Accessing Windows system variables in Java 1.4

Question

What is the best/foolproof way to get the values of environment variables in Windows when using J2SE 1.4 ?

Answer 1

You have definitely no way to access environment variables straigthly from java API. The only way to achieve that with Runtime.exec with such a code :

Process p = null;
Runtime r = Runtime.getRuntime();
String OS = System.getProperty("os.name").toLowerCase();
// System.out.println(OS);
if (OS.indexOf("windows 9") > -1) {
  p = r.exec( "command.com /c set" );
}
else if ( (OS.indexOf("nt") > -1)
       || (OS.indexOf("windows 2000") > -1 )
       || (OS.indexOf("windows xp") > -1) ) {
  // thanks to JuanFran for the xp fix!
  p = r.exec( "cmd.exe /c set" );
}

Although you can access Java variables thanks to System.getProperties(); But you would only get some env variables mapped by JVM itself, and additional data you could provide on java command line with "-Dkey=value"

For more information see http://www.rgagnon.com/javadetails/java-0150.html

Answer 2

You can use getEnv() to get environment variables:

String variable = System.getenv("WINDIR");  
System.out.println(variable);  

I believe the getEnv() function was deprecated at some point but then "undeprecated" later in java 1.5

ETA:

I see the question now refers specifically to java 1.4, so this wouldn't work for you (or at least you might end up with a deprecation warning). I'll leave the answer here though in case someone else stumbles across this question and is using a later version.

Answer 3

There's a switch to the JVM for this. From here:

Start the JVM with the "-D" switch to pass properties to the application and read them with the System.getProperty() method.

SET myvar=Hello world
SET myothervar=nothing
java -Dmyvar="%myvar%" -Dmyothervar="%myothervar%" myClass

then in myClass

String myvar = System.getProperty("myvar");
String myothervar = System.getProperty("myothervar");

Answer 4

Pass them into the JVM as -D system properties, for example:

java -D<java var>=%<environment var>%

That way you don't become tied to a particular OS.

Answer 5

Map<String, String> env = System.getenv();
for (String envName : env.keySet()) {
     System.out.format("%s=%s%n", envName, env.get(envName));
}

Answer 6

Apache Commons Exec provides with "org.apache.commons.exec.environment.EnvironmentUtils" a way to get the environment variables on JDK's prior 1.5:

(String) EnvironmentUtils.getProcEnvironment().get("SOME_ENV_VAR")