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Request object and response object analysis

2022-07-06 11:14:00 【Call me uncle】

Catalog

request object

One doGet Small projects ：

The code problem ：

Request forwarding

request Scope

response object

①:response Main methods

②: Response to the garbled problem

request object

         When the client sends a request to the server , The server created for this request request object , And in the call Servlet Of service When the method is used , Pass the object to service Method .Request Object encapsulates all the request data sent by the client .

explain ：

We use... In browsers , Any operation constitutes a request for information , Send to reuqest object , And send it to Servlet Under the interface service, Down to HttpServlet.

One doGet Small projects ：

RegisServlet.java

package com.qcby.servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.catalina.User;

@WebServlet("/regist")
public class RegisServlet extends HttpServlet{

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		String username = req.getParameter("username");
		String password = req.getParameter("password");
		
		System.out.println(username + " " + password);
	}

}

rigist.html

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<form action="/JiuYueServices/regist" method="get"> 
		 user name ：<input type="text" name="username"/>
		 password ：<input type="text" name="password"/>
		<input type="submit" value=" register ">
	</form>
</body>
</html>

<form action="/JiuYueServices/regist" method="get"> Inside JiuYueServices yes Project name

success :

The code problem ：

         because request Is to receive requests from users , The server converts the request according to the encoding format . The default encoding format on the server side is ISO-8859-1( This encoding does not support Chinese ), Our user browser defaults to utf-8 The encoding format of , So it often produces garbled code . To solve the problem of garbled code , Need to set up request The encoding format , Tell the server how to parse the data . Or after receiving the garbled code , What encoding format is used to restore

  resolvent ：

Mode one ：（ all ）

request.setCharacterEncoding("UTF-8");

Mode two ：（ With the help of String Object method , This method is valid for any request , It's all universal ）

new String(request.getParameter(name).getBytes("ISO-8859-1"),"UTF-8"))

Request forwarding

         Request forwarding is a server behavior , When the client request arrives , The server forwards , The request object is saved , In the address bar url The address will not change , After getting the corresponding , The server will send the request to the client , From beginning to end, only one request was made .

request.getRequestDispatcher(url).forward(request, response);

Two servlet：

/**
 * 
 * @author lenovo
 *          Request forwarding jump 
 *                  You can make the server jump to the client ( Or designated (Servlet)
 *            characteristic ：	
 *     1. Server side behavior       
 *     2. The address bar doesn't change 
 *     3. It's a request from beginning to end 
 *     4.request The data in servlet Share in program 
 */
@WebServlet(value="/s01")
public class Servlet01 extends HttpServlet{
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		String username  = req.getParameter("username");
		String password = req.getParameter("password");
		System.out.println("s01="+username + " " + password);
		//  Request to jump to Servlet02
		//req.getRequestDispatcher("s02").forward(req, resp);
		// Request to html page 
		req.getRequestDispatcher("RegistServlet.html").forward(req, resp);
	
	}
}
@WebServlet(value="/s02")
public class Servlet02 extends HttpServlet{
      @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    	// TODO Auto-generated method stub
             req.setCharacterEncoding("UTF-8");
    	  String username  = req.getParameter("username");
  		String password = req.getParameter("password");
  		System.out.println("s02=" + username + " " + password);
    }
}

Running, we found s01 and s02 Metropolitan output , And only once

request Scope

request Express a request , Just make a request and create a request object , His scope ： Only valid in the current request .

use : It is often used to pass parameters between different pages of the same request between servers , It is often used for control value transmission of forms .

Common methods

request.setAttribute(String name,Object value) Set domain object content
request.getAttribute(String name) Get domain object content
request.removeAttribute(String name) Delete domain object content

Two servlet

@WebServlet("/s03")
public class Servlet03 extends HttpServlet{
	
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		System.out.println(" I am a 03");
		req.setAttribute("user", "qcby");
    	req.setAttribute("age", 18);
                		
    	req.getRequestDispatcher("s04").forward(req, resp);

	}

}
@WebServlet("/s04")
public class Servlet04 extends HttpServlet{
      @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    	// TODO Auto-generated method stub
    	System.out.println(" I am a 04");
    	System.out.println(req.getAttribute("user"));
    	System.out.println(req.getAttribute("age"));
    }
}

visit ：http://localhost:8080/SecondServlet/s03

response object

 

①:response Main methods

getWriter() Get character stream ( Only corresponding string data )
getOutputStream() Obtain byte stream ( Can correspond to all data )

getWriter()

@WebServlet("/regist")
public class RegistServlet  extends HttpServlet{
	
	
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		
		
		
		PrintWriter printWriter = resp.getWriter();
		printWriter.print("success");
	
	}

}

getOutputStream()

@WebServlet("/regist")
public class RegistServlet  extends HttpServlet{
	
	
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		// PrintWriter writer = resp.getWriter();
		// writer.print("success");
		ServletOutputStream stream  = resp.getOutputStream();
		stream.write("Success".getBytes());
		
	}

}

html

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<form action="/SecondServlet/regist" method="post"> 
		 user name ：<input type="text" name="username"/>
		 password ：<input type="text" name="password"/>
		<input type="submit" value=" register ">
	</form>
</body>
</html>

②: Response to the garbled problem 

response.setCharacterEncoding("UTF-8");
response.setHeader("content-type", "text/html;charset=UTF-8");

原网站

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https://yzsam.com/2022/02/202202131633492465.html

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