浏览器从服务器下载文件的Servlet实例

Biegral 2020/8/30 11:50:55 4914

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response
		response.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：admin
			System.out.println("初始化获得的userName1："+userName1);//初始化获得的userName1：admin
			System.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 stub
		response.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>



本文转载:CSDN博客

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