Hibernate 和 Jackson（java.lang.IllegalStateException：响应提交后无法调用 sendError()）

Question

你好，Hibernate 和 Jackson 有一些问题。有两个 POJO

@Entity
@Table(name = "USERS")
public class User implements Serializable {
static final long serialVersionUID = 4235637833262722256L;

@Id
@GeneratedValue
private int id;

@Column(name = "CREATION_DATE")
private Date creationDate;

@Column(name = "FIRST_NAME")
private String firstName;

@Column(name = "LAST_NAME")
private String lastName;

@Version
@Column(name = "VERSION")
private int version;

@Column(name = "E_MAIL")
private String email;

@Column(name = "ENABLED")
private boolean enabled;

@Column(name = "LOGIN")
private String login;

@Column(name = "PASSWORD")
private String password;

@JsonManagedReference("role")
@OneToMany(mappedBy = "user", cascade = CascadeType.ALL,fetch = FetchType.EAGER)
private Set<UserRole> userRole;

为 spring 安全集成而设计的用户和他的角色。

@Entity
@Table(name = "USER_ROLES")
public class UserRole {

@Version
@Column(name = "VERSION")
int version;
@Id
@GeneratedValue
private int id;

@JsonBackReference("role")
@ManyToOne()
@JoinColumn(name = "USER_ID", referencedColumnName = "ID")
private User user;

@Column(name = "ROLE")
private String role;

并有一个控制器，它由用户 Json 通过 Jackson 制作。用方法

  @RequestMapping(value = "/login", method = RequestMethod.GET, produces = "application/json")
private @ResponseBody User checkLoginAvailability(@RequestParam String login) {
    User user = appContext.getUserService().readUserByLogin(login);
    if (user != null) {
        return user;
    }
    return new User();
}

当此方法返回没有空字段的用户时，它会抛出：

26-Oct-2014 14:31:17.652 WARNING [http-nio-8080-exec-4] 
org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.doResolveException 
Handling of [org.springframework.http.converter.HttpMessageNotWritableException]
resulted Exception java.lang.IllegalStateException: Cannot call sendError() after the response has been committed

当我添加@OneToMany(mappedBy = "user",cascade = CascadeType.ALL,fetch = FetchType.EAGER) 时出现了这个问题，以前它只是 fetch = FetchType.EAGER，但我无法用他的角色保存用户在这种情况下，表 USER_ROLE 是空的。我在杰克逊某处的无限循环中解决了该问题的一些解决方案，添加了一些注释@JsonBackReference("role") 和@JsonManagedReference("role") 但没有任何改变。我怎么解决这个问题？谢谢！

Answer 1

我建议添加@jsonignore导致循环引用的属性。这将告诉杰克逊不要序列化该属性。