In Java we can read the environment variables using System.getEnv().
System.getEnv() was introduced in the very begining of Java. deprecated in JDK 1.2 and reinstated in JDK 1.5.
we can use the following method to read environment variables.

public void readEnvVariables()
   {
       Map<String, String> envVariables = System.getenv(); 
      Set stEnvVariables = envVariables.entrySet();
      Iterator itrEnvVariables = stEnvVariables.iterator();
 
      while(itrEnvVariables.hasNext())
{
      Map.Entry mpEnvVar = (Map.Entry) itrEnvVariables.next();
   System.out.println(mpEnvVar.getKey()+"="+mpEnvVar.getValue());
 
}
   }