Java JPA获取上一个持久实体问题的ID

Question

I have read the article here but I cannot get fix my problem How to get Id of last persisted entity using JPA

I cannot get the last auto incremented primary key of the student

This is from the Servlet class

if (operation.equalsIgnoreCase("Add")) {
            student.setName(name);
            student.setAddress(address);


            int last = studentDAO.addStudent(student);
            request.setAttribute("last", last);
            request.setAttribute("student", student);

        }

This is from the session bean:

public int addStudent(Student student) {
        em.persist(student);

        em.flush();

        System.out.println(student.getStudentID());
        return student.getStudentID();
    }

I just used sout to test and see if I got the ID but it always outputs 0 every time I add a student . I cannot get the last generated id . Any help would be greatly appreciated. Thanks!

EDITED: My Student Class:

package model;

import javax.persistence.*;

@Entity
@Table
@NamedQueries({@NamedQuery(name="Student.getAll", query="Select e from Student e")})
public class Student {
    @Id
    @Column
    private int studentID;
    @Column
    private String name;
    @Column
    private String address;

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getStudentID() {
        return studentID;
    }

    public void setStudentID(int studentID) {
        this.studentID = studentID;
    }

    public Student(int studentID, String name, String address) {
        this.studentID = studentID;
        this.name = name;
        this.address = address;
    }
    public Student(){}
}

-- Solved! Answered by Peter, Thank you!

Answer 1

Id is incremented in your db? Maybe you forgot @GeneratedValue annotation above your id definition. Check this: http://www.objectdb.com/java/jpa/entity/generated