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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>1.2. System</title><link rel="stylesheet" type="text/css" href="/docbook.css" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="home" href="index.html" title="Netkiller Java 手札" /><link rel="up" href="java.html" title="第 1 章 Java 14" /><link rel="prev" href="java.html" title="第 1 章 Java 14" /><link rel="next" href="Runtime.html" title="1.3. exec 运行shell" /></head><body><a xmlns="" href="//www.netkiller.cn/">Home</a> |
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<a xmlns="" href="//www.netkiller.cn/home/about.html">About</a><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">1.2. System</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="java.html">上一页</a> </td><th width="60%" align="center">第 1 章 Java 14</th><td width="20%" align="right"> <a accesskey="n" href="Runtime.html">下一页</a></td></tr></table><hr /></div><table xmlns=""><tr><td><iframe src="//ghbtns.com/github-btn.html?user=netkiller&repo=netkiller.github.io&type=watch&count=true&size=large" height="30" width="170" frameborder="0" scrolling="0" style="width:170px; height: 30px;" allowTransparency="true"></iframe></td><td><iframe src="//ghbtns.com/github-btn.html?user=netkiller&repo=netkiller.github.io&type=fork&count=true&size=large" height="30" width="170" frameborder="0" scrolling="0" style="width:170px; height: 30px;" allowTransparency="true"></iframe></td><td><iframe src="//ghbtns.com/github-btn.html?user=netkiller&type=follow&count=true&size=large" height="30" width="240" frameborder="0" scrolling="0" style="width:240px; height: 30px;" allowTransparency="true"></iframe></td><td></td><td><a href="https://zhuanlan.zhihu.com/netkiller"><img src="/images/logo/zhihu-card-default.svg" height="25" /></a></td><td valign="middle"><a href="https://zhuanlan.zhihu.com/netkiller">知乎专栏</a> ｜ <a href="https://www.zhihu.com/club/1241768772601950208">多维度架构</a></td><td> | </td><td>微信号 netkiller-ebook </td><td> | </td><td>QQ群：128659835 请注明“读者”</td></tr></table><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="system"></a>1.2. System</h2></div></div></div>
<pre class="screen">
Java.version 运行时环境版本
java.vendor 运行时环境供应商
java.vendor.url 供应商的 URL
java.home 安装目录
java.vm.specification.version 虚拟机规范版本
java.vm.specification.vendor 虚拟机规范供应商
java.vm.specification.name 虚拟机规范名称
java.vm.version 虚拟机实现版本
java.vm.vendor 虚拟机实现供应商
java.vm.name 虚拟机实现名称
java.specification.version 运行时环境规范版本
java.specification.vendor Java 运行时环境规范供应商
java.specification.name Java 运行时环境规范名称
java.class.version Java 类格式版本号
java.class.path Java 类路径
java.library.path 加载库时搜索的路径列表
java.io.tmpdir 默认的临时文件路径
java.compiler 要使用的 JIT 编译器的名称
java.ext.dirs 一个或多个扩展目录的路径
os.name 操作系统的名称
os.arch 操作系统的架构
os.version 操作系统的版本
file.separator 文件分隔符（在 UNIX 系统中是“/”）
path.separator 路径分隔符（在 UNIX 系统中是“:”）
line.separator 行分隔符（在 UNIX 系统中是“/n”）
user.name 用户的账户名称
user.home 用户的主目录
user.dir 用户的当前工作目录
</pre>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="System"></a>1.2.1. user.dir</h3></div></div></div>
<pre class="programlisting">
public class Test {
public static void main(String[] args) {
System.out.println("Working Directory = " + System.getProperty("user.dir"));
System.out.println(System.getProperty("user.home"));
System.out.println(System.getProperty("java.version"));
System.out.println(System.getProperty("os.name"));
System.out.println(System.getProperty("java.vendor.url"));
}
}
</pre>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="idp7"></a>1.2.2. java.io.tmpdir</h3></div></div></div>
<p>改变java.io.tmpdir的默认值</p>
<pre class="programlisting">
System.setProperty("java.io.tmpdir", "/vat/tmp");
System.out.println(System.getProperty("java.io.tmpdir"));
</pre>
<p>如果你希望从外部修改这个系统属性的话，你可以使用-D这个参数，例如 java -Djava.io.tmpdir=/path/to/tmpdir</p>
<pre class="programlisting">
System.out.println(System.getProperty("java.io.tmpdir"));
</pre>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="file.encoding"></a>1.2.3. 打印当前 Java 文件的默认编码</h3></div></div></div>
<pre class="programlisting">
package cn.netkiller.test;
import java.nio.charset.Charset;
public class Test {
public Test() {
// TODO Auto-generated constructor stub
}
public static void main(String[] args) {
System.out.println(System.getProperty("file.encoding"));
System.out.println(Charset.defaultCharset());
}
}
</pre>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="idp8"></a>1.2.4. 自定义</h3></div></div></div>
<pre class="programlisting">
public static void main(String[] args) {
try {
Oracle oracle = new Oracle();
if(System.getProperty("config") == null){
System.exit(1);
}
oracle.openConfig(System.getProperty("config"));
} catch (Exception e) {
System.out.println(e.getMessage());
}
}
</pre>
<p>上面程序编译打包后运行</p>
<pre class="screen">
neo@netkiller:~/project/Oracle$ java -jar -Dconfig=jdbc.properties target/oracle-0.0.1-SNAPSHOT.jar
</pre>
</div>
<div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="idp9"></a>1.2.5. System.in 标准输入(Stdin)</h3></div></div></div>
<p>标准输入一般用于管道输入，例如：</p>
<pre class="screen">
cat test.txt | java cn.netkiller.ipo.test.StdinToStdout
</pre>
<p>下面的程序例子里从管道输入，并从标准输出打印。</p>
<pre class="programlisting">
package cn.netkiller.ipo.test;
import java.io.BufferedReader;
import java.io.InputStreamReader;
public class StdinToStdout {
public StdinToStdout() {
// TODO Auto-generated constructor stub
}
public static void main(String[] args) {
String s = "";
try {
BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
while ((s = stdIn.readLine()) != null) {
System.out.println(s);
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
</pre>
<p>默认 BufferedReader 缓冲区比较小，无法处理大于1000 行的输入，可以通过配置缓冲区来解决。</p>
<pre class="programlisting">
stdin = new BufferedReader(new InputStreamReader(System.in, "utf-8"), 1024 * 1024 * 1024); // 1G 缓冲区
</pre>
</div>
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