Question

I came across to problem with ManyToMany relations between Restaurant and Tag class. I got:

public class Tag {
    @Id
    private int id;
    private String name;
    @ManyToMany
    @JoinTable(name="restaurant_tag",
            joinColumns={@JoinColumn(name="tag_id")},
            inverseJoinColumns={@JoinColumn(name="restaurant_id")})
    private List<Restaurant> restaurants;

and:

public class Restaurant {
    @Id
    @GeneratedValue
    private int id;
    (...)
    @ManyToMany
    @JoinTable(name="restaurant_tag",
            joinColumns={@JoinColumn(name="restaurant_id")},
            inverseJoinColumns={@JoinColumn(name="tag_id")})
    private List<Tag> tags;

In my jsp I got:

<form:select multiple="true" path="tags">
<form:options items="${tagList }" itemValue="id" itemLabel="name" />
</form:select>

In my controller I got:

public ModelAndView myrestaurantadd(HttpServletRequest request,
            HttpServletResponse response, Restaurant restaurant)
            throws Exception {
restaurantDAO.saveRestaurant(restaurant);
}

When I click save button, I got error:

Field error in object ‘command’ on field ‘tags’: rejected value [[Ljava.lang.String;@5babd8cb]; codes [typeMismatch.command.tags,typeMismatch.tags,typeMismatch.java.util.List,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [command.tags,tags]; arguments []; default message [tags]]; default message [Failed to convert property value of type [java.lang.String[]] to required type [java.util.List] for property ‘tags’; nested exception is java.lang.IllegalArgumentException: Cannot convert value of type [java.lang.String] to required type [beans.Tag] for property ‘tags[0]’: no matching editors or conversion strategy found]] with root cause
org.springframework.validation.BindException: org.springframework.validation.BeanPropertyBindingResult: 1 errors

Answer 1

 [Failed to convert property value of type [java.lang.String[]] to required type [java.util.List] for property 'tags'; 

How are you handling the object at your controller. You must be accepting java.util.List in the controller handler method whereas the actual object passed is String[]. Try handling it as String[] and convert it to List in you controller.

EDIT:
With regards to your comment, I suspected something of that sort. The tags are passed from jsp in form of String[] tag and you are catching a Restaurant object which would need a List and hence the error. Try the following

public ModelAndView myrestaurantadd(HttpServletRequest request, HttpServletResponse response, Restaurant restaurant, String[] tags) throws Exception {
//Convert the String array into List<Tag> and set this list in the restaurant object
//Note that the Restaurant object obtained as the method argument with contain a null tag list, so you would need to set the tag list before saving
//Save the Restaurant object now
}