JavaWeb 文件上传下载和图片验证码

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超详细的Java知识点路线图

文件上传

这里使用的是Apache的common-fileupload包

准备工作：

下载导入jar包
common-fileupload 文件上传
common-io 文件IO
在JSP的fom标签中，添加属性：enctype=“multipart/form-data”，请求方法必须是post
表单中使用file控件上传

相关API：
ServletFileUpload类
主要方法：

isMultipartContent(Request对象）判断表单中是否有上传内容，静态
FileItemIterator getItemIterator(Request对象）获得表单项目的迭代器
setFileSizeMax(int 长度) 设置每个文件最大的大小
setSizeMax(int 长度）设置上传的总大小

FileItemIterator类表单项目的迭代器

hasNext 判断还有没有项目没有读取
FileItemStream next 读取下一个项目

FileItemStream类上传项目

getFieldName 获得表单字段的名称
getName 获得文件名
openStream 打开输入流
isFormField 判断是否是一般的表单项

Streams类文件流工具类

asString(输入流,“编码类型”) 从流中读取字符串
copy(输入流 , 输出流 , 结束是否关闭流）复制输入流的数据到输出流

/*** 上传文件的Servlet* @author xray**/
public class UploadServlet extends HttpServlet{public static final String UPLOAD_DIR = "/Users/xray/Documents/xray_mac/upload";@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doPost(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {MyLogger log = new MyLogger(UploadServlet.class);log.info("start upload...");//判断请求中是否存在上传内容if(ServletFileUpload.isMultipartContent(req)){//创建上传对象ServletFileUpload upload = new ServletFileUpload();//设置上传每个文件的最大长度upload.setFileSizeMax(1024 * 1024);//设置上传文件的总大小upload.setSizeMax(1024 * 1024 * 2);try {//获得文件项目的迭代器FileItemIterator iterator = upload.getItemIterator(req);//对迭代器进行迭代while(iterator.hasNext()){//获得每个表单项FileItemStream item = iterator.next();//获得表单项的输入流InputStream is = item.openStream();//判断该项是普通表单项目还是上传项目if(item.isFormField()){//如果是一般项目，读取文字内容String value = Streams.asString(is,"UTF-8");//判断项目的字段名switch(item.getFieldName()){case "username":log.info("用户名："+value);break;case "password":log.info("密码："+value);break;}}else{//如果是上传项目，就把文件保存到服务器的目录中 C:/xxx/aa/123.jpgString filename = UPLOAD_DIR + "/" + System.currentTimeMillis()+"-"+FilenameUtils.getName(item.getName());OutputStream out = new FileOutputStream(filename);Streams.copy(is, out, true);log.info(filename+"图片保存完毕");}}} catch (FileUploadException e) {e.printStackTrace();}}log.info("end upload...");}
}

文件下载

下载Servlet

/*** 下载文件的Servlet* @author xray**/
public class DownloadServlet extends HttpServlet{public static final String DOWNLOAD_DIR = "/Users/xray/Documents/xray_mac/download";@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {MyLogger log = new MyLogger(DownloadServlet.class);//获得文件名String filename = req.getParameter("filename");log.info("文件名:"+filename);//处理中文乱码filename = new String(filename.getBytes("ISO-8859-1"),"UTF-8");//获得服务器上磁盘文件的输入流InputStream in = new FileInputStream(DOWNLOAD_DIR+"/"+filename);//获得发送浏览器的输出流OutputStream out = resp.getOutputStream();//设置响应头resp.setHeader("content-disposition", "attachment;filename="+URLEncoder.encode(filename, "UTF-8"));//读写文件流Streams.copy(in, out, true);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req,resp);}
}

下载页面

<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body><a href="download.do?filename=Oracle超详细教程.pdf">Oracle超详细教程.pdf</a><br><a href="download.do?filename=Oracle经典教程.pdf">Oracle经典教程.pdf</a>
</body>
</html>

图片验证码

作用：提高安全性，提升黑客破解难度。
实现思路：
1、在Servlet中创建图片
2、随机生成4个字母或数字
3、随机绘制线条
4、将图片发送给浏览器
需要类：
BufferedImage 带缓冲的图片
Graphics 绘图对象
ImageIO 实现图片的IO流读写

/*** 生成验证码的Servlet**/
@WebServlet("/code.do")
public class ValidateCodeServlet extends HttpServlet{public static final String CODES = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";public static final int WIDTH = 80;public static final int HEIGHT = 35;public static final int NUMBER = 4;public static final int FONT_SIZE = 20;public static final Color[] COLORS = {Color.BLACK,Color.BLUE,Color.CYAN,Color.DARK_GRAY,Color.GREEN,Color.LIGHT_GRAY,Color.MAGENTA,Color.ORANGE,Color.PINK,Color.RED,Color.WHITE,Color.YELLOW};protected void doGet(javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse resp) throws javax.servlet.ServletException ,java.io.IOException {doPost(req,resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//创建缓冲图片对象BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_ARGB);//创建绘图对象Graphics g = image.getGraphics();//设置字体大小g.setFont(new Font("宋体",Font.PLAIN,FONT_SIZE));//设置颜色g.setColor(Color.GRAY);//填充矩形方块g.fillRect(0, 0, WIDTH, HEIGHT);//随机产生几个字母或数字Random random = new Random();char[] codes = new char[NUMBER];for(int i = 0;i < NUMBER;i++){g.setColor(COLORS[random.nextInt(COLORS.length)]);//在字符串中随机取一个字符codes[i] = CODES.charAt(random.nextInt(CODES.length()));//绘制该字符g.drawString(codes[i] + "", i * FONT_SIZE + 5, FONT_SIZE);//绘制随机的线条g.setColor(COLORS[random.nextInt(COLORS.length)]);g.drawLine(random.nextInt(WIDTH), random.nextInt(HEIGHT),random.nextInt(WIDTH), random.nextInt(HEIGHT));}//将验证码保存到Session中req.getSession().setAttribute("code", new String(codes));//取消浏览器对图片的缓存resp.addHeader("Cache-Control", "no-cache");//发送图片给浏览器ImageIO.write(image, "PNG", resp.getOutputStream());}}

登录JSP

<div id="login"><p id="title">后台管理系统</p><span id="error_msg">${error_msg}</span><form action="login.do" method="post"><input name="user_tel" type="text" placeholder="请输入手机号"><br><input name="user_password" type="password" placeholder="请输入密码"><br><input name="code" type="text" placeholder="请输入验证码"><br><img src="code.do" id="code" onclick="changeCode()"><br><input type="submit" value="登录"></form>
</div>
<script type="text/javascript">function changeCode(){document.getElementById("code").src = "code.do?x="+Math.random();}
</script>

登录Servlet中添加验证码的逻辑：

//获得用户填写的验证码
String code = req.getParameter("code");
//获得Session中的验证码
String code2 = (String) req.getSession().getAttribute("code");
//判断验证码是否正确
if(code2==null || !code2.equals(code)){req.setAttribute("error_msg", "验证码不正确");req.getRequestDispatcher("login.jsp").forward(req, resp);return;
}

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