Question

我试图从这两个实体类返回json。

Questions.java

@Entity
public class Questions {

@Id
@Column(name = "id")
private  int id;

@Column(name = "question")
private String question;

@Column(name = "type")
private String type;

@Column(name = "description")
private String description;

@Column(name = "param")
private String param;

@Column(name = "maxlength")
private int maxlength;

@Column(name = "dependency")
private String dependency;

@OneToMany(mappedBy = "questions",targetEntity = Answers.class, cascade =    CascadeType.ALL)
private Set<Answers> answers = new HashSet<>();

public int getId() {
    return id;
}

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

public String getQuestion() {
    return question;
}

public void setQuestion(String question) {
    this.question = question;
}

public String getType() {
    return type;
}

public void setType(String type) {
    this.type = type;
}

public String getDescription() {
    return description;
}

public void setDescription(String description) {
    this.description = description;
}

public String getParam() {
    return param;
}

public void setParam(String param) {
    this.param = param;
}

public int getMaxlength() {
    return maxlength;
}

public void setMaxlength(int maxlength) {
    this.maxlength = maxlength;
}

public String getDependency() {
    return dependency;
}

public Set<Answers> getAnswers() {
    return answers;
}

public void setAnswers(Set<Answers> answers) {
    this.answers = new HashSet<>(answers);
    for(Answers answers1:answers){
        answers1.setQuestions(this);
    }
}

public void setDependency(String dependency) {
    this.dependency = dependency;
}
}

Answers.java

@Entity
public class Answers {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private int id;

@Column(name = "ans_label")
private String ans_label;

@Column(name = "ans_value")
private int ans_value;

@Column(name = "ans_weightage")
private int ans_weightage;

@Column(name = "is_default")
private int is_default;

@ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
@JoinColumn(name = "ques_id", nullable = false)
private Questions questions;

public int getId() {
    return id;
}

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

public String getAns_label() {
    return ans_label;
}

public void setAns_label(String ans_label) {
    this.ans_label = ans_label;
}

public int getAns_value() {
    return ans_value;
}

public void setAns_value(int ans_value) {
    this.ans_value = ans_value;
}

public int getAns_weightage() {
    return ans_weightage;
}

public void setAns_weightage(int ans_weightage) {
    this.ans_weightage = ans_weightage;
}

public int getIs_default() {
    return is_default;
}

public void setIs_default(int is_default) {
    this.is_default = is_default;
}

public Questions getQuestions() {
    return questions;
}

public void setQuestions(Questions questions) {
    this.questions = questions;
}
}

我的控制器看起来像这样。

SaveApiController

@RequestMapping("/getData")
public @ResponseBody List<Questions> getData(){
    List<Questions> questionss=saveApiServices.getQuestions();
    return questionss;
}

我目前得到的json结果有很多重复值。

[{"id":1,"question":"१. व्यक्तिको पुरा नाम थर?", "type":"input_edittext",   
"description":"","param":"smalltext","maxlength":20,"dependency":"",
"answers": 
[{"id":0,"ans_label":"मुली","ans_value":1,"ans_weightage":0,"is_default":0,
"questions":{"id":1,"question":"१. व्यक्तिको पुरा नाम थर?",
"type":"input_edittext","description":"","param":"smalltext","maxlength":20  
,"dependency":"","answers":[{"id":0,"ans_label":"मुली","ans_value":1,
"ans_weightage":0,"is_default":0,"questions":{"id":1,
"question":"१. व्यक्तिको पुरा नाम थर ?","type":"input_edittext",
"description":"","param":"smalltext","maxlength":20,"dependency":"",
"answers":[{"id":0,"ans_label":"मुली",
"ans_value":1,"ans_weightage":0,"is_default":0,"questions":{"id":1,
"question":"१. व्यक्तिको पुरा नाम थर ?","type":"input_edittext",
"description":"","param":"smalltext","maxlength":20,"dependency":"",

我的数据库只插入了一行。在我的控制器上只找到一个问题列表。但每当抛出json输出时，它会重复很多相同的行，就像上面的json示例一样。

可能是什么问题？如果你找不到完整的解决方案，请你建议我以json格式重复相同值的原因吗？

Answer 1

杰克逊在这里进入了一个循环。您的Questions班级有Answers的链接，该班级会返回Questions。

<强>解决方案

将questions字段中的Answers字段或获取者标记为@JsonIgnored。

Answer 2

您可以尝试@JsonManagedReference和@JsonBackReference注释

为了让Jackson工作得很好，关系的两个方面之一不应该被序列化，以避免导致你的stackoverflow错误的infite循环。

@OneToMany(mappedBy = "questions",targetEntity = Answers.class, cascade =    CascadeType.ALL)
@JsonManagedReference
private Set<Answers> answers = new HashSet<>();

@ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
@JoinColumn(name = "ques_id", nullable = false)
@JsonBackReference
private Questions questions;

或

如果对获取某些实体数据不感兴趣，只需在任何一个类

中使用@JsonIgnore

杰克逊正在返回重复的行

2 个答案: