CodeseniorSoftware Tutorials

@InitBinder annotations is used to resolve type mismatch and bind exceptions occured in a form application.

In this tutorial, we will try to explain how to use @InitBinder annotation to catch submitted collections in a form application.

Lets create a JSP file as follows:

<form:form commandName="belge" action="/kullanici/belge/kaydet">
    <form:select multiple="true" path="belgeSatirlar[0].gumrukKodlari">
        <c:forEach items="${gumrukler}" var="gumruk">
            <option value="${gumruk.kod}">${gumruk.aciklama}</option>
        </c:forEach>
    </form:select>
    <form:select multiple="true" path="belgeSatirlar[1].gumrukKodlari">
        <c:forEach items="${gumrukler}" var="gumruk">
            <option value="${gumruk.kod}">${gumruk.aciklama}</option>
        </c:forEach>
    </form:select>  
</form:form>

As seen, there is a form having command "belge" and this entity contains belgeSatirlar field and belgeSatirlar contains gumrukKodlari. We can select multiple gumrukKod thanks to multiple attribute of the select element. Note that there are two select element in the form, first select element's path attribute value is "belgeSatirlar[0].gumrukKodlari" and the other's value "belgeSatirlar[1].gumrukKodlari". After submitting the form, you will get an exception: "Rejected value belgeSatirlar[0].gumrukKodlari...". To solve this problem we will use @InitBinder annotation, but lets look at Belge, BelgeSatir and GumrukKod entities.

The definition of Belge entity as follows:

@Entity
@Table(name = "BelgeKayit")
public class Belge {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "BelgeKayitId")
    private int belgeId;
    @OneToMany(mappedBy = "belge",cascade = CascadeType.ALL,fetch = FetchType.EAGER)
    private List<BelgeSatir> belgeSatirlar;
}

And the definition of BelgeSatir as follows:

@Entity
@Table(name = "BelgeSatirKayit")
public class BelgeSatir {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "BelgeSatirId")
    private int belgeSatirId;
    @ManyToMany(fetch = FetchType.EAGER)
    @JoinTable(
    name="BelgeSatir_GumrukKod",
    joinColumns = @JoinColumn( name="BasvuruNo"),
    inverseJoinColumns = @JoinColumn( name="GumrukKod")
    )
    private List<GumrukKod> gumrukKodlari;
}

And the definition of GumrukKod as follows:

@Entity
@Table(name="GumrukKodu")
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
public class GumrukKod {
    @Id
    @Column(name="KOD")
    private String kod;

    @Column(name="Aciklama")
    private String aciklama;
}

Controller Class

@Controller
@RequestMapping(value = "/kullanici", method = RequestMethod.GET)
public class UserController {
    @Autowired
    private GumrukService gumrukService;
    @InitBinder
    protected void initBinder(WebDataBinder binder) throws Exception {
        MyWebDataBinder myWebDataBinder=new MyWebDataBinder(binder);
        myWebDataBinder.registerGumrukCollectionEditor(List.class, 
                                            "belgeSatirlar.gumrukKodlari",gumrukService);
    }
}

After configuration specified at line Spring converts belgeSatirlar[0].gumrukKodlari and belgeSatirlar[1].gumrukKodlari into List collections

MyWebDataBinder Class

import org.springframework.beans.propertyeditors.CustomCollectionEditor;
import org.springframework.web.bind.WebDataBinder;
import java.util.Collection;
import java.util.List;

public class MyWebDataBinder {
    private WebDataBinder webDataBinder;
    public MyWebDataBinder(WebDataBinder webDataBinder) {
        this.webDataBinder=webDataBinder;
    }
    
    public void registerGumrukCollectionEditor(Class<?> requiredType, String field, GumrukService gumrukService) {
        webDataBinder.registerCustomEditor(requiredType, field, new GumrukCollectionEditor(List.class, gumrukService));
    }
    
    private class GumrukCollectionEditor extends CustomCollectionEditor {
        private GumrukService gumrukService;
        
        public GumrukCollectionEditor(Class<? extends Collection> collectionType, GumrukService gumrukService) {
            super(collectionType);
            this.gumrukService = gumrukService;
        }
        
        protected Object convertElement(Object element) {
            if (element instanceof GumrukKod) {
                return element;
            }
            if (element instanceof String) {
                GumrukKod gumrukKod = gumrukService.get((String) element);
                return gumrukKod;
            }
            return null;
        }
    }
}