请问，System.getProperties()，其中的key 可以自己在环境变量中设置么？急！

可以设，但不是在os的环境变量,需要在 java  -DpropertyName=value yourClass
我写了一个例子：//得到所有的系统变量。import java.util.*;public class TestVariable {
public static void main(String[] args) {
Enumeration allKey = System.getProperties().propertyNames();
System.out.println("following are all the property in jre:");
while(allKey.hasMoreElements()) {
String prpName = (String)allKey.nextElement();
System.out.println(prpName+"="+System.getProperty(prpName));
}


}
}运行:
java  TestVariable结果为：
-----------------------------------------------------
following are all the property in jre:
java.runtime.name=Java(TM) 2 Runtime Environment, Standard Edition
sun.boot.library.path=C:\Program Files\Java\j2re1.4.2_01\bin
java.vm.version=1.4.2_01-b06
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.os.patch.level=Service Pack 3
java.vm.specification.name=Java Virtual Machine Specification
user.dir=D:\temp\test
java.runtime.version=1.4.2_01-b06
java.awt.graphicsenv=sun.awt.Win32GraphicsEnvironment
java.endorsed.dirs=C:\Program Files\Java\j2re1.4.2_01\lib\endorsed
os.arch=x86
java.io.tmpdir=C:\DOCUME~1\ADMINI~1\LOCALS~1\Templine.separator=java.vm.specification.vendor=Sun Microsystems Inc.
user.variant=
os.name=Windows 2000
sun.java2d.fontpath=
java.library.path=C:\WINNT\system32;.;C:\WINNT\system32;C:\WINNT;C:\oracle\ora81\bin;C:\oracle\ora81\Apache\Perl\5.00503\bin\mswin32-x86;C:\Program Files\Oracle\jre\1.1.7\bin;C:\WINNT\system32;C:\WINNT;C:\WINNT\System32\Wbem;C:\j2sdk1.4.2_01\bin;C:\PROGRA~1\Borland\Delphi6\Bin;C:\PROGRA~1\Borland\Delphi6\Projects\Bpl;C:\Program Files\Microsoft Visual Studio\Common\Tools\WinNT;C:\Program Files\Microsoft Visual Studio\Common\MSDev98\Bin;C:\Program Files\Microsoft Visual Studio\Common\Tools;C:\Program Files\Microsoft Visual Studio\VC98\bin;
java.specification.name=Java Platform API Specification
java.class.version=48.0
java.util.prefs.PreferencesFactory=java.util.prefs.WindowsPreferencesFactory
os.version=5.0
user.home=C:\Documents and Settings\Administrator
user.timezone=
java.awt.printerjob=sun.awt.windows.WPrinterJob
file.encoding=GBK
java.specification.version=1.4
user.name=Administrator
java.class.path=.;C:\j2sdk1.4.2_01\lib\dt.jar;C:\j2sdk1.4.2_01\lib\tools.jar;C:\j2sdkee1.3.1\lib\j2ee.jar;C:\j2sdkee1.3.1\lib\j2eetools.jar;C:\j2sdkee1.3.1\lib\jhall.jar;C:\j2sdkee1.3.1\lib\j2ee-ri-svc.jar;D:\mysql\driver\mysql-connector-java-3.0.11-stable\mysql-connector-java-3.0.11-stable\mysql-connector-java-3.0.11-stable-bin.jar
java.vm.specification.version=1.0
sun.arch.data.model=32
java.home=C:\Program Files\Java\j2re1.4.2_01
java.specification.vendor=Sun Microsystems Inc.
user.language=zh
awt.toolkit=sun.awt.windows.WToolkit
java.vm.info=mixed mode
java.version=1.4.2_01
java.ext.dirs=C:\Program Files\Java\j2re1.4.2_01\lib\ext
sun.boot.class.path=C:\Program Files\Java\j2re1.4.2_01\lib\rt.jar;C:\Program Files\Java\j2re1.4.2_01\lib\i18n.jar;C:\Program Files\Java\j2re1.4.2_01\lib\sunrsasign.jar;C:\Program Files\Java\j2re1.4.2_01\lib\jsse.jar;C:\Program Files\Java\j2re1.4.2_01\lib\jce.jar;C:\Program Files\Java\j2re1.4.2_01\lib\charsets.jar;C:\Program Files\Java\j2re1.4.2_01\classes
java.vendor=Sun Microsystems Inc.
file.separator=java.vendor.url.bug=http://java.sun.com/cgi-bin/bugreport.cgi
sun.cpu.endian=little
sun.io.unicode.encoding=UnicodeLittle
sun.cpu.isalist=pentium i486 i386
-----------------------------------------------------运行:
java -DtestProp=Hello  TestVariable结果:
-----------------------------------------------------
following are all the property in jre:
java.runtime.name=Java(TM) 2 Runtime Environment, Standard Edition
sun.boot.library.path=C:\Program Files\Java\j2re1.4.2_01\bin
java.vm.version=1.4.2_01-b06
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.os.patch.level=Service Pack 3
testProp=Hello                  ----看到了吧，这个是新加的属性
java.vm.specification.name=Java Virtual Machine Specification
user.dir=D:\temp\test
java.runtime.version=1.4.2_01-b06
java.awt.graphicsenv=sun.awt.Win32GraphicsEnvironment
java.endorsed.dirs=C:\Program Files\Java\j2re1.4.2_01\lib\endorsed
os.arch=x86
java.io.tmpdir=C:\DOCUME~1\ADMINI~1\LOCALS~1\Templine.separator=java.vm.specification.vendor=Sun Microsystems Inc.
user.variant=
os.name=Windows 2000
sun.java2d.fontpath=
java.library.path=C:\WINNT\system32;.;C:\WINNT\system32;C:\WINNT;C:\oracle\ora81\bin;C:\oracle\ora81\Apache\Perl\5.00503\bin\mswin32-x86;C:\Program Files\Oracle\jre\1.1.7\bin;C:\WINNT\system32;C:\WINNT;C:\WINNT\System32\Wbem;C:\j2sdk1.4.2_01\bin;C:\PROGRA~1\Borland\Delphi6\Bin;C:\PROGRA~1\Borland\Delphi6\Projects\Bpl;C:\Program Files\Microsoft Visual Studio\Common\Tools\WinNT;C:\Program Files\Microsoft Visual Studio\Common\MSDev98\Bin;C:\Program Files\Microsoft Visual Studio\Common\Tools;C:\Program Files\Microsoft Visual Studio\VC98\bin;
java.specification.name=Java Platform API Specification
java.class.version=48.0
java.util.prefs.PreferencesFactory=java.util.prefs.WindowsPreferencesFactory
os.version=5.0
user.home=C:\Documents and Settings\Administrator
user.timezone=
java.awt.printerjob=sun.awt.windows.WPrinterJob
file.encoding=GBK
java.specification.version=1.4
user.name=Administrator
java.class.path=.;C:\j2sdk1.4.2_01\lib\dt.jar;C:\j2sdk1.4.2_01\lib\tools.jar;C:\j2sdkee1.3.1\lib\j2ee.jar;C:\j2sdkee1.3.1\lib\j2eetools.jar;C:\j2sdkee1.3.1\lib\jhall.jar;C:\j2sdkee1.3.1\lib\j2ee-ri-svc.jar;D:\mysql\driver\mysql-connector-java-3.0.11-stable\mysql-connector-java-3.0.11-stable\mysql-connector-java-3.0.11-stable-bin.jar
java.vm.specification.version=1.0
sun.arch.data.model=32
java.home=C:\Program Files\Java\j2re1.4.2_01
java.specification.vendor=Sun Microsystems Inc.
user.language=zh
awt.toolkit=sun.awt.windows.WToolkit
java.vm.info=mixed mode
java.version=1.4.2_01
java.ext.dirs=C:\Program Files\Java\j2re1.4.2_01\lib\ext
sun.boot.class.path=C:\Program Files\Java\j2re1.4.2_01\lib\rt.jar;C:\Program Files\Java\j2re1.4.2_01\lib\i18n.jar;C:\Program Files\Java\j2re1.4.2_01\lib\sunrsasign.jar;C:\Program Files\Java\j2re1.4.2_01\lib\jsse.jar;C:\Program Files\Java\j2re1.4.2_01\lib\jce.jar;C:\Program Files\Java\j2re1.4.2_01\lib\charsets.jar;C:\Program Files\Java\j2re1.4.2_01\classes
java.vendor=Sun Microsystems Inc.
file.separator=java.vendor.url.bug=http://java.sun.com/cgi-bin/bugreport.cgi
sun.cpu.endian=little
sun.io.unicode.encoding=UnicodeLittle
sun.cpu.isalist=pentium i486 i386
-----------------------------------------------------看到:testProp=Hello 这个新增的属性了吗？
哈哈