java省、市、县树的json转换遇到的溢出问题

        在开发的过程中遇到省市县树的转json问题，接下来就给出遇到的问题及解决方案：

        由于对象中存在双向引用导致的无限递归，从而在转json的过程中产生溢出，解决的方案如下通过加注解的方式来避免溢出。

        jackson中的@JsonBackReference和@JsonManagedReference，以及@JsonIgnore均是为了解决对象中存在双向引用导致的无限递归（infinite recursion）问题，这些标注均可用在属性或对应的get、set方法中。

       @JsonBackReference和@JsonManagedReference：这两个标注通常配对使用，通常用在父子关系中。        @JsonBackReference标注的属性在序列化（serialization，即将对象转换为json数据）时，会被忽略（即结果中的json数据不包含该属性的内容）。

       @JsonManagedReference标注的属性则会被序列化。在序列化时，@JsonBackReference的作用相当于@JsonIgnore，此时可以没有@JsonManagedReference。但在反序列化（deserialization，即json数据转换为对象）时，如果没有@JsonManagedReference，则不会自动注入

       @JsonBackReference标注的属性（被忽略的父或子）；如果有@JsonManagedReference，则会自动注入自动注入@JsonBackReference标注的属性。 
       @JsonIgnore：直接忽略某个属性，以断开无限递归，序列化或反序列化均忽略。当然如果标注在get、set方法中，则可以分开控制，序列化对应的是get方法，反序列化对应的是set方法。在父子关系中，当反序列化时，@JsonIgnore不会自动注入被忽略的属性值（父或子），这是它跟@JsonBackReference和@JsonManagedReference最大的区别。 

       以下为测试代码：

       AreaVO类

public class AreaVO implements Serializable {private IntegerareaId; /* 索引ID */private StringareaName; /* 地区名称 */private IntegerareaParentId; /* 地区父ID */private BooleanareaSort; /* 排序 */private Integer areaDeep; /* 地区深度，从1开始 */private StringareaRegion; /* 大区名称 */private AreaVO parentRegion;/* 父节点 */private ArrayList<AreaVO> childRegions = new ArrayList<>();/* zhua */private StringwarehouseName; /* 仓库名称*/// Constructorpublic AreaVO() {}@JsonManagedReferencepublic ArrayList<AreaVO> getChildRegions() {return childRegions;}@JsonManagedReferencepublic void setChildRegions(ArrayList<AreaVO> childRegions) {this.childRegions = childRegions;}@JsonBackReferencepublic AreaVO getParentRegion() {return parentRegion;}@JsonBackReferencepublic void setParentRegion(AreaVO parentRegion) {this.parentRegion = parentRegion;}public String getWarehouseName() {return warehouseName;}public void setWarehouseName(String warehouseName) {this.warehouseName = warehouseName;}/** * full Constructor */public AreaVO(Integer areaId, String areaName, Integer areaParentId, Boolean areaSort, Integer areaDeep, String areaRegion) {this.areaId = areaId;this.areaName = areaName;this.areaParentId = areaParentId;this.areaSort = areaSort;this.areaDeep = areaDeep;this.areaRegion = areaRegion;}public Integer getAreaId() {return areaId;}public void setAreaId(Integer areaId) {this.areaId = areaId;}public String getAreaName() {return areaName;}public void setAreaName(String areaName) {this.areaName = areaName;}public Integer getAreaParentId() {return areaParentId;}public void setAreaParentId(Integer areaParentId) {this.areaParentId = areaParentId;}public Boolean getAreaSort() {return areaSort;}public void setAreaSort(Boolean areaSort) {this.areaSort = areaSort;}public Integer getAreaDeep() {return areaDeep;}public void setAreaDeep(Integer areaDeep) {this.areaDeep = areaDeep;}public String getAreaRegion() {return areaRegion;}public void setAreaRegion(String areaRegion) {this.areaRegion = areaRegion;}@Overridepublic String toString() {return "AreaVO [" + "areaId=" + areaId + ", areaName=" + areaName + ", areaParentId=" + areaParentId + ", areaSort=" + areaSort + ", areaDeep=" + areaDeep + ", areaRegion=" + areaRegion +  "]";}}

测试main方法：

public class test {//    @JsonIgnore    public static void main(String[] args) {        JsonResult<List<AreaVO>> jsonResult = new JsonResult<List<AreaVO>>();        JsonResult<AreaVO> jsonResult1 = new JsonResult<AreaVO>();        List<AreaVO> areaVOs=new ArrayList<>();        ArrayList<AreaVO> areaVOs1=new ArrayList<>();        ArrayList<AreaVO> areaVOs2=new ArrayList<>();        ArrayList<AreaVO> areaVOs3=new ArrayList<>();        AreaVO areaVO=new AreaVO();        AreaVO areaVO1=new AreaVO();        AreaVO areaVO2=new AreaVO();        AreaVO areaVO3=new AreaVO();        areaVO.setAreaId(1);        areaVO.setAreaName("北京");        areaVO.setAreaParentId(0);        areaVO.setAreaSort(true);        areaVO.setAreaDeep(1);        areaVO.setAreaRegion("华北");        areaVO.setParentRegion(null);        areaVO1.setAreaId(36);        areaVO1.setAreaName("北京市");        areaVO1.setAreaParentId(1);        areaVO1.setAreaSort(true);        areaVO1.setAreaDeep(2);        areaVO1.setAreaRegion("华北");        areaVO1.setParentRegion(areaVO);        areaVO2.setAreaId(38);        areaVO2.setAreaName("西城区");        areaVO2.setAreaParentId(36);        areaVO2.setAreaSort(true);        areaVO2.setAreaDeep(3);        areaVO2.setAreaRegion("华北");        areaVO2.setParentRegion(areaVO1);        areaVO3.setAreaId(54);        areaVO3.setAreaName("延庆县");        areaVO3.setAreaParentId(36);        areaVO3.setAreaSort(true);        areaVO3.setAreaDeep(3);        areaVO3.setAreaRegion("华北");        areaVO3.setParentRegion(areaVO1);        areaVOs2.add(areaVO2);        areaVO1.setChildRegions(areaVOs2);        areaVOs3.add(areaVO3);        areaVO1.setChildRegions(areaVOs3);        areaVOs1.add(areaVO1);        areaVO.setChildRegions(areaVOs1);        areaVOs.add(areaVO);        jsonResult.setMsg("查询单个收货地址成功！");        jsonResult.setStatus("0");        jsonResult.setData(areaVOs);        System.out.println("-===" + jsonResult.getData());        System.out.println(JsonMapper.jsonMapper().toJson(jsonResult));    }}

测试结果：

{    "status":"0",    "msg":"查询单个收货地址成功！",    "data":[        {            "areaId":1,            "areaName":"北京",            "areaParentId":0,            "areaSort":true,            "areaDeep":1,            "areaRegion":"华北",            "childRegions":[                {                    "areaId":36,                    "areaName":"北京市",                    "areaParentId":1,                    "areaSort":true,                    "areaDeep":2,                    "areaRegion":"华北",                    "childRegions":[                        {                            "areaId":54,                            "areaName":"延庆县",                            "areaParentId":36,                            "areaSort":true,                            "areaDeep":3,                            "areaRegion":"华北",                            "childRegions":[                            ],                            "warehouseName":null                        }                    ],                    "warehouseName":null                }            ],            "warehouseName":null        }    ]}

以上问题就ok啦！