Servlet response in the related case (restyling, authentication code, ServletContext file download)

Others 2019-08-08 09:02:13 views: null

Redirect

  1. First set the status code in response to the first set

     //访问Demo1自动跳转至Demo2
    //设置状态码
    response.setStatus(302);
    //设置响应头
    response.setHeader("location","/response/responseDemo2");

  2. Complete redirection sendRedirect (String location) Method

             //访问Demo1自动跳转至Demo2
        response.sendRedirect("/response/responseDemo2");

    Redirection Features:redirect

    1. Address bar changes

    2. Redirection can access other site (server) resources

      response.sendRedirect("https://www.baidu.com");

    3. Redirection is two requests

    Forwarding features:forward

    1. Forwarding path unchanged
    2. Forwarding can only access resources at the current server
    3. Is a forwarding request, the request object can be used to share data

    Path wording:

    Category path

    1. relative path
      1. Locate the relationship between the current source and target resources
    2. Absolute path: the only resource can be determined by absolute path
      1. Rules: judge to whom the definition of the path is used
        1. Client Browser: need to add virtual directory (access path of the project)
        2. Server to use: no need to add virtual directory

Server output character data to the browser

  1. step

    1. Get the character stream output

    2. Output Data

    3. Note garbled

            //设置流的默认编码：ISO-8859-1 设置为GBK，防止乱码
        response.setCharacterEncoding("GBK");
        //告诉浏览器，服务器发送的消息体数据的编码
        //response.setHeader("content-type","text/html;charset=utf-8");
        //简单形式。设置编码
        response.setContentType("text/html;charset=utf-8");
        //获取字符输出流
        PrintWriter writer = response.getWriter();
        //输出数据
        writer.write("hello");

Server output byte data to the browser

  1. step

    1. Obtaining an output stream of bytes
    2. Output Data
            response.setContentType("text/html;charset=utf-8");
        //获取字节输出流
        ServletOutputStream outputStream = response.getOutputStream();
        //输出数据
        outputStream.write("hellow".getBytes());

Verification code

  • Essence: Pictures
  • Objective: To prevent malicious operations

servlet code:

 //创建对象，在内存中生成图片（验证码对象）
        int width=100;
        int height=50;

        BufferedImage bufferedImage=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
        //美化
        //填充背景色
        Graphics graphics=bufferedImage.getGraphics();
        //背景颜色
        graphics.setColor(Color.PINK);
        graphics.fillRect(0,0,width,height);
        //字体颜色
        graphics.setColor(Color.BLUE);
        graphics.drawRect(0,0,width-1,height-1);
        String str="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        //生成随机角标
        Random random=new Random();
        int x=0;
        for (int j = 0; j < 4; j++) {
            int i = random.nextInt(str.length());
            char A=str.charAt(i);
            graphics.drawString(A+"",x+=20,25);
        }
        //画线
        for (int i = 0; i < 4; i++) {
            int x1 = random.nextInt(100);
            int x2 = random.nextInt(100);
            int y1 = random.nextInt(50);
            int y2 = random.nextInt(50);
            graphics.drawLine( x1,  y1,  x2,  y2);
        }


        //输出演示
        ImageIO.write(bufferedImage,"jpg",response.getOutputStream());

html：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>注册</title>
    
</head>
<body>
<img id="check" src="/response/checkCodeServlet"/>
<a id="change" href="">看不清换一张</a>
</body>
</html>

Download ServletContext

  1. Download Requirements:
    1. Page displays a hyperlink
    2. After clicking a hyperlink pop-up message box download
    3. Download the complete picture file

html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<a href="/rui/downloadServlet?filename=1.jpg">图片</a>
</body>
</html>

servlet

import javax.servlet.Servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;

/**
 * @author rui
 * @create 2019-08-07 22:07
 */
@WebServlet("/downloadServlet")
public class DownloadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取参数文件名
        String filename = request.getParameter("filename");
        //找到文件真是路径
        ServletContext servletContext = this.getServletContext();
        String realPath = servletContext.getRealPath("/img/" + filename);

        //设置response的响应头类型context-type
        //获取文件类型
        String mimeType = servletContext.getMimeType(filename);
        response.setHeader("context-type",mimeType);
        //设置响应头打开方式content-disposition
        response.setHeader("content-disposition","attachment;filename="+filename);
        response.setContentType("content-disposition:attachment;filename=xxx");
        //用字节流关联
        FileInputStream fis = new FileInputStream(realPath);
        //将输入流写出到输出流
        ServletOutputStream outputStream = response.getOutputStream();
        byte[] bytes = new byte[1024 * 8];
        int len = 0;
        while ((len = fis.read(bytes)) != -1) {
            outputStream.write(bytes, 0, len);
        }
        fis.close();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

  • Tip 1.jpg web is placed under the img file file

  • problem:

    • Chinese file name problem (Chinese become "___" form)

  • solve:

    • Gets the browser version used by the client information

    • Depending on the version information, setting the coding mode filename

      1. code show as below:

      Use DownLoadUtilsTools

      import sun.misc.BASE64Encoder;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;


public class DownLoadUtils {

    public static String getFileName(String agent, String filename) throws UnsupportedEncodingException {
        if (agent.contains("MSIE")) {
            // IE浏览器
            filename = URLEncoder.encode(filename, "utf-8");
            filename = filename.replace("+", " ");
        } else if (agent.contains("Firefox")) {
            // 火狐浏览器
            BASE64Encoder base64Encoder = new BASE64Encoder();
            filename = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
        } else {
            // 其它浏览器
            filename = URLEncoder.encode(filename, "utf-8");
        }
        return filename;
    }
}

      1. Before setting in response to first add the following code:

        //解决中文文件名问题
            //获取user-agent请求头
            String header = request.getHeader("user-agent");
            filename = DownLoadUtils.getFileName(header, filename);

servlet complete code:

import javax.servlet.Servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;

/**
 * @author rui
 * @create 2019-08-07 22:07
 */
@WebServlet("/downloadServlet")
public class DownloadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取参数文件名
        String filename = request.getParameter("filename");
        //找到文件真是路径
        ServletContext servletContext = this.getServletContext();
        String realPath = servletContext.getRealPath("/img/" + filename);

        //设置response的响应头类型context-type
        //获取文件类型
        String mimeType = servletContext.getMimeType(filename);
        response.setHeader("context-type", mimeType);

        //设置响应头打开方式content-disposition
            //解决中文文件名问题
            //获取user-agent请求头
            String header = request.getHeader("user-agent");
            filename = DownLoadUtils.getFileName(header, filename);
        response.setHeader("content-disposition", "attachment;filename=" + filename);
        response.setContentType("content-disposition:attachment;filename=xxx");
        //用字节流关联
        FileInputStream fis = new FileInputStream(realPath);
        //将输入流写出到输出流
        ServletOutputStream outputStream = response.getOutputStream();
        byte[] bytes = new byte[1024 * 8];
        int len = 0;
        while ((len = fis.read(bytes)) != -1) {
            outputStream.write(bytes, 0, len);
        }
        fis.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

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Origin www.cnblogs.com/PoetryAndYou/p/11318455.html
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