export CSV file through Java JDBC

Good morning,

Running the following command from command line is ok, but cannot export
a table into a csv file through java JDBC code.

Please help!

JAVA code:
===================
public static void exec(String command)
{
try{
Process p = Runtime.getRuntime().exec(command);
p.waitFor();
p.destroy();
}catch(Exception e) {
System.err.println("exec command Error: " + e.getMessage());
}
}

SQL Command:
=================
psql -U username -d dbName -c "\copy tableName to 'result.csv' with CSV "

When call exec(commands);

Nothing happens, result.csv was not created at all?

Thanks a lot!