JSP Standard Tag Library (JSTL) technical score in the Java class library
JSP Standard Tag Library (JSTL) is an important component of the Java server page (JSP). It provides a set of labels and functions to simplify the development and maintenance of the JSP page.JSTL can help developers reduce the workload of writing Java code in the JSP page, making the readability of the page more readable and easier to maintain.
JSTL technology principles mainly include the following aspects:
1. JSTL label library: JSTL contains a series of label libraries. Through these tag libraries, various tags and functions can be used on the JSP page.The JSTL tag library contains different functions of labels, such as process control, cycle, conditional judgment, database access, and so on.By using these label libraries, some common operations can be easily completed on the JSP page without writing a lot of Java code.
2. JSTL label parser: JSTL label parser is one of the core components of JSTL. It is responsible for analyzing the label of the JSTL label library.When the web server receives a JSP request with a JSTL label, the label parser will resolve these labels and convert it to the corresponding Java code.In this way, developers can use JSTL labels on the JSP page without manual writing the corresponding Java code.
3. JSTL Standard Movement: JSTL also provides some standard actions to process logic and data operations in the JSP page.These standard actions can be declared in the form of XML tags in the JSP page and performing corresponding operations during runtime.For example, you can use <c: if> action to judge the conditions, use the <c: Foreach> action for circulating, use the <c: set> action setting variable value, and so on.
Below is a simple example, showing the usage of the JSTL label library and standard action:
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head>
<Title> JSTL Example </Title>
</head>
<body>
<H1> Welcome to Jstl </h1>
<c: set var = "name" value = "Zhang San" />
<c: if test = "$ {name eq 'Zhang San"} ">
<p> Hello, Zhang San!</p>
</c:if>
<c:choose>
<c: When test = "$ {name eq 'Li Si four'}">
<p> Hello, Li Si!</p>
</c:when>
<c:otherwise>
<p> Hello, stranger!</p>
</c:otherwise>
</c:choose>
<c:forEach var="i" begin="1" end="5">
<p> The current loop variable value is: $ {i} </p>
</c:forEach>
</body>
</html>
In the above examples, first introduce the label library of JSTL by `< %@ taglib prefix =" c "uri =" http://java.sun.com/jsp/jstl/core " %>Then use the `<C: Set>` movement to set a variable `name` value is` Zhang San `.Then use the `<C: if>` action to judge the condition. If the value of the `name` is equal to` Zhang San `, then display` hello, Zhang San!``.Next, use `<C: Choose>` and `<C: WHEN>` to make multiple branch judgments. If the value of `name` is equal to` 接 四 `, then` Hello, Li Si!`, Otherwise it will show` Hello, strangers!``.Finally, use the `<C: Foreach> Action to perform a circular operation to output the value of the current cycle variable.
Through the above examples, it can be seen that JSTL technology can significantly simplify and optimize the development of the JSP page, making it more easy to read and maintain.Developers can reduce the amount of Java code on the JSP page by using the JSTL label library and standard actions to improve the development efficiency.At the same time, JSTL also provides various functional labels and functions, which can meet different business needs and make the development of JSP pages more flexible and efficient.
