quilt<![CDATA[]]>The content contained in this tag will be expressed asPlain text,for example<![CDATA[<]]>Indicates text content“<”。
This tag is used in the XML document, let’s first look at the use of escape characters. We know that in xml,”<”、”>”、”&”The characters cannot be stored directly, otherwise the xml syntax will be checked.Report an error, If you want to use these symbols in XML, you must escape them as entities, such as”<”、”>”、”&”, so that it can be saved into the XML document.
When using the program to read, the parser will automatically convert these entities back”<”、”>”、”&”. For example:<age> age < 30 </age>
The above writing method will cause an error.It should be written like this： <age> age < 30 </age>
It is worth noting:
(1) There cannot be spaces between escaped sequence characters;
(2) The escape sequence must end with ";";
(3) "&" that appears alone will not be considered the beginning of escape;
(4) Case sensitive.
In XML, the characters that need to be escaped are:
(1)& &
(2)< <
(3)> >
(4)＂ "
(5)＇ '
But strictly speaking, only "<" and "&" are illegal in XML, and the other three can exist legally, but it is a good habit to escape them all.
No matter what, the characters before escaped or escaped will be parsed by the xml parser.For convenience,use<![CDATA[]]>to contain content that is not parsed by the XML parser. But it should be noted:
(1) This part cannot be included”]]>”；
(2) Nested use is not allowed;
(3)”]]>”This part cannot contain spaces or line breaks.
Finally, let's talk<![CDATA[]]>In terms of the relationship between xml transfer characters, do they seem to feel that the functions are repeated?
Yes, their functions are the same, but the application scenarios and requirements are somewhat different:
(1)<![CDATA[]]>All cases cannot be applied, escape characters can;
(2) For short strings<![CDATA[]]>It is long-winded to write, but it is poorly readable for long string escape characters;
(3) <![CDATA[]]>It means that the xml parser ignores parsing, so it is faster.
The role of <![CDATA[ ]]> in mybatis
When using mybatis, we write SQL in the XML mapping file. If there are some special characters in the written SQL, it will be escaped when parsing the XML file, but we do not want it to be escaped, so we need to use <![CDATA[ ]]> to solve it.
<![CDATA[ ]]> What is it, this is XML syntax. Everything inside CDATA is ignored by the parser.
If the text contains a lot of "<" characters <= and "&" characters - just like program code, it's better to put them all into the CDATA component.
But there is a problem that is <if test=""> </if> <where> </where> <choose> </choose> <trim> </trim> and other tags will not be parsed, so we only place statements with special characters in <![CDATA[ ]]> to minimize the scope of <![CDATA[ ]]>.
Examples are as follows:
<select parameterType="" resultMap="userInfo1">
<![CDATA[
SELECT newsEdit,newsId, newstitle FROM shoppingGuide WHERE 1=1 AND newsday > #{startTime} AND newsday <= #{endTime}
]]>
<if test="etidName!=''">
AND newsEdit=#{etidName}
</if>
</select>
Because there are ">" "<=" special characters here, you need to use <![CDATA[ ]]> to comment, but there is a <if> tag, so put <if> etc. outside