Spring + Thymeleaf绑定形式NullpointerException

Question

I'm currently working on an user edit form.

I have a user object with the following structure (pseudo code):

User

String name,
int age,
Address adress,
Email email,
User child,

getter/setter

Now, this object i put in as object in a Model like the following:

@RequestMapping(value = "/{login}/edit", method = RequestMethod.GET)
public ModelAndView editUserByLogin(@PathVariable("login") final String login) {
    final User currentUser = UserRepository.findPersonByLogin(login);

    ModelAndView mav = new ModelAndView(URL_EDIT_USER);
    mav.addObject(MODEL_USER, currentUser);

    return mav;
}

in my template (i use thymeleaf) i bind these object like this:

<form class="form-horizontal" method="post" >
<div class="form-group">
    <label class="col-sm-2 control-label" th:text="#{user.name}">name</label>
    <div class="col-sm-10">
        <input type="text" class="form-control" th:field="*{user.name}" />
    </div>
</div>
<div class="form-group">
    <label class="col-sm-2 control-label" th:text="#{user.address.street}">name</label>
    <div class="col-sm-10">
        <input type="text" class="form-control" th:field="*{user.address.street}" />
    </div>
</div>
<div class="form-group">
    <label class="col-sm-2 control-label" th:text="#{user.child.email.value}">name</label>
    <div class="col-sm-10">
        <input type="text" class="form-control" th:field="*{user.child.email.value}" />
    </div>
</div>
<div class="form-group">
    <label class="col-sm-2 control-label" th:text="#{user.child.address.street}">name</label>
    <div class="col-sm-10">
        <input type="text" class="form-control" th:field="*{user.child.address.street}" />
    </div>
</div>
</form>

In the GET-Method the template/html shows the correct data i expected. Now i edit the fields and submit the form, then i get the following error:

java.lang.NullPointerException: null
    at com.example.user.model.Email.hashCode(EMail.java:66) ~[classes/:na]
    at java.lang.Object.toString(Unknown Source) ~[na:1.8.0_25]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_25]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_25]
    at org.springframework.validation.FieldError.toString(FieldError.java:102) ~[spring-context-4.0.8.RELEASE.jar:4.0.8.RELEASE]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_25]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_25]
    at org.springframework.validation.AbstractErrors.toString(AbstractErrors.java:243) ~[spring-context-4.0.8.RELEASE.jar:4.0.8.RELEASE]
    at org.springframework.validation.BindException.getMessage(BindException.java:284) ~[spring-context-4.0.8.RELEASE.jar:4.0.8.RELEASE]
    at java.lang.Throwable.getLocalizedMessage(Unknown Source) ~[na:1.8.0_25]
    at java.lang.Throwable.toString(Unknown Source) ~[na:1.8.0_25]
    at java.lang.String.valueOf(Unknown Source) ~[na:1.8.0_25]
    at java.lang.StringBuilder.append(Unknown Source) ~[na:1.8.0_25]

All fields are transmitted correctly unless the email field of the child-object.

I have no idea why the error occurs, the structure is the same, the data is valid and the funny thing is when I grab the child email element in a separate object goes it

Does anyone have an idea?

Thanks in advance.

EDIT: Email class:

@Entity(name="Email")
public class Email implements Serializable
{
    private static final long serialVersionUID = 6891079722082340011L;

    @Id()
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Expose
    protected Long eMailId;
    @Expose
    protected String value;

    //getter/setter

    @Override
    public boolean equals(Object obj)
    {
        if(obj instanceof EMail){
            return value.equals(((Email) obj).getValue());
        }
        return false;
    }

    @Override
    public int hashCode()
    {
        return value.hashCode();
    }
}

The post method:

@RequestMapping(value = "/{login}/edit", method = RequestMethod.POST)
public ModelAndView updateUser(@PathVariable("login") final String login, @ModelAttribute final User webUser) {
    final Person repoUser = personRepository.findPersonByLogin(login);
    repoUser.updateWith(webUser);

    return new ModelAndView("redirect:" + URL_USERS_OVERVIEW);
}

Answer 1

The NullPointerException is happening in your Email.hashCode() method. Looking at your code this could happen if value is null.

The template you posted doesn't include the user.email.value field, so this is most likely why it is null.

Either you need to add a field for the user email, or change the hashCode method so that it handles the null value.