关于 System.getProperty

System.getProperty可以获取系统的一些环境变量，例：

import java.util.Properties;

public class PropertiesDemo {

    public static void main(String[] args) {
        Properties properties = new Properties();
        properties = System.getProperties();        
        properties.list(System.out);
    }
}

/*
输入结果：
    -- listing properties --
    java.runtime.name=Java(TM) SE Runtime Environment
    sun.boot.library.path=C:\Program Files\Java\jre7\bin
    java.vm.version=23.1-b03
    java.vm.vendor=Oracle Corporation
    java.vendor.url=http://java.oracle.com/
    path.separator=;
    java.vm.name=Java HotSpot(TM) Client VM
    file.encoding.pkg=sun.io
    user.script=
    user.country=CN
    sun.java.launcher=SUN_STANDARD
    sun.os.patch.level=Service Pack 3
    java.vm.specification.name=Java Virtual Machine Specification
    user.dir=C:\Documents and Settings\eboy\worksp...
    java.runtime.version=1.7.0_05-b05
    java.awt.graphicsenv=sun.awt.Win32GraphicsEnvironment
    java.endorsed.dirs=C:\Program Files\Java\jre7\lib\endorsed
    os.arch=x86
    java.io.tmpdir=C:\DOCUME~1\eboy\LOCALS~1\Temp\
    line.separator=
    
    java.vm.specification.vendor=Oracle Corporation
    user.variant=
    os.name=Windows XP
    sun.jnu.encoding=GBK
    java.library.path=C:\Program Files\Java\jre7\bin;C:\WIN...
    java.specification.name=Java Platform API Specification
    java.class.version=51.0
    sun.management.compiler=HotSpot Client Compiler
    os.version=5.1
    user.home=C:\Documents and Settings\eboy
    user.timezone=
    java.awt.printerjob=sun.awt.windows.WPrinterJob
    file.encoding=GBK
    java.specification.version=1.7
    user.name=eboy
    java.class.path=C:\Documents and Settings\eboy\worksp...
    java.vm.specification.version=1.7
    sun.arch.data.model=32
    java.home=C:\Program Files\Java\jre7
    sun.java.command=PropertiesDemo
    java.specification.vendor=Oracle Corporation
    user.language=zh
    awt.toolkit=sun.awt.windows.WToolkit
    java.vm.info=mixed mode, sharing
    java.version=1.7.0_05
    java.ext.dirs=C:\Program Files\Java\jre7\lib\ext;C:...
    sun.boot.class.path=C:\Program Files\Java\jre7\lib\resour...
    java.vendor=Oracle Corporation
    file.separator=\
    java.vendor.url.bug=http://bugreport.sun.com/bugreport/
    sun.cpu.endian=little
    sun.io.unicode.encoding=UnicodeLittle
    sun.desktop=windows
    sun.cpu.isalist=pentium_pro+mmx pentium_pro pentium+m...
*/

 

我要获取系统临时文件夹路径：

System.out.println(System.getProperty("java.io.tmpdir"));