版权声明:chaizepeng https://blog.csdn.net/chaizepeng/article/details/86700456
是什么
下载指的是将服务器端的文件保存到客户端的磁盘中
基本实现原理
根据对应的要下载的文件在服务器端找到对应的文件,然后获取到文件流对象,将流对象发送到客户端,然后客户端通过对返回结果中文件流的解析,将流对象转换成相应的文件保存在客户端的磁盘中,以实现下载效果
实例
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<form action="fileDownloadServlet" method="post">
<input type="hidden" name="fileName" value="ceshixzai.txt">
下载文件:下载测试文件<input type="submit" value="下载">
</form>
</body>
</html>
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(name = "FileDownloadServlet", urlPatterns = "/fileDownloadServlet")
public class FileDownloadServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doPost(request, response);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 获取下载文件名
String fileName = request.getParameter("fileName");
fileName = URLEncoder.encode(fileName, "UTF-8");
response.setHeader("Content-Disposition", "attachment;filename=" + fileName);
// 设置一个存放下载文件的目录
File file = new File("F:" + File.separator + fileName);
// 想写通用的方法的话,可以在这里进行文件的遍历查找
InputStream input = null;
OutputStream output = response.getOutputStream();;
if (file.exists()) {
input = new FileInputStream(file);
if (input != null && input.read() > 0) {
byte[] buff = new byte[1024 * 5];
int len = 0;
while ((len = input.read(buff)) > -1) {
output.write(buff, 0, len);
}
} else {
output.write("文件已经失效!".getBytes());
}
}else{
output.write("文件已经失效!".getBytes());
}
if (input != null) {
input.close();
}
if (output != null) {
output.close();
}
}
}