MySQL进行分片合并的实现步骤

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>

public class ShardContextHolder {
    private static final ThreadLocal<String> contextHolder = new ThreadLocal<>();

    public static void setShard(String shard) {
        contextHolder.set(shard);
    }

    public static String getShard() {
        return contextHolder.get();
    }

    public static void clearShard() {
        contextHolder.remove();
    }
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Service;

@Service
public class OrderService {

    @Autowired
    private JdbcTemplate jdbcTemplate;

    private String getShard(String orderId) {
        int hash = orderId.hashCode();
        int shardId = Math.abs(hash % 2); // 这里假设有2个分片
        return "ds" + shardId;
    }

    public Order getOrder(String orderId) {
        String shard = getShard(orderId);
        ShardContextHolder.setShard(shard);
        String sql = "SELECT * FROM orders WHERE order_id = ?";
        Order order = jdbcTemplate.queryForObject(sql, new Object[]{orderId}, (rs, rowNum) -> 
            new Order(rs.getString("order_id"), rs.getString("product_name"), rs.getDouble("price")));
        ShardContextHolder.clearShard();
        return order;
    }
}

import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Collectors;

@Service
public class OrderService {

    @Autowired
    @Qualifier("ds0")
    private JdbcTemplate jdbcTemplate0;

    @Autowired
    @Qualifier("ds1")
    private JdbcTemplate jdbcTemplate1;

    public List<Order> getOrdersByProductName(String productName) {
        List<Order> orders = new ArrayList<>();

        // 查询分片0
        ShardContextHolder.setShard("ds0");
        List<Order> ordersShard0 = jdbcTemplate0.query(
                "SELECT * FROM orders WHERE product_name = ?",
                new Object[]{productName},
                (rs, rowNum) -> new Order(rs.getString("order_id"), rs.getString("product_name"), rs.getDouble("price"))
        );
        orders.addAll(ordersShard0);
        ShardContextHolder.clearShard();

        // 查询分片1
        ShardContextHolder.setShard("ds1");
        List<Order> ordersShard1 = jdbcTemplate1.query(
                "SELECT * FROM orders WHERE product_name = ?",
                new Object[]{productName},
                (rs, rowNum) -> new Order(rs.getString("order_id"), rs.getString("product_name"), rs.getDouble("price"))
        );
        orders.addAll(ordersShard1);
        ShardContextHolder.clearShard();

        return orders;
    }

    // 进行排序和分页
    public List<Order> getOrdersByProductNameWithPagination(String productName, int page, int size) {
        List<Order> orders = getOrdersByProductName(productName);

        // 按价格排序
        orders = orders.stream()
                       .sorted((o1, o2) -> Double.compare(o1.getPrice(), o2.getPrice()))
                       .collect(Collectors.toList());

        // 分页
        int fromIndex = page * size;
        int toIndex = Math.min(fromIndex + size, orders.size());

        if (fromIndex > orders.size()) {
            return new ArrayList<>();
        }

        return orders.subList(fromIndex, toIndex);
    }
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.stereotype.Component;

import java.util.List;

@Component
public class TestRunner implements CommandLineRunner {

    @Autowired
    private OrderService orderService;

    @Override
    public void run(String... args) throws Exception {
        // 插入数据
        orderService.insertOrder("order1", "Product A", 100.0);
        orderService.insertOrder("order2", "Product B", 150.0);
        orderService.insertOrder("order3", "Product A", 200.0);

        // 查询单条记录
        Order order1 = orderService.getOrder("order1");
        System.out.println(order1);

        // 查询多条记录并进行合并
        List<Order> orders = orderService.getOrdersByProductName("Product A");
        orders.forEach(System.out::println);

        // 查询并分页
        List<Order> paginatedOrders = orderService.getOrdersByProductNameWithPagination("Product A", 0, 1);
        paginatedOrders.forEach(System.out::println);
    }
}