ServletContext对象
**1 ServletContext对象
1)在web应用中，由服务器创建的唯一的一个对象是ServletContext
2)ServletContext对象在每一个Servlet中取得都是相同到
3)ServletContext对象在存取方法：
存ServletContext.setAttribute(String,Object):void
取ServletContext.getAttribute(String):Object
package cn.itcast.web.servlet; import java.io.IOException; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /* * http://192.168.10.252:8080/day06/Demo11?username=jack回车 */ public class Demo11 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { //取得客户端的请求参数 String username = request.getParameter("username"); //取得唯一的一个ServletContext对象 ServletContext context = this.getServletContext(); System.out.println("Demo11:"+context.hashCode()); //将信息存入ServletContext对象 context.setAttribute("USERNAME",username); } }
package cn.itcast.web.servlet; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /* * http://192.168.10.252:8080/day06/Demo12回车 */ public class Demo12 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { //取得唯一的一个ServletContext对象 ServletContext context = this.getServletContext(); System.out.println("Demo12:"+context.hashCode()); //根据name取得ServletContext对象中的值 String username = (String) context.getAttribute("USERNAME"); //在浏览器中输出 response.setContentType("text/html;charset=UTF-8"); response.getWriter().write("用户名：" + username + "<br/>"); } }
4)在web应用中，可以取得web应用的初始化参数
package cn.itcast.web.servlet; import java.io.IOException; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class Demo2 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { ServletContext context = this.getServletContext(); String email = context.getInitParameter("email"); String tel = context.getInitParameter("tel"); if(email!=null && tel!=null){ response.setContentType("text/html;charset=UTF-8"); response.getWriter().write("赵老师邮箱：" + email + "<br/>"); response.getWriter().write("赵老师电话：" + tel + "<br/>"); } } }
<context-param> <param-name>email</param-name> <param-value>runsin0723@163.com</param-value> </context-param> <context-param> <param-name>tel</param-name> <param-value>13632334557</param-value> </context-param>
5)ServletContxt对象能够实现转发功能，即307+location
ServletContext context = this.getServletContext();
//定位需要转发的路径
RequestDispatcher rd = context.getRequestDispatcher("/success.html");
//真正转向页面
rd.forward(request,response);
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>login.html</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body> <form action="/day06/LoginServlet" method="post"> <table border="1" align="center"> <caption>用户登录[模拟MVC]</caption> <tr> <th>用户名</th> <td><input type="text" name="username"/></td> </tr> <tr> <th>密码</th> <td><input type="password" name="password"/></td> </tr> <tr> <th>验证码</th> <td> <input type="text" name="checkCode"/> </td> <td> <img src="/day06/Demo3"/> </td> </tr> <tr> <td colspan="2" align="center"> <input type="submit" value="提交"/> </td> </tr> </table> </form> </body> </html>
package cn.itcast.web.servlet; public class LoginBean { public boolean validate(String username){ boolean flag = false; if(username!=null && "jack".equals(username)){ flag = true; } return flag; } }
package cn.itcast.web.servlet; import java.io.IOException; import javax.servlet.RequestDispatcher; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class LoginServlet extends HttpServlet { public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { //取得表单提交的参数 String username = request.getParameter("username"); //调用模型层对象 LoginBean loginBean = new LoginBean(); boolean flag = loginBean.validate(username); //根据返回值，转发到不同的页面 if(flag){ ServletContext context = this.getServletContext(); //定位需要转发的路径 RequestDispatcher rd = context.getRequestDispatcher("/success.html"); //真正转向页面 rd.forward(request,response); }else{ ServletContext context = this.getServletContext(); //定位需要转发的路径 RequestDispatcher rd = context.getRequestDispatcher("/fail.html"); //真正转向页面 rd.forward(request,response); } } }
6)如果以传统方式读取资源文件（txt/xml/properties），是相对于web服务器的bin/目录而言
*7)如果以ServletContext方式读取资源文件（txt/xml/properties），是相对于web服务器的当前web应用目录而言
此时/表示:当前web应用，即day06
*8)类加载器只能加载IDE工具下src目录下的资源文件，其它目录无法加载
此时/表示:/WEB-INF/classes/目录
package cn.itcast.web.servlet; import java.io.IOException; import java.io.InputStream; import java.util.Properties; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class Demo4 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { /*传统方式 InputStream is = new FileInputStream("src/config.properties"); Properties props = new Properties(); props.load(is); System.out.println(props.getProperty("email")); */ ServletContext context = this.getServletContext(); InputStream is = context.getResourceAsStream("/doc/config.properties"); Properties props = new Properties(); props.load(is); System.out.println(props.getProperty("email")); } }
package cn.itcast.web.servlet; import java.io.IOException; import java.io.InputStream; import java.util.Properties; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class Demo5 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { //取得当前对象的字节码对象 Class clazz = this.getClass(); //取得当前对象的类加载器 ClassLoader cl = clazz.getClassLoader(); //通过类加载器加载资源文件 InputStream is = cl.getResourceAsStream("/cn/itcast/web/config/config.properties"); Properties props = new Properties(); props.load(is); System.out.println(props.getProperty("email")); } }
10)其实浏览器访问的静态资源，本质上是由一个缺省的Servlet来帮你处理的
package cn.itcast.web.servlet; import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class DownServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { //NO1获取当前config文件的方式 ServletConfig config = this.getServletConfig(); String filePath = config.getInitParameter("filePath"); //NO2 File file = new File(filePath); response.setHeader("content-disposition","attachment;filename="+file.getName()); //NO3 InputStream is = new FileInputStream(file); OutputStream os = response.getOutputStream(); byte[] buf = new byte[1024]; int len = 0; while((len=is.read(buf))>0){ os.write(buf,0,len); } is.close(); os.close(); } }
2 关于路径的问题
1)二种加载方式的区别？
服务端
ServletContext方式：
1)资源的文件的位置任意
2)加载文件时，只会以流的方式读取，不会一次性加载全部
3)/表示当前web应用，即day06
类加载器方式：
1)资源文件的位置只能放置类路径下，即IDE工具的src目录下
2)加载文件时，会一次性加载全部文件
3)/表示当前/WEB-INF/classes/
2)有关/的问题？
物理硬盘路径使用\[window系统]
网络路径使用/
如果/表示客户端路径的话，表示tomcat/webapps/目录
*3 缓存应用
1)对于浏览器的刷新而言，当浏览器缓存中有资源，也会找服务端要资源，只有在回车访问情况下，才找缓存.对于不经常变化的数据，在servlet中可以为其设置合理的缓存时间值，以避免浏览器频繁向服务器发送请求，提升服务器的性能。
2)如果要实现一种高级功能，即客户端请求动态web资源时，动态web资源发现发给客户端的数据更新了，就给客户端发送最新的数据，如果发现数据没有更新，则动态web资源就要客户端就去访问它自己缓存的数据。此种情况可以通过覆写动态web资源(即servlet)的getLastModify方法予以实现。
package cn.itcast.web.servlet; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; /* * http://localhost:8080/day06/login.html回车
* 设置静态资源[html/css/js]缓存的时间[做成一个缺省的的Servlet，路径为/] */ public class Demo6 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { String uri = request.getRequestURI(); //如果是一个html静态资源 if(uri!=null && uri.endsWith("html")){ String html = this.getServletConfig().getInitParameter("html"); if(html!=null){ long end = Long.parseLong(html)*1000 + System.currentTimeMillis(); response.setDateHeader("expires",end); } } } }
<servlet> <servlet-name>Demo6</servlet-name> <servlet-class>cn.itcast.web.servlet.Demo6</servlet-class> <init-param> <param-name>html</param-name> <param-value>86400</param-value> </init-param> <init-param> <param-name>css</param-name> <param-value>123456</param-value> </init-param> <init-param> <param-name>js</param-name> <param-value>654321</param-value> </init-param> </servlet>
package cn.itcast.web.servlet; import java.io.File; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; //缓存高级应用 public class Demo7 extends HttpServlet { protected long getLastModified(HttpServletRequest req) { System.out.println("getLastModified()"); String path = this.getServletContext().getRealPath("/doc/abc.txt"); File file = new File(path); return file.lastModified(); } public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { System.out.println("doGet()"); ServletContext context = this.getServletContext(); InputStream is = context.getResourceAsStream("/doc/abc.txt"); OutputStream os = response.getOutputStream(); byte[] buf = new byte[1024]; int len = 0; while((len=is.read(buf))>0){ os.write(buf,0,len); } is.close(); os.close(); } }
*4 response的应用
1)web容器会传入与web容器相关的HttpServletRequest和HttpServletResponse对象的实现。request和response对象即然代表请求和响应，那我们要获取客户机提交过来的数据，只需要找request对象就行了。要向客户机输出数据，只需要找response对象就行了。
2)每次浏览器请求，web容器会创建新的请求和响应对象，这二个对象的生命周期仅限于web容器内。HttpServletResponse对象服务器的响应。这个对象中封装了向客户端发送数据、发送响应头，发送响应状态码的方法。
3)对于字节方式来说，输出数字，respnse会编查ISO8859-1编码表，将码表的中的数字对应的字符取出来显示，即遇数字转字符
4)如果要输出数字，提前将数字转化成字符串
5)对于字符方式来说，可以直接输出数字
6)将中文转成字节数组时，查UTF-8码表，如果不写的话，默认查ISO8859-1码表
7)以字符方式输出中文，提前设置编码方式；以字节方式输出中文，提前设置转化编码方式
字符：
response.getOutputStream().write("中国".getBytes("UTF-8"));
字节：
response.setContentType("text/html;charset=UTF-8");
response.getWriter().write("美国");
8)HTML中的所有<meta/>标签，类似于response.setHeader()，目的是通知浏览器以特定的方式显示页面的信息
9)重定向是客户端和服务端的共同行为，
response.sendRedirect("/day06/message.html")其中/表示webapps目录
10)response常见应用：
•向客户端输出中文数据
•分别以OutputStream和PrintWriter输出
•用OutputStream输出1，客户端看到的是什么？
•中文名文件下载
•生成随机图片
•发送http头，控制浏览器定时刷新网页(refresh)
•发送http头，控制浏览器禁止缓存当前文档内容
•多学一招：使用HTML/JSP语言里面的<meta>标签来控制浏览器行为<meta http-equiv="content-type" content="text/html; charset=UTF-8">
•通过response实现请求重定向。
•请求重定向指：一个web资源收到客户端请求后，通知客户端去访问另外一个web资源，这称之为请求重定向。
•应用场景：用户登陆。
•实现方式
•response.sendRedirect(“/welcome.html”)
•实现原理：
302状态码和location头即可实现重定向
package cn.itcast.web.response; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; //向浏览器输出中文数据 public class Demo1 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { //以字节方式输出 //response.getOutputStream().write((97+"").getBytes()); //以字符方式输出 //response.getWriter().write(65); //response.getOutputStream().write("中国".getBytes("UTF-8")); response.setContentType("text/html;charset=UTF-8"); response.getWriter().write("美国"); } }
package cn.itcast.web.response; import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.net.URLEncoder; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; //中文名文件下载 public class Demo2 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { ServletContext context = this.getServletContext(); String path = context.getRealPath("/images/神奇的图片.JPG"); File file = new File(path); response.setHeader("content-disposition","attachment;filename="+URLEncoder.encode(file.getName(),"UTF-8")); InputStream is = new FileInputStream(file); OutputStream os = response.getOutputStream(); byte[] buf = new byte[1024]; int len = 0; while((len=is.read(buf))>0){ os.write(buf,0,len); } is.close(); os.close(); } }
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>download.html</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body> <a href="/day06/Demo2">下载中文文件</a> </body> </html>
package cn.itcast.web.response; import java.awt.Color; import java.awt.Font; import java.awt.Graphics; import java.awt.image.BufferedImage; import java.io.IOException; import java.util.Random; import java.util.UUID; import javax.imageio.ImageIO; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; //生成验证码图片 public class Demo3 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { response.setHeader("expires","-1"); response.setHeader("cache-control","no-cache"); response.setHeader("pragma","no-cache"); //以内存中构造一副图片 BufferedImage image = new BufferedImage(80,25,BufferedImage.TYPE_INT_RGB); //取得画笔 Graphics g = image.getGraphics(); //设置字体大小和颜色 g.setColor(Color.YELLOW); g.setFont(new Font("黑体",Font.BOLD,22)); //在图片中，画一个字符串"1A2B" g.drawString(getString(),20,20); //将内存中的图片以JPG格式输出到浏览器 ImageIO.write(image,"JPG",response.getOutputStream()); } //产生一个随机字符串 private String getString(){ String str = ""; String numberAndLetter="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"; int length = numberAndLetter.length(); for(int i=1;i<=4;i++){ if(i==1 || i==3){//数字 while(true){ Random random = new Random(); int index = random.nextInt(length); String value = numberAndLetter.substring(index,index+1); if(value.matches("[0-9]")){ str += value; break; } } }else if(i==2 || i==4){//大小字母 while(true){ Random random = new Random(); int index = random.nextInt(length); String value = numberAndLetter.substring(index,index+1); if(value.matches("[A-Za-z]")){ str += value; break; } } } } return str; } }
package cn.itcast.web.response; import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class LoginServlet extends HttpServlet { public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { String username = request.getParameter("username"); String password = request.getParameter("password"); String checkCode = request.getParameter("checkCode"); System.out.println("用户名：" + username); System.out.println("密码：" + password); System.out.println("验证码：" + checkCode); //重定向到message.html页面 //这时/表示webapps目录 response.sendRedirect("/day06/message.html"); } }
5 response细节
1)以字符或字节方式输出内容的话，只能使用其中一种
2)响应头会以叠加的方式设置，在相同的情况下，后者起决定作用
package cn.itcast.web.response; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class Demo4 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); response.setContentType("text/html;charset=GBK"); PrintWriter pw = response.getWriter(); pw.write("美国"); pw.flush(); pw.close(); } }
3)在没有关闭流的情况下，web容器帮你自动关闭所有从response中取得IO流
4)getOutputStream和getWriter方法分别用于得到输出二进制数据、输出文本数据的ServletOuputStream、Printwriter对象。
5)getOutputStream和getWriter这两个方法互相排斥，调用了其中的任何一个方法后，就不能再调用另一方法。
6)Servlet程序向ServletOutputStream或PrintWriter对象中写入的数据将被Servlet引擎从response里面获取，Servlet引擎将这些数据当作响应消息的正文，然后再与响应状态行和各响应头组合后输出到客户端。
7)Serlvet的service方法结束后，Servlet引擎将检查getWriter或getOutputStream方法返回的输出流对象是否已经调用过close方法，如果没有，Servlet引擎将调用close方法关闭该输出流对象。
