Spring-mvc 3.0 crud with checkboxes issue

I am doing an simple user crud.

My ApplicationUser has the following properties:

private Long id;
private String password;
private String username;
private Collection<Authority> myAuthorities;
private boolean isAccountNonExpired;
private boolean isAccountNonLocked;
private boolean isCredentialsNonExpired;
private boolean isEnabled;

Authority class has:

private Long id;
private String authority;
private String name;

In my jsp, my view has the following form:

<form:form modelAttribute="applicationUser"
    action="add" method="post">
    <fieldset>

    &开发者_StackOverflowlt;form:hidden path="id" />

    <legend><fmt:message key="user.form.legend" /></legend>
    <p><form:label for="username" path="username" cssErrorClass="error"><fmt:message key="user.form.username" /></form:label><br />
    <form:input path="username" /> <form:errors path="username" /></p>

    <p><form:label for="password" path="password"
        cssErrorClass="error"><fmt:message key="user.form.password" /></form:label><br />
    <form:password path="password" /> <form:errors path="password" /></p>

    <p><form:label for="password" path="password"
        cssErrorClass="error"><fmt:message key="user.form.password2" /></form:label><br />
    <form:password path="password" /> <form:errors path="password" /></p>

    <p><form:label for="myAuthorities" path="myAuthorities"
        cssErrorClass="error"><fmt:message key="user.form.autorities" /></form:label><br />
    <form:checkboxes items="${allAuthorities}" path="myAuthorities" itemLabel="name"/><form:errors path="myAuthorities" /></p>

    <p><input type="submit"/></p>
    </fieldset>
</form:form>

The jsp gets allAuthorities from this:

@ModelAttribute("allAuthorities")
public List<Authority> populateAuthorities() {
  return authorityService.findAll();
}

When I fill the form I get:

Failed to convert property value of type java.lang.String to required type java.util.Collection for property myAuthorities; nested exception is java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [com.tda.model.applicationuser.Authority] for property myAuthorities[0]: no matching editors or conversion strategy found

Which is the correct way to solve this?

HTML forms work with string values only, when your Authority is a complex bean. You need to configure a PropertyEditor to perform conversion between Authority and String:

@InitBinder 
public void initBinder(WebDataBinder b) {
    b.registerCustomEditor(Authority.class, new AuthorityEditor());
}

private class AuthorityEditor extends PropertyEditorSupport {
    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        setValue(authorityService.findById(Long.valueOf(text)));
    }

    @Override
    public String getAsText() {
        return ((Authority) getValue()).getId();
    }
}