Failed to convert from type [java.lang.String] to type [java.lang.Long]

Question

This mapping should return a Set of subscribers or subscriptions. But instead, I get the error:

There was an unexpected error (type=Bad Request, status=400). Failed to convert value of type 'java.lang.String' to required type 'org.project.notablog.domains.User'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [java.lang.Long] for value 'subscriptions'; nested exception is java.lang.NumberFormatException: For input string: "subscriptions" org.springframework.web.method.annotation.MethodArgumentTypeMismatchException: Failed to convert value of type 'java.lang.String' to required type 'org.project.notablog.domains.User'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [java.lang.Long] for value 'subscriptions'; nested exception is java.lang.NumberFormatException: For input string: "subscriptions"

Controller:

@Controller
@RequestMapping("/user")
public class UserController {


    @GetMapping("{type}/{user}/list")
    public String userList(
            Model model,
            @PathVariable User user,
            @PathVariable String type
    ) {
        model.addAttribute("userChannel", user);
        model.addAttribute("type", type);

        if ("subscriptions".equals(type)) {
            model.addAttribute("users", user.getSubscriptions());
        } else {
            model.addAttribute("users", user.getSubscribers());
        }

        return "subscriptions";
    }

}

Entity:

@Entity
@Table(name = "usr")
public class User implements UserDetails {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @NotBlank(message = "Username cannot be empty")
    private String username;

    @NotBlank(message = "Password cannot be empty")
    private String password;

    private boolean active;

    @Email(message = "Email isn't correct")
    @NotBlank(message = "Email cannot be empty")
    private String email;
    private String activationCode;

    @ElementCollection(targetClass = Role.class, fetch = FetchType.EAGER)
    @CollectionTable(name = "user_role", joinColumns = @JoinColumn(name = "user_id"))
    @Enumerated(EnumType.STRING)
    private Set<Role> roles;

    @OneToMany(mappedBy = "author", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    private Set<Message> messages;

    @ManyToMany
    @JoinTable(
            name = "user_subscriptions",
            joinColumns = { @JoinColumn(name = "author_id") },
            inverseJoinColumns = { @JoinColumn(name = "subscriber_id") }
    )
    private Set<User> subscribers = new HashSet<>();

    @ManyToMany
    @JoinTable(
            name = "user_subscriptions",
            joinColumns = { @JoinColumn(name = "subscriber_id") },
            inverseJoinColumns = { @JoinColumn(name = "author_id") }
    )
    private Set<User> subscriptions = new HashSet<>();



    public User() {
    }

    public User(String username, String password, boolean active, Set<Role> roles) {
        this.username = username;
        this.password = password;
        this.active = active;
        this.roles = roles;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        User user = (User) o;
        return Objects.equals(id, user.id);
    }

    @Override
    public int hashCode() {

        return Objects.hash(id);
    }

    public Boolean isAdmin()
    {
        return roles.contains(Role.ADMIN);
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    @Override
    public boolean isAccountNonExpired() {
        return true;
    }

    @Override
    public boolean isAccountNonLocked() {
        return true;
    }

    @Override
    public boolean isCredentialsNonExpired() {
        return true;
    }

    @Override
    public boolean isEnabled() {
        return isActive();
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public boolean isActive() {
        return active;
    }

    public void setActive(boolean active) {
        this.active = active;
    }

    public Set<Role> getRoles() {
        return roles;
    }

    public void setRoles(Set<Role> roles) {
        this.roles = roles;
    }

    @Override
    public Collection<? extends GrantedAuthority> getAuthorities() {
        return getRoles();
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getActivationCode() {
        return activationCode;
    }

    public void setActivationCode(String activationCode) {
        this.activationCode = activationCode;
    }

    public Set<Message> getMessages() {
        return messages;
    }

    public void setMessages(Set<Message> messages) {
        this.messages = messages;
    }

    public Set<User> getSubscribers() {
        return subscribers;
    }

    public void setSubscribers(Set<User> subscribers) {
        this.subscribers = subscribers;
    }

    public Set<User> getSubscriptions() {
        return subscriptions;
    }

    public void setSubscriptions(Set<User> subscriptions) {
        this.subscriptions = subscriptions;
    }
}

Freemarker template:

<#import "parts/common.ftlh" as c>

<@c.page>
    <h3>${author.username}</h3>
    <div>${type}</div>
    <ul class="list-group">
        <#list users as user>
            <li class="list-group-item">
                <a href="/user-messages/${user.id}">${user.getUsername()}</a>
            </li>
        </#list>
    </ul>
</@c.page>

I've already tried everything that came to my mind, but I can't figure out what the problem is.

Answer 1

With this

    @PathVariable User user,

you are referring to variable within your path {type}/{user}/list, which is just a String, probably the userId.

It should be something like

    @PathVariable("user") String userId

after which you can load the user, like User user = userService.getUser(userId); UserService or UserRepository must be wired into the Controller for this.