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_" role="presentation">_jvsta2a_12["sysRole"]->com.dyoon.cmms.pojo.SysRole__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_" role="presentation">_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_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_" role="presentation">_jvsta2a_8["userModifyLog"]->com.dyoon.cmms.pojo.UserModifyLog__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")





	@ResponseBody





	public 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")





	@ResponseBody





	public 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。

原文地址：https://blog.csdn.net/baidu_28283827/article/details/53675121