How Do I Create Many to Many Hibernate Mapping for Additional Property from the Join Table?

You need to use @EmbeddedId and @Embeddable annotations to solve this issue:

Lecturer Class:

@Entity
@Table(name="LECTURER")
public class Lecturer {

@OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.lecturer", cascade=CascadeType.ALL)
Set<LecturerCourse> lecturerCourses == new HashSet<LecturerCourse>();

//all others properties Setters and getters are less relevant.

}

Course class:

@Entity
@Table(name="COURSE")
public class Course {

@OneToMany(fetch = FetchType.LAZY, mappedBy = "pk.course", cascade=CascadeType.ALL)
Set<LecturerCourse> lecturerCourses == new HashSet<LecturerCourse>();

//all others properties Setters and getters are less relevant.

}

LecturerCourse Class:

@Entity
@Table(name = "lecturer_course")
@AssociationOverrides({
        @AssociationOverride(name = "pk.lecturer", 
            joinColumns = @JoinColumn(name = "LECTURER_ID")),
        @AssociationOverride(name = "pk.course", 
            joinColumns = @JoinColumn(name = "COURSE_ID")) })
public class LecturerCourse {

    private LecturerCourseID pk = new LecturerCourseID();

    @Column(name = "CAPACITY", nullable = false, length = 10)
    private String capacity;

    @EmbeddedId
    public LecturerCourseID getPk() {
        return pk;
    }

}

Now the Primary Key:

@Embeddable
public class LecturerCourseID implements java.io.Serializable {

    private Lecturer lecturer;
    private Course course;

    @ManyToOne
    public Stock getLecturer() {
        return lecturer;
    }

    public void setLecturer(Lecturer lecturer) {
        this.lecturer= lecturer;
    }

    @ManyToOne
    public Course getCourse() {
        return course;
    }

    public void setCourse(Course course) {
        this.course= course;
    }

}

now Your Main should be something like this:

Lecturer lecturer1 = new Lecturer();
Course math = new Course();
LecturerCourse lecturer1math  = new LecturerCourse();
lecturer1math.setCapacity("capacity");
lecturer1math.setLecturer(lecturer1);
lecturer1math.setCourse(math);
lecturer1.getLecturerCourses().add(lecturer1math);

//saving object
session.save(lecturer1);

You need to be sure that class marked as @Embeddable should implement Serializable marker interface.

Hope it helps.