JSP click the link and download the file of

 
/** 
*  Achieve file save function  
* 
* @param text 
*  The file content  
* @param fileName 
*  The file name  
* @return 
*/ 
protected String renderFile(String text, String fileName) 
throws IOException 
{ 
response.addHeader("Content-Disposition", "attachment; filename=" 
+ fileName); 
response.setContentType("application/octet-stream"); 
response.setCharacterEncoding("GB2312"); 
response.getWriter().write(text); 
response.flushBuffer(); 
response.getWriter().close(); 
return null; 
} 

Download action:

 
/** *//** 
*  Provides a method for downloading  
* @return 
*/ 
public String down() 
{ 
String dir = getFullPath() + "/upload/file/"; 
try 
{ 
if (!FileUtils.exists(dir)) 
{ 
new File(dir).mkdirs(); 
} 
Random r = new Random(System.currentTimeMillis()); 
Integer randomInt = r.nextInt(); 
this.renderFile("test content:" + randomInt,randomInt + ".txt"); 
} 
catch (IOException e) 
{ 
e.printStackTrace(); 
this.renderText(e.getMessage()); 
} 
return null; 
} 

Page link call:

 
<a href="${ctx}/va/va!down.do" > download </a>