从jsp页面上的select标签获取bean

Question

I use Spring, jsp and Hibernate in my project. I have two entities Employee and Department . Dapartment is a part of Employee and they have relationship one-to-many

    @Entity
    @Table(name = "employee")
    public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    @OneToOne
    @JoinColumn(name = "dep_id")
    private Department department;

I create controller, DAO and jsp pages for view.

My problem: I want to update data of Employee in my jsp page. Before this I add Employee and list of departments in model

In controller:

 model.addAttribute("employee", employeeDao.find(id));
 model.addAttribute("departments", departmentDao.list());

In JSP:

<form method="post">
   <select value="${employee.department}">
     <c:forEach items="${departments}" var ="dep">
        <option value="${dep}">${dep.name}</option>
     </c:forEach>
</form>

In controller (post request)

@RequestMapping(value = "/{id}", method = RequestMethod.POST)
    public String updateEmployee(@PathVariable("id") long id, Employee employee) {
        employee.setId(id);
        employeeDao.update(employee);

        return "redirect:/employees";
    }

but value employee.department=null Why?

Of course, on jsp page in "select" tag I can create variable dep I mean:

<select name ="dep">
   <option value="${dep.id}">${dep.name}</option>
</select>

and then in controller using id of department i will be able to get department from database and update Employee. Is it right way?

Answer 1

You have not posted your full Controller however if we assume the initial get request looks like:

@RequestMapping(value = "/{id}", method = RequestMethod.GET)
      public ModelAndView loadForEdit(@PathVariable("id") long id)
      model.addAttribute("employee", employeeDao.find(id));
      model.addAttribute("departments", departmentDao.list());
      return new ModelAndView(...);
}

Then on loadForEdit() we load an Employee and Departments for edit and set them in the model for rendering the edit page.

Now, on submit, the POST method updateEmployee(...) knows nothing about this previous Employee and Department and therefore the framework is simply passing in a new instance to updateEmployee(...).

If you refactor along the lines of the following, then on the call to both the GET and POST handlers, the method annotated with @ModelAttribute(value = "employee") will execute. In the first case it will be added to the model, as previously, and in the second case the Employee will be retrieved, the fields bound to the updated values amd will then be passed to your POST handler.

@RequestMapping(value = "/{id}", method = RequestMethod.Get)
public String loadForEdit(){
    return "nextView";
}

@RequestMapping(method = RequestMethod.POST)
public String updateEmployee(value = "/{id}", @ModelAttribute("employee") Employee employee)   
{
    return "redirect:/employees";
}

@ModelAttribute(value = "employee") 
public Employee getEmployee(@PathVariable("id") long id) 
{ 
    return  employeeDao.find(id);
}

@ModelAttribute(value = "departments") 
public List<Department>  getDepartments() 
{ 
    return  departmentDao.list());
}

There is a lot of flexibility on how you can handle this:

See 'Using @ModelAttribute on a method argument' in:

http://docs.spring.io/spring/docs/current/spring-framework-reference/html/mvc.html

@RequestMapping(value="/owners/{ownerId}/pets/{petId}/edit", method =
> RequestMethod.POST) public String processSubmit(@ModelAttribute Pet
> pet) { } 

Given the above example where can the Pet instance come from? There are several options:

1. It may already be in the model due to use of @SessionAttributes — see the section called “Using @SessionAttributes to store model attributes in the HTTP session between requests”.
2. It may already be in the model due to an @ModelAttribute method in the same controller — as explained in the previous section. [My suggestion]
3. It may be retrieved based on a URI template variable and type converter (explained in more detail below).
4. It may be instantiated using its default constructor. [current position]

Answer 2

Sory, I forgot to publish the decision to solve. Thanks to all who helped me to find right solution. In controller:

 @RequestMapping(value = "/{id}", method = RequestMethod.GET)
    public String getEmployee(@PathVariable("id") long id, Model model) {
        model.addAttribute("employee", employeeDao.find(id));
        model.addAttribute("departments", departmentDao.list());
        return "employees/view";
    }

Then we need to edit view. On JSP-page:

<%@ taglib prefix="sf" uri="http://www.springframework.org/tags/form"%>

<sf:form modelAttribute="employee" method="post">
   <sf:select path="department" id="select-departments"  >
     <c:forEach items="${departments}" var="dep" varStatus="status">
       <option value="${dep.id}">${dep.name}</option>
     </c:forEach>
   </sf:select>
</sf:form>

We also need to create department's editor:

public class DepartmentEditor extends PropertyEditorSupport {

    private DepartmentDao departmentDao;

    public DepartmentEditor(DepartmentDao departmentDao) {
        this.departmentDao = departmentDao;
    }

    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        long id = Long.parseLong(text);
        Department department = departmentDao.find(id);
        setValue(department);
    }
}

And at the and we need to add some code in controller:

 @InitBinder
    protected void initBinder(WebDataBinder binder) {
        binder.registerCustomEditor(Department.class, new DepartmentEditor(departmentDao));
    }
@RequestMapping(value = "/{id}", method = RequestMethod.POST)
    public String updateEmployee(@PathVariable("id") long id, @ModelAttribute Employee employee) {
        employee.setId(id);
        employeeDao.update(employee);
        return "redirect:/employees";
    }