java的System.getProperties属性

System可以获取很多环境有关的属性：

-- listing properties --java.runtime.name=Java(TM) SE Runtime Environmentsun.boot.library.path=C:\Program Files\Java\jdk1.8.0_65\jre...java.vm.version=25.65-b01java.vm.vendor=Oracle Corporationjava.vendor.url=http://java.oracle.com/path.separator=;java.vm.name=Java HotSpot(TM) Client VMfile.encoding.pkg=sun.iouser.script=user.country=CNsun.java.launcher=SUN_STANDARDsun.os.patch.level=Service Pack 1java.vm.specification.name=Java Virtual Machine Specificationuser.dir=E:\eclipseWorkspace\TestIojava.runtime.version=1.8.0_65-b17java.awt.graphicsenv=sun.awt.Win32GraphicsEnvironmentjava.endorsed.dirs=C:\Program Files\Java\jdk1.8.0_65\jre...os.arch=x86java.io.tmpdir=C:\Users\ADMINI~1\AppData\Local\Temp\line.separator=java.vm.specification.vendor=Oracle Corporationuser.variant=os.name=Windows 7sun.jnu.encoding=GBKjava.library.path=C:\Program Files\Java\jdk1.8.0_65\bin...java.specification.name=Java Platform API Specificationjava.class.version=52.0sun.management.compiler=HotSpot Client Compileros.version=6.1user.home=C:\Users\Administratoruser.timezone=java.awt.printerjob=sun.awt.windows.WPrinterJobfile.encoding=GBKjava.specification.version=1.8user.name=Administratorjava.class.path=E:\eclipseWorkspace\TestIo\target\tes...java.vm.specification.version=1.8sun.arch.data.model=32java.home=C:\Program Files\Java\jdk1.8.0_65\jresun.java.command=org.eclipse.jdt.internal.junit.runner...java.specification.vendor=Oracle Corporationuser.language=zhawt.toolkit=sun.awt.windows.WToolkitjava.vm.info=mixed mode, sharingjava.version=1.8.0_65java.ext.dirs=C:\Program Files\Java\jdk1.8.0_65\jre...sun.boot.class.path=C:\Program Files\Java\jdk1.8.0_65\jre...java.vendor=Oracle Corporationfile.separator=\java.vendor.url.bug=http://bugreport.sun.com/bugreport/sun.cpu.endian=littlesun.io.unicode.encoding=UnicodeLittlesun.desktop=windowssun.cpu.isalist=pentium_pro+mmx pentium_pro pentium+m...