jackson的对象到JSON转换问题 导入java.io.File； 导入java.lang.reflect.Array； 导入java.lang.reflect.Field； 导入java.math.BigDecimal； 导入java.sql.Time； 导入java.sql.Timestamp； 导入java.util.ArrayList； 导入java.util.Date； 导入java.util.List； 导入org.apache.commons.lang3.StringUtils； 导入org.json.simple.JSONArray； 导入org.json.simple.JSONObject； 导入org.json.simple.parser.JSONParser； 导入com.fasterxml.jackson.annotation.jsonautodect.Visibility； 导入com.fasterxml.jackson.annotation.PropertyAccessor； 导入com.fasterxml.jackson.databind.ObjectMapper； 导入com.fasterxml.jackson.databind.ObjectWriter； 导入com.report.mongo.MakeMD5Checksum； 导入com.report.mongo.MongoService； 导入job.com.rpt.bootstrap.ApplicationConfigCache； import service.com.rpt.db.MongoDataService； import service.com.rpt.util.RPTUtil； 公共类DTOtoJSONTest{ 公共静态void main（字符串[]args）引发异常{ //TODO自动生成的方法存根 Address studentAddress1=新地址（）； studentaddress 1.adrLine1=“studentaddress 1 adrLine1”； studentaddress 1.adrLine2=“studentaddress 1 adrLine2”； studentaddress 1.city=“studentaddress 1城市”； studentAddress1.postalCode=1； Address studentAddress2=新地址（）； studentaddress 2.adrLine1=“studentaddress 2 adrLine1”； studentaddress 2.adrLine2=“studentaddress 2 adrLine2”； studentaddress 2.city=“studentaddress 2城市”； 学生地址2.postalCode=2； StudentDTO StudentDTO=新StudentDTO（）； studentDTO.name=“BK”； studentDTO.roll=1； 学生年龄=40； studentDTO.dateOfBirth=新日期（）； studentDTO.gender=“M”； studentDTO.addresses=新地址[2]； studentDTO.addresses[0]=studentAddress1； 学生地址[1]=学生地址2； studentDTO.sportsInterests=新字符串[3]； studentDTO.sportsInterests[0]=新字符串（“Fooball”）； studentDTO.sportsInterests[1]=新字符串（“排球”）； studentDTO.sportsInterests[2]=新字符串（“Carom”）； GurdianInfo父亲=新的GurdianInfo（）； father.gurdianName=“父亲姓名”； father.relation=“父亲”； 父地址=新地址（）； father.address.adrLine1=“father addressline1”； father.address.adrLine2=“father addressline2”； father.address.city=“父城”； father.address.postalCode=11； father.gurdianCntactInfo=新ArrayList（）； ContactInfo fContactInfo=新的ContactInfo（）； fContactInfo.isPrimary=true； fContactInfo.cellNumber=“1234”； fContactInfo.emailId=“”； fContactInfo.type=“单元格”； 父.gurdianCntactInfo.add（fContactInfo）； fContactInfo=新联系人信息（）； fContactInfo.isPrimary=false； fContactInfo.cellNumber=“5678”； fContactInfo.emailId=“”； fContactInfo.type=“单元格”； 父.gurdianCntactInfo.add（fContactInfo）； fContactInfo=新联系人信息（）； fContactInfo.isPrimary=false； fContactInfo.cellNumber=“”； fContactInfo.emailId=“父亲电子邮件”； fContactInfo.type=“电子邮件”； 父.gurdianCntactInfo.add（fContactInfo）； studentDTO.gurdianInfo=新建ArrayList（）； studentDTO.gurdianInfo.add（父亲）； GurdianInfo母亲=新的GurdianInfo（）； mother.gurdianName=“父名”； 母亲关系=“父亲”； mother.address=新地址（）； mother.address.adrLine1=“Father addressline1”； mother.address.adrLine2=“Father addressline2”； mother.address.city=“父城”； mother.address.postalCode=11； mother.gurdianCntactInfo=新的ArrayList（）； ContactInfo mContactInfo=新的ContactInfo（）； mContactInfo.isPrimary=true； mContactInfo.cellNumber=“PQRS”； mContactInfo.emailId=“”； mContactInfo.type=“单元格”； mother.gurdianCntactInfo.add（mContactInfo）； mContactInfo=新联系人信息（）； mContactInfo.isPrimary=false； mContactInfo.cellNumber=“”； mContactInfo.emailId=“母亲电子邮件”； mContactInfo.type=“电子邮件”； mother.gurdianCntactInfo.add（mContactInfo）； studentDTO.gurdianInfo.add（母亲）； 课程详细信息：课程详细信息=新课程详细信息（）； 课程详情。课程名称=“MCA”； 课程详情.standard=“硕士”； CoursolamDetail.subjects=新字符串[3]； 课程详情。科目[0]=“SUB0”； 课程详情。科目[1]=“SUB1”； 课程详情。科目[2]=“SUB2”； studentDTO.curloamdetail=课程详情； //上面的部分只是创建了一个对象 //主代码从下面开始 ObjectMapper mapperObj=新的ObjectMapper（）； mapperObj.setVisibility（PropertyAccessor.FIELD，Visibility.ANY）； JSONObject studentJSON=新的JSONObject（）； convertToJSON（studentDTO，studentJSON）； System.out.println（studentJSON.toJSONString（））；//此行打印{} } 公共静态void convertToJSON（Object-Object，JSONObject-JSONObject）引发异常{ ObjectMapper mapperObj=新的ObjectMapper（）； mapperObj.setVisibility（PropertyAccessor.FIELD，Visibility.ANY）； 字符串jsonStr=mapperbj.writeValueAsString（对象）； ; JSONParser=新的JSONParser（）； JSONObject local=（JSONObject）parser.parse（jsonStr）； jsonObject=本地； writeValueAsString（对象）； System.out.println（“在CONEVRSION之后**************”+jsonObject.toJSONString（））；//此行打印JSON }

}

在上面的代码中，我试图使用jackson将一个对象转换为JSON对象。对象正在转换为JSON对象，但问题是JSON对象仅在convertToJSON方法中可用（它打印JSON）。我无法在main方法中打印JSON。在main方法中，它打印“{}”。请帮忙

---

感谢您将

convertToJSON

中的

jsonObject

的引用更改为新对象

studentJson

保持相同的空对象。convertToJSON应返回JSONObject。不带走

import java.io.File;
import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.math.BigDecimal;
import java.sql.Time;
import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

import org.apache.commons.lang3.StringUtils;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;

import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectWriter;
import com.report.mongo.MakeMD5Checksum;
import com.report.mongo.MongoService;

import job.com.rpt.bootstrap.ApplicationConfigCache;
import service.com.rpt.db.MongoDataService;
import service.com.rpt.util.RPTUtil;

public class DTOtoJSONTest {

public static void main(String[] args) throws Exception{
    // TODO Auto-generated method stub

    Address studentAddress1 = new Address();
    studentAddress1.adrLine1 = "studentAddress1 adrLine1";
    studentAddress1.adrLine2 = "studentAddress1 adrLine2";
    studentAddress1.city = "studentAddress1 City";
    studentAddress1.postalCode = 1;

    Address studentAddress2 = new Address();
    studentAddress2.adrLine1 = "studentAddress2 adrLine1";
    studentAddress2.adrLine2 = "studentAddress2 adrLine2";
    studentAddress2.city = "studentAddress2 City";
    studentAddress2.postalCode = 2;

    StudentDTO studentDTO = new StudentDTO();
    studentDTO.name = "BK";
    studentDTO.roll = 1;
    studentDTO.age = 40;
    studentDTO.dateOfBirth = new Date();
    studentDTO.gender = "M";

    studentDTO.addresses = new Address[2];
    studentDTO.addresses[0] = studentAddress1;
    studentDTO.addresses[1] = studentAddress2;


    studentDTO.sportsInterests = new String[3];
    studentDTO.sportsInterests[0] = new String("Fooball");
    studentDTO.sportsInterests[1] = new String("VollyBall");
    studentDTO.sportsInterests[2] = new String("Carom");



    GurdianInfo father = new GurdianInfo();
    father.gurdianName = "Father Name";
    father.relation = "Father";
    father.address = new Address();
    father.address.adrLine1 = "Father addressline1";
    father.address.adrLine2 = "Father addressline2";
    father.address.city = "Father City";
    father.address.postalCode = 11;

    father.gurdianCntactInfo = new ArrayList<ContactInfo>();

    ContactInfo fContactInfo = new ContactInfo();
    fContactInfo.isPrimary = true;
    fContactInfo.cellNumber = "1234";
    fContactInfo.emailId = "";
    fContactInfo.type = "Cell";

    father.gurdianCntactInfo.add(fContactInfo);

    fContactInfo = new ContactInfo();
    fContactInfo.isPrimary = false;
    fContactInfo.cellNumber = "5678";
    fContactInfo.emailId = "";
    fContactInfo.type = "Cell";

    father.gurdianCntactInfo.add(fContactInfo);

    fContactInfo = new ContactInfo();
    fContactInfo.isPrimary = false;
    fContactInfo.cellNumber = "";
    fContactInfo.emailId = "father email";
    fContactInfo.type = "email";

    father.gurdianCntactInfo.add(fContactInfo);

    studentDTO.gurdianInfo = new ArrayList<GurdianInfo>();
    studentDTO.gurdianInfo.add(father);


    GurdianInfo mother = new GurdianInfo();
    mother.gurdianName = "Father Name";
    mother.relation = "Father";
    mother.address = new Address();
    mother.address.adrLine1 = "Father addressline1";
    mother.address.adrLine2 = "Father addressline2";
    mother.address.city = "Father City";
    mother.address.postalCode = 11;

    mother.gurdianCntactInfo = new ArrayList<ContactInfo>();

    ContactInfo mContactInfo = new ContactInfo();
    mContactInfo.isPrimary = true;
    mContactInfo.cellNumber = "PQRS";
    mContactInfo.emailId = "";
    mContactInfo.type = "Cell";

    mother.gurdianCntactInfo.add(mContactInfo);

    mContactInfo = new ContactInfo();
    mContactInfo.isPrimary = false;
    mContactInfo.cellNumber = "";
    mContactInfo.emailId = "mother email";
    mContactInfo.type = "email";

    mother.gurdianCntactInfo.add(mContactInfo);
    studentDTO.gurdianInfo.add(mother);

    CurriculamDetail curriculamDetail = new CurriculamDetail();
    curriculamDetail.curriculamName = "MCA";
    curriculamDetail.standard = "MASTERS";
    curriculamDetail.subjects = new String[3];
    curriculamDetail.subjects[0] = "SUB0";
    curriculamDetail.subjects[1] = "SUB1";
    curriculamDetail.subjects[2] = "SUB2";
    studentDTO.curriculamDetail = curriculamDetail;
    //Above part just creates an object
    // Main code starts below
    ObjectMapper mapperObj = new ObjectMapper();

    mapperObj.setVisibility(PropertyAccessor.FIELD, Visibility.ANY);
    JSONObject studentJSON = new JSONObject();
        convertToJSON(studentDTO, studentJSON);
        System.out.println(studentJSON.toJSONString()); //This line prints {}
    }


public static void convertToJSON(Object object, JSONObject jsonObject) throws Exception{

    ObjectMapper mapperObj = new ObjectMapper();
    mapperObj.setVisibility(PropertyAccessor.FIELD, Visibility.ANY);

    String jsonStr = mapperObj.writeValueAsString(object); 
    ;
    JSONParser parser = new JSONParser();
    JSONObject local = (JSONObject)parser.parse(jsonStr);
    jsonObject = local;
        mapperObj.writeValueAsString(object);
    System.out.println("AFTER CONEVRSION ****************** " + jsonObject.toJSONString());  //This line prints JSON 

}