MyBatis查询返回Map时设置值为null的字段也在结果集中

使用Mybatis的查询，很多时候都要返回Map，Mybatis默认若field的值为null时候不返回字段的名称，导致结果集map没有对应的key。

然而很多时候为了前端的使用方便还是要返回字段的key。

若MyBatis一个查询的如下

<select id="queryById"  resultType="Map" parameterType="Object">
select id,user_name,user_code from customer where id = #{id}
</select>

当查询的一条记录如下

mysql> select id,user_name, user_code from customer limit 1;
+----+--------------+-----------+
| id | user_name    | user_code |
+----+--------------+-----------+
|  1 | MassiveStars |      NULL |
+----+--------------+-----------+

返回的Map只有id和user_name两个key

Mybatis的配置文件中有一个callSettersOnNulls属性可解决此问题，mybatis-config.xml如下。

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD SQL MAP Config 3.2//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

<settings>
<setting name="callSettersOnNulls" value="true"/>
</settings>

</configuration>

若报下列错误，则 mybatis-config.xml中各标签的顺序有错误，正确的顺序依次为properties、settings、typeAliases、typeHandlers、objectFactory、objectWrapperFactory、plugins、environments、databaseIdProvider、mappers。

Caused by: org.xml.sax.SAXParseException; lineNumber: 17; columnNumber: 17; 元素类型为 "configuration" 的内容必须匹配 "(properties?,settings?,typeAliases?,typeHandlers?,objectFactory?,objectWrapperFactory?,plugins?,environments?,databaseIdProvider?,mappers?)"。
at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:198)
at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.error(ErrorHandlerWrapper.java:134)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:437)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:368)
at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:325)
at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.handleEndElement(XMLDTDValidator.java:1994)
at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.endElement(XMLDTDValidator.java:879)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1782)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2973)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:606)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:510)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:848)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:777)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141)
at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:243)
at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(DocumentBuilderImpl.java:347)
at org.apache.ibatis.parsing.XPathParser.createDocument(XPathParser.java:254)

MyBatis在3.2版本中加入此特性，若还是不生效，检查项目的MyBatis版本是不是大于等于3.2。