mybatis动态sql实现逻辑代码详解

Nice MsSql

2022-05-23 0 794

<?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

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
https://www.jb51.net/article/219617.htm

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);
		}