引用：http://www.cnblogs.com/zhuaijun/archive/2012/05/27/2520284.html
第一种：
就是直接给出下载的地址，这种方式很不好，因为会暴露你的地址，带来很多不安全的因素，可以说是千万不要用这种
第二种：
下载页面
<%@ page language="java" import="java.util.*" pageEncoding="GB18030"%>
<html>
<head>
<title>download</title>
</head>
<body>
<a href="xia.jsp?filename=新建文档.txt">新建文档.txt</a>
</body>
</html>
然后编写如下页面
<%@ page contentType="text/html;charset=gbk"%>
<%@ page language="java" import="java.io.*,java.net.*" pageEncoding="gbk"%>
<html>
<head>
<title>test</title>
</head>
<body>
<%
response.setContentType("text/html");
javax.servlet.ServletOutputStream ou = response.getOutputStream();
String filepath="uploadfile/";
String filename=new String(request.getParameter("filename").getBytes("ISO8859_1"),"GB2312").toString();
System.out.println("DownloadFile filepath:" + filepath);
System.out.println("DownloadFile filename:" + filename);
java.io.File file = new java.io.File(filepath + filename);
if (!file.exists()) {
System.out.println(file.getAbsolutePath() + " 文件不存在!");
return;
}
// 读取文件流
java.io.FileInputStream fileInputStream = new java.io.FileInputStream(file);
// 下载文件
// 设置响应头和下载保存的文件名
if (filename != null && filename.length() > 0) {
response.setContentType("application/x-msdownload");
response.setHeader("Content-Disposition", "attachment; filename=" + new String(filename.getBytes("gb2312"),"iso8859-1") + "");
if (fileInputStream != null) {
int filelen = fileInputStream.available();
//文件太大时内存不能一次读出,要循环
byte a[] = new byte[filelen];
fileInputStream.read(a);
ou.write(a);
}
fileInputStream.close();
ou.close();
}
%>
</body>
</html>
第三种方法
使用servlet 首先配置web.xml
<servlet>
<servlet-name>DownloadFile</servlet-name>
<servlet-class>libin123.com.cn.servlet.DownloadFile</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>DownloadFile</servlet-name>
<url-pattern>/downloadfile</url-pattern>
</servlet-mapping>
编写DownloadFile.java类
package libin123.com.cn.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.sun.image.codec.jpeg.ImageFormatException;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageDecoder;
public class DownloadFile extends HttpServlet {
private static final long serialVersionUID = 1L;
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html");
javax.servlet.ServletOutputStream out = response.getOutputStream();
String filepath=request.getRealPath("/") + "uploadfile/";
String filename=new String(request.getParameter("filename").getBytes("ISO8859_1"),"GB2312").toString();
System.out.println("DownloadFile filepath:" + filepath);
System.out.println("DownloadFile filename:" + filename);
java.io.File file = new java.io.File(filepath + filename);
if (!file.exists()) {
System.out.println(file.getAbsolutePath() + " 文件不存在!");
return;
}
// 读取文件流
java.io.FileInputStream fileInputStream = new java.io.FileInputStream(file);
// 下载文件
// 设置响应头和下载保存的文件名
if (filename != null && filename.length() > 0) {
response.setContentType("application/x-msdownload");
response.setHeader("Content-Disposition", "attachment; filename=" + new String(filename.getBytes("gb2312"),"iso8859-1") + "");
if (fileInputStream != null) {
int filelen = fileInputStream.available();
//文件太大时内存不能一次读出,要循环
byte a[] = new byte[filelen];
fileInputStream.read(a);
out.write(a);
}
fileInputStream.close();
out.close();
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<!DOCTYPE HTML PUBLIC -//W3C//DTD HTML 4.01 Transitional//EN>");
out.println("<HTML>");
out.println(" <HEAD><TITLE>A Servlet</TITLE></HEAD>");
out.println(" <BODY>");
out.print(" This is ");
out.print(this.getClass().getName());
out.println(", using the POST method");
out.println(" </BODY>");
out.println("</HTML>");
out.flush();
out.close();
}
}
下载页面
<%@ page language="java" import="java.util.*" pageEncoding="GB18030"%>
<html>
<head>
</head>
<body>
<a href="downloadfile?filename=新建文档.txt">新建文档.txt</a>
</body>
</html>