mybatis动态sql实现逻辑代码详解_Sql Server

mybatis动态sql实现逻辑代码详解

2021-09-22 18:04_东极 Sql Server

mybatis通过将sql配置xml文件中,通过解析xml动态标签来实现动态sql，本文以xml文件为例给大家介绍mybatis动态sql的实现代码，感兴趣的朋友一起看看吧

<?xml version = "1.0" ?>
<!DOCTYPE script SYSTEM "script-1.0.dtd">
<script namespace="user">
<common id="commonOrder">
order by id desc
</common>
<sql id="queryUser">
select * from user
<where>
<if test='id != null '>
id = #{id}
</if>
<if test="names != null and names.size() >0">
and name in
<foreach collection="names" item="item" separator="," open="(" close=")">
${item}
</foreach>
</if>
</where>
<ref id="commonOrder"/>
</sql>
<sql id="updateUser">
update user set name = ${name}
<where>
<if test='id != null '>
id = #{id}
</if>
</where>
</sql>
</script>

1.xml文件读取

xml标签编写规则

<!ELEMENT script (#PCDATA | sql | common)*>
<!ATTLIST script
namespace CDATA #REQUIRED
>
<!ELEMENT sql (#PCDATA | trim | where | set | foreach | choose | if | ref)*>
<!ATTLIST sql
id CDATA #REQUIRED
>
<!ELEMENT common (#PCDATA | trim | where | set | foreach | choose | if)*>
<!ATTLIST common
id CDATA #REQUIRED
>
<!ELEMENT ref (#PCDATA)*>
<!ATTLIST ref
id CDATA #REQUIRED
>
<!ELEMENT trim (#PCDATA | trim | where | set | foreach | choose | if)*>
<!ATTLIST trim
prefix CDATA #IMPLIED
prefixOverrides CDATA #IMPLIED
suffix CDATA #IMPLIED
suffixOverrides CDATA #IMPLIED
>
<!ELEMENT where (#PCDATA | trim | where | set | foreach | choose | if | ref)*>
<!ELEMENT set (#PCDATA | trim | where | set | foreach | choose | if)*>
<!ELEMENT foreach (#PCDATA | trim | where | set | foreach | choose | if)*>
<!ATTLIST foreach
collection CDATA #REQUIRED
item CDATA #IMPLIED
index CDATA #IMPLIED
open CDATA #IMPLIED
close CDATA #IMPLIED
separator CDATA #IMPLIED
>
<!ELEMENT choose (when* , otherwise?)>
<!ELEMENT when (#PCDATA | trim | where | set | foreach | choose | if)*>
<!ATTLIST when
test CDATA #REQUIRED
>
<!ELEMENT otherwise (#PCDATA | trim | where | set | foreach | choose | if)*>
<!ELEMENT if (#PCDATA | trim | where | set | foreach | choose | if)*>
<!ATTLIST if
test CDATA #REQUIRED
>

DocumentBuilderFactory 是jdk自带的解析xml文件操作,位于 javax.xml.parsers 包,如图其是一个抽象类,因此无法被实例化

mybatis动态sql实现逻辑代码详解

需要通过 newInstance 来实例化

mybatis动态sql实现逻辑代码详解

实例化对象后的属性 setValidating(true); 即通过xml的验证规则进行xml格式验证

setNamespaceAware 设置忽略命名空间，对于xml文件的命名空间的定义,详见

private Document buildXml(InputStream scriptFile)
throws ParserConfigurationException, SAXException, IOException {
DocumentBuilderFactory factory = DocumentBuilderFactory
.newInstance();
//默认情况下，解析器不验证文档。将这个参数设置为 true 可打开验证功能。
factory.setValidating(true);
//是否设置命名空间
factory.setNamespaceAware(false);
//确定是否要忽略文件中的注释。其默认值为 false。
factory.setIgnoringComments(true);
//确定是否要忽略元素内容中的空白（类似于浏览器对待 HTML 的方式）。其默认值为 false。
factory.setIgnoringElementContentWhitespace(false);
//定解析器是否要将 CDATA 节点转换为文本，以及是否要和周围的文本节点合并（如果适用的话）。其默认值为 false。
factory.setCoalescing(false);
//确定是否要展开外部实体引用。如果为 true，外部数据将插入文档。其默认值为 true
factory.setExpandEntityReferences(true);
DocumentBuilder builder = factory.newDocumentBuilder();
//设置验证规则文件 dtd文件
builder.setEntityResolver(new EntityResolver() {
@Override
public InputSource resolveEntity(String publicId,
String systemId) throws SAXException, IOException {
return new InputSource(new ClassPathResource("script-1.0.dtd").getInputStream());
}
});
//设置错误解析器
builder.setErrorHandler(new ErrorHandler() {
@Override
public void error(SAXParseException exception)
throws SAXException {
throw exception;
}
@Override
public void fatalError(SAXParseException exception)
throws SAXException {
throw exception;
}
@Override
public void warning(SAXParseException exception)
throws SAXException {
}
});
return builder.parse(scriptFile);
}