struts2文件下载

<action name="test" class="com.TestAction" method="importToFile">
    	<result name="success" type="stream">    
        <param name="contentType">unknown</param>    
        <param name="inputName">downloadFile</param> <!--下载文件的文件流名称，在action中需要给它一个get方法返回下载文件的流-->   
        <param name="contentDisposition">attachment;filename="${downloadFileName}"</param>  
        <param name="bufferSize">4096</param>    
    </result>   
    </action>

public InputStream getDownloadFile() throws InvalidResultSetAccessException, IOException, SQLException {
		String path = request.getSession().getServletContext().getRealPath("/temp");
		File dir = new File(path);
		if (!dir.exists())
			dir.mkdir();
		parent_code = request.getParameter("parent_code");
		String fileName = "shopbarcode_"+parent_code+".txt";
		File file = new File(dir,fileName);
		FileWriter writer = new FileWriter(file);
		DB db = new DB();
		writeToFile(db, writer, parent_code);
		writer.close();
		return ServletActionContext.getServletContext().getResourceAsStream("/temp/"+fileName);
	}


public String importToFile() {
		setDownloadFileName("test.txt");
		return SUCCESS;
	}