mybatis查询结果返回至实体类的示例代码

2023-07-21 19:17:03 83

近期，利用mybatis做一个简单查询，先看主要代码：

Service层：

packagecom.example1.service;

importjava.util.List;

importorg.apache.log4j.Logger;
importorg.springframework.beans.factory.annotation.Autowired;
importorg.springframework.stereotype.Service;

importcom.example1.dao.OrderMapper;
importcom.example1.pojo.Order;

@Service
publicclassOrderService{

privateLoggerlog=Logger.getLogger(OrderService.class);

@Autowired
privateOrderMapperorderMapper;

publicvoidfindOrders(){
Listorders=orderMapper.findOrders();
for(Orderorder:orders){
log.info(order.getId()+":"+order.getName());
}
}
}

dao层：

packagecom.example1.dao;
importjava.util.List;
importcom.example1.pojo.Order;
publicinterfaceOrderMapper{
publicListfindOrders();
}






SELECT*FROMt_order

Order类：

packagecom.example1.pojo;

publicclassOrder{

privateStringid;
privateStringname;
publicStringgetId(){
returnid;
}
publicvoidsetId(Stringid){
this.id=id;
}
publicStringgetName(){
returnname;
}
publicvoidsetName(Stringname){
this.name=name;
}
@Override
publicStringtoString(){
return"Order[id="+id+",name="+name+"]";
}
}

配置妥当，执行，结果报错了：

java.lang.ClassCastException:java.util.HashMapcannotbecasttocom.example1.pojo.Order
atcom.example1.service.OrderService.findOrders(OrderService.java:26)
atcom.example1.service.OrderService$$FastClassBySpringCGLIB$$b6b2c61a.invoke()
atorg.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
atorg.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:717)
atorg.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
atorg.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99)
atorg.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:281)
atorg.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96)
atorg.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
atorg.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
atorg.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
atorg.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:653)
atcom.example1.service.OrderService$$EnhancerBySpringCGLIB$$e285c4bb.findOrders()
atcom.example1.controller.OrderController.findOrders(OrderController.java:22)
atsun.reflect.NativeMethodAccessorImpl.invoke0(NativeMethod)
atsun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
atsun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
atjava.lang.reflect.Method.invoke(Method.java:498)
atorg.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:219)
atorg.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:132)
atorg.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:100)
atorg.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:604)
atorg.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:565)
atorg.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
atorg.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)
atorg.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
atorg.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
atorg.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778)
atjavax.servlet.http.HttpServlet.service(HttpServlet.java:617)
atjavax.servlet.http.HttpServlet.service(HttpServlet.java:723)
atorg.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
atorg.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
atorg.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
atorg.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
atorg.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
atorg.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
atorg.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
atorg.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
atorg.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:879)
atorg.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:617)
atorg.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1778)
atjava.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*FROMt_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：

packagecom.example1.service;

importjava.util.List;
importjava.util.Map;

importorg.apache.log4j.Logger;
importorg.springframework.beans.factory.annotation.Autowired;
importorg.springframework.stereotype.Service;

importcom.alibaba.fastjson.JSONArray;
importcom.alibaba.fastjson.JSONObject;
importcom.example1.dao.OrderMapper;
importcom.example1.pojo.Order;

@Service
publicclassOrderService{

privateLoggerlog=Logger.getLogger(OrderService.class);

@Autowired
privateOrderMapperorderMapper;

publicvoidfindOrders(){
Listorders=orderMapper.findOrders();
for(MaporderMap:orders){
StringorderJsonStr=JSONObject.toJSONString(orderMap);
Orderorder=(Order)JSONArray.parseObject(orderJsonStr,Order.class);
log.info(order.getId()+":"+order.getName());
}
}
}

dao层：

packagecom.example1.dao;

importjava.util.List;
importjava.util.Map;

publicinterfaceOrderMapper{

publicListfindOrders();
}

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://www.nhooo.com/article/190478.htm

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毛票票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毛票票！

mybatis查询结果返回至实体类的示例代码

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