How to read Environment Variable in Java.

Question

Hi,
I am trying to read a environment variable $TMP which has a value of /apps/bea/pt847/psoft5/tmp in UNIX.
I have written the following code and getting Null pointer exception when calling the method logmessage. Any help with reading environment variable is appreciated.
public static void logMessage(String message) {
       SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss ");
       Date now = new Date();
       Properties p = null;   
       try
          p = getEnvVars("$TMP");
          System.out.println("the current value of TEMP is : " + p.getProperty("$TMP"));
       catch (Throwable e) {
          e.printStackTrace();
       try
       BufferedWriter os = new BufferedWriter(new FileWriter("/tmp/pscas_signon_log.txt", true));
       os.write(formatter.format(now));
       os.write(message);
       os.write("\n");
       os.write("tmp_env = " + p.getProperty("$TMP"));
       os.write("\n");
       os.close();
       catch(IOException _ex) { }
    public static Properties getEnvVars(String env_var) throws Throwable {
       Properties envVars = new Properties();
       Process p = Runtime.getRuntime().exec(env_var);
       BufferedReader br = new BufferedReader( new InputStreamReader( p.getInputStream() ) );
       String line = null;
       while( (line = br.readLine()) != null ) {
          int idx = line.indexOf( '=' );
          String key = line.substring( 0, idx );
          String value = line.substring( idx+1 );
          envVars.setProperty( key, value );
          // System.out.println( key + " = " + value );
       return envVars;
    }

Answer 1

Updated code:
public static void logMessage(String message) {
       SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss ");
       Date now = new Date();
       Properties p = null;   
       try
          p = getEnvVars("$TMP");
          System.out.println("the current value of TEMP is : " + System.getProperty("$TMP"));
       catch (Throwable e) {
          e.printStackTrace();
       try
       BufferedWriter os = new BufferedWriter(new FileWriter("/tmp/pscas_signon_log.txt", true));
       os.write(formatter.format(now));
       os.write(message);
       os.write("\n");
       os.write("tmp_env = " + System.getProperty("$TMP"));
       os.write("\n");
       os.close();
       catch(IOException _ex) { }
    public static Properties getEnvVars(String env_var) throws Throwable {
       Properties envVars = new Properties();
       Process p = Runtime.getRuntime().exec(env_var);
       BufferedReader br = new BufferedReader( new InputStreamReader( p.getInputStream() ) );
       String line = null;
       while( (line = br.readLine()) != null ) {
          int idx = line.indexOf( '=' );
          String key = line.substring( 0, idx );
          String value = line.substring( idx+1 );
          envVars.setProperty( key, value );
          // System.out.println( key + " = " + value );
       return envVars;
    }and this is the error message..
java.io.IOException: $TMP: not found
        at java.lang.UNIXProcess.forkAndExec(Native Method)
        at java.lang.UNIXProcess.<init>(UNIXProcess.java:72)
        at java.lang.Runtime.execInternal(Native Method)
        at java.lang.Runtime.exec(Runtime.java:602)
        at java.lang.Runtime.exec(Runtime.java:461)
        at java.lang.Runtime.exec(Runtime.java:397)
        at java.lang.Runtime.exec(Runtime.java:359)
        at SimpleCasValidator.getEnvVars(SimpleCasValidator.java:108)
        at SimpleCasValidator.logMessage(SimpleCasValidator.java:81)