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Don't you know the relationship between JSP and servlet?

2022-07-07 03:07:00 【60 year old procedural ape】

List of articles

What is? Servlet

1、servlet Is running on the Web Small in server Java Program .servlet Usually by HTTP（ Hypertext transfer protocol ） Receive and respond come from Web Client requests .

2、Servlet yes JavaEE One of the norms , A specification is an interface .

Servlet Sample code for the program ：

public class HelloServlet implements Servlet {
/**
* service  Methods are designed to handle requests and responses 
* @param servletRequest
* @param servletResponse
* @throws ServletException
* @throws IOException
*/
@Override
	public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws
	ServletException, IOException {
		System.out.println("Hello Servlet  Was interviewed ");
	}
}

web.xml Configuration in ：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0">
  
<!-- servlet  Label to  Tomcat  To configure  Servlet  Program  -->
<servlet>
	<!--servlet-name  label  Servlet  The program has an alias （ It's usually a class name ） -->
	<servlet-name>HelloServlet</servlet-name>
  
	<!--servlet-class  yes  Servlet  The full class name of the program -->
	<servlet-class>com.atguigu.servlet.HelloServlet</servlet-class>
</servlet>
  
<!--servlet-mapping  Label to  servlet  Program configuration access address -->
<servlet-mapping>
	<!--servlet-name  The tag is used to tell the server , Which address do I currently configure  Servlet  Program usage -->
	<servlet-name>HelloServlet</servlet-name>
  
	<!--url-pattern  Tag configuration access address  <br/> /  When the server parses the slash , The address is ：http://ip:port/ Project path  <br/> /hello  The address is ：http://ip:port/ Project path /hello <br/> -->
	<url-pattern>/hello</url-pattern>
</servlet-mapping>
</web-app

Usually in the actual project development , It's all about inheritance HttpServlet class The way to achieve Servlet Program .

Servlet Class code ：

public class HelloServlet2 extends HttpServlet {
	/**
	* doGet（） stay  get  Call when requested 
	* @param req
	* @param resp
	* @throws ServletException
	* @throws IOException
	*/
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException,
	IOException {
		System.out.println("HelloServlet2  Of  doGet  Method ");
	}
  	
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException,
	IOException {
	System.out.println("HelloServlet2  Of  doPost  Method ");
	}
  
}

web.xml Configuration in ：
Just configure as above

What is? Jsp

jsp All change is java server pages.Java The server page of .
jsp Its main function is to replace Servlet Program returns html Page data .
because Servlet Program returns html Page data is a very complicated thing . Development costs and maintenance costs are very high .

Servlet Comes back html Code of page data :

public class PringHtml extends HttpServlet {
    
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException,
	IOException {
    
		//  Through the return flow of the response  html  The page data 
		resp.setContentType("text/html; charset=UTF-8");
		PrintWriter writer = resp.getWriter();
		writer.write("<!DOCTYPE html>\r\n");
		writer.write(" <html lang=\"en\">\r\n");
		writer.write(" <head>\r\n");
		writer.write(" <meta charset=\"UTF-8\">\r\n");
		writer.write(" <title>Title</title>\r\n");
		writer.write(" </head>\r\n");
		writer.write(" <body>\r\n");
		writer.write("  This is a  html  The page data  \r\n");
		writer.write(" </body>\r\n");
		writer.write("</html>\r\n");
		writer.write("\r\n");
	}
}

jsp Send back a simple html Page code :

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
 This is a  html  The page data 
</body>
</html>

jsp and Servlet The connection of

jsp A page is essentially a Servlet Program .

When we first visited jsp On the page .Tomcat The server will help us jsp Page translation becomes a java Source file . And compile it into by .class Bytecode program . We turn on Translated java It's not difficult to find the content of the source file is ：

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We track the source code and find ,HttpJspBase class . It directly inherits HttpServlet class . in other words .jsp Translated java class , It indirectly inherited HttpServlet class . in other words , The translation is a Servlet Program .

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