Hibernate懒加载导致json数据对象传输异常的问题---（非常重要）

1. 异常：

[console_demo][WARN] [2016-12-15 19:49:35] org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver.handleHttpMessageNotWritable(407) | Failed to write HTTP message: org.springframework.http.converter.HttpMessageNotWritableException: Could not write content: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.HashMap["ckRequirePartLists"]->java.util.ArrayList[0]->com.dyoon.cmms.pojo.CkRequirePartList["ckPurchaseBill"]->com.dyoon.cmms.pojo.CkPurchaseBill["applyOperator"]->com.dyoon.cmms.pojo.UserOperator_$$_jvsta2a_12["sysRole"]->com.dyoon.cmms.pojo.SysRole_$$_jvsta2a_8["userModifyLog"]->com.dyoon.cmms.pojo.UserModifyLog_$$_jvsta2a_6["handler"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.HashMap["ckRequirePartLists"]->java.util.ArrayList[0]->com.dyoon.cmms.pojo.CkRequirePartList["ckPurchaseBill"]->com.dyoon.cmms.pojo.CkPurchaseBill["applyOperator"]->com.dyoon.cmms.pojo.UserOperator_$$_jvsta2a_12["sysRole"]->com.dyoon.cmms.pojo.SysRole_$$_jvsta2a_8["userModifyLog"]->com.dyoon.cmms.pojo.UserModifyLog_$$_jvsta2a_6["handler"])

2. 原因：

使用注解@ResponseBody返回由Hibernate DAO直接获得的pojo对象内存在Lazy关联对象，执行Jason转换时，会从数据库加载该对象，而此时session已关闭，导致加载失败，进而导致Jason转换失败。

3  解决：

方法一：在不影响数据完整性的情况下，使用set方法手动置空pojo类的Lazy关联对象。（这样如果关联的对象比较多，可能漏的。）

方法二：使用@JsonIgnore注释掉pojo类的Lazy关联对象。（这种如果在其他的地方需要用关联的对象转json,这样就会导致失效。）

方法三：自定义类，二次封装所需的pojo对象的属性。

4. 事例：以下对第三种方法做展示

jsp页面：

function showPartDetails(purchBillId){      $.ajax({type:"post",url:"${rootPath }/depot/purchase/getPartByPurchBillId?purchBillId="+purchBillId,success : function(data){ alert(data.requirePartListBeans[0].partName);}});         }

通过ajax发送请求到controller，服务器处理结果，将结果以json的格式发送给前端。

常规下的controller如下：

        @RequestMapping(value = "/getPartByPurchBillId")@ResponseBodypublic Map<String,Object> getPartByPurchBillId(@RequestParam(value="purchBillId") Integer purchBillId) throws JsonProcessingException {Map<String, Object> map = new HashMap<>();List<CkRequirePartList> ckRequirePartLists = purchaseService.getPartByPurchBillId(purchBillId);map.put("requirePartListBeans", ckRequirePartLists);         return map;}

但是由于hibernate懒加载的问题，requirePartListBeans不能正常的转换为json，这时候将前端要获取的属性数据封装成一个类，以下为假如前端要获取的3条数据：

public class RequirePartListBean {private String partNumber;private String partName;private BigDecimal partQuantity;public String getPartNumber() {return partNumber;}public void setPartNumber(String partNumber) {this.partNumber = partNumber;}public String getPartName() {return partName;}public void setPartName(String partName) {this.partName = partName;}public BigDecimal getPartQuantity() {return partQuantity;}public void setPartQuantity(BigDecimal partQuantity) {this.partQuantity = partQuantity;}}

更改后的controller为：

        @RequestMapping(value = "/getPartByPurchBillId")@ResponseBodypublic Map<String,Object> getPartByPurchBillId(@RequestParam(value="purchBillId") Integer purchBillId) throws JsonProcessingException {Map<String, Object> map = new HashMap<>();List<CkRequirePartList> ckRequirePartLists = purchaseService.getPartByPurchBillId(purchBillId);RequirePartListBean r = null;List<RequirePartListBean> requirePartListBeans = new ArrayList<>();for (CkRequirePartList ckRequirePartList : ckRequirePartLists) {r = new RequirePartListBean();r.setPartName(ckRequirePartList.getModPartCatalog().getPartName());r.setPartNumber(ckRequirePartList.getModPartCatalog().getPartNumber());r.setPartQuantity(ckRequirePartList.getPartQuantity());requirePartListBeans.add(r);}map.put("requirePartListBeans", requirePartListBeans);return map;}

前端ajax通过success响应数据，

success : function(data){ alert(data.requirePartListBeans[0].partName);}

至此，问题得到解决。还有问题的可以留言。