Getting environment variables in Java

It is divided into some environment variables that get Java itself and the environment variables related to the operating system.

• Get some of the JVM-related variables

Set an environment variable at run time debug to True:java-ddebug=true YourClass
Set an environment variable in the program debug to True: system.setproperty ("Debug", "true");
Get an environment variable debug: String debug = System.getproperty ("Debug");

Some of the environment variables are listed in the following table, which are already defined by Java and can be obtained through System.getproperty ("key") in the program, and more environment variables see the JDK documentation.

Property name	Description
Java.version	Java Runtime version
Java.home	installation directory for Java
Java.class.version	Version number of the Java class format
Java.class.path	Find paths for Java classes
Java.io.tmpdir	The default temp directory
Java.compiler	A timely compiler used by Java
Java.ext.dirs	Directory for Java expansion packs
Os.name	Name of the operating system
Os.arch	Architecture of the operating system
Os.version	Version of the operating system
File.separator	File delimiter ("/" under Unix)
Path.separator	Path delimiter (under Unix as ': ')
Line.separator	Line break ('/n ' under Unix)
User.Name	User account Name
User.home	User Directory
User.dir	User's current working directory

Other specific references can be found in the following code instance program.

• Get environment variables for operating system

Note that this is the environment variable that gets the operating system, not some variables related to the JVM.
Perhaps in order to create a JVM is the operating system platform atmosphere, or to emphasize the platform-independent Java, not know Java has put system.getenv (String) function obsolete. So in general Java can only get some of its own defined variables, but not with the operating system environment variables, can only run by Java's "-D" parameter to set some of the variables to be passed to it.
So the only way is to judge the operating system first, then use the operating system commands to bring up the list of environment variables, try to obtain the output list.

• Code implementation

Import Java.io.bufferedreader;import java.io.ioexception;import Java.io.inputstreamreader;import Java.util.HashMap Import Java.util.map;import Java.util.properties;public class Systemvalue {/** * get system-related values by using systems */public static Voi  D getsystemproperties () {Properties pp = system.getproperties ();  System.out.println ("System ' s Properties:");  System.out.println ();  Java.util.Enumeration en = Pp.propertynames ();   while (En.hasmoreelements ()) {String Nexte = (string) en.nextelement ();   System.out.print (nexte + "=" + Pp.getproperty (nexte));  System.out.println ();  }} public static void Getcustomproperties (String key) {map map = GETENV (); SYSTEM.OUT.PRINTLN (key + "=" + map.get (key));  public static map GetEnv () {map map = new HashMap ();  Process p = null;  Runtime r = Runtime.getruntime ();  String OS = System.getproperty ("Os.name"). toLowerCase ();  System.out.println ("os=" +os);   try {if (Os.indexof ("Windows 9") >-1) {p = r.exec ("command.com/c set"); } else if ((Os.indexof ("NT") >-1) | | (Os.indexof ("Windows 1") >-) | | (Os.indexof ("Windows XP") >-1))   {p = r.exec ("cmd.exe/c set");   } else {//Unix P = r.exec ("env");   } bufferedreader br = new BufferedReader (new InputStreamReader (p. getInputStream ()));   String Line;    while (line = Br.readline ()) = null) {string[] str = line.split ("=");   Map.put (Str[0], str[1]);  }} catch (IOException IoE) {ioe.printstacktrace (); } return map;  } public static void Main (string[] args) {//getsystemproperties (); Getcustomproperties ("Java_home"); }}

Getting environment variables in Java

Getting environment variables in Java