struts2文件下载时报错java.lang.IllegalStateException?报错

下载没有问题，可以下载，但是一点击下载或点击取消，后台都会报这个错误

下载部分的代码：

public InputStream getContentStream() {
		String id = obj.getId();
		Connection conn = null;
		ResultSet rs = null;
		java.sql.Statement sm = null;
		try {
			conn = DataSourceUtil.getConnection();
			sm=conn.createStatement();
			String sql = "SELECT FILE_NAME,UPLOAD_FILE FROM T_ATTACHMENT WHERE ID = '" + id + "'";
			rs = sm.executeQuery(sql);
			FileUpload fileUpload = new FileUpload();
			InputStream inputStream = null;
			if(rs.next()){
				fileUpload.setFileName(rs.getString(1));
				Blob blob=rs.getBlob(2);  
				inputStream = blob.getBinaryStream();
			}
			String fileName = fileUpload.getFileName();
			obj.setFileName(URLEncoder.encode(fileName, "UTF-8"));
			return inputStream;
		} catch (SQLException e) {
			log.info(e.toString());
		}catch (UnsupportedEncodingException e) {
			log.info(e.toString());
		}
		return null;
	}