Logging with NullPointerException?

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Log runtime Exceptions in Java using log4j

I am developing a desktop application. I used Log4j to write log. How can I write log with NullPointerException? I didn't predict that could happen.

Catch the exception then log it. OR, are you having trouble getting Log4J to work? — case1352, Oct 31 '12 at 02:12

score 1 · Answer 1 · answered Oct 31 '12 at 02:18

1

If you mean just how to print the exception to the log, assuming the configuration is OK:

try {
     ....something
} catch(RuntimeException e) {
     log.error("Got unexpected exception", e);
}

NullPointerException inherits from RuntimeExepction so you can safely catch it and any other runtime ones with the above code. The above code will NOT catch any exception which is inherit from Exception but not from RuntimeException.

answered Oct 31 '12 at 02:18

IllegalArgumentException

680
4
10

And `RuntimeException` inherits from `Exception`. It would be best to catch `Exception` in this case because you don't know when a `RuntimeException` would raise explicitly. – Luiggi Mendoza Oct 31 '12 at 02:22
Not sure that was the intention. He wrote "I didn't predict that could happen" so I assumed he want to catch only exceptions which are unpredictable. I know that's not the best design, and it's really up to the developer if he wishes to catch all types, like with Throwable or only a portion which he can't handle explicitly. – IllegalArgumentException Oct 31 '12 at 02:25

Metalhead · Answer 2 · 2012-10-31T02:28:03.917

If I understand your question properly, you do not want to put Try catch statements throughout your code to handle NullPointer Exception as it is not expected.

Simple way to handle is to put a null check before using the object reference for any operation. Also , place these null checks only on those objects where you can expect that it might not be initialized due to some other exception or error scenario.

i.e

if (objectReference!=null)
           objectReference.CallSomeMethod();

Another example

String listofDefaulters =null;
  String defaulters = getDefauter();
/**you might expect that you will always get defaulters from the method call but it might happen dat it can return null value also. 
 So always put a null check where you are not 100% sure if value will not be null**/
  if (defaulters !=null)
     defaulters.doSomeOperation();

score 0 · Answer 3 · answered Oct 31 '12 at 02:25

If you want to do aspect oriented programming, you may want to write an advice around Exception including NullPointerException and perform the logging e.g. below:

 @Aspect
 public class ExceptionLogging {
   private static Logger log = null;

   @Pointcut ("call(* *.*(..)))
   public void exceptionLogMethods(){
   }

   @AfterThrowing(pointcut="exceptionLogMethods()", throwing="e")
   public void handleException(Throwable ex, JoinPoint jointPoint) {
      log = Logger.getLogger(jointPoint.getThis().getClass());
      log.debug(jointPoint.getThis().getClass() + ex.getMessage());
   }
  }

score 0 · Answer 4 · answered Oct 31 '12 at 02:32

You can use the class Preconditions too in the Guava libraries for customize the exceptions and the messages.

The method Preconditions#checkNotNull(T, java.lang.Object) throws a NullPointerException if the reference T is null.

void method(String name) {
    Preconditions.checkNotNull(name, "The name is null.");

    // do something with the name
}

void otherMethod() {
    try {
        method("zerone"); // OK
        method(null); // throws NPE
    } catch(RuntimeExcetion e) {
        LOG.error(e.getMessage(), e);  // Message: "The name is null."
    }
}

Logging with NullPointerException?

4 Answers4