![CDATA[]] and escape characters explained

I. Introduction

At the DAO layer, SQL statements related to entity classes are usually configured in XML files, as follows:

<select id="queryUsrnmTypOprorder" parameterClass="java.util.HashMap"resultMap="queryCasprjstfsetListMap"> <![CDATA[ select a.usrnm, a.typ, a.oprorder from fset a inner join casprjstfapr using (stfaprid) where casprjstfapr.jugsumid =#jugsumid# and casprjstfapr.blnorg = #blnorg# and isvld = '1' order by a.typ asc,span> a.oprorder asc ]]> </select>

The content contained by the tag ![CDATA[]] will be represented as plain text, for example, ![CDATA[]] means the text content "<".

This tag is used in xml documents, let's take a look at the use of escape characters.We know that in xml, characters such as "<", ">", "&" cannot be stored directly, otherwise an error will be reported during the xml syntax check. If you want to use these symbols in xml, you must escape them asEntities, such as "<", ">", "&", can be saved into the xml document.

The parser will automatically convert these entities back to "<", ">", and "&" when read by the program.For example:

2. Attention

1. There must be no spaces between escape sequence characters;
2. Escape sequences must end with ";";
3. A single occurrence of "&" is not considered the beginning of an escape;
4. Case sensitive.

In XML, characters that need to be escaped are:

But strictly speaking, only "<" and "&" are illegal in XML, the other three can exist legally, but, escaping them all is a good practice.

In any case, the characters before escaping and the characters after escaping will be parsed by the xml parser. For convenience, use ![CDATA[]] to includeContent not parsed by the xml parser.But it should be noted that:

1. This section can no longer contain "]]>";
2. Nesting is not allowed;
The
3. ”]]>” part cannot contain spaces or line breaks.

Finally, let's talk about the relationship between ![CDATA[]] and xml transfer characters. Do they seem to have duplicate functions?

3. Application scenarios and requirements

1. ![CDATA[]] is not applicable in all cases, escape characters are OK;
2. It is verbose for short strings ![CDATA[]], but less readable for long strings with escape characters;
3. ![CDATA[]] means that the xml parser ignores parsing, so it is faster.