Unexpected NullPointerException When Parsing XML to POJOs Using JAXB 2.3.1
I'm having trouble with I'm sure I'm missing something obvious here, but I'm relatively new to this, so bear with me. I'm working with a `NullPointerException` when trying to unmarshal an XML document into a list of POJOs using JAXB version 2.3.1. The XML structure contains nested elements, and I'm using annotations on my Java classes to define the mapping. Here’s the XML input I'm working with: ```xml <library> <book> <title>Effective Java</title> <author>Joshua Bloch</author> </book> <book> <title>Clean Code</title> <author>Robert C. Martin</author> </book> </library> ``` My POJO classes are structured like this: ```java import javax.xml.bind.annotation.*; import java.util.List; @XmlRootElement(name = "library") @XmlAccessorType(XmlAccessType.FIELD) public class Library { @XmlElement(name = "book") private List<Book> books; // getters and setters } @XmlAccessorType(XmlAccessType.FIELD) public class Book { private String title; private String author; // getters and setters } ``` When I attempt to unmarshal the XML, I use the following code: ```java JAXBContext context = JAXBContext.newInstance(Library.class); Unmarshaller unmarshaller = context.createUnmarshaller(); Library library = (Library) unmarshaller.unmarshal(new File("library.xml")); ``` However, I receive a `NullPointerException` on the line where I attempt to access the `books` list in my `Library` class after unmarshalling. I’ve double-checked the XML structure and the field names in my POJOs, and they seem to match correctly. I've also tried adding `@XmlElementWrapper(name = "books")` to the `books` list field, but that didn't solve the scenario. I’m not sure what else to check or adjust to resolve this question. Can anyone point me in the right direction? Am I missing something in the JAXB annotations or configuration? Am I missing something obvious? Is there a better approach? My team is using Java for this application. What am I doing wrong?