关于后端:Apache-Calcite-动态数据管理框架整合-csv-实战笔记

序言

咱们在 Apache Calcite 动态数据治理框架介绍 介绍了 calcite 的基本功能，本文一起来看一下如何实现一个 csv 的 sql 查问。

入门例子

依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>calcite-learn</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>pom</packaging>
    <modules>
        <module>calcite-learn-basic</module>
    </modules>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <calcite.version>1.20.0</calcite.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.apache.calcite</groupId>
            <artifactId>calcite-core</artifactId>
            <version>${calcite.version}</version>
        </dependency>
        <dependency>
            <groupId>org.apache.calcite</groupId>
            <artifactId>calcite-example-csv</artifactId>
            <version>${calcite.version}</version>
        </dependency>
        <!-- Add other dependencies, e.g., database driver -->
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

测试 csv

创立文件夹：

D:\github\calcite-learn\calcite-learn-basic\src\main\resources\csv

上面防对应的测试 csv 文件：

• depts.csv

EMPNO:long,NAME:string,DEPTNO:int,GENDER:string,CITY:string,EMPID:int,AGE:int,SLACKER:boolean,MANAGER:boolean,JOINEDAT:date
100,"Fred",10,,,30,25,true,false,"1996-08-03"
110,"Eric",20,"M","San Francisco",3,80,,false,"2001-01-01"
110,"John",40,"M","Vancouver",2,,false,true,"2002-05-03"
120,"Wilma",20,"F",,1,5,,true,"2005-09-07"
130,"Alice",40,"F","Vancouver",2,,false,true,"2007-01-01"

测试类

package com.github.houbb.calcite.learn.basic;

import org.apache.calcite.adapter.csv.CsvSchema;
import org.apache.calcite.adapter.csv.CsvTable;
import org.apache.calcite.jdbc.CalciteConnection;
import org.apache.calcite.schema.SchemaPlus;

import java.io.File;
import java.sql.*;
import java.util.Properties;

public class CsvDemo {public static void main(String[] args) throws Exception {
        // 0. 获取 csv 文件的门路，留神获取到文件所在下层门路就能够了
        String path = "D:\\github\\calcite-learn\\calcite-learn-basic\\src\\main\\resources\\csv\\";

        // 1. 构建 CsvSchema 对象，在 Calcite 中，不同数据源对应不同 Schema，比方 CsvSchema、DruidSchema、ElasticsearchSchema 等
        CsvSchema csvSchema = new CsvSchema(new File(path), CsvTable.Flavor.SCANNABLE);

        // 2. 构建 Connection
        // 2.1 设置连贯参数
        Properties info = new Properties();
        // 不辨别 sql 大小写
        info.setProperty("caseSensitive", "false");
        // 2.2 获取规范的 JDBC Connection
        Connection connection = DriverManager.getConnection("jdbc:calcite:", info);
        // 2.3 获取 Calcite 封装的 Connection
        CalciteConnection calciteConnection = connection.unwrap(CalciteConnection.class);

        // 3. 构建 RootSchema，在 Calcite 中，RootSchema 是所有数据源 schema 的 parent，多个不同数据源 schema 能够挂在同一个 RootSchema 下
        // 以实现查问不同数据源的目标
        SchemaPlus rootSchema = calciteConnection.getRootSchema();

        // 4. 将不同数据源 schema 挂载到 RootSchema，这里增加 CsvSchema
        rootSchema.add("csv", csvSchema);

        // 5. 执行 SQL 查问，通过 SQL 形式拜访 csv 文件
        String sql = "select * from csv.depts";
        Statement statement = calciteConnection.createStatement();
        ResultSet resultSet = statement.executeQuery(sql);

        // 6. 遍历打印查问后果集
        printResultSet(resultSet);
    }

    public static void printResultSet(ResultSet resultSet) throws SQLException {
        // 获取 ResultSet 元数据
        ResultSetMetaData metaData = resultSet.getMetaData();

        // 获取列数
        int columnCount = metaData.getColumnCount();
        System.out.println("Number of columns:" + columnCount);

        // 遍历 ResultSet 并打印后果
        while (resultSet.next()) {
            // 遍历每一列并打印
            for (int i = 1; i <= columnCount; i++) {String columnName = metaData.getColumnName(i);
                String columnValue = resultSet.getString(i);
                System.out.println(columnName + ":" + columnValue);
            }
            System.out.println(); // 换行}
    }

}

测试成果

Number of columns: 10
EMPNO: 100
NAME: Fred
DEPTNO: 10
GENDER: 
CITY: 
EMPID: 30
AGE: 25
SLACKER: true
MANAGER: false
JOINEDAT: 1996-08-03

EMPNO: 110
NAME: Eric
DEPTNO: 20
GENDER: M
CITY: San Francisco
EMPID: 3
AGE: 80
SLACKER: null
MANAGER: false
JOINEDAT: 2001-01-01

EMPNO: 110
NAME: John
DEPTNO: 40
GENDER: M
CITY: Vancouver
EMPID: 2
AGE: null
SLACKER: false
MANAGER: true
JOINEDAT: 2002-05-03

EMPNO: 120
NAME: Wilma
DEPTNO: 20
GENDER: F
CITY: 
EMPID: 1
AGE: 5
SLACKER: null
MANAGER: true
JOINEDAT: 2005-09-07

EMPNO: 130
NAME: Alice
DEPTNO: 40
GENDER: F
CITY: Vancouver
EMPID: 2
AGE: null
SLACKER: false
MANAGER: true
JOINEDAT: 2007-01-01

参考资料

Apache Calcite 疾速入门指南

Apache Calcite 精简入门与学习领导

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