在所有对象的参数上运行java

Question

用户(id、名字、名字）；

@RequestMapping(value = "/users/update", method = RequestMethod.POST)
    public User updateUser(@ModelAttribute("User") User user) {
        //persist.save(user);
        return user;
    }

在post请求中，用户可以发送值为null的参数，我想确定这些参数是谁。

@modelattribute将这些值强制转换为user模型，并将null值赋予未与用户一起发送的空参数。

{
    "id": 1,
    "firstName": "itzik",
    "lastName": null, 
}

我正在尝试确定哪些参数保存值null以防止它们在保存之前损坏我的整个数据记录。

谢谢！

public class User {

    private int id;
    private String uid;
    private String firstName;
    private String lastName;
    private String email;
    private String phone;
    private int permission;
    private int department;
    private boolean deleted;

    public User(String uid, String firstName, String lastName, String email, String phone, int permission, int department, boolean deleted) {
        this.uid = uid;
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
        this.phone = phone;
        this.permission = permission;
        this.department = department;
        this.deleted = deleted;
    }
}

Answer 1

当您使用Spring框架时，有一个序列化/反序列化发生在“幕后”，这涉及到您的POJO。

@RequestMapping(value = "/users/update", method = RequestMethod.POST)
public User updateUser(@ModelAttribute("User") User user) {
    //persist.save(user);
    return user;
}

...HTTP协议将带来表示用户的文本/JSON内容，但不会发送用户的实例。同样，当您的在方法中返回user；时，您返回的是user的实例，但是客户机得到的是一个表示您的用户的序列化Json（这是因为Spring会在幕后为您序列化类）。

因此，Spring将寻找user的构造函数，并将Json字符串反序列化为user实例。

public User(String lastName) {
    this.lastName = Objects.requireNonNull(lastName, "lastName should not be null");
}

...然后，当Spring试图初始化user实例时，它就会接收到一个NullPointerException并将其直接报告给调用方。你的方法甚至不会被调用。

完整示例：

public class User {

    private final int id; //<- make all fields final (they can't change any longer after construction)
    private final String uid;
    private final String firstName;
    private final String lastName;
    private final String email;
    private final String phone;
    private final int permission;
    private final int department;
    private final boolean deleted;

    public User(String uid, String firstName, String lastName, String email, String phone, int permission, int department, boolean deleted) {
        this.uid = Objects.requireNonNull(uid); //<- wrap all sets by requireNonNull
        this.firstName = Objects.requireNonNull(firstName);
        this.lastName = Objects.requireNonNull(lastName);
        this.email = Objects.requireNonNull(email);
        this.phone = Objects.requireNonNull(phone);
        this.permission = Objects.requireNonNull(permission);
        this.department = Objects.requireNonNull(department);
        this.deleted = Objects.requireNonNull(deleted);
    }
}