java中獲取系統屬性以及環境變數
System.getEnv（）和System.getProperties（）的區別
從概念上講，系統屬性和環境變數都是名稱與值之間的對映。兩種機制都能用來將使用者定義的資訊傳遞給 Java 程序。環境變數產生更多的全域性效應，因為它們不僅對Java 子程序可見，而且對於定義它們的程序的所有子程序都是可見的。在不同的作業系統上，它們的語義有細微的差別，比如，不區分大小寫。因為這些原因，環境變數更可能有意料不到的副作用。最好在可能的地方使用系統屬性。環境變數應該在需要全域性效應的時候使用，或者在外部系統介面要求使用環境變數時使用（比如PATH）。
程式碼如下：
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);
}
}
輸入如下：
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
以下是property的輸出：
--------------------------------------
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
個人認為比較重要的系統屬性：
java.home：Java 安裝目錄 (比如D:/JavaStudio/jdk15/jre)
java.class.path：Java 類路徑
java.vm.version：Java虛擬機器版本號(比如：1.5.0-b64）
java.version：Java版本號(比如：1.5.0)
os.name：作業系統的名稱(比如：Windows XP)
os.version：作業系統的版本(比如：Windows XP 的版本為5.1)
user.home：使用者的主目錄 (比如：C:/Documents and Settings/zhangsan)
user.name：當前使用者名稱
user.country：當前使用者所屬國家
user.dir：使用者的當前工作目錄比較重要的環境變數（Windows作業系統）：
%COMPUTERNAME% 返回計算機的名稱。
%COMSPEC% 返回命令列直譯器可執行程式的準確路徑。
%WINDIR% 返回作業系統目錄的位置。
%OS% 返回作業系統的名稱。Windows 2000 將作業系統顯示為 Windows_NT。
%PATH% 指定可執行檔案的搜尋路徑。
%USERDOMAIN% 返回包含使用者帳戶的域的名稱。
%USERNAME% 返回當前登入的使用者的名稱。
下面是一篇在jdk1.4中得到環境變數的方法：
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",""));
}
}