如何从网站下载文件-Java / Jsp

浅浅的花香味﹌ 2023-02-15 07:38 35阅读 0赞

在这里，我显示了一个简单的Java示例，以演示如何让用户从网站下载文件。 无论您使用的是struts，JSP，Spring还是其他Java框架，其逻辑都是相同的。

1）首先，我们必须设置**HttpServletResponse响应，**以告知浏览器系统将返回应用程序文件而不是正常的html页面

response.setContentType("application/octet-stream");
    response.setHeader("Content-Disposition",
    "attachment;filename=downloadfilename.csv");

我们还可以在**附件中**指定下载文件名**； filename =** ，上面的示例导出一个csv文件名“ downloadfilename.csv”供用户下载。

2）有两种方法可以让用户从网站下载文件

**从物理位置读取文件**

File file = new File("C:\\temp\\downloadfilename.csv");
    FileInputStream fileIn = new FileInputStream(file);
    ServletOutputStream out = response.getOutputStream();
    
    byte[] outputByte = new byte[4096];
    //copy binary contect to output stream
    while(fileIn.read(outputByte, 0, 4096) != -1)
    {
    	out.write(outputByte, 0, 4096);
    }
    fileIn.close();
    out.flush();
    out.close();

**将数据库数据或字符串直接导出到InputStream以供用户下载。**

StringBuffer sb = new StringBuffer("whatever string you like");
    InputStream in = new ByteArrayInputStream(sb.toString().getBytes("UTF-8"));
    ServletOutputStream out = response.getOutputStream();
    
    byte[] outputByte = new byte[4096];
    //copy binary contect to output stream
    while(in.read(outputByte, 0, 4096) != -1)
    {
    	out.write(outputByte, 0, 4096);
    }
    in.close();
    out.flush();
    out.close();

3）完成

在这里，我展示了我的struts示例，以演示如何直接将数据写入InputStream并将其输出为“ temp.cvs”以供用户下载。

public ActionForward export(ActionMapping mapping, ActionForm form,
    	HttpServletRequest request, HttpServletResponse response)
    	throws Exception {
    				
    	//tell browser program going to return an application file 
            //instead of html page
            response.setContentType("application/octet-stream");
            response.setHeader("Content-Disposition","attachment;filename=temp.csv");
    				
    	try 
    	{
    		ServletOutputStream out = response.getOutputStream();
    		StringBuffer sb = generateCsvFileBuffer();
    					
    		InputStream in = 
                        new ByteArrayInputStream(sb.toString().getBytes("UTF-8"));
    					
    		byte[] outputByte = new byte[4096];
    		//copy binary contect to output stream
    		while(in.read(outputByte, 0, 4096) != -1)
    		{
    			out.write(outputByte, 0, 4096);
    		}
    		in.close();
    		out.flush();
    		out.close();
    					
    	  }
    	  return null;
    	}
    
    private static StringBuffer generateCsvFileBuffer()
    {
    	StringBuffer writer = new StringBuffer();
    
    	writer.append("DisplayName");
    	writer.append(',');
    	writer.append("Age");
    	writer.append(',');
    	writer.append("HandPhone");
    	writer.append('\n');
    
            writer.append("mkyong");
    	writer.append(',');
    	writer.append("26");
    	writer.append(',');
    	writer.append("0123456789");
    	writer.append('\n');
    			
    	return writer;
    }

这是[Servlet代码中][Servlet]的[文件下载示例][Servlet]

标签： [下载文件][Link 1] [java][] [struts][]

> 翻译自: [https://mkyong.com/java/how-to-download-file-from-website-java-jsp/][https_mkyong.com_java_how-to-download-file-from-website-java-jsp]

[Servlet]: http://www.mkyong.com/servlet/servlet-code-to-download-text-file-from-website-java/
[Link 1]: https://mkyong.com/tag/download-file/
[java]: https://mkyong.com/tag/java/
[struts]: https://mkyong.com/tag/struts/
[https_mkyong.com_java_how-to-download-file-from-website-java-jsp]: https://mkyong.com/java/how-to-download-file-from-website-java-jsp/