java, playframework, ajax, json - 将 Object 转换为 JSON 时发生无限递归

Question

我需要将此对象列表转换为 JSON，以便我可以将其传递给我的 AJAX。

到目前为止我有（使用java playframework）

Application.java

@Transactional
public static Result fetchOptions(String strCategoryId, String strCategoryName) {

    Main mainAppModel = new Main();
    mainAppModel.populateOptions(strCategoryId, strCategoryName);
    return ok(Json.toJson(mainAppModel));
  }

Main.java

  public void populateCountryOptions() {
    Countries countriesDb = new Countries();
    lstCountries = countriesDb.getCountriesByRegion(strRegionId);
  }

  public void populateLocationOptions() {
    Locations locationsDb = new Locations();
    lstLocations = locationsDb.getLocationByCountry(strCountryId);
  }

  public void populateDepartmentOptions() {
    Departments departmentsDb = new Departments();
    lstDepartments = departmentsDb.getDepartmentByLocationId(strLocationId);
  }

  public void populateOptions(String strCategoryId, String strCategoryName) {
    switch (strCategoryName) {
      case "region":
        strRegionId = strCategoryId;
        populateCountryOptions();
        break;
      case "country":
        strCountryId = strCategoryId;
        populateLocationOptions();
        break;
      case "location":
        strLocationId = strCategoryId;
        populateDepartmentOptions();
        break;
      default:
        break;
    }
  }

conf/routes

POST    /fetchOptions/:strCategoryId/:strCategoryName   controllers.Application.fetchOptions(strCategoryId: String, strCategoryName: String)

Departments.java（删除了 getter 和 setter）

package models.db;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

import play.db.jpa.JPA;

@Table(name = "DEPARTMENTS")
@Entity
public class Departments {

  @Id
  @Column(name = "DEPARTMENT_ID")
  private String strDepartmentId;

  @Column(name = "DEPARTMENT_NAME")
  private String strDepartmentName;

  @Column(name = "MANAGER_ID")
  private String strManagerId;

  @Column(name = "LOCATION_ID")
  private String strLocationId;


  @SuppressWarnings("unchecked")
  public List<Departments> getDepartmentByLocationId(String strLocationId) {

    StringBuilder sb = new StringBuilder();
    sb.append(" SELECT ");
    sb.append("         DEPARTMENT_ID ");
    sb.append("         , DEPARTMENT_NAME ");
    sb.append("         , MANAGER_ID ");
    sb.append("         , LOCATION_ID ");
    sb.append(" FROM  ");
    sb.append("         DEPARTMENTS ");
    sb.append(" WHERE ");
    sb.append("         LOCATION_ID = '" + strLocationId + "'");
    sb.append(" ORDER BY  ");
    sb.append("         DEPARTMENT_NAME ASC ");

    List<Departments> lstDepartments = new ArrayList<Departments>();
    try {
      lstDepartments = JPA.em().createNativeQuery(sb.toString(), Departments.class).getResultList();
    } catch (Exception e) {
      // TODO: handle exception
    }

    return lstDepartments;

  }
}

Countries.java（对比）

package models.db;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

import play.db.jpa.JPA;

@Table(name = "COUNTRIES")
@Entity
public class Countries {


  @Id
  @Column(name = "COUNTRY_ID")
  private String strCountryId;

  @Column(name = "COUNTRY_NAME")
  private String strCountryName;

  @Column(name = "REGION_ID")
  private String strRegionId;

  @SuppressWarnings("unchecked")
  public List<Countries> getCountriesByRegion(String strRegionId) {

    StringBuilder sb = new StringBuilder();
    sb.append(" SELECT ");
    sb.append("         COUNTRY_ID ");
    sb.append("         , COUNTRY_NAME ");
    sb.append("         , REGION_ID ");
    sb.append(" FROM  ");
    sb.append("         COUNTRIES ");
    sb.append(" WHERE ");
    sb.append("         REGION_ID = '" + strRegionId + "'");
    sb.append(" ORDER BY ");
    sb.append("         COUNTRY_NAME ASC ");

    List<Countries> lstCountries = new ArrayList<Countries>();
    try {
      lstCountries = JPA.em().createNativeQuery(sb.toString(), Countries.class).getResultList();
    } catch (Exception e) {
      // TODO: handle exception
    }

    return lstCountries;
  }


}

我认为不再需要 javascript，因为错误发生在将 mainAppModel 对象返回为 Json 时。
所以我在 Main.java 上有 3 个方法，在 Application.java 上使用相同的方法。如果我使用 populateCountryOptions() 和 populateLocationOptions() Json 工作正常，但每当我使用 populateDepartmentOptions() 发生无限递归。该模型看起来彼此相似。我不知道是什么导致了这个错误。感谢您的帮助！

Answer 1

你需要在这里休息：

case "location":
        strLocationId = strCategoryId;
        populateDepartmentOptions();
    break;

Answer 2

因为我无法修复错误。我通过覆盖 .toString() 手动创建自己的 JSON

虽然这不是我的问题的具体答案，但无论如何我都会 post 帮助其他可能遇到与 .toJson() 方法相同问题的人

这是我的代码：

Main.java

已添加

@Override
  public String toString() {
    return "{\"lstCountries\":" + lstCountries + ",\"lstLocations\":" + lstLocations
        + ",\"lstDepartments\":" + lstDepartments + "}";
  }

Countries.java

@Override
  public String toString() {
    return "{\"strCountryId\":\"" + strCountryId + "\",\"strCountryName\":\"" + strCountryName
        + "\",\"strRegionId\":\"" + strRegionId + "\"}";
  }

Locations.java

@Override
  public String toString() {
    return "{\"strLocationId\":\"" + strLocationId + "\",\"strStreetAddress\":\""
        + strStreetAddress + "\",\"strPostalCode\":\"" + strPostalCode + "\",\"strCity\":\""
        + strCity + "\",\"strStateProvince\":\"" + strStateProvince + "\",\"strCountryId\":\""
        + strCountryId + "\"}";
  }

Departments.java

@Override
  public String toString() {
    return "{\"strDepartmentId\":\"" + strDepartmentId + "\",\"strDepartmentName\":\""
        + strDepartmentName + "\",\"strManagerId\":\"" + strManagerId + "\",\"strLocationId\":\""
        + strLocationId + "\"}";
  }

Application.java

然后我将 return 更改为：

@Transactional
  public static Result fetchOptions(String strCategoryId, String strCategoryName) {

    Main mainAppModel = new Main();
    mainAppModel.populateOptions(strCategoryId, strCategoryName);
    return ok(Json.toJson(mainAppModel.toString()));
  }

javascript

这是获取国家/地区列表的ajax

$.ajax({
        type : 'POST',
        url : "/fetchOptions/" + region + "/region",
        dataType: "json",
        success : function(data) {
            data = JSON.parse(data);
            //some codes here..
            //use data.lstCountries for Countries List
        },
        error : function(error) {
            alert("Error: " + error.status);
        }
     });

java, playframework, ajax, json - 将 Object 转换为 JSON 时发生无限递归

java, playframework, ajax, json - Infinite recursion occurs when converting Object to JSON

java

ajax

json

playframework

infinite-recursion

Application.java

Main.java

conf/routes

Departments.java（删除了 getter 和 setter）

Countries.java（对比）

Main.java

Countries.java

Locations.java

Departments.java

Application.java

javascript