参考 : 

        Servlet之文件预览_httpservletresponse 设置文件预览-CSDN博客 

        java如何获取文件的媒体类型（MIME类型）？ - Java中文网 

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.URL;
import java.net.URLConnection;@Controller
public class YuLangController {@RequestMapping("/yl/{fileName}")public void yl(@PathVariable("fileName") String fileName, HttpServletResponse response) throws Exception {URL url = new File(fileName).toURI().toURL();URLConnection connection = url.openConnection();String contentType = connection.getHeaderField("content-type");response.setContentType(contentType);// 输出文件 fileName为相对路径 fileName= [System.getProperty("user.dir")+File.separator+fileName]InputStream is = new FileInputStream(fileName);OutputStream os = response.getOutputStream();BufferedOutputStream bos = new BufferedOutputStream(os);byte[] buffer = new byte[1024];int len = -1;while ((len = is.read(buffer)) != -1) {bos.write(buffer, 0, len);}// 关闭流bos.flush();bos.close();is.close();}
}