System.getProperties() メソッドの呼び出しでシステムに定義されているプロパティ、すなわちシステム プロパティを取得することができます。 Java 実行環境の情報、 OS の情報、実行ユーザの情報などを取得することができます。試しに次のコードを実行してみました。

Properties props = System.getProperties();
for (Enumeration enum = props.propertyNames(); enum.hasMoreElements();) {
    String key = (String) enum.nextElement();
    String value = props.getProperty(key);
    System.out.println("key=" + key + ", value=" + value);
}

• 出力結果

key=java.runtime.name, value=Java(TM) 2 Runtime Environment, Standard Edition
key=sun.boot.library.path, value=C:\Program Files\Java\j2re1.4.2_06\bin
key=java.vm.version, value=1.4.2_06-b03
key=java.vm.vendor, value=Sun Microsystems Inc.
key=java.vendor.url, value=http://java.sun.com/
key=path.separator, value=;
key=java.vm.name, value=Java HotSpot(TM) Client VM
key=file.encoding.pkg, value=sun.io
key=user.country, value=JP
key=sun.os.patch.level, value=Service Pack 4
key=java.vm.specification.name, value=Java Virtual Machine Specification
key=user.dir, value=D:\work\eclipse-ws\test
key=java.runtime.version, value=1.4.2_06-b03
key=java.awt.graphicsenv, value=sun.awt.Win32GraphicsEnvironment
key=java.endorsed.dirs, value=C:\Program Files\Java\j2re1.4.2_06\lib\endorsed
key=os.arch, value=x86
key=java.io.tmpdir, value=C:\DOCUME~1\uguu\LOCALS~1\Temp\
key=line.separator, value=

key=java.vm.specification.vendor, value=Sun Microsystems Inc.
key=user.variant, value=
key=os.name, value=Windows 2000
key=sun.java2d.fontpath, value=
key=java.library.path, value=C:\Program Files\Java\j2re1.4.2_06\bin;.;C:\WINNT\system32;C:\WINNT;C:\WINNT\system32;C:\WINNT;C:\WINNT\System32\Wbem;C:\usr\svn-win32-1.1.2\bin;C:\usr\j2sdk1.4.2_06\bin;C:\Program Files\Justsystem\JSLIB32;C:\usr\mysql-4.0.23\bin
key=java.specification.name, value=Java Platform API Specification
key=java.class.version, value=48.0
key=java.util.prefs.PreferencesFactory, value=java.util.prefs.WindowsPreferencesFactory
key=os.version, value=5.0
key=user.home, value=C:\Documents and Settings\uguu
key=user.timezone, value=
key=java.awt.printerjob, value=sun.awt.windows.WPrinterJob
key=file.encoding, value=MS932
key=java.specification.version, value=1.4
key=user.name, value=uguu
key=java.class.path, value=D:\work\eclipse-ws\test\bin
key=java.vm.specification.version, value=1.0
key=sun.arch.data.model, value=32
key=java.home, value=C:\Program Files\Java\j2re1.4.2_06
key=java.specification.vendor, value=Sun Microsystems Inc.
key=user.language, value=ja
key=awt.toolkit, value=sun.awt.windows.WToolkit
key=java.vm.info, value=mixed mode
key=java.version, value=1.4.2_06
key=java.ext.dirs, value=C:\Program Files\Java\j2re1.4.2_06\lib\ext
key=sun.boot.class.path, value=C:\Program Files\Java\j2re1.4.2_06\lib\rt.jar;C:\Program Files\Java\j2re1.4.2_06\lib\i18n.jar;C:\Program Files\Java\j2re1.4.2_06\lib\sunrsasign.jar;C:\Program Files\Java\j2re1.4.2_06\lib\jsse.jar;C:\Program Files\Java\j2re1.4.2_06\lib\jce.jar;C:\Program Files\Java\j2re1.4.2_06\lib\charsets.jar;C:\Program Files\Java\j2re1.4.2_06\classes
key=java.vendor, value=Sun Microsystems Inc.
key=file.separator, value=\
key=java.vendor.url.bug, value=http://java.sun.com/cgi-bin/bugreport.cgi
key=sun.cpu.endian, value=little
key=sun.io.unicode.encoding, value=UnicodeLittle
key=sun.cpu.isalist, value=pentium i486 i386

分かりづらいので、並び替え、表にしました。

key	value
awt.toolkit	sun.awt.windows.WToolkit
file.encoding	MS932
file.encoding.pkg	sun.io
file.separator	\
java.awt.graphicsenv	sun.awt.Win32GraphicsEnvironment
java.awt.printerjob	sun.awt.windows.WPrinterJob
java.class.path	D:\work\eclipse-ws\test\bin
java.class.version	48
java.endorsed.dirs	C:\Program Files\Java\j2re1.4.2_06\lib\endorsed
java.ext.dirs	C:\Program Files\Java\j2re1.4.2_06\lib\ext
java.home	C:\Program Files\Java\j2re1.4.2_06
java.io.tmpdir	C:\DOCUME~1\uguu\LOCALS~1\Temp\
java.library.path	C:\Program Files\Java\j2re1.4.2_06\bin;.;C:\WINNT\system32;C:\WINNT;C:\WINNT\system32;C:\WINNT;C:\WINNT\System32\Wbem;C:\usr\svn-win32-1.1.2\bin;C:\usr\j2sdk1.4.2_06\bin;C:\Program Files\Justsystem\JSLIB32;C:\usr\mysql-4.0.23\bin
java.runtime.name	Java(TM) 2 Runtime Environment, Standard Edition
java.runtime.version	1.4.2_06-b03
java.specification.name	Java Platform API Specification
java.specification.vendor	Sun Microsystems Inc.
java.specification.version	1.4
java.util.prefs.PreferencesFactory	java.util.prefs.WindowsPreferencesFactory
java.vendor	Sun Microsystems Inc.
java.vendor.url	http://java.sun.com/
java.vendor.url.bug	http://java.sun.com/cgi-bin/bugreport.cgi
java.version	1.4.2_06
java.vm.info	mixed mode
java.vm.name	Java HotSpot(TM) Client VM
java.vm.specification.name	Java Virtual Machine Specification
java.vm.specification.vendor	Sun Microsystems Inc.
java.vm.specification.version	1
java.vm.vendor	Sun Microsystems Inc.
java.vm.version	1.4.2_06-b03
line.separator
os.arch	x86
os.name	Windows 2000
os.version	5
path.separator	;
sun.arch.data.model	32
sun.boot.class.path	C:\Program Files\Java\j2re1.4.2_06\lib\rt.jar;C:\Program Files\Java\j2re1.4.2_06\lib\i18n.jar;C:\Program Files\Java\j2re1.4.2_06\lib\sunrsasign.jar;C:\Program Files\Java\j2re1.4.2_06\lib\jsse.jar;C:\Program Files\Java\j2re1.4.2_06\lib\jce.jar;C:\Program Files\Java\j2re1.4.2_06\lib\charsets.jar;C:\Program Files\Java\j2re1.4.2_06\classes
sun.boot.library.path	C:\Program Files\Java\j2re1.4.2_06\bin
sun.cpu.endian	little
sun.cpu.isalist	pentium i486 i386
sun.io.unicode.encoding	UnicodeLittle
sun.java2d.fontpath
sun.os.patch.level	Service Pack 4
user.country	JP
user.dir	D:\work\eclipse-ws\test
user.home	C:\Documents and Settings\uguu
user.language	ja
user.name	uguu
user.timezone
user.variant