-align: left">1. 查看可安装JDK版本</p>
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<pre><span style="color: rgba(0, 0, 0, 1)"># yum search java | grep -i --color JDK</span></pre>
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<p> ※ 使用指令列出所有可安装版本号，并选中想要安装版本号，执行后续步骤。</p>
<p> </p>
<p> 2. 安装指定版本JDK</p>
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<div class="line number1 index0 alt2"><code class="html plain"># yum install java-1.8.0-openjdk java-1.8.0-openjdk-devel</code></div>
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<p> ※ 安装期间会有确认提示，输入y继续即可。看到Complete! 即安装完成，默认安装至/usr/lib/jvm下。</p>
<p> </p>
<p>3. 查看安装情况</p>
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<div class="line number1 index0 alt2"><code class="html plain"># java -version</code></div>
<div class="line number2 index1 alt1"><code class="html plain">openjdk version "1.8.0_232"</code></div>
<div class="line number3 index2 alt2"><code class="html plain">OpenJDK Runtime Environment (build 1.8.0_232-b09)</code></div>
<div class="line number4 index3 alt1"><code class="html plain">OpenJDK 64-Bit Server VM (build 25.232-b09, mixed mode)</code></div>
<div class="line number5 index4 alt2"><code class="html plain">// 查看安装目录，l为链接，d为文件夹</code></div>
<div class="line number6 index5 alt1"><code class="html plain"># cd /usr/lib/jvm</code></div>
<div class="line number7 index6 alt2"><code class="html plain"># ll</code></div>
<div class="line number8 index7 alt1"><code class="html plain">total 4</code></div>
<div class="line number9 index8 alt2"><code class="html plain">lrwxrwxrwx 1 root root 26 Jan 2 10:05 java -> /etc/alternatives/java_sdk</code></div>
<div class="line number10 index9 alt1"><code class="html plain">lrwxrwxrwx 1 root root 32 Jan 2 10:05 java-1.8.0 -> /etc/alternatives/java_sdk_1.8.0</code></div>
<div class="line number11 index10 alt2"><code class="html plain">lrwxrwxrwx 1 root root 40 Jan 2 10:05 java-1.8.0-openjdk -> /etc/alternatives/java_sdk_1.8.0_openjdk</code></div>
<div class="line number12 index11 alt1"><code class="html plain">drwxr-xr-x 7 root root 4096 Jan 2 10:05 java-1.8.0-openjdk-1.8.0.232.b09-0.el7_7.x86_64</code></div>
<div class="line number13 index12 alt2"><code class="html plain">lrwxrwxrwx 1 root root 34 Jan 2 10:05 java-openjdk -> /etc/alternatives/java_sdk_openjdk</code></div>
<div class="line number14 index13 alt1"><code class="html plain">lrwxrwxrwx 1 root root 21 Jan 2 10:05 jre -> /etc/alternatives/jre</code></div>
<div class="line number15 index14 alt2"><code class="html plain">lrwxrwxrwx 1 root root 27 Jan 2 10:05 jre-1.8.0 -> /etc/alternatives/jre_1.8.0</code></div>
<div class="line number16 index15 alt1"><code class="html plain">lrwxrwxrwx 1 root root 35 Jan 2 10:05 jre-1.8.0-openjdk -> /etc/alternatives/jre_1.8.0_openjdk</code></div>
<div class="line number17 index16 alt2"><code class="html plain">lrwxrwxrwx 1 root root 51 Jan 2 10:05 jre-1.8.0-openjdk-1.8.0.232.b09-0.el7_7.x86_64 -> java-1.8.0-openjdk-1.8.0.232.b09-0.el7_7.x86_64/jre</code></div>
<div class="line number18 index17 alt1"><code class="html plain">lrwxrwxrwx 1 root root 29 Jan 2 10:05 jre-openjdk -> /etc/alternatives/jre_openjdk</code></div>
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<p> </p>
<p>4. 配置环境变量</p>
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<div class="line number1 index0 alt2"><code class="html plain"># vim /etc/profile</code></div>
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<p> 在profile末尾追加环境变量JAVA_HOME、CLASSPATH、PATH</p>
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<div class="line number1 index0 alt2"><code class="bash functions">export</code> <code class="bash plain">JAVA_HOME=</code><code class="bash plain">/usr/lib/jvm/java-1</code><code class="bash plain">.8.0-openjdk-1.8.0.232.b09-0.el7_7.x86_64</code></div>
<div class="line number2 index1 alt1"><code class="bash functions">export</code> <code class="bash plain">CLASSPATH=.:$JAVA_HOME</code><code class="bash plain">/jre/lib/rt</code><code class="bash plain">.jar:$JAVA_HOME</code><code class="bash plain">/jre/lib/dt</code><code class="bash plain">.jar:$JAVA_HOME</code><code class="bash plain">/lib/tool</code><code class="bash plain">.jar</code></div>
<div class="line number3 index2 alt2"><code class="bash functions">export</code> <code class="bash plain">PATH=$PATH:$JAVA_HOME</code><code class="bash plain">/bin</code></div>
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<li>rt.jar:Java基础库，即Java doc里面看到的所有类。</li>
<li>dt.jar:运行环境类库，主要为swing包，使用swing时可以加上。</li>
<li>tool.jar是系统编译（javac）时要使用的一个类库。</li>
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<p> ※CLASSPATH加载类库各版本并不相同，具体可视情况而定，以上配置仅供参考。</p>
<p>5. 使配置生效:source /etc/profile</p>
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<div class="line number1 index0 alt2"><code class="java plain"># source /etc/profile</code></div>
<div class="line number2 index1 alt1"><code class="java plain"># java -version</code></div>
<div class="line number3 index2 alt2"><code class="java plain">openjdk version </code><code class="java string">"1.8.0_232"</code></div>
<div class="line number4 index3 alt1"><code class="java plain">OpenJDK Runtime Environment (build </code><code class="java value">1.8</code><code class="java plain">.0_232-b09)</code></div>
<div class="line number5 index4 alt2"><code class="java plain">OpenJDK </code><code class="java value">64</code><code class="java plain">-Bit Server VM (build </code><code class="java value">25.232</code><code class="java plain">-b09, mixed mode)</code></div>
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<p> ※source指令报错请仔细确认步骤4内容是否有误。</p>
<p>6. 写一个Hello World！</p>
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<div class="line number1 index0 alt2"><code class="java plain"># cat HelloWorld.java </code></div>
<div class="line number2 index1 alt1"><code class="java keyword">public</code> <code class="java keyword">class</code> <code class="java plain">HelloWorld{</code></div>
<div class="line number3 index2 alt2"><code class="java spaces"> </code><code class="java keyword">public</code> <code class="java keyword">static</code> <code class="java keyword">void</code> <code class="java plain">main(String[] args){</code></div>
<div class="line number4 index3 alt1"><code class="java spaces"> </code><code class="java plain">System.out.println(</code><code class="java string">"HelloWorld"</code><code class="java plain">);</code></div>
<div class="line number5 index4 alt2"><code class="java spaces"> </code><code class="java plain">}</code></div>
<div class="line number6 index5 alt1"><code class="java plain">}</code></div>
<div class="line number7 index6 alt2"><code class="java plain"># javac HelloWorld.java </code></div>
<div class="line number8 index7 alt1"><code class="java plain"># java HelloWorld</code></div>
<div class="line number9 index8 alt2"><code class="java plain">HelloWorld</code></div>
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<p> </p>
<p>7. END</p>
<p> 至此一个简单的JDK安装过程就完成了，下面是一些闲谈。</p>
<p> Java的JDK有两套：一个时Oracle的JDK，另外一个就是本文记载的OpenJDK了。</p>
<p> Oracle JDK可用于开发Java Web应用程序，独立应用程序以及其他图形用户界面。基于Java标准版规范实现，并且完全基于Java编程语言。版本发行缓慢，但是更具有稳定性。</p>
<p> OpenJDK基本可完成Oracle JDK的所有任务。OpenJDK是Java SE平台版的开源和免费实现，是使用C ++和Java编程语言编写的。版本发行迅速，可以根据应用程序的要求修改性能，可伸缩性和实现，以根据需要调整Java虚拟机。</p>
<p> ※Oracle JDK的构建过程基于OpenJDK，因此OpenJDK与Oracle JDK之间<strong>没有技术差异</strong>。因此不必纠结选择OracleJDK或者OpenJDK，只需安装其一便可进行Java的开发和学习。</p>
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<p>8. 参考</p>
<p>CentOS下安装JDK</p>
<p>JDK和OpenJDK的区别</p>
<p> </p>
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<div id="HistoryToday" class="c_ad_block"> <span style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">(3) 此时会弹出“新建系统变量”对话框。在“变量名”文本框中输入 JAVA_HOME，在“变量值”文本框中输入 JDK 的安装路径，图 4 所示。最后单击“确定”按钮，保存 JAVA_HOME 变量。</span></div>
<br style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">
<div style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif; text-align: center"><img style="border-style: none; max-width: 100%" src="http://c.biancheng.net/uploads/allimg/181109/3-1Q10913515WB.gif" alt="新建JAVA_HOME系统变量"><br>图 4 新建JAVA_HOME系统变量</div>
<br style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif"><span style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">(4) 在图 3 所示的“系统变量”列表框中双击 Path 变量，进入“编辑系统变量”对话框。在“变量值”文本框的最前端添加</span><code style="display: inline-block; margin: auto 2px; padding: 0 4px; color: rgba(51, 51, 51, 1); border: 1px solid rgba(221, 221, 221, 1); background: rgba(246, 246, 246, 1); border-radius: 2px; font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">.;％JAVA__HOME%\bin;</code><span style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">内容，如图 5 所示。最后单击“确定”按钮。</span><br style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif"><br style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">
<div style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif; text-align: center"><img style="border-style: none; max-width: 100%" src="http://c.biancheng.net/uploads/allimg/181109/3-1Q10913523S03.gif" alt="编辑Path系统变量"><br>图 5 编辑Path系统变量</div>
<br style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif"><span style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">提示：</span><span style="font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif; color: rgba(178, 34, 34, 1)">字符串“<code style="display: inline-block; margin: auto 2px; padding: 0 4px; color: rgba(51, 51, 51, 1); border: 1px solid rgba(221, 221, 221, 1); background: rgba(246, 246, 246, 1); border-radius: 2px; font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">.;％JAVA_HOME%\bin;</code>”中的两个分号是不可缺少的，它们用于分隔多个环境变量。</span><span style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">第一个分号前是一个英文状态半角下的句号，表示命令行下的当前目录；第二个分号前则是 JDK 的 bin 目录。</span>
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<p><span style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">(3) 此时会弹出“新建系统变量”对话框。在“变量名”文本框中输入 JAVA_HOME，在“变量值”文本框中输入 JDK 的安装路径，图 4 所示。最后单击“确定”按钮，保存 JAVA_HOME 变量。</span><br style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif"><br style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif"></p>
<div style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif; text-align: center"><img style="border-style: none; max-width: 100%" src="http://c.biancheng.net/uploads/allimg/181109/3-1Q10913515WB.gif" alt="新建JAVA_HOME系统变量"><br>图 4 新建JAVA_HOME系统变量</div>
<p><br style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif"><span style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">(4) 在图 3 所示的“系统变量”列表框中双击 Path 变量，进入“编辑系统变量”对话框。在“变量值”文本框的最前端添加</span><code style="display: inline-block; margin: auto 2px; padding: 0 4px; color: rgba(51, 51, 51, 1); border: 1px solid rgba(221, 221, 221, 1); background: rgba(246, 246, 246, 1); border-radius: 2px; font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">.;％JAVA__HOME%\bin;</code><span style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">内容，如图 5 所示。最后单击“确定”按钮。</span><br style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif"><br style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif"></p>
<div style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif; text-align: center"><img style="border-style: none; max-width: 100%" src="http://c.biancheng.net/uploads/allimg/181109/3-1Q10913523S03.gif" alt="编辑Path系统变量"><br>图 5 编辑Path系统变量</div>
<p><br style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif"><span style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">提示：</span><span style="font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif; color: rgba(178, 34, 34, 1)">字符串“<code style="display: inline-block; margin: auto 2px; padding: 0 4px; color: rgba(51, 51, 51, 1); border: 1px solid rgba(221, 221, 221, 1); background: rgba(246, 246, 246, 1); border-radius: 2px; font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">.;％JAVA_HOME%\bin;</code>”中的两个分号是不可缺少的，它们用于分隔多个环境变量。</span><span style="color: rgba(68, 68, 68, 1); font-family: "Helvetica Neue", 微软雅黑, "Microsoft Yahei", Helvetica, Arial, sans-serif">第一个分号前是一个英文状态半角下的句号，表示命令行下的当前目录；第二个分号前则是 JDK 的 bin 目录。</span></p><br><br>
来源：https://www.cnblogs.com/du-jun/p/12221540.html
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