I've had instances of our Java code catch a NullPointerException
, but when I try to log the StackTrace (which basically ends up calling Throwable.printStackTrace()
), all I get is:
java.lang.NullPointerException
Has anyone else come across this? I tried googling for "java null pointer empty stack trace" but didn't come across anything like this.
In Java, the java. lang. NullPointerException is thrown when a reference variable is accessed (or de-referenced) and is not pointing to any object. This error can be resolved by using a try-catch block or an if-else condition to check if a reference variable is null before dereferencing it.
Simply put, a stack trace is a representation of a call stack at a certain point in time, with each element representing a method invocation. The stack trace contains all invocations from the start of a thread until the point it's generated. This is usually a position at which an exception takes place.
How to avoid the NullPointerException? To avoid the NullPointerException, we must ensure that all the objects are initialized properly, before you use them. When we declare a reference variable, we must verify that object is not null, before we request a method or a field from the objects.
What Causes NullPointerException. The NullPointerException occurs due to a situation in application code where an uninitialized object is attempted to be accessed or modified. Essentially, this means the object reference does not point anywhere and has a null value.
You are probably using the HotSpot JVM (originally by Sun Microsystems, later bought by Oracle, part of the OpenJDK), which performs a lot of optimization. To get the stack traces back, you need to pass the option -XX:-OmitStackTraceInFastThrow
to the JVM.
The optimization is that when an exception (typically a NullPointerException) occurs for the first time, the full stack trace is printed and the JVM remembers the stack trace (or maybe just the location of the code). When that exception occurs often enough, the stack trace is not printed anymore, both to achieve better performance and not to flood the log with identical stack traces.
To see how this is implemented in the HotSpot JVM, grab a copy of it and search for the global variable OmitStackTraceInFastThrow
. Last time I looked at the code (in 2019), it was in the file graphKit.cpp.
As you mentioned in a comment, you're using log4j. I discovered (inadvertently) a place where I had written
LOG.error(exc);
instead of the typical
LOG.error("Some informative message", e);
through laziness or perhaps just not thinking about it. The unfortunate part of this is that it doesn't behave as you expect. The logger API actually takes Object as the first argument, not a string - and then it calls toString() on the argument. So instead of getting the nice pretty stack trace, it just prints out the toString - which in the case of NPE is pretty useless.
Perhaps this is what you're experiencing?
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