图片服务器——实现阶段（数据库实现）

一、封装数据库操作

创建DBUtil类，创建一个单例类辅助创建连接，其中URL为数据库连接字符串，用户名，密码都是固定的。

private static final String URL = "jdbc:mysql://127.0.0.1:3306/image_server?
characterEncoding=utf8&useSSL=true" 
private static final String USERNAME = "root"; 
private static final String PASSWORD = "1002";

这个类主要包含三个方法

// 这是一个获取单例的方法
public static DataSource getDataSource() { } 
// 获取链接
public static Connection getConnection() { } 
// 关闭链接
public static void close(Connection conn, PreparedStatement statement, 
                         ResultSet resultSet) {}

类的实现代码

public class DBUtil {
    private static final String URL = "jdbc:mysql://127.0.0.1:3306/image_server?characterEncoding=utf8&useSSL=true";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "1002";
    private static volatile DataSource dataSource = null;

    public static DataSource getDataSource() {
        //通过这个方法创建DataSource的实例
        if (dataSource == null) {
            synchronized (DBUtil.class) {
                if(dataSource == null){
                    dataSource = new MysqlDataSource();
                    MysqlDataSource tmpDataSource = (MysqlDataSource) dataSource;
                    tmpDataSource.setURL(URL);
                    tmpDataSource.setUser(USERNAME);
                    tmpDataSource.setPassword(PASSWORD);
                }
            }
        }
        return dataSource;
    }
    public static Connection getConnection() {
        try {
            return getDataSource().getConnection();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }
    public static void close(Connection connection, PreparedStatement statement, ResultSet resultSet){
        try {
            if(resultSet != null){
                resultSet.close();
            }
            if(statement != null){
                statement.close();
            }
            if(connection != null){
                connection.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

创建Image类

public class Image {
    private int imageId;
    private String imageName;
    private int size;
    private String uploadTime;
    private String contentType;
    private String path;
    private String md5;
}

创建ImageDao类

public class ImageDao { 
     public boolean insert(Image image) { 
         return false; 
     } 
     public Image[] selectAll() { 
         return null; 
     } 
     public Image selectOne(int imageId) { 
         return null; 
     } 
     public boolean delete(int imageId) { 
         return false; 
     } 
}

实现ImageDao.insert方法

 public void insert(Image image){
        //1.获取数据库连接
        Connection connection = DBUtil.getConnection();
        //2.创建并拼装 sql 语句
        String sql = "insert into image_table values(null,?,?,?,?,?,?)";
        PreparedStatement statement = null;
        try {
            statement = connection.prepareStatement(sql);
            statement.setString(1,image.getImageName());
            statement.setInt(2,image.getImageId());
            statement.setString(3,image.getuuploadTime());
            statement.setString(4,image.getContentType());
            statement.setString(5,image.getPath());
            statement.setString(6,image.getMd5());
            //3.执行 sql 语句
            int ret = statement.executeUpdate();
            if(ret != 1){
                //程序出现问题，抛出一个异常
                throw new JavaImageServerException("插入数据库出错！");
            }

        } catch (SQLException | JavaImageServerException e) {
            e.printStackTrace();
        }finally {
            //4.关闭连接和 statement
            DBUtil.close(connection,statement,null);
        }
    }

实现ImageDao.selectAll

 public List selectAll(){
        List images = new ArrayList<>();
        //1.获取数据库连接
        Connection connection = DBUtil.getConnection();
        //2.构造 sql 语句
        String sql = "select * from image_table";
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        try {
            //3.执行 sql 语句
            statement = connection.prepareStatement(sql);
            resultSet = statement.executeQuery();
            //4.处理结果集\
            while (resultSet.next()){
                Image image = new Image();
                image.setImageId(resultSet.getInt("imageId"));
                image.setImageName(resultSet.getString("imageName"));
                image.setSize(resultSet.getInt("size"));
                image.setuploadTime(resultSet.getString("uploadTime"));
                image.setContentType(resultSet.getString("contentType"));
                image.setPath(resultSet.getString("path"));
                image.setMd5(resultSet.getString("md5"));
                images.add(image);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            //5.关闭连接
            DBUtil.close(connection,statement,resultSet);
        }
        return images;
    }

实现ImageDao.selectOne方法

public Image selectOne(int imageId){
        //1.获取数据库连接
        Connection connection = DBUtil.getConnection();
        //2.构造sql语句
        String sql = "select *from image_table where imageId = ?";
        PreparedStatement statement = null;
        ResultSet resultSet = null;
        //3.执行sql语句
        try {
            statement = connection.prepareStatement(sql);
            statement.setInt(1,imageId);
            resultSet = statement.executeQuery();
            //4.处理结果集
            if (resultSet.next()){
                Image image = new Image();
                image.setImageId(resultSet.getInt("imageId"));
                image.setImageName(resultSet.getString("imageName"));
                image.setSize(resultSet.getInt("size"));
                image.setuploadTime(resultSet.getString("uploadTime"));
                image.setContentType(resultSet.getString("contentType"));
                image.setPath(resultSet.getString("path"));
                image.setMd5(resultSet.getString("md5"));
                return image;
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            //5.关闭连接
            DBUtil.close(connection,statement,resultSet);
        }
        return null;
    }

实现ImageDao.delete方法

public void delete(int imageId)  {
        //1.获取数据库连接
        Connection connection = DBUtil.getConnection();
        //2.拼装 sql 语句
        String sql = "delete from image_table where imageId = ?";
        PreparedStatement statement = null;
        //3.执行 sql 语句
        try {
            statement = connection.prepareStatement(sql);
            statement.setInt(1,imageId);
            int ret = statement.executeUpdate();
            if(ret != 1){
                throw new JavaImageServerException("删除数据库出错！");
            }
        } catch (SQLException |JavaImageServerException e) {
            e.printStackTrace();
        } finally {
            DBUtil.close(connection,statement,null);
        }

    }