why i am getting nullpointerexception in JSP page for Spring DAO methods? - spring

Question

here, whenever I trying to access or call the DAO method (which is written in #Repository class) in the JSP page in My spring MVC Project using Hibernate, it showing NullPointerException.
it works fine when I accessing this method in Controller class, it just throwing an exception in the JSP page.
and here expection i am getting,
SEVERE: Servlet.service() for servlet [jsp] threw exception
java.lang.NullPointerException
at com.lms.service.BookDetailsServiceImpl.getBookStatusForLibrarianById(BookDetailsServiceImpl.java:62)
here is my code,
in pom.xml,
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.libmansystem</groupId>
<artifactId>LibraryManagementSystems</artifactId>
<packaging>war</packaging>
<version>1.0</version>
<name>LibraryManagementSystems Maven Webapp</name>
<url>http://maven.apache.org</url>
<properties>
<springframework.version>5.0.2.RELEASE</springframework.version>
<springsecurity.version>5.0.0.RELEASE</springsecurity.version>
<hibernate.version>5.4.14.Final</hibernate.version>
<mysql.connector.version>8.0.20</mysql.connector.version>
<c3po.version>0.9.5.5</c3po.version>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>1.8</maven.compiler.source>
<maven.compiler.target>1.8</maven.compiler.target>
</properties>
<dependencies>
<!-- Spring MVC support -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>${springframework.version}</version>
</dependency>
<!-- Spring Transactions -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-tx</artifactId>
<version>${springframework.version}</version>
</dependency>
<!-- Spring ORM -->
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-orm</artifactId>
<version>${springframework.version}</version>
</dependency>
<!-- Hibernate Core -->
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-core</artifactId>
<version>${hibernate.version}</version>
</dependency>
<!-- Add MySQL and C3P0 support -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>${mysql.connector.version}</version>
</dependency>
<dependency>
<groupId>com.mchange</groupId>
<artifactId>c3p0</artifactId>
<version>${c3po.version}</version>
</dependency>
<!-- Servlet, JSP and JSTL support -->
<dependency>
<groupId>javax.servlet.jsp.jstl</groupId>
<artifactId>jstl-api</artifactId>
<version>1.2</version>
<exclusions>
<exclusion>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
</exclusion>
<exclusion>
<groupId>javax.servlet.jsp</groupId>
<artifactId>jsp-api</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.glassfish.web</groupId>
<artifactId>jstl-impl</artifactId>
<version>1.2</version>
<exclusions>
<exclusion>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
</exclusion>
<exclusion>
<groupId>javax.servlet.jsp</groupId>
<artifactId>jsp-api</artifactId>
</exclusion>
<exclusion>
<groupId>javax.servlet.jsp.jstl</groupId>
<artifactId>jstl-api</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<finalName>LibraryManagementSystems</finalName>
<pluginManagement>
<plugins>
<plugin>
<!-- Add maven co-ordinates for : maven-war-plugin -->
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>3.2.3</version>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
entity class,
#Entity
#Table(name = "book_status_forlibrarian")
public class BookStatusForLibrarian {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "s_id")
private Integer id;
#Column(name = "status")
private String status;
public BookStatusForLibrarian() {
}
public BookStatusForLibrarian(Integer id, String status) {
this.id = id;
this.status = status;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getStatus() {
return status;
}
public void setStatus(String status) {
this.status = status;
}
#Override
public String toString() {
return "BookStatusForLibrarian [id=" + id + ", status=" + status + "]";
}
}
Dao interface and class,
public interface BookDetailsDAO {
public BookStatusForLibrarian getBookStatusForLibrarianById(int statusId);
}
#Repository
public class BookDetailsDAOImpl implements BookDetailsDAO{
private SessionFactory sessionFactory;
#Autowired
public BookDetailsDAOImpl(SessionFactory sessionFactory)
{
this.sessionFactory = sessionFactory;
}
public BookDetailsDAOImpl()
{
}
#Override
public BookStatusForLibrarian getBookStatusForLibrarianById(int statusId) {
Session theSession = sessionFactory.getCurrentSession();
BookStatusForLibrarian theBookStatusForLibrarian = theSession.get(BookStatusForLibrarian.class, statusId);
return theBookStatusForLibrarian;
}
}
my service interface and class,
public interface BookDetailsService {
public BookStatusForLibrarian getBookStatusForLibrarianById(int statusId);
}
#Service
public class BookDetailsServiceImpl implements BookDetailsService {
#Autowired
BookDetailsDAO theBookDetailsDAO;
#Override
#Transactional
public BookStatusForLibrarian getBookStatusForLibrarianById(int statusId) {
System.out.println("inside service ");
return theBookDetailsDAO.getBookStatusForLibrarianById(statusId);
}
}
my controller,
#Controller
public class HomePageController {
#GetMapping("/homepage")
public String getHomePage()
{
return "homepage";
}
}
in my JSP page I am getting exception,
/WEB-INF/view/homepage.jsp,
<%#page import="com.lms.service.NonServiceMethod"%>
<%#page import="com.lms.dao.BookDetailsDAOImpl"%>
<%#page import="com.lms.service.BookDetailsServiceImpl"%>
<%#page import="com.lms.service.BookDetailsService"%>
<%#page import="com.lms.entity.BookStatusForLibrarian"%>
<%# page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%# taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%# taglib prefix="form" uri="http://www.springframework.org/tags/form" %>
<%# page isELIgnored="false"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Show All Book</title>
</head>
<body>
<%
System.out.println("getting exception while calling Spring DAO method (which is written in #Repository class) in JSP page");
BookDetailsServiceImpl theBookDetailsService = new BookDetailsServiceImpl();
BookStatusForLibrarian getBookStatus= theBookDetailsService.getBookStatusForLibrarianById(3);
%>
</body>
</html>
and here expection i am getting,
SEVERE: Servlet.service() for servlet [jsp] threw exception
java.lang.NullPointerException
at com.lms.service.BookDetailsServiceImpl.getBookStatusForLibrarianById(BookDetailsServiceImpl.java:62)
please help me.

Answer 1

If you create the service in the JSP, it is not a Spring bean. There is no dependency injection done by Spring, you DAO is not injected in your service (NullPointerException). The correct way to pass the model (BookStatusForLibrarian) into the view (JSP) is to use the Controller.
#Controller
public class HomePageController {
#Autowired
BookDetailsService bookDetailsService;
#GetMapping("/homepage")
public String getHomePage(Model model) {
BookStatusForLibrarian bookStatus = bookDetailsService.getBookStatusForLibrarianById(3);
model.addAttribute("bookStatus", bookStatus);
return "homepage";
}
}
Then you can use bookStatus directly in the JSP without <% %> just like this: ${bookStatus.id}