Request对象和Response对象详解

Request

1.获取请求的基本信息

1>获取请求的url和uri

2>获取url后面的请求参数部分的字符串

3>获取请求方式

4>获取主机名,IP地址

5>获取 Contexpath

String url = request .getRequestURL().toString();

System. out .println( url );

String uri = request .getRequestURI().toString();

System. out .println( uri );

String params = request .getQueryString();

System. out .println( params );

String method = request .getMethod();

System. out .println( method );

String addr = request .getRemoteHost() + request .getRemotePort() + request .getRemoteAddr() +

     "==user=" + request .getRemoteUser();

System. out .println( "addr: " + addr );

String contextPath = request .getContextPath();

response .sendRedirect( contextPath + "/index.jsp" );

2.通过 Referer 请求头实现防盗链

Referer请求头的值表示从哪个网页上的链接访问到当前链接

盗链: 其他站点通过超链接链接到自己的站点,从而实现资源的盗窃称为盗链.

@WebServlet ( "/NewsServlet" )

public class NewsServlet extends HttpServlet {

     private static final long serialVersionUID = 1L;

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

         response .setContentType( "text/html;charset=utf-8" );

       

       String referer = request .getHeader( "Referer" );

        if ( referer == null || "" .equals( referer ) || ! referer .contains( "localhost/" )) {

            response .sendRedirect( request .getContextPath() + "/index.jsp" );

       }

       

        response .getWriter().write( "习大大吃包子...." );

    }

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

       doGet( request , response );

    }

}

如果Referer为空或者不是从自己的站点访问过来就重定向到自己站点的主页.

2.获取请求参数

Map params = request .getParameterMap();

for (String name : params .keySet()) {

   String value = request .getParameter( name );

   System. out .println( "name=" + name + ", value=" + value );

}

解决请求乱码问题:

request.setCharacterEncoding(" Utf -8");

如果上面的代码只能解决POST的乱码问题, 则可以自行进行解码操作

String userName = request .getParameter( "username" );

userName =  new String( userName .getBytes( "ISO8859-1" ), "UTF-8" );

前段使用 UTF-8 进行编码, 传输到服务器, 服务器可以使用 ISO8859-1 解码得到UTF-8编码后的码值, 然后通过new String(bytes, charset)的方式进行解码.

3.设置和获取域属性

Object attr = request .getAttribute( "attr" );

request .setAttribute( "key" , "value" );

request .removeAttribute( "attr" );

Enumeration attributeNames = request .getAttributeNames();

一般我们的应用是servlet处理数据, 将处理好的数据放到request域中,然后带到jsp页面上进行展示操作.

4. 请求转发与请求包含

请求转发:

request .getRequestDispatcher( "/DispatcherTest2" ).forward( request , response );

或

this .getServletContext().getRequestDispatcher( "/DispatcherTest2" ).forward( request , response );

Note:

    1)一次请求只能转发一次, 否则会发生下面的异常: -- 可以得到第一次转发获取的数据

java.lang.IllegalStateException : Cannot forward after response has been committed

    2)当有数据已经写到客户端时再请求转发也会抛出异常.

    3)若转发前有数据写入到response缓冲区,则请求转发会清空response缓冲区的实体内容, 但不会清空请求头信息.

请求包含:

当需要将多个servlet的输出合并到一块打给浏览器时可以使用请求包含

request .getRequestDispatcher( "/DispatcherTest2" ).include( request , response );

或

this.getServletContext().getRequestDispatcher("/DispatcherTest2").include(request, response);

Notice:

    1)被包含的Servlet程序不能改变响应消息的状态码和响应头，如果它里面存在这样的语句，这些语句的执行结果将被忽略.

    2)常被用来进行页面布局

请求重定向:

response .sendRedirect( request .getContextPath() + "/DispatcherTest2" );

Notice:

1) 不能在数据已经发送到浏览器之后再进行请求重定向:

java.lang.IllegalStateException : Cannot call sendRedirect() after the response has been committed

2) 在请求重定向之前写入到response缓冲区的数据会被清空

3) 一次请求只能重定向一次

Summary:

请求重定向地址栏会发生变化.请求转发地址栏不发生变化.

请求重定向两次请求两次响应.请求转发一次请求一次响应.

如果需要在资源跳转时利用request域传递域属性则必须使用请求转发

如果希望资源跳转后修改用户的地址栏则使用请求重定向

如果使用请求转发也可以重定向也可以,则优先使用请求转发,减少浏览器对服务器的访问次数减轻服务器的压力.

Response

1.response

    ServletResponse -- 通用的response提供了一个响应应该具有最基本的属性和方法

        |

        |-HttpServletResponse -- 在ServletResponse的基础上针对于HTTP协议增加了很多强化的属性和方法

2.输出数据

 1)getOutputStream字节输出流

response.getOutputStream().write("中国".getBytes(" utf -8"));

string.getBytes()如果没有指定编码方式,会使用平台默认的编码方式

2)getWriter字符输出流

response .getWriter().write( "北京" );

    Notice: getWriter和getOutputStream在一次请求中只能使用一个

    使用字符输出流输出中文时, 由于网线上只能输出高低电平,如果没有指定编码方式,那么服务器在发送数据时会使用默认的ISO-8859-1对数据编码(该码表中没有汉字, 因此汉字会被编码为?, 传送到浏览器上的数据实际就是?).

3)解决乱码

    1> 通知服务器发送数据时使用utf-8编码

response.setCharacterEncoding(" utf -8");

    2> 通知浏览器接受数据时使用utf-8解码

response.setHeader("Content-Type", "text/ html ; charset = utf -8");

    3> Notice:

        a. response对象中对Content-Type响应头进行了封装,可以使用一下代码代替 2>

response .setContentType( "text/html;charset=utf-8" );

        b. 如果设置了Content-Type,服务器会自动的设置 characterEncoding,因此解决乱码只需要设置Content-Type响应头一行代码就可以了,但是为了代码的可读性更高,一般还是建议同时设置 characterEncoding 和 Content-Type.

3)实现下载

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

     response .setHeader( "Content-Disposition" , "attachment;filename=" + URLEncoder. encode ( "美女.jpg" ) );

    InputStream in = new FileInputStream( this .getServletContext().getRealPath( "美女.jpg" ));

    OutputStream out = response .getOutputStream();

     byte [] bytes = new byte [1024];

     int len = -1;

     while (-1 != ( len = in .read( bytes ))) {

        out .write( bytes , 0, len );

    }

     in .close();

}

4) 实现定时刷新

    1.Servlet实现

response .setContentType( "text/html;charset=utf-8" );

response .getWriter().write( "恭喜您注册成功, 3秒后回到主页" );

response .setHeader( "Refresh" , "3;url=OutServlet" );

    2.html实现

< meta charset = "UTF-8" >

< meta http-equiv = "Refresh" content = "3; url=index.jsp" >

< title > Insert title here title >

head >

< body >

    恭喜您注册成功, 3秒后回到主页....

body >

5)控制浏览器是否缓存

response .setIntHeader( "Expires" , -1);

response .setHeader( "Cache-Control" , "no-cache" );

response .setHeader( "Pragma" , "no-cache" );

response .getWriter().write( new Date(). toLocaleString () );

6)实现请求重定向

response .sendRedirect( this .getServletContext().getContextPath());

7)输出验证码图片

package com.inetsoft.response;

import java.awt.Color;

import java.awt.Font;

import java.awt.Graphics2D;

import java.awt.image.BufferedImage;

import java.io.IOException;

import java.util.Random;

import javax.imageio.ImageIO;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

/**

 * @Description : 用于输出验证码图片的 Servlet

 * @Warning :

 * @Author DreamLi

 * @Package Day04 - Response - Request  --   com.inetsoft.response.ValidServlet

 * @Date : 2017年12月17日 下午4:51:22

 * @Version : 1.0.0

 */

@WebServlet ( "/ValidServlet" )

public class ValidServlet extends HttpServlet {

    

     private static final long serialVersionUID = -70985881600765636L;

     private Random rand = new Random();

     public void doGet(HttpServletRequest request , HttpServletResponse response )

            throws ServletException, IOException {

        //设置响应头让浏览器不再缓存验证码图片

        response .setDateHeader( "Expires" , -1);

        response .setHeader( "Cache-Control" , "no-cache" );

        response .setHeader( "Pragma" , "no-cache" );

       

        //创建验证码图片

        //1.创建一张图片到内存中

        int width = 120;

        int height = 30;

       BufferedImage img = new BufferedImage( width , height , BufferedImage. TYPE_INT_RGB );

        //2.获取该图片上的画笔

       Graphics2D g = (Graphics2D) img .getGraphics();

        //3.设置背景色以及图片边框

        g .setColor( new Color(199,237,204));

        g .fillRect(0, 0, width , height );

        g .setColor(Color. black );

        g .drawRect(0, 0, width -1, height -1);

        //4.设置干扰线

        int lineNum = randNumber(3,7); //干扰线的条数

        for ( int i = 0; i < lineNum ; i ++){

            g .setColor( new Color(randNumber(0,255),randNumber(0,255),randNumber(0,255)));

            g .drawLine(randNumber(0, width ), randNumber(0, height ),randNumber(0, width ), randNumber(0, height ) );

       }

        //5.设置验证码内容

        int row = 10;

        int col = 22;

        g .setFont( new Font( "黑体" , Font. BOLD , 20));

       StringBuffer buffer = new StringBuffer();

        for ( int i = 0; i < 4; i ++){

            g .setColor( new Color(randNumber(0,255),randNumber(0,255),randNumber(0,255)));

            double theta = Math. toRadians (randNumber(-50, 50));

            g .rotate( theta , row , col );

            int num = randNumber(0, 9);

            buffer .append( num );

            g .drawString( num + "" , row , col );

            g .rotate(0- theta , row , col );

            row += 30;

       }

        //将验证码加入到session

         request .getSession().setAttribute( "valid" , buffer .toString());

       System. out .println( buffer );

        //6.写入到输出流中

       ImageIO. write ( img , "jpg" , response .getOutputStream());

    }

     /**

     * 产生一个区间里面的随机数

     * @param left 区间左值

     * @param right 区间右值

     * @return 区间里面的一个随机数

     */

     private int randNumber( int left , int right ){

        return   rand .nextInt( right - left ) + left ;

    }

     public void doPost(HttpServletRequest request , HttpServletResponse response )

            throws ServletException, IOException {

       doGet( request , response );

    }

}

最后, 附上demo地址:   https://github.com/DreamLi1314/Day04-Response-Request.git