System.getEnv（）和System.getProperties（）的差别
从概念上讲，系统属性 和环境变量 都是名称与值之间的映射。两种机制都能用来将用户定义的信息传递给 Java 进程。环境变量产生很多其它的全局效应，由于它们不仅对Java 子进程可见，并且对于定义它们的进程的全部子进程都是可见的。在不同的操作系统上，它们的语义有细微的区别，比方，不区分大写和小写。由于这些原因，环境变量更可能有意料不到的副作用。最好在可能的地方使用系统属性。环境变量应该在须要全局效应的时候使用，或者在外部系统接口要求使用环境变量时使用（比方 PATH）。
代码例如以下：
public static void main(String [] args)
{
Map
m = System.getenv();
for
( Iterator it = m.keySet().iterator(); it.hasNext(); )
{
String
key = (String ) it.next();
String
value = (String ) m.get(key);
System.out.println(key
+":" +value);
}
System.out.println(
"--------------------------------------" );
Properties
p = System.getProperties();
for
( Iterator it = p.keySet().iterator(); it.hasNext(); )
{
String
key = (String ) it.next();
String
value = (String ) p.get(key);
System.out.println(key
+":" +value);
}
}
输入例如以下：
ANT_HOME:D:/program/devel/ant
PROCESSOR_ARCHITECTURE:x86
LOGONSERVER://RJ-WEIJIANJUN
HOMEDRIVE:C:
CATALINA_HOME:D:/program/server/Tomcat5.5
DXSDK_DIR:d:/Program
Files/Microsoft DirectX SDK (August 2008)/
VS80COMNTOOLS:C:/Program
Files/Microsoft Visual Studio 8/Common7/Tools/
SESSIONNAME:Console
HOMEPATH:/Documents and
Settings/Administrator
TMP:C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp
windir:C:/WINDOWS
PROCESSOR_IDENTIFIER:x86 Family
6 Model 15 Stepping 13, GenuineIntel
VS90COMNTOOLS:e:/Program
Files/Microsoft Visual Studio 9.0/Common7/Tools/
SystemDrive:C:
USERPROFILE:C:/Documents and
Settings/Administrator
PATHEXT:.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH
CommonProgramFiles:C:/Program
Files/Common Files
NUMBER_OF_PROCESSORS:2
ComSpec:C:/WINDOWS/system32/cmd.exe
COMPUTERNAME:RJ-WEIJIANJUN
OS:Windows_NT
USERNAME:Administrator
CLIENTNAME:Console
TEMP:C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp
USERDOMAIN:RJ-WEIJIANJUN
ALLUSERSPROFILE:C:/Documents
and Settings/All Users
lib:C:/Program Files/SQLXML
4.0/bin/
PROCESSOR_LEVEL:6
SystemRoot:C:/WINDOWS
ClusterLog:C:/WINDOWS/Cluster/cluster.log
APPDATA:C:/Documents and
Settings/Administrator/Application Data
Path:C:/WINDOWS/system32;C:/WINDOWS;C:/WINDOWS/System32/Wbem;C:/Program
Files/Microsoft SQL Server/80/Tools/Binn/;C:/Program Files/Microsoft SQL
Server/90/DTS/Binn/;C:/Program Files/Microsoft SQL
Server/90/Tools/binn/;C:/Program Files/Microsoft SQL
Server/90/Tools/Binn/VSShell/Common7/IDE/;C:/Program Files/Microsoft Visual
Studio 8/Common7/IDE/PrivateAssemblies/;D:/program/devel/flex_sdk2/bin;D:/program/devel/ant/bin;C:/Program
Files/Java/jdk1.6.0_07/bin;%JONAS_ROOT%/bin/nt;d:/program/devel/ant/bin
JAVA_HOME:C:/Program
Files/Java/jdk1.6.0_07
FP_NO_HOST_CHECK:NO
PROCESSOR_REVISION:0f0d
ProgramFiles:C:/Program Files
下面是property的输出：
--------------------------------------
java.runtime.name:Java(TM) 2
Runtime Environment, Standard Edition
sun.boot.library.path:D:/Program
Files/MyEclipse 6.5/jre/bin
java.vm.version:1.5.0_11-b03
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:Service Pack
2
java.vm.specification.name:Java
Virtual Machine Specification
user.dir:D:/dev/eclipse/mye65/workspace/jmx
java.runtime.version:1.5.0_11-b03
java.awt.graphicsenv:sun.awt.Win32GraphicsEnvironment
java.endorsed.dirs:D:/Program
Files/MyEclipse 6.5/jre/lib/endorsed
os.arch:x86
java.io.tmpdir:C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp/
line.separator:
java.vm.specification.vendor:Sun
Microsystems Inc.
user.variant:
os.name:Windows 2003
sun.jnu.encoding:GBK
java.library.path:D:/Program
Files/MyEclipse
6.5/jre/bin;.;C:/WINDOWS/system32;C:/WINDOWS;C:/WINDOWS/system32;C:/WINDOWS;C:/WINDOWS/System32/Wbem;C:/Program
Files/Microsoft SQL Server/80/Tools/Binn/;C:/Program Files/Microsoft SQL
Server/90/DTS/Binn/;C:/Program Files/Microsoft SQL
Server/90/Tools/binn/;C:/Program Files/Microsoft SQL
Server/90/Tools/Binn/VSShell/Common7/IDE/;C:/Program Files/Microsoft Visual
Studio
8/Common7/IDE/PrivateAssemblies/;D:/program/devel/flex_sdk2/bin;D:/program/devel/ant/bin;C:/Program
Files/Java/jdk1.6.0_07/bin;%JONAS_ROOT%/bin/nt;d:/program/devel/ant/bin
java.specification.name:Java
Platform API Specification
java.class.version:49.0
sun.management.compiler:HotSpot
Client Compiler
os.version:5.2
user.home:C:/Documents and
Settings/Administrator
user.timezone:Asia/Shanghai
java.awt.printerjob:sun.awt.windows.WPrinterJob
file.encoding:GBK
java.specification.version:1.5
java.class.path:D:/dev/eclipse/mye65/workspace/jmx/bin;D:/program/lib/jmx/jmxtools.jar;D:/program/lib/log/commons-logging-1.1.1.jar;D:/program/lib/log/log4j-1.2.15.jar;D:/program/lib/registry/registry.jar
user.name:Administrator
java.vm.specification.version:1.0
java.home:D:/Program
Files/MyEclipse 6.5/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:1.5.0_11
java.ext.dirs:D:/Program
Files/MyEclipse 6.5/jre/lib/ext
sun.boot.class.path:D:/Program
Files/MyEclipse 6.5/jre/lib/rt.jar;D:/Program Files/MyEclipse
6.5/jre/lib/i18n.jar;D:/Program Files/MyEclipse
6.5/jre/lib/sunrsasign.jar;D:/Program Files/MyEclipse 6.5/jre/lib/jsse.jar;D:/Program
Files/MyEclipse 6.5/jre/lib/jce.jar;D:/Program Files/MyEclipse
6.5/jre/lib/charsets.jar;D:/Program Files/MyEclipse 6.5/jre/classes
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
个人觉得比較重要的系统属性：
java.home：Java 安装文件夹 (比方D:/JavaStudio/jdk15/jre)
java.class.path：Java 类路径
java.vm.version：Java虚拟机版本(比方：1.5.0-b64）
java.version：Java版本(比方：1.5.0)
os.name：操作系统的名称(比方：Windows XP)
os.version：操作系统的版本号(比方：Windows XP 的版本号为5.1)
user.home：用户的主文件夹 (比方：C:/Documents and Settings/zhangsan)
user.name：当前username
user.country：当前用户所属国家
user.dir：用户的当前工作文件夹
比較重要的环境变量（Windows操作系统）：
%COMPUTERNAME% 返回计算机的名称。
%COMSPEC% 返回命令行解释器可运行程序的准确路径。
%WINDIR% 返回操作系统文件夹的位置。
%OS% 返回操作系统的名称。Windows 2000 将操作系统显示为 Windows_NT。
%PATH% 指定可运行文件的搜索路径。
%USERDOMAIN% 返回包括用户帐户的域的名称。
%USERNAME% 返回当前登录的用户的名称。
以下是一篇在jdk1.4中得到环境变量的方法：
Access user
defined environment variable inside the java program with jdk1.4
In JDK 1.4
System.getenv() is deprecated. (In JDK 1.5 it is un-deprected again.) The
getProperty method is now the correspoding method to get the variables. For
example: System.getProperty("java.class.path",""). But it
doesn't work for user defined environment variable. This problem can be solved
by using the following code:
import java.io.BufferedReader;
import java.io.InputStreamReader;
/**
* Environment class simulates the System.getenv() method which is deprecated
* on java 1.4.2
*
* @author v-josp
*/
public class TestRoot
{
//result of all enviornment variables
private static BufferedReader commandResult;
static
{
String cmd = null;
String os = null;
//getting the OS name
os = System.getProperty("os.name").toLowerCase();
// according to OS set the command to execute
if(os.startsWith("windows"))
{
cmd = "cmd /c SET";
}
else
{
cmd="env";
}
try
{
//execute the command and get the result in the form of InputStream
Process p = Runtime.getRuntime().exec(cmd);
//parse the InputStream data
InputStreamReader isr = new InputStreamReader(p.getInputStream());
commandResult= new BufferedReader(isr);
}
catch (Exception e)
{
System.out.println("OSEnvironment.class error: " + cmd +
":" + e);
}
}
/**
* This method is used to get the path of the given enviornment variable. This
* method tries to simulates the System.getenv() which is deprecated on java
1.4.2
*
* @param String - name of the environment variable
* @param String - default value
* @return
*/
public static String getenv(String envName,String defaultValue)
{
String line = null;
try
{
while ((line = commandResult.readLine()) != null)
{
if(line.indexOf(envName)>-1)
{
return line.substring(line.indexOf(envName)+envName.length()+1);
}
}
return defaultValue;
}
catch (Exception e)
{
return defaultValue;
}
}
public static void
main(String args[])
{
System.out.println(TestRoot.getenv("CLASSPATH",""));
}
}