java: Detailed explanation of the request object of the http module

Article Directory

background

In Java, the request object and response object of the HTTP module represent the objects used when the client sends a request to the server and the server sends a response to the client, respectively.

inheritance relationship

ServletRequest		--	接口
	|   继承
HttpServletRequest	-- 接口
	|	实现
org.apache.catalina.connector.RequestFacade 类(tomcat)

Get data request

The request object contains information about the client request, such as request method, request URL, request header, request body, etc. Commonly used attributes and methods include:

Get request line data

Get request method: GET
- String getMethod()
(*) Get virtual directory: /day14
- String getContextPath()
Get Servlet path: /demo1
- String getServletPath()
Obtain the get method request parameters: name=zhangsan
- String getQueryString()
(*) Get request URI: /day14/demo1
- String getRequestURI(): /day14/demo1
- StringBuffer getRequestURL():http://localhost/day14/demo1
- URL: Uniform Resource Locator: http://localhost/day14/demo1
- URI: Uniform Resource Identifier: /day14/demo1
Obtain protocol and version: HTTP/1.1
- String getProtocol()
Get the IP address of the client machine:
- String getRemoteAddr()

Following is a simple Java Servlet example that demonstrates how to use the request object to handle HTTP requests and responses:

package cn.xxx.web.request;

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;

/**
 * 演示Request对象获取请求行数据
 */

@WebServlet("/requestDemo1")
public class RequestDemo1 extends HttpServlet {
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        /*
            1. 获取请求方式 ：GET
                * String getMethod()
            2. (*)获取虚拟目录：/day14
                * String getContextPath()
            3. 获取Servlet路径: /requestDemo1
                * String getServletPath()
            4. 获取get方式请求参数：name=zhangsan
                * String getQueryString()
            5. (*)获取请求URI：/day14/demo1
                * String getRequestURI():		/day14/requestDemo1
                * StringBuffer getRequestURL()  :http://localhost/day14/requestDemo1
            6. 获取协议及版本：HTTP/1.1
                * String getProtocol()

            7. 获取客户机的IP地址：
                * String getRemoteAddr()

         */
        //1. 获取请求方式 ：GET
        String method = request.getMethod();
        System.out.println(method);
        //2.(*)获取虚拟目录：/day14
        String contextPath = request.getContextPath();
        System.out.println(contextPath);
        //3. 获取Servlet路径: /demo1
        String servletPath = request.getServletPath();
        System.out.println(servletPath);
        //4. 获取get方式请求参数：name=zhangsan
        String queryString = request.getQueryString();
        System.out.println(queryString);
        //5.(*)获取请求URI：/day14/demo1
        String requestURI = request.getRequestURI();
        StringBuffer requestURL = request.getRequestURL();
        System.out.println(requestURI);
        System.out.println(requestURL);
        //6. 获取协议及版本：HTTP/1.1
        String protocol = request.getProtocol();
        System.out.println(protocol);
        //7. 获取客户机的IP地址：
        String remoteAddr = request.getRemoteAddr();
        System.out.println(remoteAddr);
    }
}

Get request header data

(*) String getHeader(String name): Get the value of the request header by the name of the request header
Enumeration<String> getHeaderNames(): Get all request header names

package cn.xxx.web.request;

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;
import java.util.Enumeration;

@WebServlet("/requestDemo2")
public class RequestDemo2 extends HttpServlet {
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        //演示获取请求头数据
        
        //1.获取所有请求头名称
        Enumeration<String> headerNames = request.getHeaderNames();
        //2.遍历
        while(headerNames.hasMoreElements()){
    
    
            String name = headerNames.nextElement();
            //根据名称获取请求头的值
            String value = request.getHeader(name);
            System.out.println(name+"---"+value);
        }

    }
}

package cn.xxx.web.request;

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;
import java.util.Enumeration;

@WebServlet("/requestDemo3")
public class RequestDemo3 extends HttpServlet {
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        //演示获取请求头数据:user-agent

        String agent = request.getHeader("user-agent");
        //判断agent的浏览器版本
        if(agent.contains("Chrome")){
    
    
            //谷歌
            System.out.println("谷歌来了...");
        }else if(agent.contains("Firefox")){
    
    
            //火狐
            System.out.println("火狐来了...");
        }

    }
}

Get request body data

Only the POST request method has a request body, and the request parameters of the POST request are encapsulated in the request body.

Get the stream object
* BufferedReader getReader(): Get the character input stream, only character data can be manipulated
- ServletInputStream getInputStream(): Get byte input stream, which can operate all types of data (explained after file upload knowledge points)
Then get the data from the stream object

package cn.xxx.web.request;

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("/requestDemo5")
public class RequestDemo5 extends HttpServlet {
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        //获取请求消息体--请求参数

        //1.获取字符流
        BufferedReader br = request.getReader();
        //2.读取数据
        String line = null;
        while((line = br.readLine()) != null){
    
    
            System.out.println(line);
        }

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
    }
}

Example: Anti-leech

package cn.xxx.web.request;

import javax.servlet.ServletContext;
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("/requestDemo4")
public class RequestDemo4 extends HttpServlet {
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        //演示获取请求头数据:referer

        String referer = request.getHeader("referer");
        System.out.println(referer);//http://localhost/day14/login.html

        //防盗链
        if(referer != null ){
    
    
            if(referer.contains("/day14")){
    
    
                //正常访问
               // System.out.println("播放电影....");
                response.setContentType("text/html;charset=utf-8");
                response.getWriter().write("播放电影....");
            }else{
    
    
                //盗链
                //System.out.println("想看电影吗？来优酷吧...");
                response.setContentType("text/html;charset=utf-8");
                response.getWriter().write("想看电影吗？来优酷吧...");
            }
        }

    }
}

Other functions

General way to get request parameters

Regardless of the get or post request method, the following methods can be used to obtain request parameters

String getParameter(String name): Obtain the parameter value according to the parameter name username=zs&password=123
String[] getParameterValues(String name): Obtain the array of parameter values according to the parameter name hobby=xx&hobby=game
Enumeration getParameterNames(): Get the parameter names of all requests
Map<String,String[]> getParameterMap(): Get the map collection of all parameters

package cn.xxx.web.request;

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;
import java.util.Enumeration;
import java.util.Map;
import java.util.Set;

@WebServlet("/requestDemo6")
public class RequestDemo6 extends HttpServlet {
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        //post 获取请求参数

        //根据参数名称获取参数值
        String username = request.getParameter("username");
       /* System.out.println("post");
        System.out.println(username);*/

       //根据参数名称获取参数值的数组
        String[] hobbies = request.getParameterValues("hobby");
        /*for (String hobby : hobbies) {
            System.out.println(hobby);
        }*/

        //获取所有请求的参数名称

        Enumeration<String> parameterNames = request.getParameterNames();
        /*while(parameterNames.hasMoreElements()){
            String name = parameterNames.nextElement();
            System.out.println(name);
            String value = request.getParameter(name);
            System.out.println(value);
            System.out.println("----------------");
        }*/

        // 获取所有参数的map集合
        Map<String, String[]> parameterMap = request.getParameterMap();
        //遍历
        Set<String> keyset = parameterMap.keySet();
        for (String name : keyset) {
    
    
            
            //获取键获取值
            String[] values = parameterMap.get(name);
            System.out.println(name);
            for (String value : values) {
    
    
                System.out.println(value);
            }

            System.out.println("-----------------");
        }


    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        //get 获取请求参数
/*
        //根据参数名称获取参数值
        String username = request.getParameter("username");
        System.out.println("get");
        System.out.println(username);*/

        this.doPost(request,response);
    }
}

Chinese garbled characters:
* Get method: tomcat 8 has solved the get method garbled problem
* post method: garbled characters
Solution: Before getting parameters, set the encoding of the request request.setCharacterEncoding("utf-8");

package cn.xxx.web.request;

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;
import java.util.Enumeration;
import java.util.Map;
import java.util.Set;

@WebServlet("/requestDemo7")
public class RequestDemo7 extends HttpServlet {
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        //1.设置流的编码
        request.setCharacterEncoding("utf-8");

        //获取请求参数username
        String username = request.getParameter("username");

        System.out.println(username);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    

        this.doPost(request,response);
    }
}

request forwarding

A resource jump method inside the server

step:
1. Get the request forwarder object through the request object: RequestDispatcher getRequestDispatcher(String path)
2. Use the RequestDispatcher object to forward: forward(ServletRequest request, ServletResponse response)
Features:
1. The browser address bar path does not change
2. It can only be forwarded to the internal resources of the current server.
3. forwarding is a request

package cn.xxx.web.request;

import javax.servlet.RequestDispatcher;
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("/requestDemo8")
public class RequestDemo8 extends HttpServlet {
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        System.out.println("demo8888被访问了。。。");
        //转发到demo9资源
/*
        RequestDispatcher requestDispatcher = request.getRequestDispatcher("/requestDemo9");
        requestDispatcher.forward(request,response);
        */

        //存储数据到request域中
        request.setAttribute("msg","hello");

        request.getRequestDispatcher("/requestDemo9").forward(request,response);
        //request.getRequestDispatcher("http://www.xxx.cn").forward(request,response);

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    

        this.doPost(request,response);
    }
}

share data

Domain object: a scoped object that can share data within the scope
request domain: represents the scope of a request, generally used to share data among multiple resources forwarded by the request
method:
1. void setAttribute(String name, Object obj): store data
2. Object getAttitude(String name): get value by key
3. void removeAttribute(String name): Remove key-value pairs by key

package cn.xxx.web.request;

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("/requestDemo9")
public class RequestDemo9 extends HttpServlet {
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    

        //获取数据
        Object msg = request.getAttribute("msg");
        System.out.println(msg);

        System.out.println("demo9999被访问了。。。");

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    

        this.doPost(request,response);
    }
}

Get ServletContext

ServletContext getServletContext()

package cn.xxx.web.request;

import javax.servlet.ServletContext;
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("/requestDemo10")
public class RequestDemo10 extends HttpServlet {
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    


        ServletContext servletContext = request.getServletContext();

        System.out.println(servletContext);

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    

        this.doPost(request,response);
    }
}