元素类型为 "configuration" 的内容必须匹配 "(properties?,settings?,typeAliases?,typeHandlers?...)

在运行mybatis配置文件的时候，出现错误：

Caused by: org.xml.sax.SAXParseException: 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:203) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.error(ErrorHandlerWrapper.java:134) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:396) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:327) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:284) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.handleEndElement(XMLDTDValidator.java:1994) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.impl.dtd.XMLDTDValidator.endElement(XMLDTDValidator.java:879) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(XMLDocumentFragmentScannerImpl.java:1783) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:2970) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:606) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:510) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:848) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:777) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:141) ~[na:1.8.0_91]
    at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(DOMParser.java:243) ~[na:1.8.0_91]

配置文件如下：mybatis-configuration.xml

<configuration>
    
    <typeAliases>
        <typeAlias alias="User" type="mybatis.User" />
    typeAliases>

    
    <properties resource="jdbc.properties" />

    
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}" />
                <property name="url" value="${jdbc.url}" />
                <property name="username" value="${jdbc.user}" />
                <property name="password" value="${jdbc.password}" />
            dataSource>
        environment>
    environments>
    
    <mappers>
        <mapper resource="User.xml" />
    mappers>
configuration>

jdbc.properties文件如下：

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/springdb
jdbc.user=root
jdbc.password=root

找了老半天，才发现配置文件 configuration 中的元素，不但有类型限制，也有顺序限制。必须按照（properties?,settings?,typeAliases?,typeHandlers?…)顺序排放，

于是我将元素放在元素前面。即如下所示：

    "jdbc.properties" />
    <typeAliases>
        <typeAlias alias="User" type="mybatis.User" />
    typeAliases>

然后问题解决，读取数据库成功，运行成功！