通过Servlet使用commons-fileupload处理上传下载文件
1. FileUtil类
处理文件，保存上传文件。

2. FileService类
 下载文件,通过页面传递文件id获得文件信息


4. JdbcHelper类
  数据库连接工具类
import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import org.slf4j.Logger;import org.slf4j.LoggerFactory;public class JdbcHelper {//private static final Logger logger = LoggerFactory.getLogger(JdbcHelper.class);//private static final String DRIVER = "com.mysql.jdbc.Driver";private static final String URL = "jdbc:mysql://localhost:3306/abc?useUnicode=true&characterEncoding=utf-8";private static final String USER = "root";private static final String PASSWORD = "root";//private Connection conn = null;public JdbcHelper() {try {Class.forName(DRIVER);conn = DriverManager.getConnection(URL, USER, PASSWORD);} catch (ClassNotFoundException e) {logger.error("could not get a connection ", e);} catch (SQLException e) {logger.error("connect DB error", e);}}public Connection getConnection(){return this.conn;}public void closeQuietly(ResultSet rs, PreparedStatement psmt, Connection conn){if(rs != null){try {rs.close();} catch (Exception e) {logger.error("close ResultSet error");}}rs = null;if(psmt != null){try {psmt.close();} catch (Exception e) {logger.error("close PreparedStatement error", e);}}psmt = null;if(conn != null){try {conn.close();} catch (Exception e) {logger.error("close Connection error", e);}}conn = null;}}