浏览器从服务器下载文件的Servlet实例

测试两种下载：浏览器通过服务器下载其他网站文件（http协议）；浏览器下载服务器本地硬盘里的文件（file协议）

1.工具类downloadUtils.java的核心部分

//服务器使客户端可以从远程url下载文件public void download(String fileUrl, HttpServletResponse response) throws ServletException, IOException {String fileName = fileUrl.substring(fileUrl.lastIndexOf("/") +1, fileUrl.length());// 文件名称URL url = new URL(fileUrl);URLConnection conn = url.openConnection();int filesize = conn.getContentLength(); // 取数据长度BufferedInputStream bis = new BufferedInputStream(conn.getInputStream());// 清空responseresponse.reset();// 文件名称转换编码格式为utf-8,保证不出现乱码,这个文件名称用于浏览器的下载框中自动显示的文件名response.addHeader("Content-Disposition",        "attachment;filename=" + new String(fileName.getBytes("utf-8"), "iso8859-1"));response.addHeader("Content-Length", "" + filesize);BufferedOutputStream os = new BufferedOutputStream(response.getOutputStream());response.setContentType("application/octet-stream");// 从输入流中读入字节流，然后写到文件中byte[] buffer = new byte[1024];int nRead;while ((nRead = bis.read(buffer, 0, 1024)) > 0) { // bis为网络输入流os.write(buffer, 0, nRead);}bis.close();os.flush();os.close();}

2.Servlet核心部分webxmlServlet.java（只需看doGet方法即可，其他的可不看）：

package test;import java.io.IOException;import javax.servlet.ServletConfig;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * Servlet implementation class webxmlServlet */public class webxmlServlet extends HttpServlet {private static final long serialVersionUID = 1L;           /**     * @see HttpServlet#HttpServlet()     */    public webxmlServlet() {        super();        // TODO Auto-generated constructor stub    }        public void init()    {        String userName;String userName1;String path;try {ServletConfig config = getServletConfig();userName = config.getInitParameter("username");userName1 = this.getInitParameter("username");path = config.getInitParameter("path");System.out.println("初始化获得的userName："+userName);//初始化获得的userName：adminSystem.out.println("初始化获得的userName1："+userName1);//初始化获得的userName1：adminSystem.out.println("初始化获得的path："+path);//初始化获得的path：null} catch (Exception e) {e.printStackTrace();}    }/** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubresponse.getWriter().append("Served at: ").append(request.getContextPath());System.out.println("webxmlServlet的doGet开始。。。");//1.服务器使客户端从网络上下载文件String url  = "http://apps.bdimg.com/libs/accounting.js/0.3.2/accounting.min.js";fileDownload fd = new fileDownload();//fd.download(url, response);//2.服务器从本地拿文件给和客户端String localUrl = "file:///D:/test/test1.txt";fd.download(localUrl, response);}/** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

注意：doGet方法中写了两种测试方法：

1.一种是浏览器从其他网站下资源，本地的服务器只是提供这种链接下载的服务，使客户端可以不需要能访问这个url即可下载此资源，服务器代为传输下载，即服务器提供链接和传输中介服务。使用http协议。

2.另一种是浏览器从服务器的本地设备中获取，即服务器从自己硬盘中拿出文件给客户端。使用本地文本传输协议file协议。这种更常见。

3.这两种服务都需要使用协议不管是http协议还是本地文本传输协议file协议。

4.doGet中这个两种方法必须有分开测试，即测试一个注释一个，不然一个测试I/O流关闭后会导致另一个报错，你也可以new两次fileDownload。我是为了测试效果，才测一个注掉一个。

为了让你的servlet运行起来，我给出web.xml
3.web.xml（需要手动在WEB-INF目录下手动新建目录classes/log4j.properties）

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">  <welcome-file-list>    <welcome-file>login.jsp</welcome-file>  </welcome-file-list>  <context-param>    <param-name>path</param-name>    <param-value>/WEB-INF/config.properties</param-value>  </context-param>  <context-param>    <param-name>log4jConfigLocation</param-name>    <param-value>/WEB-INF/classes/log4j.properties</param-value>  </context-param>  <servlet>    <description>This is the description of my J2EE component</description>    <display-name>This is the display name of my J2EE component</display-name>    <servlet-name>CheckAccount</servlet-name>    <servlet-class>com.ht.servlet.CheckAccount</servlet-class>    <init-param>      <param-name>username</param-name>      <param-value>admin</param-value>    </init-param>  </servlet>  <servlet-mapping>    <servlet-name>CheckAccount</servlet-name>    <url-pattern>/CheckAccount</url-pattern>  </servlet-mapping>  <servlet>    <description>This is the description of my J2EE component</description>    <display-name>This is the display name of my J2EE component</display-name>    <servlet-name>webxmlServlet</servlet-name>    <servlet-class>test.webxmlServlet</servlet-class>    <init-param>      <param-name>username</param-name>      <param-value>admin</param-value>    </init-param>  </servlet>  <servlet-mapping>    <servlet-name>webxmlServlet</servlet-name>    <url-pattern>/webxmlServlet</url-pattern>  </servlet-mapping>  <session-config>    <session-timeout>40</session-timeout>  </session-config>  <error-page>    <error-code>404</error-code>    <location>/login.jsp</location>  </error-page>  <error-page>    <error-code>500</error-code>    <location>/login.jsp</location>  </error-page>   <!--  <filter>  <filter-name>Encoding</filter-name>  <filter-class>ghjf.test.filter.SetCharacterEncodingFilter</filter-class>  <init-param>     <param-name>encoding</param-name>     <param-value>UTF-8</param-value>  </init-param></filter><filter-mapping>   <filter-name>Encoding</filter-name>   <url-pattern>/*</url-pattern></filter-mapping> --></web-app>

在启动servlet后，需要测试。

4.用浏览器打开点击链接测试的HTML页面testServletDownload.html：

<!doctype html><html> <head>  <meta http-equiv="Content-Type" content="text/html; charset=utf-8">  <title>测试客户端下载文件页面</title> </head> <body><a href="http://localhost:8080/demoProj/webxmlServlet">点我下载文件</a> </body></html>