@Entity
public class Employee implements Serializable{
    private Set<Department> departments = new HashSet<Department>();//所属部门
    @ManyToMany(cascade=CascadeType.REFRESH, fetch=FetchType.EAGER)
    @JoinTable(name="employee_department", joinColumns=@JoinColumn(name="username"),
            inverseJoinColumns=@JoinColumn(name="department_id"))
    public Set<Department> getDepartments() {
        return departments;
    }
    public void setDepartments(Set<Department> departments) {
        this.departments = departments;
    }
    
    public void addDepartment(Department department){
        if(!this.departments.contains(department)) this.departments.add(department);
    }
    public void removeDepartment(Department department){
        if(this.departments.contains(department)) this.departments.remove(department);
    }
}

@Entity
public class Department implements Serializable{

    private Set<Employee> employees = new HashSet<Employee>();//员工
        @ManyToMany(mappedBy="departments", cascade=CascadeType.REFRESH)
    public Set<Employee> getEmployees() {
        return employees;
    }
    public void setEmployees(Set<Employee> employees) {
        this.employees = employees;
    }

    public String list(){
        StringBuffer hql = new StringBuffer();
        hql.append("o.visible=?");
        List pr = new ArrayList();
        pr.add(true);
        if("true".equals(ef.getQuery())) { 
            if(ef.getDepartment()!=null && !"".equals(ef.getDepartment())) {
                System.out.println(ef.getDepartment());
                hql.append(" and o.departments in (select d from Department d where id =?)");//问题是这句hql怎么写
                pr.add(ef.getDepartment());//ef.getDepartment()接收回来的部门id,初始化问号

            }
        }
        pl = new PageList<Employee>(Integer.valueOf(ReadMessageConnection.getMessageConnection("employeePageSize")), ef.getFirstIndex());
        pl.setQueryResult(employeeManager.getScrollData(Employee.class, pl.getFirstindex(), pl
                .getMaxresult(), hql.toString(), pr.toArray()));
        return "list";
    }