瀏覽器從伺服器下載檔案的Servlet例項
阿新 • • 發佈：2018-12-27
測試兩種下載：瀏覽器通過伺服器下載其他網站檔案（http協議）；瀏覽器下載伺服器本地硬盤裡的檔案（file協議）
1.工具類downloadUtils.java的核心部分
//伺服器使客戶端可以從遠端url下載檔案 public void download(String fileUrl, HttpServletResponse response) throws ServletException, IOException { String fileName = fileUrl.substring(fileUrl.lastIndexOf("/") +1, fileUrl.length());// 檔名稱 URL url = new URL(fileUrl); URLConnection conn = url.openConnection(); int filesize = conn.getContentLength(); // 取資料長度 BufferedInputStream bis = new BufferedInputStream(conn.getInputStream()); // 清空response response.reset(); // 檔名稱轉換編碼格式為utf-8,保證不出現亂碼,這個檔名稱用於瀏覽器的下載框中自動顯示的檔名 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"); // 從輸入流中讀入位元組流，然後寫到檔案中 byte[] buffer = new byte[1024]; int nRead; while ((nRead = bis.read(buffer, 0, 1024)) > 0) { // bis為網路輸入流 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("初始化獲得的userName："+userName);//初始化獲得的userName：admin System.out.println("初始化獲得的userName1："+userName1);//初始化獲得的userName1：admin System.out.println("初始化獲得的path："+path);//初始化獲得的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 stub response.getWriter().append("Served at: ").append(request.getContextPath()); System.out.println("webxmlServlet的doGet開始。。。"); //1.伺服器使客戶端從網路上下載檔案 String url = "http://apps.bdimg.com/libs/accounting.js/0.3.2/accounting.min.js"; fileDownload fd = new fileDownload(); // fd.download(url, response); //2.伺服器從本地拿檔案給和客戶端 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方法中寫了兩種測試方法：
1.一種是瀏覽器從其他網站下資源，本地的伺服器只是提供這種連結下載的服務，使客戶端可以不需要能訪問這個url即可下載此資源，伺服器代為傳輸下載，即伺服器提供連結和傳輸中介服務。使用http協議。
2.另一種是瀏覽器從伺服器的本地裝置中獲取，即伺服器從自己硬碟中拿出檔案給客戶端。使用本地文字傳輸協議file協議。這種更常見。
3.這兩種服務都需要使用協議不管是http協議還是本地文字傳輸協議file協議。
4.doGet中這個兩種方法必須有分開測試，即測試一個註釋一個，不然一個測試I/O流關閉後會導致另一個報錯，你也可以new兩次fileDownload。我是為了測試效果，才測一個注掉一個。
3.web.xml（需要手動在WEB-INF目錄下手動新建目錄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>4.用瀏覽器開啟點選連結測試的HTML頁面testServletDownload.html：
<!doctype html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>測試客戶端下載檔案頁面</title>
</head>
<body>
<a href="http://localhost:8080/demoProj/webxmlServlet">點我下載檔案</a>
</body>
</html>