例子 - 文件下载 - 《Java Web 笔记》

超链接指向的资源如果能被浏览器解析，则点击后显示；不能的话则展示下载提示框 ``` <!DOCTYPE html>

图片


- 针对以上问题，我们想让浏览器弹窗提示下载，无论什么类型
- download.html

<!DOCTYPE html>

<!-- 超链接指向的资源如果能被浏览器解析，则点击后显示；不能的话则展示下载提示框-->
<a href="/WebDemo_war_exploded/downloadServlet?filename=图标.png">图片</a>


- DownloadServlet
> response.setHeader("content-disposition","attachment;filename="+filename);

package com.code.web;

import com.code.web.util.DownloadUtils;

import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.ServletOutputStream; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.FileInputStream; import java.io.IOException;

@WebServlet(“/downloadServlet”) public class DownloadServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    ServletContext servletContext = this.getServletContext();
    // 文件地址
    String filename = request.getParameter("filename");
    String realPath = servletContext.getRealPath("/imgs/" + filename);
    // 设置响应体文件类型
    String mimeType = servletContext.getMimeType(realPath);
    response.setHeader("content-type",mimeType);
    // 防止中文乱码
    String header = request.getHeader("user-agent");
    filename = DownloadUtils.getileName(header, filename);
    // 打开响应体方式
    response.setHeader("content-disposition","attachment;filename="+filename);
    // 响应体图片字节数据
    FileInputStream fileInputStream = new FileInputStream(realPath);
    ServletOutputStream outputStream = response.getOutputStream();
    byte[] buff = new byte[1024*8];
    int len = 0;
    while ((len = fileInputStream.read(buff)) != -1){
        outputStream.write(buff,0,len);
    }
    fileInputStream.close();
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    this.doPost(request, response);
}

}

<a name="xSeNm"></a>
#### 防止中文名乱码工具类

package com.code.web.util;

import java.io.UnsupportedEncodingException; import java.net.URLEncoder; import java.util.Base64;

public class DownloadUtils {

public static String getileName(String agent,String filename) throws UnsupportedEncodingException {
    if (agent.contains("MSIE")) {
        // IE浏览器
        filename = URLEncoder.encode(filename, "utf-8");
        filename = filename.replace("+", " ");
    } else if (agent.contains("Firefox")) {
        // 火狐浏览器
        Base64.Encoder encoder = Base64.getEncoder();
        String str = encoder.encodeToString(filename.getBytes("utf-8"));
        filename = "=?utf-8?B?" + str + "?=";
    } else {
        // 其它浏览器
        filename = URLEncoder.encode(filename, "utf-8");
    }
    return filename;
}

} ```