Question

如何在spring 3.2 mvc中接收复杂对象？

在下面的简单示例中，我有两个模型类，具有多对一关系。添加新的Employee对象时，我想使用html select来选择它的部门。

当我发帖添加新的员工时，我收到以下错误：

无法将java.lang.String类型的属性值转换为属性部门所需类型hu.pikk.model.Department;嵌套异常是java.lang.IllegalStateException：无法将类型[java.lang.String]的值转换为属性部门所需的类型[hu.pikk.model.Department]：找不到匹配的编辑器或转换策略

我应该如何实施编辑器或转换策略？是否应该注意最佳做法或陷阱？

我已经阅读了spring mvc文档，以及一些文章和stackoverflow问题，但说实话，我发现它们有点令人困惑，而且很多时候太短，太过分了。

型号：

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private int employeeId;
    @NotEmpty
    private String name;

    @ManyToOne
    @JoinColumn(name="department_id")
    private Department department;
    //getters,setters
}

@Entity
public class Department {
    @Id
    @GeneratedValue
    private int departmentId;
    @Column
    private String departmentName;

    @OneToMany
    @JoinColumn(name = "department_id")
    private List<Employee> employees;
    //getters,setters
}

在我的控制器类中：

@RequestMapping(value = "/add", method = RequestMethod.GET)
private String addNew(ModelMap model) {
    Employee newEmployee = new Employee();
    model.addAttribute("employee", newEmployee);
    model.addAttribute("departments", departmentDao.getAllDepartments());
    return "employee/add";
}
@RequestMapping(value = "/add", method = RequestMethod.POST)
private String addNewHandle(@Valid Employee employee, BindingResult bindingResult, ModelMap model, RedirectAttributes redirectAttributes) {
    if (bindingResult.hasErrors()) {
        model.addAttribute("departments", departmentDao.getAllDepartments());
        return "employee/add";
    }
    employeeDao.persist(employee);
    redirectAttributes.addFlashAttribute("added_employee", employee.getName());
    redirectAttributes.addFlashAttribute("message", "employee added...");
    return "redirect:list";     
}

在add.jsp中：

<f:form commandName="employee" action="${pageContext.request.contextPath}/employee/add" method="POST">
    <table>
        <tr>
            <td><f:label path="name">Name:</f:label></td>
            <td><f:input path="name" /></td>
            <td><f:errors path="name" class="error" /></td>
        </tr>
        <tr>
            <td><f:label path="department">Department:</f:label></td>
        <td><f:select path="department">
                <f:option value="${null}" label="NO DEPARTMENT" />
                <f:options items="${departments}" itemLabel="departmentName" itemValue="departmentId" />
            </f:select></td>
            <td><f:errors path="department" class="error" /></td>
        </tr>
    </table>
    <input type="submit" value="Add Employee">
</f:form>

Answer 1

问题是，当控制器收到POST时，它不知道如何将id字符串转换为Department对象。我发现基本上有三种方法可以解决这个问题：

不使用spring表单jstl，而是使用自定义名称的简单html选择，并在Controller中使用@RequestParam读取它，访问数据库并填充它。
实现Converter接口，并将其注册为bean。
实现PropertyEditor接口。通过扩展PropertyEditorSupport类，可以更轻松地完成此任务。

我选择了第三种选择。（稍后当我将有一些时间时，我将使用探索的前两个选项编辑此答案。）

2。实现转换器＆lt; String，Department＆gt;接口

@Component 
public class DepartmentConverter implements Converter<String,Department>{
    @Autowired
    private DepartmentDao departmentDao;
    @Override
    public Department convert(String id){
        Department department = null;
        try {
            Integer id = Integer.parseInt(text);
            department = departmentDao.getById(id);
            System.out.println("Department name:" + department.getDepartmentName());
        } catch (NumberFormatException ex) {
            System.out.println("Department will be null");
        }
        return department;
    }
}

在spring beans配置文件中：

<mvc:annotation-driven conversion-service="conversionService"/>
<bean id="conversionService"
  class="org.springframework.context.support.ConversionServiceFactoryBean">
    <property name="converters">
        <list>
            <bean class="package.DepartmentConverter"/>
        </list>
    </property>
</bean>

3。扩展PropertyEditorSupport类

public class SimpleDepartmentEditor extends PropertyEditorSupport {

    private DepartmentDao departmentDao;

    public SimpleDepartmentEditor(DepartmentDao departmentDao){
        this.departmentDao = departmentDao;
    }
    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        Department department = null;
        try {
            Integer id = Integer.parseInt(text);
            department = departmentDao.getById(id);
            System.out.println("Department name:" + department.getDepartmentName());
        } catch (NumberFormatException ex) {
            System.out.println("Department will be null");
        }
        setValue(department);
    }
}

在Controller内部，我需要添加一个@InitBinder：

    @InitBinder
    protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) {
        binder.registerCustomEditor(Department.class, new SimpleDepartmentEditor(departmentDao));
    }

Answer 2

我认为你在这里遇到了下一个情况。当Spring尝试反序列化在Employee中收到的addNewHandle实体时，它找到了String类型的属性department，但在目标实体中它有Department类型，那么，因为你有没有转换为这种转换注册，它失败了。因此，要解决此问题，您可以实现自己的转换器（Converter），它获取String并返回Department并在conversionService中注册它，或者您可以通过覆盖{{3}来实现自己的JSON反序列化策略使用department注释@JsonDeserialize(using=<your Jacson custom deserializer>.class)属性。希望这会有所帮助。

如何在弹簧3.2 mvc中接收复杂物体？

2 个答案:

2。实现转换器＆lt; String，Department＆gt;接口

3。扩展PropertyEditorSupport类