When passing a -D parameter in Java, what is the proper way of writing the command-line and then accessing it from code?
For example, I have tried writing something like this...
if (System.getProperty("test").equalsIgnoreCase("true"))
{
//Do something
}
And then calling it like this...
java -jar myApplication.jar -Dtest="true"
But I receive a NullPointerException. What am I doing wrong?
I suspect the problem is that you've put the "-D" after the -jar. Try this:
java -Dtest="true" -jar myApplication.jar
From the command line help:
java [-options] -jar jarfile [args...]
In other words, the way you've got it at the moment will treat -Dtest="true" as one of the arguments to pass to main instead of as a JVM argument.
(You should probably also drop the quotes, but it may well work anyway - it probably depends on your shell.)
That should be:
java -Dtest="true" -jar myApplication.jar
Then the following will return the value:
System.getProperty("test");
The value could be null, though, so guard against an exception using a Boolean:
boolean b = Boolean.parseBoolean( System.getProperty( "test" ) );
Note that the getBoolean method delegates the system property value, simplifying the code to:
if( Boolean.getBoolean( "test" ) ) {
// ...
}
Integer.getInteger("test"); Long.getLong("test") assuming you have -Dtest=123You're giving parameters to your program instead to Java. Use
java -Dtest="true" -jar myApplication.jar
instead.
Consider using
"true".equalsIgnoreCase(System.getProperty("test"))
to avoid the NPE. But do not use "Yoda conditions" always without thinking, sometimes throwing the NPE is the right behavior and sometimes something like
System.getProperty("test") == null || System.getProperty("test").equalsIgnoreCase("true")
is right (providing default true). A shorter possibility is
!"false".equalsIgnoreCase(System.getProperty("test"))
but not using double negation doesn't make it less hard to misunderstand.
System.getProperty("test", "true").equalsIgnoreCase("true") would be the better way to write the last condition.
compareToIgnoreCaseinstead ofequalsIgnoreCasefor locale-agnostic identifiers; otherwise you may run into the Turkish four-Is problem, among others.