mybatis查询结果返回至实体类的示例代码

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();

}

"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

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$niSVW$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.proceniSVWssRequest(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.StandardConthttp://extValve.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

"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

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

for (Map orderMap : orders) {

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：

https://jb51.net/article/190478.htm

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