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request，response

作者：互联网

1、HttpServletResponse

web服务器接收到客户端的http请求，会针对这个请求，分别创建一个代表请求的HttpServletRequest对象，代表响应的一个HttpServletResponse；

1、简单分类

负责向浏览器发送数据的方法

ServletOutputStream getOutputStream() throws IOException;
​
PrintWriter getWriter() throws IOException;

 

负责向浏览器发送响应头的方法

void setCharacterEncoding(String var1);
​
void setContentLength(int var1);
​
void setContentLengthLong(long var1);
​
void setContentType(String var1);    void setDateHeader(String var1, long var2);
​
    void addDateHeader(String var1, long var2);
​
    void setHeader(String var1, String var2);
​
    void addHeader(String var1, String var2);
​
    void setIntHeader(String var1, int var2);
​
    void addIntHeader(String var1, int var2);

 

响应的状态码

int SC_CONTINUE = 100;
int SC_SWITCHING_PROTOCOLS = 101;
int SC_OK = 200;
int SC_CREATED = 201;
int SC_ACCEPTED = 202;
int SC_NON_AUTHORITATIVE_INFORMATION = 203;
int SC_NO_CONTENT = 204;
int SC_RESET_CONTENT = 205;
int SC_PARTIAL_CONTENT = 206;
int SC_MULTIPLE_CHOICES = 300;
int SC_MOVED_PERMANENTLY = 301;
int SC_MOVED_TEMPORARILY = 302;
int SC_FOUND = 302;
int SC_SEE_OTHER = 303;
int SC_NOT_MODIFIED = 304;
int SC_USE_PROXY = 305;
int SC_TEMPORARY_REDIRECT = 307;
int SC_BAD_REQUEST = 400;
int SC_UNAUTHORIZED = 401;
int SC_PAYMENT_REQUIRED = 402;
int SC_FORBIDDEN = 403;
int SC_NOT_FOUND = 404;
int SC_METHOD_NOT_ALLOWED = 405;
int SC_NOT_ACCEPTABLE = 406;
int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
int SC_REQUEST_TIMEOUT = 408;
int SC_CONFLICT = 409;
int SC_GONE = 410;
int SC_LENGTH_REQUIRED = 411;
int SC_PRECONDITION_FAILED = 412;
int SC_REQUEST_ENTITY_TOO_LARGE = 413;
int SC_REQUEST_URI_TOO_LONG = 414;
int SC_UNSUPPORTED_MEDIA_TYPE = 415;
int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
int SC_EXPECTATION_FAILED = 417;
int SC_INTERNAL_SERVER_ERROR = 500;
int SC_NOT_IMPLEMENTED = 501;
int SC_BAD_GATEWAY = 502;
int SC_SERVICE_UNAVAILABLE = 503;
int SC_GATEWAY_TIMEOUT = 504;
int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

 

2、下载文件

  1. 向浏览器输出消息

  2. 下载文件

    1. 要获取下载文件的路径

    2. 要下载的文件名是什么

    3. 设置想办法让浏览器能够支持下载我们需要下载的东西

    4. 获取下载文件的输入流

    5. 创建缓冲区

    6. 获取OutputStream对象

    7. 将FileOutputStream流写入到buffer缓冲区

    8. 使用OutputStream将缓冲区中的数据输出到客户端！

    文件下载案例

    public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1. 要获取下载文件的路径
        String realPath = "E:\\Java\\IDEA\\project\\Javaweb\\javaweb-02-servlet\\response\\target\\classes\\搭建.jpg";
        System.out.println("下载的文件路径:"+realPath);
        //2. 要下载的文件名是什么
        String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
        //3. 设置想办法让浏览器能够支持(Content-disposition)下载我们需要下载的东西,中文文件名URLEncoder.encode编码，否则有可能乱码
        resp.setHeader("Content-disposition","attachment;filename="+fileName+ URLEncoder.encode(fileName,"UTF-8"));
        //4. 获取下载文件的输入流
​
        FileInputStream in = new FileInputStream(realPath);
​
​
        //5. 创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
​
        //6. 获取OutputStream对象
        ServletOutputStream out = resp.getOutputStream();
        //7. 将FileOutputStream流写入到buffer缓冲区 使用OutputStream将缓冲区中的数据输出到客户端！
        while ((len -in.read(buffer)) > 0){
            out.write(buffer,0,len);
        }
        in.close();
        out.close();
    }
​
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
​
    }
}

     

web.xml

<servlet>
    <servlet-name>filedown</servlet-name>
    <servlet-class>com.uestc.servlet.FileServlet</servlet-class>
</servlet>
​
<servlet-mapping>
    <servlet-name>filedown</servlet-name>
    <url-pattern>/down</url-pattern>
</servlet-mapping>

 

3、验证码功能

验证码怎么来的？

类

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
​
        //如何让浏览器3s自动刷新一次；
        resp.setHeader("refresh","3");
​
        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D g = (Graphics2D) image.getGraphics(); //笔
        //设置图片的背景颜色
        g.setColor(Color.white);
        g.fillRect(0,0,80,20);
        //给图片写数据
        g.setColor(Color.blue);
        g.setFont(new Font(null,Font.BOLD,20));
        g.drawString(makeNum(),0,20);
​
        //告诉浏览器，这个请求用图片的方式打开
        resp.setContentType("image/jpeg");
        //网站存在缓存，不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");
​
        //把图片写给浏览器
        boolean write = ImageIO.write(image,"jpg", resp.getOutputStream());
​
    }
​
    //生成随机数
    private String makeNum(){
        Random random = new Random();
        String num = random.nextInt(9999999)+"";
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 7-num.length(); i++) {
            sb.append("0");
        }
        String s = sb.toString() + num;
        return num;
​
    }
​
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

 

web.xml

<servlet>
    <servlet-name>ImageServlet</servlet-name>
    <servlet-class>com.uestc.servlet.ImageServlet</servlet-class>
</servlet>
​
<servlet-mapping>
    <servlet-name>ImageServlet</servlet-name>
    <url-pattern>/img</url-pattern>
</servlet-mapping>

 

4、实现重定向

一个web资源收到客户端请求，他会通知客户端取访问另外一个web资源，这个过程叫做重定向。

常见场景：

void sendRedirect(String var1) throws IOException;
测试

   @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
​
        /*
        resp.setHeader("Location","/r/img");
        resp.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY);//302
         */
​
        resp.sendRedirect("/r/img");//重定向
​
    }

 

web.xml

<servlet>
    <servlet-name>RedirectServlet</servlet-name>
    <servlet-class>com.uestc.servlet.RedirectServlet</servlet-class>
</servlet>
​
<servlet-mapping>
    <servlet-name>RedirectServlet</servlet-name>
    <url-pattern>/red</url-pattern>
</servlet-mapping>

 

面试题，请你聊聊重定向和转发的区别？

相同点

不同点

 

2、HttpServletRequest

HttpServletRequest代表客户端的请求，用户通过Http协议访问服务器，HTTP请求中的所有信息会被封装到HttpServletRequest，通过这个HttpServletRequest的方法，获得客户端的所有信息。

1、获取前端传递的参数及请求转发

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
​
    req.setCharacterEncoding("utf-8");
    resp.setCharacterEncoding("utf-8");
​
    String username = req.getParameter("username");
    String password = req.getParameter("password");
    String[] hobbys = req.getParameterValues("hobbys");
    System.out.println("===============================");
    //后台接收中文乱码问题
    System.out.println(username);
    System.out.println(password);
    System.out.println(Arrays.toString(hobbys));
    System.out.println("===============================");
​
    System.out.println(req.getContextPath());
    //通过请求转发
    //这里的 / 代表当前的web应用
    req.getRequestDispatcher("/success.jsp").forward(req,resp);
​
​
}

 

请求转发和重定向的区别

相同点

不同点

 

标签：String,int,resp,req,request,void,SC,response
来源： https://www.cnblogs.com/mhy123/p/16476526.html