System.getProperty("user.dir")

今天写一个小程序，需要获取当前项目的根目录。百度搜索得知System.getProperty("user.dir")该方法可以做到。看到这行代码不由让我思考：“user.dir”是一个什么玩意？System.getProperty("key")该方法到底有多少个key？于是经过对api的研究，发现了System.getProperties()这个方法可以获取到所有的key值;代码如下：

public void getSystemKey(){

    File sysFile = new File("d:/study","sysFile.properties");
    Properties sysPro = System.getProperties();
    try {
        sysPro.store(new FileOutputStream(sysFile), "Properties ClASS");
    } catch (FileNotFoundException e1) {
        e1.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    
}

得到的sysFile.properties文件内容如下：

#Properties ClASS
#Wed Mar 18 16:04:29 CST 2015
java.runtime.name=Java(TM) SE Runtime Environment
sun.boot.library.path=D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\jre\bin
java.vm.version=11.3-b02
java.vm.vendor=Sun Microsystems Inc.
java.vendor.url=http://java.sun.com/
path.separator=;
java.vm.name=Java HotSpot(TM) Client VM
file.encoding.pkg=sun.io
sun.java.launcher=SUN_STANDARD
user.country=CN
sun.os.patch.level=
java.vm.specification.name=Java Virtual Machine Specification
user.dir=D:\workspace\study\2015-3-17Java-FileUpDown
java.runtime.version=1.6.0_13-b03
java.awt.graphicsenv=sun.awt.Win32GraphicsEnvironment
java.endorsed.dirs=D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\jre\lib\endorsed
os.arch=x86
java.io.tmpdir=C:\Users\ADMINI~1\AppData\Local\Temp\
line.separator=

java.vm.specification.vendor=Sun Microsystems Inc.
user.variant=
os.name=Windows Vista
sun.jnu.encoding=GBK
java.library.path=D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\bin;.;C:\Windows\Sun\Java\bin;C:\Windows\system32;C:\Windows;D:/InstallFiles/Genuitec/Common/binary/com.sun.java.jdk.win32.x86_1.6.0.013/jre/bin/client;D:/InstallFiles/Genuitec/Common/binary/com.sun.java.jdk.win32.x86_1.6.0.013/jre/bin;C:\ProgramData\Oracle\Java\javapath;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;D:\InstallFiles\dzpk\Java\jdk1.6.0_24\lib
java.specification.name=Java Platform API Specification
java.class.version=50.0
sun.management.compiler=HotSpot Client Compiler
os.version=6.2
user.home=C:\Users\Administrator
user.timezone=Asia/Shanghai
java.awt.printerjob=sun.awt.windows.WPrinterJob
file.encoding=GBK
java.specification.version=1.6
java.class.path=D:\workspace\study\2015-3-17Java-FileUpDown\WebRoot\WEB-INF\classes;D:\workspace\study\2015-3-17Java-FileUpDown\WebRoot\WEB-INF\lib\poi-3.11-20141221.jar;D:\workspace\study\2015-3-17Java-FileUpDown\WebRoot\WEB-INF\lib\commons-logging-1.1.3.jar;D:\workspace\study\2015-3-17Java-FileUpDown\WebRoot\WEB-INF\lib\junit-4.11.jar;D:\workspace\study\2015-3-17Java-FileUpDown\WebRoot\WEB-INF\lib\log4j-1.2.17.jar
user.name=Administrator
java.vm.specification.version=1.0
java.home=D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\jre
sun.arch.data.model=32
user.language=zh
java.specification.vendor=Sun Microsystems Inc.
awt.toolkit=sun.awt.windows.WToolkit
java.vm.info=mixed mode
java.version=1.6.0_13
java.ext.dirs=D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\jre\lib\ext;C:\Windows\Sun\Java\lib\ext
sun.boot.class.path=D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\jre\lib\resources.jar;D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\jre\lib\rt.jar;D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\jre\lib\sunrsasign.jar;D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\jre\lib\jsse.jar;D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\jre\lib\jce.jar;D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\jre\lib\charsets.jar;D:\InstallFiles\Genuitec\Common\binary\com.sun.java.jdk.win32.x86_1.6.0.013\jre\classes;D:\InstallFiles\Genuitec\Common\plugins\com.genuitec.eclipse.j2eedt.core_8.6.1.me201010211225\data\libraryset\EE_5\javaee.jar;D:\InstallFiles\Genuitec\Common\plugins\com.genuitec.eclipse.j2eedt.core_8.6.1.me201010211225\data\libraryset\EE_5\jsf-impl.jar;D:\InstallFiles\Genuitec\Common\plugins\com.genuitec.eclipse.j2eedt.core_8.6.1.me201010211225\data\libraryset\EE_5\jsf-api.jar;D:\InstallFiles\Genuitec\Common\plugins\com.genuitec.eclipse.j2eedt.core_8.6.1.me201010211225\data\libraryset\EE_5\jstl-1.2.jar
java.vendor=Sun Microsystems Inc.
file.separator=\
java.vendor.url.bug=http://java.sun.com/cgi-bin/bugreport.cgi
sun.io.unicode.encoding=UnicodeLittle
sun.cpu.endian=little
sun.desktop=windows
sun.cpu.isalist=pentium_pro+mmx pentium_pro pentium+mmx pentium i486 i386 i86

关于这个user.dir，有网友说是用户工作目录，理由就是user.dir是user  directory的缩写；我觉得这个说法不对，个人理解user.dir只是一个key而已。