Mysql中，Blob是一个二进制大型对象，是一个可以存储大量数据的容器，它能容纳不同大小的数据

MySQL 的四种Blob类型：(除了在存储的最大信息量上不同外，它们是等同的，如果存储的文件过大，数据库的性能会下降)

public class JDBCTest03 {
    // 插入图片，在数据库设置对应图片字段的Blob类型
    // 插入Blob类型的数据必须使用PreparedStatement，因为Blob类型的数据无法使用字符串拼写
    public void testInsertBlob() throws ClassNotFoundException, SQLException, FileNotFoundException {
        String sql = "INSERT INTO customers(name, email, birth, picture)"
                + "VALUES(?,?,?,?)";
        String driverClass = "com.mysql.jdbc.Driver";
        String jdbcurl = "";
        Class.forName(driverClass);
        Connection connection = DriverManager.getConnection(jdbcurl,"user","password");
        PreparedStatement preparedStatement = connection.prepareStatement(sql);

        InputStream inputStream = new FileInputStream("picture.jpg");
        preparedStatement.setBlob(4,inputStream);
        preparedStatement.executeUpdate();

        preparedStatement.close();
        connection.close();
    }

    // 读取图片
    // 读取blob数据：
    // 1. 使用getBlob方法读取到Blob对象
    // 2.调用Blob的getBinaryStream()方法得到输入流。再使用IO操作即可
    public void readBlob() throws ClassNotFoundException, SQLException, IOException {
        String sql = "SELECT id, name customerName, email, birth, picture "
                + "FROM customers WHERE id = 13";
        String driverClass = "com.mysql.jdbc.Driver";
        String jdbcurl = "";
        Class.forName(driverClass);
        Connection connection = DriverManager.getConnection(jdbcurl,"user","password");
        PreparedStatement preparedStatement = connection.prepareStatement(sql);
        ResultSet resultSet = preparedStatement.executeQuery();
        if(resultSet.next()){
            int id = resultSet.getInt(1);
            String name = resultSet.getString(2);
            String email = resultSet.getString(3);
            Blob picture = resultSet.getBlob(5);

            InputStream in = picture.getBinaryStream();

            OutputStream out = new FileOutputStream("newPicture.jpg");
            byte[] buffer = new byte[1024];
            int len = 0;
            while ((len = in.read(buffer)) != -1){
                out.write(buffer,0,len);
            }
            in.close();
            out.close();
        }
        resultSet.close();
        preparedStatement.close();
        connection.close();
    }    
}