mybatis查询结果返回至实体类的示例代码

近期，利⽤mybatis做⼀个简单查询，先看主要代码：Service层：

package com.example1.service;

import java.util.List;

import org.apache.log4j.Logger;

import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;

import com.example1.dao.OrderMapper;import com.example1.pojo.Order;

@Service

public class OrderService {

private Logger log = Logger.getLogger(OrderService.class);

@Autowired

private OrderMapper orderMapper;

public void findOrders() {

List orders = orderMapper.findOrders(); for (Order order : orders) {

log.info(order.getId() + \" : \" + order.getName()); } }}

dao层：

package com.example1.dao;import java.util.List;

import com.example1.pojo.Order;public interface OrderMapper { public List findOrders();}

SELECT * FROM t_order

Order类：

package com.example1.pojo;

public class Order {

private String id; private String name; public String getId() { return id; }

public void setId(String id) { this.id = id; }

public String getName() { return name; }

public void setName(String name) { this.name = name; }

@Override

public String toString() {

return \"Order [id=\" + id + \ }}

配置妥当，执⾏，结果报错了：

java.lang.ClassCastException: java.util.HashMap cannot be cast to com.example1.pojo.Order at com.example1.service.OrderService.findOrders(OrderService.java:26)

at com.example1.service.OrderService$$FastClassBySpringCGLIB$$b6b2c61a.invoke() at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)

at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:717) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)

at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99)

at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:281) at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)

at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:653)

at com.example1.service.OrderService$$EnhancerBySpringCGLIB$$e285c4bb.findOrders() at com.example1.controller.OrderController.findOrders(OrderController.java:22) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498)

at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:219)

at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132) at

org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:100) at

org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:604) at

org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:565) at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)

at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778) at javax.servlet.http.HttpServlet.service(HttpServlet.java:617) at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)

at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:879)

at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:617) at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1778) at java.lang.Thread.run(Thread.java:745)

可以看出，java.util.HashMap不能直接存储到具体的实体类。解决办法：

⼀、dao层通过resultType指定返回类型

SELECT * FROM t_order

⼆、查询结果返回list，然后遍历list，将map转换成相应的java对象修改后的Service层：

package com.example1.service;

import java.util.List;import java.util.Map;

import org.apache.log4j.Logger;

import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;

import com.alibaba.fastjson.JSONArray;import com.alibaba.fastjson.JSONObject;import com.example1.dao.OrderMapper;import com.example1.pojo.Order;

@Service

public class OrderService {

private Logger log = Logger.getLogger(OrderService.class);

@Autowired

private OrderMapper orderMapper;

public void findOrders() {

List

String orderJsonStr = JSONObject.toJSONString(orderMap);

Order order = (Order) JSONArray.parseObject(orderJsonStr,Order.class); log.info(order.getId() + \" : \" + order.getName()); } }}

dao层：

package com.example1.dao;

import java.util.List;import java.util.Map;

public interface OrderMapper {

public List

其中，关于map转java对象的⽅法有好多种，具体可以参考本⼈另⼀篇⽂章：

以上两种⽅法均实际测试通过。到此这篇关于mybatis查询结果返回⾄实体类的⽰例代码的⽂章就介绍到这了,更多相关mybatis结果返回实体类内容请搜索以前的⽂章或继续浏览下⾯的相关⽂章希望⼤家以后多多⽀持！