In -depth analysis

In -depth analysis JSP Standard Tag Library (JSTL) is an extended label library of JavaseerVer Pages (JSP). It provides a set of labels and functions to simplify the development and maintenance of the JSP page.The JSTL label library contains the core label library and XML processing tag library (XML). It can handle common data operation, process control, internationalization and formatting, XML processing and other tasks. JSTL's technical principles are mainly based on JSP and its label analysis and processing process.In the JSP page, the JSTL label is parsed and converted into the corresponding Java code from the JSP compiler, and then executed in the Servlet generated by JSP.The core label library of JSTL contains the following important tags: 1. `<C: OUT>` Tags: Value for output variables or expressions.Below is an example: jsp <c:set var="name" value="John" /> <c:out value="${name}" /> This code will output the value of the variable name (John). 2. `<C: Set>` Tags: Used to set the value of the variable.Below is an example: jsp <c:set var="age" value="25" /> This code will set the value of the AGE variable to 25. 3. `<C: FOREACH>` Tags: For circular iteration.Below is an example: jsp <c:forEach items="${names}" var="name"> <c:out value="${name}" /> </c:forEach> This code traverses the names of names and outputs the value of each element. 4. `<C: if>` Tags: for conditional judgment.Below is an example: jsp <c:if test="${age > 18}"> <p> Adults </p> </c:if> <c:if test="${age <= 18}"> <p> Minor </p> </c:if> This code will determine the output content based on the value of the AGE variable. JSTL's XML processing tag library provides some labels for processing XML documents, such as `<x: FOREACH>` and `<x: PARSE>`.In addition, JSTL also provides labels for formatting and localized support for the date, numerical value. The advantage of using the JSTL tag library is that the readability and maintenance of the JSP page can be improved.By using JSTL tags, business logic and expression can be pulled out of the JSP page, reducing the redundancy of the code, and improving the relictory and maintenance of the code.In addition, JSTL also provides some high -level data operations, process control and internationalization functions, making the development of the JSP page more convenient and flexible. In summary, JSTL is a very practical Java class library that provides rich labels and functions to simplify the development and maintenance of the JSP page.Through in -depth understanding of JSTL's technical principles and use methods, we can develop dynamic web applications more efficiently. Hope the above content will help you!