spring mvc的表单类型转换(custom property editor)

spring mvc的表单类型转换太强大了，目前用到了两个简单的，

一个是将表单中的file自动映射成byte[],这样文件上传（如果使用blob）就无需写任何代码了。

另一个是将表单中的yyyy-MM-dd格式映射成java.util.Date，

假设User.java中有如下这两种特殊的属性：

public class User implements Serializable{    private Date birth;    private byte[] icon;}```注册这两种属性编辑器只需在Controller中定义如下这样一个initBinder方法:<div class="se-preview-section-delimiter"></div>

这里写代码片
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@Controller("userController")@RequestMapping(value = "/user")public class UserController {    @RequestMapping(value = "create", method = RequestMethod.POST)    public String create(@ModelAttribute("user") User user,            RedirectAttributes redirectAttributes) {        userService.createUser(user);        redirectAttributes.addFlashAttribute("message", "create success!");        return SUCCESS;    }        @InitBinder    protected void initBinder(            WebDataBinder binder) throws ServletException {        binder.registerCustomEditor(byte[].class,                new ByteArrayMultipartFileEditor());                 SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");                dateFormat.setLenient(false);                binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));    }}

ByteArrayMultipartFileEditor和CustomDateEditor都是spring直接提供的。
自定义的：

  public class User implements Serializable{    public Set<Role> roles = new HashSet<Role>();    }

public class Role implements Serializable {    private Long id;    private String name;

UserController如下：

@RequestMapping(value = "create", method = RequestMethod.GET)public String createForm(ModelMap model) {    model.addAttribute("roleList", roleService.findAllRoles());    User user = new User();    model.addAttribute(user);    return "user/user_new";}

public class RoleEditor extends PropertyEditorSupport {2    private RoleService roleService;    public RoleEditor(RoleService roleService) {        this.roleService = roleService;    }    @Override    public void setAsText(String text) throws IllegalArgumentException {        if (text != null) {            Role role = roleService.findRoleById(Long.valueOf(text));            setValue(role);        } else {            setValue(null);        }    }}

并在UserController中的initBinder方法中注册该编辑器

@InitBinderprotected void initBinder(        WebDataBinder binder) throws ServletException {    //@see http://forum.springsource.org/showthread.php?59612-Service-injection-amp-PropertyEditor    binder.registerCustomEditor(Role.class, new RoleEditor(roleService));}

这时在UserController的create方法中取得的User对象就是已经绑定了roles的了

@RequestMapping(value = "create", method = RequestMethod.POST)public String create(@ModelAttribute("user") User user,        RedirectAttributes redirectAttributes) {    userService.createUser(user);    redirectAttributes.addFlashAttribute("message", "create success!");    return SUCCESS;}

值得注意的是，你必须要覆写Role的equals和hashCode方法，不然当你进入修改页面时，user的role属性不会自动的check上。