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import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Downloads extends HttpServlet {
private static final long serialVersionUID = 1L;
// 字符编码
private final String ENCODING = "GB2312";
// 内容类型
private final String CONTENT_TYPE = "text/html;charset=gb2312";
// 要下载的文件存放的路径
private String downloadfiledir = "C:\\Users\\786108\\Downloads\\apache-tomcat-7.0.41\\webapps\\uploadFile\\upload\\";
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 设置request对象的字符编码
request.setCharacterEncoding(ENCODING);
// 从request中取出要下载文件的名字
String filename = request.getParameter("filename");
// 判断传输过来的filename是否合法
if (filename == null || filename.trim().equals("")) {
// 设置response对象的ContentType
response.setContentType(CONTENT_TYPE);
// 输出错误信息
PrintWriter out = response.getWriter();
out.println("<font color=red>输入的文件名无效！</font>");
out.close();
} else {
// 下载文件的完整路径名
String fullfilename = downloadfiledir + filename;
System.out.println("下载文件：" + fullfilename);
// 根据文件的类型设置response对象的ContentType
String contentType = getServletContext().getMimeType(fullfilename);
if (contentType == null)
contentType = "application/octet-stream";
response.setContentType(contentType);
// 设置response的头信息
response.setHeader("Content-disposition", "attachment;filename=\""
+ filename + "\"");
InputStream is = null;
OutputStream os = null;
try {
is = new BufferedInputStream(new FileInputStream(fullfilename));
// 定义输出字节流
ByteArrayOutputStream baos = new ByteArrayOutputStream();
// 定义response的输出流
os = new BufferedOutputStream(response.getOutputStream());
// 定义buffer
byte[] buffer = new byte[4 * 1024]; // 4k Buffer
int read = 0;
// 从文件中读入数据并写到输出字节流中
while ((read = is.read(buffer)) != -1) {
baos.write(buffer, 0, read);
}
// 将输出字节流写到response的输出流中
os.write(baos.toByteArray());
} catch (IOException e) {
e.printStackTrace();
} finally {
// 关闭输出字节流和response输出流
os.close();
is.close();
}
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 调用doGet()方法
doGet(request, response);
}
}

 


本文转自    拖鞋崽      51CTO博客，原文链接:http://blog.51cto.com/1992mrwang/1243222