如何在对象的 JSON 属性中排除（在输出类中）？

Question

假设我是一个将转换为 JSON 的输出类：

StudentSummary.java

public class StudentSummary {

    private StudentList studentList;

    // getters setters
}

和

StudentList.java

public class StudentList {

    private int numberOfStudents;
    private int totalExpenditures;
    private List<Student> students;

    // getters setters
}

进行服务调用后，我得到以下 JSON 输出：

{ 
 "studentSummary": {
     "studentList": {
         "numberOfStudents": 500,
         "totalExpenditures": 250000,
         "students": [ /* students listed */ ]
     }
}

我想从 JSON 中排除 studentList StudentSummary 类：

{ 
 "studentSummary": {
     "studentList": {
         "numberOfStudents": 500,
         "totalExpenditures": 250000
      }
  }
}

我已经尝试使用（在 StudentSummary 输出类中）@JsonIgnore 和 @JsonProperties，通过指定仅排除 "studentList.students"，但这没有任何作用。

编辑：进一步澄清，为什么我不能在 StudentList 类中进行更改，这是因为它被另一个服务使用，而 StudentSummary 类的服务属于不同的服务，所以我只能在里面进行更改后一个类，不修改前一个服务。

Answer 1

总结

这将解决您的问题：

public class StudentSummary {

    @JsonIgnoreProperties(value = { "students" })
    public StudentList studentList = new StudentList();

您不需要编辑StudentList 类。

所有测试类定义

学生

public class Student {

    String name = "Student" + Math.random()*100;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

学生名单

public class StudentList {

    int numberOfStudents;
    int totalExpenditures;
    List<Student> students = new ArrayList<>();

    public StudentList(){
        for(int i =0; i<10; i++){
            students.add(new Student());
        }
    }

    public int getNumberOfStudents() {
        return numberOfStudents;
    }

    public void setNumberOfStudents(int numberOfStudents) {
        this.numberOfStudents = numberOfStudents;
    }

    public int getTotalExpenditures() {
        return totalExpenditures;
    }

    public void setTotalExpenditures(int totalExpenditures) {
        this.totalExpenditures = totalExpenditures;
    }

    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }

    //getters setters
}

学生总结

public class StudentSummary {

    @JsonIgnoreProperties(value = { "students" })
    public StudentList studentList = new StudentList();

    public StudentSummary(){
        studentList = new StudentList();
    }

    public StudentList getStudentList() {
        return studentList;
    }

    public void setStudentList(StudentList studentList) {
        this.studentList = studentList;
    }

    //getters setters
}

主类

ObjectMapper mapper = new ObjectMapper();

StudentSummary summary = new StudentSummary();
String test = mapper.writeValueAsString(summary);
System.out.println(test);
System.out.print("DONE");

Answer 2

如果不能修改类的源代码，需要创建Mixin类来省略Studentlist ...

点击以下链接查看 Jackson Mixin..

How can I tell jackson to ignore a property for which I don't have control over the source code?

Answer 3

您可以使用@JsonIgnoreProperties 或@JsonIgnore 在JSON 序列化时忽略类的任何属性。例如

***public class StudentList {
int numberOfStudents;
int totalExpenditures;
@JsonIgnore
List<Student> students;
//getters setters
}***

或者

***@JsonIgnoreProperties(value = { "students" })
public class StudentList {
int numberOfStudents;
int totalExpenditures;
List<Student> students;
//getters setters
}***

Answer 4

我相信从这个问题你不能接触StudentList 类，一切都应该从StudentSummary 类处理。我的想法是创建另一个类SpecialStudent 并覆盖学生列表的setter/getter，然后将@JsonIgnore 属性放在它们上面。以下是相同的示例。让我知道这是否有帮助

class SpecialStudent extends StudentList{
    @JsonIgnore
    @Override
    public List<Student> getStudents()
    {
        return students;
    }
    /**
     * @param students the students to set
     */
    @Override
    @JsonIgnore
    public void setStudents(List<Student> students)
    {
        this.students = students;
    }
}

学生总结应该是这样的

public class StudentSummary
{
    SpecialStudent studentList;

    /**
     * @return the studentList
     */
    public StudentList getStudentList()
    {
        return studentList;
    }

    /**
     * @param studentList the studentList to set
     */
    public void setStudentList(SpecialStudent studentList)
    {
        this.studentList = studentList;
    }

}

测试类

StudentSummary sum = new  StudentSummary();
        SpecialStudent l = new SpecialStudent();
        l.setNumberOfStudents(4);
        l.setTotalExpenditures(12);
        sum.setStudentList(l);


        ObjectMapper mapper = new ObjectMapper();
        String json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(sum);

        System.out.println(json);

输出

{
  "studentList" : {
    "numberOfStudents" : 4,
    "totalExpenditures" : 12
  }
}

Answer 5

我建议阅读here

基本上，如果你不能修改类本身的任何东西，那么你需要全局告诉杰克逊如何在序列化配置上处理这个（通过对象映射器上的混合注释）

Answer 6

由于您无法更改 StudentList;您不需要在 StudentSummary 中包含 StudentList 的实例。因此，您可以进行如下映射：

 public class StudentSummary {

    int numberOfStudents;
    int totalExpenditures;

    public StudentSummary (){
         StudentList studentList = new StudentList();
         this.numberOfStudents = studentList.getNumberOfStudents();
         this.totalExpenditures = studentList.getTotalExpenditures();
    }

    //getters setters for numberOfStudents & totalExpenditures
  }