java -D的用途

java已有默认系统属性，通过：System.getProperties().list(System.out);查看，结果如下：
-- listing properties --
java.runtime.name=java(TM) SE Runtime Environment
sun.boot.library.path=D:\java\jdk1.6.0_23\jre\bin
java.vm.version=19.0-b09
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
user.country=CN
sun.java.launcher=SUN_STANDARD
sun.os.patch.level=
java.vm.specification.name=java Virtual Machine Specification
user.dir=E:\workspace\javad\javad
java.runtime.version=1.6.0_23-b05
java.awt.graphicsenv=sun.awt.Win32GraphicsEnvironment
java.endorsed.dirs=D:\java\jdk1.6.0_23\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 7
sun.jnu.encoding=GBK
java.library.path=D:\java\jdk1.6.0_23\bin;.;C:\Windows\...
java.specification.name=java Platform API Specification
java.class.version=50.0
sun.management.compiler=HotSpot Client Compiler
os.version=6.1
user.home=C:\Users\Administrator
user.timezone=
java.awt.printerjob=sun.awt.windows.WPrinterJob
file.encoding=GBK
java.specification.version=1.6
user.name=Administrator
java.class.path=E:\workspace\javad\javad\target\test-...
java.vm.specification.version=1.0
sun.arch.data.model=32
java.home=D:\java\jdk1.6.0_23\jre
java.specification.vendor=Sun Microsystems Inc.
user.language=zh
awt.toolkit=sun.awt.windows.WToolkit
java.vm.info=mixed mode, sharing
java.version=1.6.0_23
java.ext.dirs=D:\java\jdk1.6.0_23\jre\lib\ext;C:\Wi...
sun.boot.class.path=D:\java\jdk1.6.0_23\jre\lib\resources...
java.vendor=Sun Microsystems Inc.
file.separator=\
java.vendor.url.bug=http://java.sun.com/cgi-bin/bugreport...
sun.cpu.endian=little
sun.io.unicode.encoding=UnicodeLittle
sun.desktop=windows
sun.cpu.isalist=pentium_pro+mmx pentium_pro pentium+m...
可以使用java -D修改这些属性，也可以创建自己的程序属性，如：java -Djava.io.tmpdir=d:\，修改临时文件存放目录