jsp 起航 和Servlet通过attribute通信

 @WebServlet(name = "ticketServlet",urlPatterns = {"/tickets"},loadOnStartup = 1)
 @MultipartConfig(fileSizeThreshold = 5242880,
 maxFileSize = 20971520L,//20MB
 maxRequestSize = 41943040L//40MB
 )
 public class TicketServlet extends HttpServlet{
     //线程可见性
     private volatile int TICKET_ID_SEQUENCE = 1;
     private Map<Integer,Ticket> ticketDatabase = new LinkedHashMap<>();

     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {

         //使用请求参数做了一个菜单
         String action = req.getParameter("action");
         if (action == null){
             action = "list";//默认ticket列表
         }
         switch (action){
             case "create":
                 this.showTicketForm(req,resp);//展示表单
                 break;
             case "view":
                 this.viewTicket(req,resp);//具体一张
                 break;
             case  "download":
                 this.downloadAttachment(req,resp);//下载附件
                 break;
             default:
                 this.listTickets(req,resp);//展示ticket
                 break;
         }
     }

     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         req.setCharacterEncoding("UTF-8");
         String action = req.getParameter("action");
         if(action == null){
             action = "list";
         }
         switch (action){
             case "create":
                 this.createTicket(req,resp);//表单提交实际创建方法
                 break;
             case "list":
             default:
                 resp.sendRedirect("tickets");//重定向 get
                 break;

         }

     }

     private void listTickets(HttpServletRequest request,HttpServletResponse response) throws IOException, ServletException {
         request.setAttribute("ticketDatabase",this.ticketDatabase);
         request.getRequestDispatcher("/WEB-INF/jsp/view/listTickets.jsp").forward(request,response);
     }

     private void viewTicket(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
         //从ticket列表进入某张ticket所需要id
         String idString = request.getParameter("ticketId");
         Ticket ticket = this.getTicket(idString, response);
         if(ticket == null)
             return;
         request.setAttribute("ticketId",idString);
         request.setAttribute("ticket",ticket);

         request.getRequestDispatcher("/WEB-INF/jsp/view/viewTicket.jsp")
                 .forward(request,response);
     }

     private Ticket getTicket(String id, HttpServletResponse response) throws IOException {
         //id.len == ''  一般合法性检查  有没有
         if (id == null || id.length()==0){
             response.sendRedirect("tickets");
             return null;
         }
         try {
             //parse异常
             Ticket ticket = this.ticketDatabase.get(Integer.parseInt(id));
             //都考虑失败 没有的情况
             if (ticket == null) {
                 response.sendRedirect("tickets");
                 return null;
             }
             return ticket;
         }catch (Exception e){
             response.sendRedirect("tickets");
             return null;
         }
     }

     private void showTicketForm(HttpServletRequest req,HttpServletResponse resp) throws IOException, ServletException {
 //        内部转发，而不是重定向，用户浏览器不会收到重定向状态码，浏览器URL也不改变
 //        内部请求处理转发至应用程序不同部分，forward后，Servlet代码没有控制权再操作响应对象。
         req.getRequestDispatcher("/WEB-INF/jsp/view/ticketForm.jsp").forward(req,resp);
     }

     private void downloadAttachment(HttpServletRequest request, HttpServletResponse response) throws IOException {
        //下载某一个attachment
         String idString = request.getParameter("ticketId");
         Ticket ticket = this.getTicket(idString, response);
         if(ticket == null)
             return;

         String name = request.getParameter("attachment");
         if(name == null)
         {
             response.sendRedirect("tickets?action=view&ticketId=" + idString);
             return;
         }

         Attachment attachment = ticket.getAttachment(name);
         if(attachment == null)
         {
             response.sendRedirect("tickets?action=view&ticketId=" + idString);
             return;
         }
         //header 内容位置   文件名
         response.setHeader("Content-Disposition",
                 "attachment; filename=" +
                         new String(attachment.getName().getBytes("UTF-8"),"ISO8859-1"));

         response.setContentType("application/octet-stream");
         //流
         ServletOutputStream stream = response.getOutputStream();
         stream.write(attachment.getContents());
     }

     private void createTicket(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
         Ticket ticket = new Ticket();
         ticket.setCustomerName(req.getParameter("customerName"));
         ticket.setSubject(req.getParameter("subject"));
         ticket.setBody(req.getParameter("body"));

         Part filePart = req.getPart("file1");
         if (filePart!=null){
             Attachment attachment = this.processAttachment(filePart);
             if (attachment!=null)
                 ticket.addAttachment(attachment);
         }
         int id;
         synchronized (this){
             id = this.TICKET_ID_SEQUENCE++;
             this.ticketDatabase.put(id,ticket);
         }
         resp.sendRedirect("tickets?action=view&ticketId="+id);
     }

     private Attachment processAttachment(Part filePart) throws IOException {
         InputStream inputStream = filePart.getInputStream();//用户输入流
         ByteArrayOutputStream outputStream = new ByteArrayOutputStream();//写入attachment做准备

         int read;
         final byte[] bytes  = new byte[1024];//buffer
         while((read=inputStream.read(bytes))!=-1){//有多少
             outputStream.write(bytes,0,read);//写多少
         }

         Attachment attachment = new Attachment();
         attachment.setName(filePart.getSubmittedFileName());
         attachment.setContents(outputStream.toByteArray());

         return attachment;
     }

【展示ticket表单】

 <%--<%@ page contentType="text/htmlcharset=UTF-8" %>--%>
 <%@ page session="false" %>
 <html>
 <head>
     <title>Create a Ticket</title>
 </head>
 <body>
     <%--//编码类型multipart/form-data--%>
 <form method="POST" action="tickets" enctype="multipart/form-data">
     <%--//隐藏域提交 action value = create--%>
     <input type="hidden" name="action" value="create"/>
     Your Name<br/>
     <input type="text" name="customerName"/><br/><br/>
     Subject<br/>
     <input type="text" name="subject"/><br/><br/>
     Body<br/>
     <textarea name="body" rows="5" cols="30"></textarea><br/><br/>
     <b>Attachments</b><br/>
     <input type="file" name="file1"/><br/><br/>
     <input type="submit" value="提交"/>
 </form>
 </body>
 </html>

【查看Ticket】

 <%@ page import="net.mypla.model.Ticket" %>
 <%@ page session="false" %>
 <%
     String ticketId = (String) request.getAttribute("ticketId");
     Ticket ticket = (Ticket) request.getAttribute("ticket");
 %>
 <html>
 <head>
     <title>客户支持系统</title>
 </head>
 <body>
     <h2>Ticket #<%= ticketId%>: <%=ticket.getSubject()%></h2>
     <i>Customer Name - <%= ticket.getCustomerName()%></i><br /><br />
     <%= ticket.getBody()%><br /><br />
     <%
         if(ticket.getNumberOfAttachments()>0){
             %>Attachments:<%
             int i = 0;
             for(Attachment a:ticket.getAttachments()){
                 if(i++>0)
                     out.print(",");
                 %><a href="<c:url value="/tickets">
                     <c:param name="action" value="download"/>
                     <c:param name="ticketId" value="<%= ticketId%>"/>
                     <c:param name="attachment" value="<%= a.getName()%>"/>
                 </c:url>"><%= a.getName()%></a><%
             }
         }
     %><br/>
     <a href="<c:url value="/tickets" />">Return to list tickets</a>
 </body>
 </html>

【查看tickets列表】

 <%@ page session="false" import="java.util.Map" %>
 <%@ page import="net.mypla.model.Ticket" %>
 <%
     @SuppressWarnings("unchecked")
     Map<Integer,Ticket> ticketDatabase = (Map<Integer, Ticket>) request.getAttribute("ticketDatabase");
 %>
 <html>
 <head>
     <title>消费者支持系统</title>
 </head>
 <body>
     <h2>Tickets</h2>

     <a href="<c:url value="/tickets"><c:param name="action" value="create"/></c:url>">Create Ticket</a><br/><br/>
     <%
         if(ticketDatabase.size() == 0){
             %><i>There are no tickets in the system.</i><%
         }
         else{
             for(int id : ticketDatabase.keySet()){
                 String idString = Integer.toString(id);
                 Ticket ticket = ticketDatabase.get(id);
                 %>Ticket #<%= idString%>:<a href="<c:url value="/tickets">
                     <c:param name="action" value="view"/>
                     <c:param name="ticketId" value="<%= idString%>"/></c:url>"><%= ticket.getSubject()%></a>
         ( customer:<%= ticket.getCustomerName() %>)<br /><%
         }
 }
 %>
 </body>
 </html>

【部署描述符】

<jsp-config>
    <jsp-property-group>
        <url-pattern>*.jsp</url-pattern>
        <url-pattern>*.jspf</url-pattern>
        <page-encoding>UTF-8</page-encoding>
        <scripting-invalid>false</scripting-invalid>
        <include-prelude>/WEB-INF/jsp/base.jspf</include-prelude>
        <!--jsp转换器删除响应输出中空白，只留指令、声明、脚本、jsp标签-->
        <trim-directive-whitespaces>true</trim-directive-whitespaces>
        <default-content-type>text/html</default-content-type>
    </jsp-property-group>
</jsp-config>