Need help with EJB3.0 Stateless Session Bean code

[Ravi Desigan]

Hello,

Recently in an interview they asked me to develop code for the following scenario:

Student: ID, Name
Course: ID, Name
A student can take many courses and a course can have many students.
1).Write skeleton code of entity bean (or whatever technologies you like) classes to model Student and Course and student course registration.
2). Write a skeleton Student DAO class that support
2.1). add a new student along with their course registrations.
2.2). Delete a student.
2.3).Get all students, sorted by their name, for a given course with course name as input.
Bonus Points:
2.4). What if we want to record course scores?  What possible changes need to be made?
                       Explain briefly.
2.5). How to find all students who don’t register for a given course?  

I am a self-learner and a newcomer to EJB3.0, I wrote the code as given in the attachments. They failed me. What have I done wrong?

This is my EJB3.0 Stateless Session Bean that caters to the business requirements:

@Stateless
@TransactionManagement(TransactionManagementType.CONTAINER)
public class CourseManagerBean implements CourseManager {
	@Resource
	private SessionContext context;
	
	@PersistenceContext(unitName="myPersistenceUnit") 
	private EntityManager entityManager;
	
	public CourseManagerBean() {}
	
	@TransactionAttribute(TransactionAttributeType.REQUIRED)
	public void addStudent(String id, String name, Set<Course> courses)
	{
		try 
		{
			Student student = new Student();
			student.setStudentId(id);
			student.setStudentName(name);
			student.setCourses(myCourses);
			entityManager.persist(student);
	   	} catch (Throwable th) {
			context.setRollbackOnly();
		}
	}
	
	@TransactionAttribute(TransactionAttributeType.REQUIRED)
	public void deleteStudent(String id) 
	{
		try 
		{
			entityManager.remove(entityManager.merge(id));
    	} catch (Throwable th) {
			context.setRollbackOnly();
		}
	}

	@TransactionAttribute(TransactionAttributeType.REQUIRED)
	public ArrayList<Student> getSortedStudentList(String course)
	{
		try {
			StudentComparator sc = new StudentComparator();
			Course student_course = (Course) entityManager.createQuery("Select object (o) from Course o "
		 		+ " where o.courseId like '%course%'").getSingleResult();
		 
			ArrayList<Student> myStudents = new ArrayList<Student>(Arrays.asList(student_course.getStudents()));
			return myStudents.sort(sc);
		} catch (Throwable th) {
			context.setRollbackOnly();
		}
	
	}
	
	@TransactionAttribute(TransactionAttributeType.REQUIRED)
	public ArrayList<Student> getStudentNotInCourse(String course)
	{
		try 
		{
			Query q = entityManager.createNativeQuery("Select s.Student_id from Student s "
					+ "where not exists (Select sc.sc_Student_id from Student_Course sc where "
					+ "sc.sc_student_id = s.Student_id " 
					+ "and sc.sc_course_id = ?)", myPersistenceUnit.persistence.Student.class) ;
			q.setParameter(1, course);
			return new ArrayList<Student>(Arrays.asList(q.getResultList()));
		} catch (Throwable th) {
			context.setRollbackOnly();
		}
    
	}
	
	@TransactionAttribute(TransactionAttributeType.REQUIRED)
	public void addScore(String studentId, String courseId, float score)
	{
		 try
		 {
		     Query query = entityManager.createQuery("UPDATE STUDENT_COURSE e SET "
					 + "e.COURSE_SCORE = ? where e.COURSE_ID = ? and e.STUDENT_ID = ? ");
			 query.setParameter(1, score);
			 query.setParameter(2, courseId);
			 query.setParamater(3, studentId);
			 query.executeUpdate();
		 } catch (Throwable th) {
			 context.setRollbackOnly();
		 } 
	}
	
}

Here are my 2 Entity Beans: Student and Course

@Entity 
@Table(name = "STUDENT") 
public class Student implements java.io.Serializable 
{ 
	
	private String studentId;
	private String studentName;
	private Set<Course> studentCourses;
	
	public Student() {
		  
	}
	  
	public Student(String id, String name, Set<Course> courses) {
	  studentId = id;
	  studentName = name;
	  studentCourses = courses;
	}
	
	@ManyToMany
	  @JoinTable(name="STUDENT_COURSE",
	       joinColumns=
	                @JoinColumn(name="SC_STUDENT_ID",
	                     referencedColumnName="STUDENT_ID"),
	       inverseJoinColumns=
	                @JoinColumn(name="SC_COURSE_ID",
	                     referencedColumnName="COURSE_ID") )
	public Set<Course> getCourses(){
		return this.studentCourses;
	}
	
	public void setCourses(Set<Course> courses) {
		studentCourses = courses;
	}
	  
	
   @Id 
   @Column(name="STUDENT_ID", nullable=false) 
   public String getStudentId() {
   	  return studentId;
   }
  
   public void setStudentId(String id) {
	  this.studentId = id;
   }
  
   @Column(name="STUDENT_NAME", nullable=false)
   public String getStudentName() {
	  return this.studentName;
   }
  
   public void setStudentName(String name) {
	  this.studentName = name;
   }
}

@Entity
@Table(name="COURSE")
public class Course implements java.io.Serializable
{
	private String courseId;
	private String courseName;
	private Set<Student> students;
	
	public Course() {
		
	}
	
	public Course(String courseId, String courseName, Set<Student> students)
	{
		this.courseId = courseId;
		this.courseName = courseName;
		this.students = students;
	}
	
	@ManyToMany
	  @JoinTable(name="STUDENT_COURSE",
	       joinColumns=
	                @JoinColumn(name="SC_COURSE_ID",
	                     referencedColumnName="COURSE_ID"),
	       inverseJoinColumns=
	                @JoinColumn(name="SC_STUDENT_ID",
	                     referencedColumnName="STUDENT_ID") )
	public Set<Student> getStudents() 
	{
		return students;
	}
	
	public void setStudents(Set<Student> students) 
	{
		this.students = students;
	}
	
	 @Id 
	 @Column(name="COURSE_ID", nullable=false) 
	 public String getCourseId() 
	 {
		 return courseId;
	 }
	
	 public void setCourseId(String courseId) 
	 {
		 this.courseId = courseId;
	 }
	 
	 @Column(name="COURSE_NAME", nullable=false)
	 public String getCourseName() 
	 {
		 return courseName;
	 }
	 
	 public void setCourseName(String courseName)
	 {
		 this.courseName = courseName;
	 }
}

[Ravi Desigan]

Here are my 3 tables, STUDENT, COURSE AND STUDENT_COURSE:

CREATE TABLE STUDENT (   STUDENT_ID    VARCHAR2(10) NOT NULL,   STUDENT_NAME  VARCHAR2(50) NOT NULL,   PRIMARY KEY(STUDENT_ID) ); CREATE TABLE COURSE (   COURSE_ID     VARCHAR2(10) NOT NULL,   COURSE_NAME   VARCHAR2(50) NOT NULL,   PRIMARY KEY(COURSE_ID) ); CREATE TABLE STUDENT_COURSE (    SC_STUDENT_ID    VARCHAR2(10) NOT NULL,    SC_COURSE_ID     VARCHAR2(10) NOT NULL,    PRIMARY KEY(SC_STUDENT_ID, SC_COURSE_ID),    FOREIGN KEY(SC_STUDENT_ID) REFERENCES STUDENT(STUDENT_ID) ON UPDATE CASCADE ON DELETE RESTRICT,    FOREIGN KEY(SC_COURSE_ID) REFERENCES COURSE(COURSE_ID) ON UPDATE CASCADE ON DELETE RESTRICT );

[Frits Walraven]

I am a self-learner and a newcomer to EJB3.0, I wrote the code as given in the attachments. They failed me. What have I done wrong?

Did they tell you why they weren't happy with your effort?

I find it a brave attempt but I have some questions/remarks:

where is your DAO  "2). Write a skeleton Student DAO class that support"

In a bidirectional @ManyToMany relationship you need to designate an owner (by the mappedBy element of the annotation) otherwise you create 2 unidirectional relationships

Why do you have try-catch blocks?

[Ravi Desigan]

Hello,

Thanks for the reply.

I find it extremely tough to learn EJB3.1 on my own, because I am unable to set-up a successful test environment using Software/tools.

I have read a lot since the above interviewers failed me (I couldn't ask them for clarifications as they had sent me home this test via some recruiters) and I changed my entities to what it appears like below in quotes.

I think they mean by DAO class, the Session bean which will access the database using NamedQuery, NativeQuery and such. I am still working on the right version of this, but have attached the version I started with in the original reply in quotes.

Please see my newly modified entities, I have included mappedBy clause as per your valuable suggestion.

The STUDENT Entity Bean:

import java.util.Set;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.JoinColumn;

@Entity 
@Table(name = "STUDENT") 
public class Student implements java.io.Serializable 
{ 
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	private int studentId;
	private String studentName;
	private Set<Course> courses;
	
	public Student() {
		  
	}
	  
	public Student(int id, String name) {
	  studentId = id;
	  studentName = name;
	}
	
	public Course addCourse(Course inCourse) {
		this.getCourses().add(inCourse);
		inCourse.addStudent(this);
		return inCourse;
	}
	
	public Course removeCourse(Course inCourse) {
		getCourses().remove(inCourse);
		inCourse.removeStudent(this);
		return inCourse;
	}

	
	@ManyToMany
	  @JoinTable(name="STUDENT_COURSE",
	       joinColumns=
	                @JoinColumn(name="SC_STUDENT_ID",
	                     referencedColumnName="STUDENT_ID"),
	       inverseJoinColumns=
	                @JoinColumn(name="SC_COURSE_ID",
	                     referencedColumnName="COURSE_ID") )
	public Set<Course> getCourses(){
		return this.courses;
	}
	
	public void setCourses(Set<Course> courses) {
		courses = courses;
	}
	  
	
   @Id 
   @Column(name="STUDENT_ID", nullable=false) 
   public int getStudentId() {
   	  return studentId;
   }
  
   public void setStudentId(int id) {
	  this.studentId = id;
   }
  
   @Column(name="STUDENT_NAME", nullable=false)
   public String getStudentName() {
	  return this.studentName;
   }
  
   public void setStudentName(String name) {
	  this.studentName = name;
   }
}
 

The COURSE Entity bean:

import java.util.Set;
import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;
import javax.persistence.Table;
import javax.persistence.JoinColumn;

@Entity
@Table(name="COURSE")
public class Course implements Serializable
{
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	private int courseId;
	private String courseName;
    private Set<Student> students;
		
	
	public Course() {
		
	}
	
	public Course(int courseId, String courseName)
	{
		this.courseId = courseId;
		this.courseName = courseName;
	}
	
	 @Id 
	 @Column(name="COURSE_ID", nullable=false) 
	 public int getCourseId() 
	 {
		 return courseId;
	 }
	
	 public void setCourseId(int courseId) 
	 {
		 this.courseId = courseId;
	 }
	 
	 @Column(name="COURSE_NAME", nullable=false)
	 public String getCourseName() 
	 {
		 return courseName;
	 }
	 
	 public void setCourseName(String courseName)
	 {
		 this.courseName = courseName;
	 }
	 
	 @ManyToMany(mappedBy = "courses")
     public Set<Student> getStudents() 
		{
			return students;
		}
		
		public void setStudents(Set<Student> students) 
		{
			this.students = students;
		}
		
		public void addStudent(Student s1) {
			
			this.getStudents().add(s1);
		
		}
		
		public void removeStudent(Student s1) {
			this.getStudents().remove(s1);
		}
}
 

[Frits Walraven]

I find it extremely tough to learn EJB3.1 on my own, because I am unable to set-up a successful test environment using Software/tools.

I could help you with this, what have you been using until now? And where did you get stuck? I am using the following tools:

Eclipse (Juno)

Derby database (db-derby-10.11.1.1)

Squirrel - to check the database

I think they mean by DAO class, the Session bean which will access the database using NamedQuery, NativeQuery and such.

The DAO normally is a seperate class in a seperate layer of your application. I would suggest using a CDI bean for this (EJB is to heavy for this and the overall transaction is managed from your CourseManagerBean).

You would get something like this:

@Stateless
@TransactionManagement(TransactionManagementType.CONTAINER)  // default so no need to specify
public class CourseManagerBean implements CourseManager {
    @Inject
    private CourseDao dao
     
    public CourseManagerBean() {} // default, so no need to specify
     
    @TransactionAttribute(TransactionAttributeType.REQUIRED) // default, so no need to specify
    public void addStudent(String id, String name, Set<Course> courses)
    {
       Student student = new Student();
       student.setStudentId(id);
       student.setStudentName(name);
       student.setCourses(myCourses);
       dao.addStudent(student);
    }
}

and

public class CourseDao implements CourseService {

    @PersistenceContext(unitName="myPersistenceUnit") 
    private EntityManager entityManager;

    public void addStudent(String id, String name, Set<Course> courses)
    {
        entityManager.persist(student);
    }
   
}

Another question: have you thought about cascade options?

[Ravi Desigan]

Oh, if you or someone could help me with Software setup, that would be the best award for me!

I have installed Eclipse - Indigo, MYSQL database and Jboss application server version 7.1.1 Final.

Initially I had installed Eclipse Neon, but on learning the hardway it does not work with JDK1.8, I uninstalled it. And then I installed Eclipse Indigo.

Now I am able to deploy my EJB into Jboss 7.1.1 server under Eclipse Indigo and am able to connect with database.

But on client EJB launch as Java Application, I am getting a SASL exception which says, all authentication mechanisms failed.

This is the exact error I am getting:

ERROR: JBREM000200: Remote connection failed: javax.security.sasl.SaslException: Authentication failed: all available authentication mechanisms failed
javax.naming.NamingException: Failed to create remoting connection [Root exception is java.lang.RuntimeException: javax.security.sasl.SaslException: Authentication failed: all available authentication mechanisms failed]
at org.jboss.naming.remote.client.ClientUtil.namingException(ClientUtil.java:36)
at org.jboss.naming.remote.client.InitialContextFactory.getInitialContext(InitialContextFactory.java:121)
at javax.naming.spi.NamingManager.getInitialContext(NamingManager.java:684)
at javax.naming.InitialContext.getDefaultInitCtx(InitialContext.java:307)
at javax.naming.InitialContext.init(InitialContext.java:242)
at javax.naming.InitialContext.<init>(InitialContext.java:216)
at jayashree.statestreettest.clientutility.JNDIlookup.getInitialContext(JNDIlookup.java:22)
at jayashree.statestreettest.client.CreateStudentClient.doLookup(CreateStudentClient.java:58)
at jayashree.statestreettest.client.CreateStudentClient.main(CreateStudentClient.java:40)
Caused by: java.lang.RuntimeException: javax.security.sasl.SaslException: Authentication failed: all available authentication mechanisms failed
at org.jboss.naming.remote.protocol.IoFutureHelper.get(IoFutureHelper.java:87)
at org.jboss.naming.remote.client.NamingStoreCache.getRemoteNamingStore(NamingStoreCache.java:56)
at org.jboss.naming.remote.client.InitialContextFactory.getOrCreateCachedNamingStore(InitialContextFactory.java:166)
at org.jboss.naming.remote.client.InitialContextFactory.getOrCreateNamingStore(InitialContextFactory.java:139)
at org.jboss.naming.remote.client.InitialContextFactory.getInitialContext(InitialContextFactory.java:104)
... 7 more
Caused by: javax.security.sasl.SaslException: Authentication failed: all available authentication mechanisms failed
at org.jboss.remoting3.remote.ClientConnectionOpenListener$Capabilities.handleEvent(ClientConnectionOpenListener.java:365)
at org.jboss.remoting3.remote.ClientConnectionOpenListener$Capabilities.handleEvent(ClientConnectionOpenListener.java:214)
at org.xnio.ChannelListeners.invokeChannelListener(ChannelListeners.java:72)
at org.xnio.channels.TranslatingSuspendableChannel.handleReadable(TranslatingSuspendableChannel.java:189)
at org.xnio.channels.TranslatingSuspendableChannel$1.handleEvent(TranslatingSuspendableChannel.java:103)
at org.xnio.ChannelListeners.invokeChannelListener(ChannelListeners.java:72)
at org.xnio.nio.NioHandle.run(NioHandle.java:90)
at org.xnio.nio.WorkerThread.run(WorkerThread.java:184)
at ...asynchronous invocation...(Unknown Source)
at org.jboss.remoting3.EndpointImpl.doConnect(EndpointImpl.java:270)
at org.jboss.remoting3.EndpointImpl.doConnect(EndpointImpl.java:251)
at org.jboss.remoting3.EndpointImpl.connect(EndpointImpl.java:349)
at org.jboss.remoting3.EndpointImpl.connect(EndpointImpl.java:333)
at org.jboss.naming.remote.client.EndpointCache$EndpointWrapper.connect(EndpointCache.java:105)
at org.jboss.naming.remote.client.NamingStoreCache.getRemoteNamingStore(NamingStoreCache.java:55)
... 10 more
Exception in thread "main" java.lang.NullPointerException
at jayashree.statestreettest.client.CreateStudentClient.main(CreateStudentClient.java:42)

I have spent days trying to get the server work with MYSQL database and then be able to deploy my EJB. Now this! I feel like hitting on a wall.

[Frits Walraven]

But on client EJB launch as Java Application, I am getting a SASL exception which says, all authentication mechanisms failed.

The easiest way to connect as a client to an EJB is by using a Servlet. An Application client is tricky and needs some extra configuration.

Just create a Dynamic Web Project in Eclipse and inject the EJB in the Servlet. For example:

@WebServlet("/StudentCourseServlet")
public class StudentCourseServlet extends HttpServlet {

        @EJB
        private CourseManager service;
       
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
                PrintWriter writer = response.getWriter();
                writer.write("<html><head></head><body>");

                // Get your data from the request 
                String id= request.getParameter("id");
                String name= request.getParameter("name");
                String courseName= request.getParameter("course");
                
                // create a course from the String
                Course course = new Course(courseName)
                ...

                // Call your business service layer 
                Student s = service.addStudent(id, name, courses);
		
                writer.write("The student : " + s.toString() + " has been added");
                writer.write("<h1>done</h1>");
                writer.write("</body></html>"); 
        }
}

And call your EJB from a browser and provide the parameters in the URL, for example:

http://localhost:8080/StudentCourseProject/StudentCourseServlet?id=5&name=student&course=maths

[Ravi Desigan]

That is really a good suggestion. I tried to set up such an environment (that is, also including a Web project with servlet) in my Jboss environment yesterday, but there also I got some exceptions. Will try some more. Thank you very much.