JavaWeb -- 服务器传递给Servlet的对象 -- ServletConfig, ServletContext,Request, Response
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1. ServletConfig
有一些东西不合适在程序中写死,应该写在web.xml中,比如 文字怎么显示, 访问数据库名 和 密码, servlet要读取的配置文件 等等。。
<servlet> <servlet-name>Test</servlet-name> <servlet-class>com.kevin.Test</servlet-class> <init-param> <param-name>data1</param-name> <param-value>data11.log</param-value> </init-param> <init-param> <param-name>data2</param-name> <param-value>data2.log</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>Test</servlet-name> <url-pattern>/Test2</url-pattern> </servlet-mapping>
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubString servletConfig1 = this.getServletConfig().getInitParameter("data1");//获取指定名的参数response.getOutputStream().write(("WebTest2.Test " + servletConfig1).getBytes());Enumeration<String> e = this.getServletConfig().getInitParameterNames(); //获取所有参数名while(e.hasMoreElements()) //获取所有参数{String name = (String) e.nextElement();String data = this.getServletConfig().getInitParameter(name);response.getOutputStream().write((" "+data).getBytes());}}
2. ServletContext: 服务已启动就会对应每个Web应用产生一个ServletContext, 停服务器才销毁对象。
应用:聊天室等
应用一: l多个Servlet通过ServletContext对象实现数据共享。
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubString data = "aaaa";this.getServletContext().setAttribute("data1", data); //写入}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubString data = (String) this.getServletContext().getAttribute("data1"); //读取response.getOutputStream().write(data.getBytes());}
<context-param> <param-name>data2</param-name> <param-value>context-param in web.xml</param-value> </context-param>
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubString data = (String) this.getServletContext().getInitParameter("data2");//获取ServletContext参数response.getOutputStream().write(data.getBytes());}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubString data = "dataaaaaaaaa";this.getServletContext().setAttribute("data3", data); //线程不安全。实际开发不能用RequestDispatcher rd = this.getServletContext().getRequestDispatcher("/1.jsp"); //带数据请求转发jsprd.forward(request, response);}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stub //注意路径是对Tomcat服务器里面的资源,而不是Eclipse项目的资源显示InputStream in = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties"); //获取字节流String path = this.getServletContext().getRealPath("/WEB-INF/classes/db.properties");//获取绝对路径,能获取到文件名Properties props = new Properties();props.load(in);String url = props.getProperty("URL");String username = props.getProperty("username");String password = props.getProperty("password");response.getOutputStream().write((url + " " + username + " " + password).getBytes());}
如果读取资源文件的程序不是Servlet的话,就只能用类装载器去读。
String path = UserDao.class.getClassLoader().getResource("db.properties").getpath();
通过类装载器的getResource()获得一个URL,再获得其绝对路径, 再通过普通的InputStream 读取文件。
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stub//程序以什么码表输出,就要控制浏览器用什么码表显示response.setHeader("Content-type", "text/html;charset=UTF-8");String data = "中国人";OutputStream out = response.getOutputStream();out.write(data.getBytes("UTF-8"));}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubresponse.setCharacterEncoding("UTF-8"); //控制response 以UTF-8编码response.setHeader("content-type","text/html;charset=UTF-8"); //http头, 控制浏览器以UTF-8显示String data = "中国";PrintWriter out = response.getWriter();out.write(data);}
控制文件下载
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubString path = this.getServletContext().getRealPath("/download/apple.png");String filename = path.substring(path.lastIndexOf("/")+1); //截取文件名 //System.out.println(filename);response.setHeader("content-disposition", "attachment;filename=" + URLEncoder.encode(filename, "UTF-8"));//用URL防止中文文件名乱码问题InputStream in = null;OutputStream out = null;try{in = new FileInputStream(path);out = response.getOutputStream();int len = 0;byte[] buf = new byte[1024];while( (len=in.read(buf)) > 0 ){out.write(buf, 0, len);}}finally{try{in.close();out.close();}catch (Exception e){e.printStackTrace();}}}
输出随机认证图片,防恶意注册
private static final int width = 120; private static final int height = 40;protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubBufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);Graphics g = image.getGraphics();setBackGround(g);setBorder(g);drawRandomLine(g);drawRandomNum((Graphics2D)g);response.setContentType("image/jpeg"); //设置头, 浏览器以图片方式打开response.setDateHeader("expries", -1); //设置头, 不让浏览器缓存response.setHeader("Cache-Control", "no-cache");response.setHeader("Pragma", "no-cache");ImageIO.write(image, "jpg", response.getOutputStream());}private void drawRandomNum(Graphics2D g) { //添加随机汉字// TODO Auto-generated method stub//[\u4e00 ~ \u9fa5]g.setColor(Color.BLUE);g.setFont(new Font(null, Font.BOLD, 20));String base = "\u7684\u4e00\u662f\u4e86\u6211\u4e0d\u4eba\u5728\u4ed6\u6709\u8fd9\u4e2a\u4e0a\u4eec\u6765";int x = 5;for(int i=0; i<4; i++){String ch = base.charAt(new Random().nextInt(base.length())) + "";//System.out.println(ch);int degreen = new Random().nextInt()%30;g.rotate(degreen*Math.PI/180, x, 25); //翻转汉字g.drawString(ch, x, 25);g.rotate(-degreen*Math.PI/180, x, 25);x += 30;}} private void drawRandomLine(Graphics g) { //加干扰线// TODO Auto-generated method stubg.setColor(Color.green);for(int i=0; i<8; i++){int x1 = new Random().nextInt(width);int y1 = new Random().nextInt(height);int x2 = new Random().nextInt(width);int y2 = new Random().nextInt(height);g.drawLine(x1, y1, x2, y2);}}private void setBorder(Graphics g) { //设置边框// TODO Auto-generated method stubg.setColor(Color.blue);g.drawRect(1, 1, width-2, height-2);}private void setBackGround(Graphics g) { //设置背景颜色// TODO Auto-generated method stubg.setColor(Color.WHITE);g.fillRect(0, 0, width, height);}
Html调用上面的Servlet, 点击即可更换随机图片
<?xml version="1.0" encoding="UTF-8" ?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Insert title here</title><script type="text/javascript">function changeImage(img) {img.src = img.src + "?" + new Date().getTime();}</script></head><body><form action=""><pre>User :<input type="text" name="username"/> <br />Passwd :<input type="password" name="passwd"/> <br />CheckCode:<input type="text" name="checkcode"/> <br /><img src="Demo4" alt="ChangeOne" onclick="changeImage(this)" style="cursor: hand"/></pre></form></body></html>
注册完成后实现 几秒跳转,转发
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubtest2(request, response); //实用}private void test2(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { //利用meta标签实现refresh, 跳转到jsp显示页面String message = "<meta http-equiv='refresh' content='3;url=http://www.baidu.com'>"+ "Register successfully!! Will goto .... <a href='http://www.baidu.com'>Clicked here!!</a></meta>"; this.getServletContext().setAttribute("message", message);this.getServletContext().getRequestDispatcher("/1.jsp").forward(request, response); //转发}private void test1(HttpServletResponse response) throws IOException {response.setCharacterEncoding("UTF-8");response.setContentType("text/html;charset=UTF-8");response.setHeader("refresh", "3;url=/WebTest2/1.jsp");response.getWriter().write("Register successfully!! Will goto .... "+ "<a href='http://www.baidu.com'>Clicked here!!</a>");}
1.jsp
<body><font color="red"><% java.util.Date d = new java.util.Date(); %><h1>Today's date is <%= d.toString() %> and this jsp page worked!</h1><%String message = (String)application.getAttribute("message");out.write(message);%></font></body>
上面的方法是转发, 注意和下面的重定向的区别
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stub/*response.setStatus(302); //实用http响应头重定向response.setHeader("location", "/WebTest2/1.html");*/response.sendRedirect("/WebTest2/1.html"); //API方法重定向}
控制缓存 // 缓存时间需要在当前时间的基础上添加。
response.addDateHeader("expires",System.currentTimeMillis() + 1000*3600);
Response要注意的一些细节:
4. Request
Request 常用方法
l获得客户机信息
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubtest3(request);}private void test3(HttpServletRequest request) throws IOException { //获得客户机请求参数(客户端提交的数据)Enumeration<String> e = request.getParameterNames();while(e.hasMoreElements()){String name = e.nextElement();String value = request.getParameter(name);System.out.println(name + "=" + value);}String[] values = request.getParameterValues("name");for(int i=0; values!=null && i<values.length; i++){if(!values[i].trim().equals(""))System.out.println("name=" + values[i]);}Map<String, String[]> map = request.getParameterMap();User user = new User();try {BeanUtils.populate(user, map);} catch (Exception e1) {// TODO Auto-generated catch blocke1.printStackTrace();}System.out.println(user.getPasswd());}private void test2(HttpServletRequest request) { //获得客户机请求头String headValue = request.getHeader("Accept-Language");System.out.println(headValue);Enumeration<String> e = request.getHeaders("Accept-Language");while(e.hasMoreElements()){String value = e.nextElement();System.out.println(value);}e = request.getHeaderNames();while(e.hasMoreElements()){String name = e.nextElement();String value = request.getHeader(name);System.out.println(name + "=" + value);}}private void test1(HttpServletRequest request) { // 获得客户机信息System.out.println(request.getRequestURI());System.out.println(request.getRequestURL());System.out.println(request.getQueryString());System.out.println(request.getRemoteAddr());System.out.println(request.getRemoteHost());System.out.println(request.getRemotePort());System.out.println(request.getMethod());}/** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubSystem.out.println("+++++++++++++++++++");InputStream in = request.getInputStream();int len = 0;byte[] buf = new byte[1024]; while( (len=in.read(buf))>0 ){System.out.println(new String(buf, 0, len));}}
上面User类为 , 请求数据为 ....?name=kevin&name=xiang&passwd=123456
public class User {private String[] name;private String passwd;public String[] getName() {return name;}public void setName(String[] name) {this.name = name;}public String getPasswd() {return passwd;}public void setPasswd(String passwd) {this.passwd = passwd;}}
Request 请求中会夹带中文, 解决乱码问题
如果是Post方式提交的请求带中文参数,可以设置编码
//post方式提交request.setCharacterEncoding("UTF-8");System.out.println("post username=" + request.getParameter("username"));
如果是Get方式 或 超链接方式 提交的请求带中文参数, 只能手动转码
String name = request.getParameter("username"); //Get方式提交name = new String(name.getBytes("iso8859-1"), "UTF-8");System.out.println("get name=" + name);
Request请求转发
和ServletContext一样Request 也可以做到请求转发,而且更实用,由于Request域不同于ServletContext域,每个请求都会有一个Request,所以用setAttribute()方法传递数据,不会有线程安全问题,具有实用性。
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubString data = "xxxxxx";request.setAttribute("data", data);request.getRequestDispatcher("/1.jsp").forward(request, response);//请求转发}
5. Web工程中各种地址的写法
首先“/” 加斜杠, 看地址使用的对象是谁。如果是服务器使用,斜杠就代表当前Web应用。 如果是浏览器使用,斜杠就代表网站,网站下面才有Web应用。
例一: 转发, 转发是给服务器使用,所以斜杠是代表当前Web应用
request.getRequestDispatcher("/1.html");
例二: 重定向, 重定向是给浏览器使用的,所以斜杠是代表网站,后面还需要接Web应用名
response.sendRedirect("/WebTest2/1.html");
书写路径时, 如果是Web工程中的资源文件用“/”斜杠, 如果是要获取硬盘上的文件,用“C:\\” 反斜杠
6. 域, ServletContext域 和 request域
对于域 需要有两个理解, 首先是一个容器,然后有自己的作用范围。
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