Tomcat12-Troubleshooting-Java-Exceptions

Troubleshooting Common Java Exceptions

• Below is an example of NullPointer Exception

   Exception in thread "main" java.lang.NullPointerException
    at com.example.myproject.Object1.getValue(Object1.java:16)
    at com.example.myproject.Object2.getNumericValue(Object2.java:25)
    at com.example.myproject.Object3.main(Object3.java:14)
  

  • In this case we need to navigate to the file Object1 and review the method called getValue() to determine what happened
  • The remaining lines give the further information about how the exception was arrived at.
• Most of the times we'll have something different to the above, but the above given can be taken as a basic example of how to find out the issue.
• Let us look at the below log once

   Exception in thread "main" java.lang.NullPointerException
    at com.example.myproject.Object1.getValue(Object1.java:16)
    at com.example.myproject.Object2.getNumericValue(Object2.java:25)
    at com.example.myproject.Object3.main(Object3.java:14)
   Caused by: java.lang.IllegalReferenceException
    at com.example.myproject.Object1.getParentValue(Object1.java:22)
  

  • This means that we have a NullPointer exception in Object1 at the getValue() method occured as Object1 and getParentValue() method thrown a IllegalReferenceException and this is the initial cause of the problem.
  • If we have multiple Caused by sections then the lowest is the initial cause of the problem.