Spring MVC - 是否存在显示表单验证错误消息的替代方法（不使用@ModelAtrribute和@Valid）？

Question

Trying to get Spring annotation based validation working in a simple webapp. While using @ModelAttribute along with @Valid, I am getting validation error next to the field, however when I am adding object to model, not getting error messages.

Suggest any alternative approach to display form validation error message(ie without using @ModelAtrribute along with @Valid)

Below is the code:

EmployeeModel.java

@Entity
@Table(name = "Employee")
public class EmployeeModel implements Serializable {

    /**
     *
     */
    private static final long serialVersionUID = 1L;

    @Id
    @Column(name = "ID")
    @NotNull(message = "ID is required")
    private Integer employee_id;

    @Column(name = "Name")
    @NotEmpty(message = "Name is required")
    private String employee_name;

    @Column(name = "Manager")
    private String manager;

    public Integer getEmployee_id() {
        return employee_id;
    }

    public void setEmployee_id(Integer employee_id) {
        this.employee_id = employee_id;
    }

    public String getEmployee_name() {
        return employee_name;
    }

    public void setEmployee_name(String employee_name) {
        this.employee_name = employee_name;
    }

    public String getManager() {
        return manager;
    }

    public void setManager(String manager) {
        this.manager = manager;
    }

    @Override
    public String toString() {
        return "Employee [id=" + employee_id + ", Name=" + employee_name
                + ", Manager=" + manager + "]";
    }
}

Code snippet in Controller

@RequestMapping(value = "/save", method = RequestMethod.POST)
public String saveEmployee(Model model, @Valid EmployeeModel employee, BindingResult result) {
    if (result.hasErrors()) {
        model.addAttribute("employee", employee);
        //model.addAttribute(employee);
        return "EmployeeForm";
    }
    employeeService.addEmployee(employee);
    return "forward:/";
}

View:

<form:form action="save" method="post" modelAttribute="employee">
                <tr>
                    <td><form:label path="employee_id">Employee ID:</form:label></td>
                    <td><form:input path="employee_id" /></td>
                    <td><form:errors path="employee_id"/></td>
                </tr>
                <tr>
                    <td><form:label path="employee_name">Employee Name:</form:label></td>
                    <td><form:input path="employee_name" /></td>
                    <td><form:errors path="employee_name"/></td>
                </tr>
                <tr>
                    <td><form:label path="manager">Manager:</form:label></td>
                    <td><form:input path="manager" /></td>
                </tr>
                <tr>
                    <td colspan="2" align="center"><input type="submit"
                        value="Save"></td>
                </tr>
            </form:form>

In case I use the commented line

//model.addAttribute(employee)

I get exception stating: java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'employee' available as request attribute.

Replacing the commented line with

model.addAttribute("employee",employee)

Page gets loaded with the previous value entered which means invalid object is not getting replaced, still error message is not displayed.

The above can be achieved using @ModelAttribute along with @Valid, but is there any other alternative ie without using @ModelAtrribute?

What is the difference in working with @ModelAttribute and Model, as till now I considered both works in similar way?

Answer 1

@ModelAttribute populates the fields of a class, which then populates an attribute of the model to be passed back to the view.

Also you make following change on your saveEmployee method. You do not need to add attribute to model. @ModelAttribute automatically add for you.

@RequestMapping(value = "/save", method = RequestMethod.POST)
public String saveEmployee(@Valid @ModelAttribute(name = "employee") EmployeeModel employee, BindingResult result) {
    if (result.hasErrors()) {
        return "EmployeeForm";
    }
    employeeService.addEmployee(employee);
    return "forward:/";
}