Understand the common list of JSP built-in objects

JSP built-in objects overview: What should you know?

In JSP (Java Server Pages) development, there are many built-in objects available for developers to use. These built-in objects are automatically created by the JSP container when executing the JSP file, and developers do not need to manually create or initialize them. Correct understanding and use of these built-in objects can improve the development efficiency and quality of JSP pages. This article will introduce several commonly used JSP built-in objects and give specific code examples.

1. request object (javax.servlet.http.HttpServletRequest):
   The request object is an instance of the HttpServletRequest type, representing an HTTP request. It provides methods for accessing HTTP requests, including obtaining request parameters, obtaining request header information, obtaining the requested URL, etc. The following is a sample code using the request object:

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

2. response object (javax.servlet.http.HttpServletResponse):
   The response object is an instance of the HttpServletResponse type, representing the HTTP response . It provides methods to access HTTP responses, including setting response status codes, setting response types, sending redirects, etc. The following is a sample code using the response object:

   <%
     response.sendRedirect("https://www.example.com");
   %>

3. session object (javax.servlet.http.HttpSession):
   session object is an instance of the HttpSession type, representing the relationship with the client conversations between clients. It provides methods to access the session, including getting and setting session properties, destroying the session, etc. The following is a sample code using the session object:

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

4. out object (javax.servlet.jsp.JspWriter):
   out object is an instance of the JspWriter type, representing the client The output stream output from the terminal. It provides methods for outputting text, HTML tags, etc. The following is a sample code using the out object:

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

5. application object (javax.servlet.ServletContext):
   The application object is an instance of the ServletContext type and represents the entire Web application. It provides methods to access global variables of Web applications and obtain initialization parameters of Web applications. The following is a sample code using the application object:

   <%
     application.setAttribute("count", 0);
     int count = (int)application.getAttribute("count");
     count++;
     application.setAttribute("count", count);
   %>

The above are several commonly used JSP built-in objects. By using these built-in objects correctly, HTTP requests and responses can be processed more conveniently. Manage session state and output page content. In actual development, there are other built-in objects, such as pageContext objects, config objects, etc., which are also worthy of further understanding and mastery by developers.

I hope this article can help readers have a deeper understanding and application of JSP built-in objects. By skillfully using these built-in objects, you can improve the development efficiency and maintainability of web applications and provide users with a better experience.

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