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<title>csdn_几个实用的Servlet应用例子---入门、cookie、session及上传文件</title>
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<td WIDTH="50%" bordercolor="#FFFFFF" CLASS="t1" bgcolor="#F0F0F0" align="center" nowrap>几个实用的Servlet应用例子---入门、cookie、session及上传文件</td>
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<P
class=MsoNormal><BR> Servlet可以被认为是服务端的applet，它被WEB服务器加载和执行，前端可以显示页面和获得页面数据，后台可以操纵数据库，能完成JavaBean的很多功能。在这里我较为详细的说说Servlet在Cookie，Session和上传文件上的应用，在说明时我给出一些能编绎运行的小例子，最后给出一个文件上传例子以加深印象。
<BR> 我们先来看看SERVLET程序的基本构架： <BR>式1：<BR> package test;<BR> import
javax.servlet.*; <BR> import javax.servlet.http.*; <BR> import
java.io.*; <BR> import java.util.*; <BR> public class test extends
HttpServlet { <BR> public void init(ServletConfig config) throws
ServletException { <BR> super.init(config);<BR>} <BR> public void
service(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException { <BR> int f =1; switch(f){ <BR> case
1:firstMothed(request,respponse);break; <BR>} <BR>}<BR> public void
firstMothed(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
<BR> response.setContentType("text/html");<BR> OutputStreamWriter osw =
new <BR> OutputStreamWriter(response.getOutputStream());
<BR> PrintWriter out = new PrintWriter
(response.getOutputStream());<BR> out.println("< html>");
<BR> out.println("< head>< title>Servlet1< /title><
/head>");<BR> out.println("< body>你好！"); <BR> out.println("<
/body>< /html>"); <BR> out.close(); <BR>} <BR>}
<BR>式2：<BR> package test; <BR> import javax.servlet.*; <BR> import
javax.servlet.http.*;<BR> import java.io.*; <BR> import java.util.*;
<BR> public class test extends HttpServlet { <BR> public void
init(ServletConfig config) throws ServletException
{<BR> super.init(config);<BR>}<BR> public void doGet(HttpServletRequest
request, HttpServletResponse response) throws ServletException,
IOException
{<BR> response.setContentType("text/html");<BR> OutputStreamWriter osw =
new OutputStreamWriter(response.getOutputStream());<BR> PrintWriter out =
new PrintWriter (response.getOutputStream());<BR> out.println("<
html>"); <BR> out.println("< head>< title>Servlet1<
/title>< /head>"); <BR> out.println("<
body>你好！");<BR> out.println("< /body><
/html>");<BR> out.close();<BR>}<BR> public void
doPost(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException
{<BR> response.setContentType("text/html");<BR> OutputStreamWriter osw =
new OutputStreamWriter(response.getOutputStream()); <BR> PrintWriter out
= new PrintWriter (response.getOutputStream()); <BR> out.println("<
html>");<BR> out.println("< head>< title>Servlet1<
/title>< /head>"); <BR> out.println("< body>你好！");
<BR> out.println("< /body>< /html>"); <BR> out.close();
<BR>} <BR>} <BR> 式1适合于作总控模块，此SERVLET作中间调度，根据不同的f值调用不同的SERVLET或方法。
<BR>式2适合于对html的get和post有不同要求的情况。<BR> 但这并不是绝对的，式2就完全可以代替式1，只要在doGet()方法中写上doPost就与式1完全一样。<BR>在init方法中执行的语句，只要这个servlet被启动了就一直有效，比如，我们在init()中new了一个对象，那么这个对象的内存空间就永远存在，除非显式地把这个对象赋为null，或重启服务。<BR> HttpServletRequest和HttpServletResponse两个对象实现http请求，它们有很多有用的方法，在下面的cookie和session管理中会细加描述。<BR> 1，
cookie管理 cookie用于在客户端保存个人所特有的信息，它采取在客户机写临时文件的机制。 <BR> package test;
<BR> import javax.servlet.*; <BR> import javax.servlet.http.*;
<BR> import java.io.*; <BR> import java.util.*; <BR> public class test
extends HttpServlet {<BR> public void init(ServletConfig config) throws
ServletException {<BR> super.init(config);<BR>}<BR> public void
service(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException {<BR> //写cookie <BR> String CookieName
="js79"; //若是汉字则需编码 <BR> String CookieValue = "yesky";//若是汉字则需编码
<BR> Cookie cookie = new Cookie(CookieName,CookieValue);
<BR> cookie.setMaxAge(age); // age = Integer.MAX_VALUE
永不过期<BR> cookie.setPath("/");<BR> //读cookie <BR> String value =
null;<BR> Cookie[] cookies = request.getCookies();<BR> if (cookies !=
null) {<BR> for (int i=0; i< cookies.length; i++) { <BR> if
(cookies[i].getName().equals(CookieName))<BR> value =
cookies[i].getValue(); <BR> break; <BR>}
<BR>}<BR>}<BR> response.setContentType("text/html");
<BR> OutputStreamWriter osw = new
OutputStreamWriter(response.getOutputStream());<BR> PrintWriter out = new
PrintWriter (response.getOutputStream());<BR> out.println("<
html>");<BR> out.println("< head>< title>test<
/title>< /head>"); <BR> out.println("cookie键:"+CookieName+"<
br>"); <BR> out.println("cookie值: "+value); <BR> out.println("<
/body>< /html>");<BR> out.close();<BR>}<BR>}<BR> 2,session管理
<BR> Session在Servlet中是很有用的，它比cookie安全可靠灵活，但是管理起来有点麻烦，用得不好会造成服务器的开销很大，浪费资源。下面是一个基于Session管理一个对象的简单例子。
<BR>一个简单的bean对象TestObject<BR> package test; <BR> public class TestObject
extends Object {<BR> int id = 0; public String cur="";<BR>} <BR> package
test;<BR> import javax.servlet.*; <BR> import javax.servlet.http.*;
<BR> import java.io.*; <BR> import java.util.*;<BR> public class
TestMan extends HttpServlet { <BR> public void init(ServletConfig config)
throws ServletException {<BR> super.init(config);<BR>}<BR> public void
doGet(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException { <BR> int f =
1;<BR> if(request.getParameter("f")!=null)<BR> f =
<BR> Integer.parseInt(request.getParameter("f")); <BR> switch(f){
<BR> case 1: this.getResult(request,response); <BR> break;<BR> case
2:<BR> this.setSession(request,response);<BR> break; <BR>} <BR>}
<BR> public void doPost(HttpServletRequest request, HttpServletResponse
response) throws ServletException, IOException {
<BR> doGet(request,response);<BR>}<BR> public void
getResult(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {<BR> TestObject testObject =
null;<BR> testObject = getStatus(request,response);<BR> String html =
testObject.id; doWrite( response,html); <BR>}<BR> public void
setSession(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {<BR> HttpSession session =
request.getSession(); <BR> TestObject testObject = null; <BR> testObject
= getStatus(request,response); <BR> String tmp = null; <BR> tmp =
request.getParameter("id");<BR> if(tmp != null) testObject.id = tmp;
<BR> session.putValue("testObject ",article);
<BR> getResult(request,response);<BR>} <BR> private TestObject
getStatus(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException {<BR> HttpSession session =
request.getSession(); <BR> TestObject testObject = null;
<BR> if(session!=null){<BR> if(session.getValue("testObject
")!=null){<BR> testObject = (TestObject)session.getValue("testObject
");<BR>} <BR> else{<BR> testObject = new TestObject
();<BR>}<BR>}<BR> else{ <BR> testObject = new TestObject ();
<BR>}<BR> return testObject; <BR>}<BR> private void
doWrite(HttpServletResponse response,String html) throws
ServletException, IOException { <BR> PrintWriter out =
response.getWriter();<BR> out.println(html);
<BR> out.close();<BR>}<BR> /////////////////////////////////////////////////////////
<BR>} <BR> 若能轻松搞定上面的例子，相信读者对SERVLET已有了较为深刻的理解。
<BR>下面再介绍一个上传文件例子，其中汲及到了下载的免费JavaBean
(如有感兴趣的朋友，可来函索要免费JavaBean源代码,Email:js79@yesky.com)
<BR> 上传基本原理：由页面发出一个http请求，服务端得到请求后，解析多媒体协议，读出文件内容，写文件内容到服务器，所有的这些功能都封装到JavaBean中。<BR> 上传文件的必需条件：Browser端<
form>表单的ENCTYPE属性值必须为
multipart/form-data，它告诉我们传输的数据要用到多媒体传输协议，由于多媒体传输的都是大量的数据，所以规定上传文件必须是post方法，<
input>的type属性必须是file。 <BR> package upload;<BR> import
javax.servlet.*; <BR> import javax.servlet.http.*; <BR> import
java.io.*; <BR> import java.util.*; <BR> public class UpLoadServlet
extends HttpServlet {<BR> public void init(ServletConfig config) throws
ServletException{ <BR> super.init(config);<BR>} <BR> public void
doGet(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException {<BR> PrintWriter out =
response.getWriter();<BR> out.println("< HTML>< HEAD><
TITLE>UpLoad< /TITLE>"<BR> +"< meta http-equiv='Content-Type'
content='text/html; charset=gb2312'>" <BR> +"< /HEAD>"
<BR> +"< body>"); <BR> out.println("< div align='center'
valign='top'>"<BR> +"< span
class='nava'>请你选择上传的文件(请注意文件大小只能在20K之内)< /span>< BR>"
<BR> +"< form ENCTYPE='multipart/form-data' method=post action=''>"
<BR> +"< input type='file' name='file'>" <BR> +"< input
type='submit' value='发送'>" <BR> +"< /form>"<BR> +"<
/div>"); <BR> out.println("< /body><
/html>");<BR> out.close(); <BR>} <BR> ////////<BR> public void
doPost(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException {<BR> PrintWriter out =
response.getWriter(); <BR> int tmpID = 1; try {<BR> MultipartRequest
multi = new MultipartRequest(request,"/home/js79/html/", 5 * 1024 *
1024);<BR>}<BR> catch(Exception e){<BR> tmpID = -1;
System.out.println(e);<BR>} <BR> if(tmpID == 1){<BR> out.println("<
HTML>< HEAD>< TITLE>UpLoad< /TITLE>" <BR> +"<
meta http-equiv='Content-Type' content='text/html;
charset=gb2312'>"<BR> +"< /HEAD>"<BR> +"< body>");
<BR> out.println("上传成功！< /body>< /html>"); <BR>}
<BR> else{<BR> out.println("< HTML>< HEAD><
TITLE>UpLoad< /TITLE>"<BR> +"< meta http-equiv='Content-Type'
content='text/html; charset=gb2312'>" <BR> +"<
/HEAD>"<BR> +"< body>");<BR> out.println("上传不成功！<
/body>< /html>");<BR>} <BR> out.close();<BR>}<BR>} </P>
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