通过jdbc连接Mysql并查询的步骤_jdbc查询mysql

从mysql中对表进行查询：

 
        Connection connection = null;
        PreparedStatement preparedStatement = null;
        ResultSet resultSet = null;
        try {
            // 1.注册驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            // 2.创建连接
            connection = DriverManager.getConnection(
                    "jdbc:mysql://hadoop102:3306/gmall_realtime_config?" +
                    "user=root&password=000000&useUnicode=true&" +
                    "characterEncoding=utf8&serverTimeZone=Asia/Shanghai&useSSL=false");
            // 3.预编译sql，获取数据库操作对象
            preparedStatement = connection.prepareStatement(
                    "select * from gmall_realtime_config.table_process where sink_type = 'dwd'");
            // 4.执行sql查询，获取数据集
            resultSet = preparedStatement.executeQuery();
            // 5.获取元数据信息
            ResultSetMetaData metaData = resultSet.getMetaData();
            // 6.处理查询结果。将查询信息 写入到 hashmap中
            while (resultSet.next()){
                JSONObject jsonObject = new JSONObject();
                for (int i = 1; i <= metaData.getColumnCount(); i++) {
                    String columnName = metaData.getColumnName(i);
                    String columnValue = resultSet.getString(i);
                    jsonObject.put(columnName,columnValue);
                }
                TableProcess tableProcess = JSON.toJavaObject(jsonObject, TableProcess.class);
                if (tableProcess != null){
                    String sourceTable = tableProcess.getSourceTable();
                    String sourceType = tableProcess.getSourceType();
                    String putKey = sourceTable + ":" + sourceType;
                    hashMap.put(putKey,tableProcess);
                }
            }
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
        // 7.关闭连接
            if (resultSet!= null) resultSet.close();
            if (preparedStatement != null) preparedStatement.close();
            if (connection != null) connection.close();
        }