當(dāng)xxxMaaper.java的方法返回值類型是List<A>，而xxxMappper.xml中對(duì)應(yīng)的sql的resultType指定為B對(duì)象，這樣是不會(huì)包錯(cuò)的(即使A與B不存在關(guān)系)

1.集合對(duì)象原本就是存儲(chǔ)對(duì)象,可以是不同的對(duì)象List

2.直接處理List類型常常會(huì)出現(xiàn)類型轉(zhuǎn)換異常,jdk5出現(xiàn)泛型,使得程序員向list中存放相同類型對(duì)象

3.泛型作用于編譯階段,僅為了防止類型混亂而出現(xiàn),類型轉(zhuǎn)換異常

4.mybatis結(jié)果集封裝bean時(shí)采用反射,是在運(yùn)行時(shí)進(jìn)行的,此時(shí)再看泛型容易進(jìn)入誤區(qū)

public class A}public class B{}

@Service()public class AImpl implements AService {private AMapper aMapper ;public List<B> increTrade(Map<String, Object> map) {List<B> lst =aMapper.increTrade(map); //這里debug看到list是A類型,此時(shí)泛型誤導(dǎo)人return lst;}}public interface AMapper {List<B>increTrade(Map<String, Object> map);}AMapper 對(duì)應(yīng)的xml文件

<select parameterType='java.util.Map' resultType='cn.easier.admin.model.A'>//-------------</select>List中map泛型對(duì)應(yīng)mybatis的返回類型List<Map<String,Object>>在mybatis對(duì)應(yīng)

resultType='java.util.HashMap'

</select> <select resultType='java.util.HashMap' >SELECT DATE_FORMAT( report_date, ’%Y%m’ ) label , COUNT( 0 ) valueFROM t_smoke_detector_record WHERE tsdr_type != '火災(zāi)告警'GROUP BY label </select>

@ApiOperation(value = '按照月份統(tǒng)計(jì)報(bào)警條數(shù)',notes = '按照月份統(tǒng)計(jì)報(bào)警條數(shù)')@GetMapping(value = 'warnCountStatistics')@ActionLog(value = '按照月份統(tǒng)計(jì)所有報(bào)警條數(shù)') public List<Map<String,Object>> warnCountStatistics(){List list = smokeDetectorRecordMapper.selectWarnCountBymonths();return list;

返回結(jié)果

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