Request and response description

Request and Response explain

Simple function description

From the literal meaning of the word , We understand that a person is asking , One is to respond .

We write Servlet When coding, we often see these two parameters .

We need to know what role these two parameterizers play .

Quote the description of dark horse

request: Get request data

The browser will send HTTP Request to the background server [Tomcat]
HTTP Your request will contain a lot of request data [ Request line + Request header + Request body ]
Background server [Tomcat] Would be right HTTP The data in the request is parsed and the parsing result is stored in an object. The stored object is request object , So we can request Object to get the relevant parameters of the request
After obtaining the data, you can continue the subsequent business , For example, obtaining the user name and password can realize the related business of login operation

response: Set response data

After business processing , The background needs to return the result of business processing to the front end, that is, response data, and encapsulate the response data into response In the object
Background server [Tomcat] Can parse response object , according to [ Response line + Response head + Response body ] Format splicing result browser final parsing result , Display the content in the browser for users to browse

Code test cases

package jgd;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 java.io.BufferedReader;import java.io.IOException;@WebServlet("/dod/*")public class ServletDemo8 extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// super.doGet(req, resp);//  Get request method         String method = req.getMethod();        System.out.println(" Request mode :"+method);//  Get virtual access directory ( Project access path )        String contextPath = req.getContextPath();        System.out.println(" Virtual directory :"+contextPath);//  obtain url        StringBuffer requestURL = req.getRequestURL();        System.out.println("url"+requestURL.toString());//  Get resource identifier         String requestURI = req.getRequestURI();        System.out.println(" Resource identifier "+requestURI);//  Get request parameters         String queryString = req.getQueryString();        System.out.println(" Request parameters "+queryString);//  Get a request header of the browser version         String agent = req.getHeader("user-agent");// obtain         System.out.println(" browser "+agent);    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// super.doPost(req, resp);//  obtain post Of 2 Request body // 1: Get character input stream         BufferedReader br = req.getReader();//  Reading data         String line = br.readLine();        System.out.println(line);//  After one request ,request After the object is destroyed , The flow will automatically close     }}

package jgd;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 java.io.IOException;@WebServlet("/demo9")public class ServletDemo9 extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        String name = req.getParameter("name");        resp.setHeader("content-type", "text/html;character=utf-8");        resp.setContentType("text/html;charset=utf-8");//html// resp.setContentType("text/plain; charset=utf-8");  Text // charset=UTF-8. If the method is getWriter() Call before method is called , Then the character encoding of the response will only start from the given content type   Set in . If the method is in the getWriter() The method is called or is called after it is submitted. ,//  The character encoding of the response will not be set , In the use of http In the case of an agreement , The method is designed as follows   Set up  Content-type Physical header .        resp.getWriter().write("<h1>" + name + ", Welcome </h1>");    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// super.doPost(req, resp);        System.out.println("POST...");    }}

== Please see the code comments for the points needing attention ==

==request Object is the object used to encapsulate the requested data
response Object is an object used to encapsulate response data ==

Of course, this is just our little understanding

Request Inheritance system

Then we will find that in different Servlet The writing of these two parameters in is also different .

package jgd;import javax.servlet.*;import javax.servlet.annotation.WebServlet;import java.io.IOException;@WebServlet("/demo1")public class ServletDemo01 implements Servlet {    public void init(ServletConfig servletConfig) throws ServletException {    }    public ServletConfig getServletConfig() {        return null;    }    public void service(ServletRequest servletRequest, ServletResponse servletResponse) throws ServletException, IOException {        //Servlet When interviewed service Automatically         System.out.println("servlet hello world");    }    public String getServletInfo() {        return null;    }    public void destroy() {    }}

package jgd;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 java.io.IOException;@WebServlet("/jgdabc/666")// Multiple access paths can be configured , This is an exact match //@WebServlet(urlPatterns = {"/demo7","/demo07"})//@WebServlet(urlPatterns = "/user/*")  Directory matching // When both exact matching and directory matching are satisfied , Precise matching has higher priority //@WebServlet("*.do")  Extension matching // Any match // /*  Has a higher priority than ///@WebServlet("/")//@WebServlet("/*")public class ServletDemo7 extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        System.out.println("demo7get...");    }    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// super.doPost(req, resp);    }}

One is existing in inheritance Servlet Method parameter body , One is HttpServlet Of doGet（） and doPost（） In the parameter body of the two methods . We can obviously find that the writing of these two parameters is different . But it is still an implementation request and an implementation response .

Now let's look at Request, Presumably, it also has its own inheritance system .

ServletRequest and HttpServletRequest All are Java Provided . Then it is implemented by Tomcat To complete . The implementation class is RequestFacade.

== This class implements HttpServletRequest Interface , It also indirectly realizes ServletRequest Interface .
Servlet Class service Method 、doGet Method or doPost The method is ultimately determined by Web The server [Tomcat]
To invoke the , therefore Tomcat The specific implementation class of method parameter interface is provided , And completed the creation of the object ==

The verification method is that you put request Print out , You can understand .