java - 如何在 Java8 中创建 Json 数组并且仅在设置值时打印 json？

Question

我正在尝试使用 fasterxml jackson 生成以下内容..但我陷入困境。我似乎不知道如何创建数组。

{
   "setAccId":"12345",
   "groupOf":null,
   "isEnabled":false,
   "list":[
      {
         "student":"jim",
         "type":"S_A",
         "retro":null
      },
      {
         "student":"bob",
         "type":"S_A",
         "retro":null
      }
   ],
   "sort":[]
}

我有两个类。一个具有 Json 属性，另一个是我打印它的位置。

Below class (DynamicJsonHelper) is where I have all the json properties

package com.company.jsonfc;

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonPropertyOrder({
"accId",
"groupOf",
"isEnabled"
})

public class DynamicJsonHelper {

    public String accId;
    public String groupOf;
    public List studentList;

    @JsonProperty("accId")
    public void setAccId(String accId) {
        this.accId = accId;
    }

    @JsonProperty("groupOf")
    public void setGroupOf(String groupOf) {
        this.groupOf = groupOf;
    }

    @JsonProperty("isEnabled")
    public boolean isEnabled() {
        return false;
    }

    @JsonProperty("studentList")
    public List<StudentList> studentList() {
        return studentList;
    }

}

Student List Class (as suggested)

class StudentList {
    String student;
    String type;
    String retro; 
}

And here is class (PrintJson) where I call it.

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.JsonNodeFactory;

import com.company.jsonfc.DynamicJsonHelper;

@JsonInclude(JsonInclude.Include.NON_NULL)
public class PrintJson {

    @Test
    public void create_json() throws JsonProcessingException {
    final JsonNodeFactory factory = JsonNodeFactory.instance;

    DynamicJsonHelper dynamicJsonHelper = new DynamicJsonHelper();
    String jsonString;
    ObjectMapper mapper = new ObjectMapper();

    dynamicJsonHelper.setAccId("12345");

    jsonString = mapper.writeValueAsString(dynamicJsonHelper);
    System.out.println(jsonString);
    }

}

This results in printing the following:

{
   "setAccId":"12345",
   "groupOf":null,
   "isEnabled":false
   "studentList":null
}

1) 如何在末尾添加 list:[ ... ] 数组和 sort: [ ] ？

2)在PrintJson类中，我没有为groupOf设置值，但它仍然是在Json中创建的。我如何设置它，以便如果我设置值，它就会被打印..否则它不会包含在正在打印的 json 中。

如果您使用我的代码并为我提供示例以便更好地理解，我将不胜感激

Answer 1

1) How do I add the list:[ ... ] array & the sort: [ ] at the end too?

答案:您可以再创建两个类，第一个类用于 list和一个 sort 。现在上课DynamicJsonHelper您可以添加它们，就像添加 accId 一样或isEnabled并且它们将被打印。确保将所需的字段添加为两个类中的实例变量。例如，对于列表，您可以有一个类，例如:

class StudentList{
    String student;
    String type;
    String retro;
}

现在在您的类中添加一个字段 DynamicJsonHelper如List<StudentList> 。同样，您可以对 sort 执行此操作.

2) In class PrintJson, I don't set value for groupOf but it is still created in Json. How do I set it so if I set value, it is printed.. otherwise it is not included in the json being printed.

回答:您可以或者使用对象映射器并将其设置为在序列化期间忽略空字段。例如:mapper.setSerializationInclusion(Include.NON_NULL);或者您可以在类级别将其设置为忽略空值(如果有)。例如:

@JsonInclude(Include.NON_NULL)
class Test
{
  String t;
}

正如上面 aBnormaLz 的评论中提到的，如果类型像 isEnabled 那样是原始类型，则不起作用。因此，请考虑将其更改为 boolean 值，并确保其他字段也同样如此。

编辑:

@JsonPropertyOrder({
"accId",
"groupOf",
"isEnabled"
})
@JsonInclude(JsonInclude.Include.NON_NULL)

public class DynamicJsonHelper {

public String accId;
public String groupOf;
public List<Student> studentList;

@JsonProperty("accId")
public void setAccId(String accId) {
    this.accId = accId;
}

@JsonProperty("groupOf")
public void setGroupOf(String groupOf) {
    this.groupOf = groupOf;
}

@JsonProperty("isEnabled")
public boolean isEnabled() {
    return false;
}

@JsonProperty("studentList")
public void setStudentList(List<Student> list) {
    this.studentList = list;
}

}

class Student {
private String student;
private String type;
private String retro; 

public Student(String student, String type, String retro) {
    this.student = student;
    this.type = type;
    this.retro = retro;
}

public String getStudent() {
    return student;
}

public void setStudent(String student) {
    this.student = student;
}

public String getType() {
    return type;
}

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

public String getRetro() {
    return retro;
}

public void setRetro(String retro) {
    this.retro = retro;
}    
}

class HelperTest{

public static void main(String[] args) throws JsonProcessingException {
    DynamicJsonHelper dynamicJsonHelper = new DynamicJsonHelper();
    String jsonString;
    ObjectMapper mapper = new ObjectMapper();

    dynamicJsonHelper.setAccId("12345");

    List<Student> list = Arrays.asList(new Student("s1", "t1", "r1"), new Student("s2", "t2", "r2"));

    dynamicJsonHelper.setStudentList(list);
    jsonString = mapper.writeValueAsString(dynamicJsonHelper);
    System.out.println(jsonString);

}
}

执行程序后output如下图:

{
   "accId": "12345",
   "isEnabled": false,
   "studentList": [
                    {
                      "student": "s1",
                      "type": "t1",
                      "retro": "r1"
                    },
                    {
                      "student": "s2",
                      "type": "t2",
                      "retro": "r2"
                    }
                   ]
}