Must-learn JSP built-in object knowledge: Understand what are the commonly used built-in objects in JSP

Necessary knowledge for learning JSP built-in objects: To master the built-in objects in jsp, you need specific code examples

JSP (JavaServer Pages) is a dynamic web page Development technology, its advantage lies in combining the characteristics of dynamic programming languages ​​​​(such as Java) and static pages. In JSP, built-in objects play an important role to facilitate developers for data processing and page rendering. This article will introduce some commonly used JSP built-in objects and provide specific code examples to deepen understanding.

1. request object (HttpServletRequest): represents the client's request and encapsulates various information of the HTTP request, such as request parameters, request headers, request methods, etc. Through the request object, we can obtain and process the data submitted by the user. The following is a sample code for obtaining request parameters:

<%
    String username = request.getParameter("username");
%>

2. response object (HttpServletResponse): represents the server's response and encapsulates various information of the HTTP response, such as response status code and response headers , response body, etc. Through the response object, we can send data to the client or set some properties of the response. The following is a sample code for setting the response header:

<%
    response.setContentType("text/html;charset=UTF-8");
%>

3. out object (JspWriter): represents the output stream of the JSP page, and content can be output to the client through the out object. In JSP, we can use the built-in out object to output HTML, text and other content. The following is a sample code that outputs text:

<%
    out.println("Hello, World!");
%>

4. session object (HttpSession): represents the user session and is used to share data between multiple requests from the same user. Through the session object, we can save and obtain data between multiple pages or requests. The following is a sample code to save and obtain session data:

<%
    session.setAttribute("username", "John");
    String storedUsername = (String) session.getAttribute("username");
%>

5. application object (ServletContext): represents the context of the entire application and can share data between different components of the application . Through the application object, we can share data between different JSP pages. The following is a sample code for saving and obtaining application data:

<%
    application.setAttribute("count", 10);
    int storedCount = (int) application.getAttribute("count");
%>

6. pageContext object (PageContext): represents the context of the JSP page and encapsulates references to other built-in objects. Through the pageContext object, we can easily obtain other built-in objects, such as request, response, etc. The following is a sample code to obtain other built-in objects:

<%
    request.setAttribute("name", "Alice");
    String storedName = (String) pageContext.getAttribute("name");
%>

In JSP development, it is very important to master the use of these built-in objects. By using these objects rationally, we can develop dynamic web pages more flexibly and efficiently. At the same time, learning and practicing code examples is also very necessary. Through actual operations, you can better understand and master the usage of built-in objects.

To summarize, this article introduces the commonly used built-in objects in JSP: request, response, out, session, application and pageContext, and provides specific code examples to deepen understanding. Through study and practice, I believe readers can become more proficient in the usage of JSP built-in objects and improve development efficiency.

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