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Introduction to the nine built-in objects of JSP in web development and their functions

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Feb 01, 2024 am 08:43 AM

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Introduction to the nine built-in objects of JSP in web development and their functions

JSP nine built-in objects and their role in web development

JSP (JavaServer Pages) is a web page based on Java language Development technology that allows developers to embed Java code in HTML or XML pages. JSP pages are executed on the server side and the resulting HTML or XML code is sent to the client browser.

There are nine objects built into JSP that can provide various functions in web development. The nine built-in objects are:

request: represents the request issued by the client. It contains information about the request, such as the requested URL, request method, request headers, etc.
response: Indicates the server's response to the request. It contains information about the response, such as response status code, response headers, response body, etc.
session: Represents a session between the client and the server. It contains information about the session, such as session ID, session properties, etc.
application: Represents the entire application. It contains information about the application, such as application properties, application-scoped listeners, etc.
config: Indicates the configuration information of the JSP page. It contains information about the JSP page, such as the path to the JSP page, the initialization parameters of the JSP page, etc.
out: Represents the output stream of the JSP page. It can be used to output HTML or XML code to the client browser.
page: Represents the JSP page itself. It can be used to access the properties and methods of a JSP page.
pageContext: Represents the context of the JSP page. It contains information about the JSP page, such as the properties of the JSP page, the output stream of the JSP page, etc.
exception: Indicates an exception that occurs in the JSP page. It contains information about the exception such as exception type, exception message, etc.

These nine built-in objects play an important role in web development. They can help developers easily implement various functions, such as obtaining request information, generating responses, managing sessions, accessing application properties, configuring JSP pages, outputting HTML or XML code, accessing properties and methods of JSP pages, getting JSP page Context and handling exceptions in JSP pages, etc.

The following are several examples of using JSP built-in objects:

Use the request object to obtain the request parameters:

String name = request.getParameter("name");

Use the response object to set Response header:

response.setHeader("Content-Type", "text/html");

Use session object to store session properties:

session.setAttribute("user", user);

Use application object to access application properties:

String appName = application.getInitParameter("appName");

Use the config object to obtain the initialization parameters of the JSP page:

String initParam = config.getInitParameter("initParam");

Use the out object to output HTML or XML code:

out.println("<html><body><h1 id="Hello-World">Hello World!</h1></body></html>");

Use the page object to access the properties and methods of the JSP page:

String pageEncoding = page.getPageEncoding();

Use the pageContext object to obtain the context of the JSP page:

PageContext pageContext = this.getJspContext();

Use exception Object handling exceptions in JSP pages:

try {
  // 代码
} catch (Exception e) {
  exception = e;
}

JSP built-in objects are very important tools in JSP development. Mastering the use of these built-in objects can help developers easily implement various functions and improve development efficiency.

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