mybatis查询结果返回至实体类的代码示例

本篇文章小编给大家分享一下mybatis查询结果返回至实体类的代码示例，文章代码介绍的很详细，小编觉得挺不错的，现在分享给大家供大家参考，有需要的小伙伴们可以来看看。

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 + ", name=" + name + "]";
 }
}

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

dao层：

package com.example1.dao;
 
import java.util.List;
import java.util.Map;
 
public interface OrderMapper {
 
 public List