Spring Boot 数据访问与数据库集成详解

接着在 application.properties 中配置连接信息。这里开启了 Hibernate 的自动更新策略，开发阶段很方便，但生产环境建议改为 validate 或 none。

server.port=8080
spring.datasource.url=jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone=UTC
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.username=root
spring.datasource.password=123456
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

实体与仓库

定义一个 Product 实体类，使用 JPA 注解映射表结构。注意字段命名规范，Getter/Setter 方法要完整。

import javax.persistence.*;
import java.util.List;

@Entity
@Table(name = "product")
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String productId;
    private String productName;
    private double price;
    private int sales;

    public Product() {}

    public Product(String productId, String productName, double price, int sales) {
        this.productId = productId;
        this.productName = productName;
        this.price = price;
        this.sales = sales;
    }

    // Getter and Setter methods omitted for brevity
    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
    public String getProductId() { return productId; }
    public void setProductId(String productId) { this.productId = productId; }
    public String getProductName() { return productName; }
    public void setProductName(String productName) { this.productName = productName; }
    public double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
    public int getSales() { return sales; }
    public void setSales(int sales) { this.sales = sales; }

    @Override
    public String toString() {
        return "Product{" +
                "id=" + id +
                ", productId='" + productId + '\'' +
                ", productName='" + productName + '\'' +
                ", price=" + price +
                ", sales=" + sales +
                '}';
    }
}

Repository 接口继承 JpaRepository 即可获取基础 CRUD 方法，还可以自定义查询方法，比如按销量排序。

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import java.util.List;

@Repository
public interface ProductRepository extends JpaRepository<Product, Long> {
    List<Product> findBySalesGreaterThan(int sales);
}

控制器与测试

Controller 层负责暴露 REST API，注入 Repository 后直接调用。测试时可以使用@SpringBootTest 启动上下文。

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import java.util.List;

@RestController
@RequestMapping("/api/products")
public class ProductController {
    @Autowired
    private ProductRepository productRepository;

    @GetMapping("/")
    public List<Product> getAllProducts() {
        return productRepository.findAll();
    }

    @PostMapping("/")
    public Product addProduct(@RequestBody Product product) {
        return productRepository.save(product);
    }

    @GetMapping("/top-selling")
    public List<Product> getTopSellingProducts(@RequestParam int topN) {
        List<Product> products = productRepository.findBySalesGreaterThan(0);
        products.sort((p1, p2) -> p2.getSales() - p1.getSales());
        if (products.size() > topN) {
            return products.subList(0, topN);
        }
        return products;
    }
}

与 H2 集成

H2 内存数据库非常适合开发和单元测试，无需安装额外服务。

配置差异

主要区别在于依赖和 URL 配置。H2 依赖同样放在 runtime 范围，URL 指向内存数据库。

spring.datasource.url=jdbc:h2:mem:testdb
spring.datasource.driver-class-name=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password
spring.h2.console.enabled=true
spring.h2.console.path=/h2-console

实体类和 Repository 的定义与 MySQL 场景基本一致，这使得代码在不同环境间迁移变得非常容易。

与 MyBatis 集成

如果你更喜欢手写 SQL，MyBatis 是更好的选择。它通过 Mapper 接口和 XML 文件分离关注点。

依赖与配置

添加 MyBatis Starter 依赖，并指定 Mapper XML 的位置。

<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.3.0</version>
</dependency>

mybatis.mapper-locations=classpath:mapper/*.xml
mybatis.type-aliases-package=com.example.demo.entity

Mapper 与 XML

Mapper 接口标记为 @Mapper，XML 文件中定义具体的 SQL 语句。这种方式在处理复杂查询时比 JPA 更灵活。

import org.apache.ibatis.annotations.Mapper;
import java.util.List;

@Mapper
public interface ProductMapper {
    List<Product> findAll();
    int insert(Product product);
    List<Product> findBySalesGreaterThan(int sales);
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.demo.mapper.ProductMapper">
    <resultMap id="ProductResultMap" type="com.example.demo.entity.Product">
        <id property="id" column="id"/>
        <result property="productId" column="product_id"/>
        <result property="productName" column="product_name"/>
        <result property="price" column="price"/>
        <result property="sales" column="sales"/>
    </resultMap>
    <select id="findAll" resultMap="ProductResultMap"> SELECT * FROM product </select>
    <insert id="insert" parameterType="com.example.demo.entity.Product">
        INSERT INTO product (product_id, product_name, price, sales) VALUES (#{productId}, #{productName}, #{price}, #{sales})
    </insert>
    <select id="findBySalesGreaterThan" parameterType="int" resultMap="ProductResultMap">
        SELECT * FROM product WHERE sales > #{sales}
    </select>
</mapper>

事务管理

事务是保证数据一致性的关键。Spring Boot 通过 @Transactional 注解轻松开启事务。

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import java.util.List;

@Service
public class ProductService {
    @Autowired
    private ProductRepository productRepository;

    @Transactional
    public void addProduct(Product product) {
        productRepository.save(product);
    }

    @Transactional(readOnly = true)
    public List<Product> getAllProducts() {
        return productRepository.findAll();
    }
}

注意读写分离，只读查询加上 readOnly = true 可以优化性能。如果多个方法需要在一个事务中执行，可以在 Service 类级别添加注解。

实际应用场景

在实际项目中，我们通常会结合 Controller、Service 和 Repository 构建完整的分层架构。例如电商系统中的商品管理，需要处理库存扣减、订单创建等涉及多步操作的场景，此时事务管理尤为重要。

下面是一个整合后的示例，展示了从启动类到测试类的完整流程。

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import org.springframework.web.bind.annotation.*;
import javax.persistence.*;
import java.util.List;

@SpringBootApplication
public class ProductApplication {
    public static void main(String[] args) {
        SpringApplication.run(ProductApplication.class, args);
    }

    @Autowired
    private ProductService productService;

    public void run(String... args) {
        productService.addProduct(new Product("P001", "手机", 1000.0, 100));
        productService.addProduct(new Product("P002", "电脑", 5000.0, 50));
        productService.addProduct(new Product("P003", "电视", 3000.0, 80));
        productService.addProduct(new Product("P004", "手表", 500.0, 200));
        productService.addProduct(new Product("P005", "耳机", 300.0, 150));
    }
}

@Entity
@Table(name = "product")
class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String productId;
    private String productName;
    private double price;
    private int sales;

    public Product() {}

    public Product(String productId, String productName, double price, int sales) {
        this.productId = productId;
        this.productName = productName;
        this.price = price;
        this.sales = sales;
    }

    public Long getId() { return id; }
    public void setId(Long id) { this.id = id; }
    public String getProductId() { return productId; }
    public void setProductId(String productId) { this.productId = productId; }
    public String getProductName() { return productName; }
    public void setProductName(String productName) { this.productName = productName; }
    public double getPrice() { return price; }
    public void setPrice(double price) { this.price = price; }
    public int getSales() { return sales; }
    public void setSales(int sales) { this.sales = sales; }

    @Override
    public String toString() {
        return "Product{" +
                "id=" + id +
                ", productId='" + productId + '\'' +
                ", productName='" + productName + '\'' +
                ", price=" + price +
                ", sales=" + sales +
                '}';
    }
}

@Repository
interface ProductRepository extends JpaRepository<Product, Long> {
    List<Product> findBySalesGreaterThan(int sales);
}

@Service
class ProductService {
    @Autowired
    private ProductRepository productRepository;

    @Transactional
    public void addProduct(Product product) {
        productRepository.save(product);
    }

    @Transactional(readOnly = true)
    public List<Product> getAllProducts() {
        return productRepository.findAll();
    }

    @Transactional(readOnly = true)
    public List<Product> getTopSellingProducts(int topN) {
        List<Product> products = productRepository.findBySalesGreaterThan(0);
        products.sort((p1, p2) -> p2.getSales() - p1.getSales());
        if (products.size() > topN) {
            return products.subList(0, topN);
        }
        return products;
    }
}

@RestController
@RequestMapping("/api/products")
class ProductController {
    @Autowired
    private ProductService productService;

    @GetMapping("/")
    public List<Product> getAllProducts() {
        return productService.getAllProducts();
    }

    @PostMapping("/")
    public void addProduct(@RequestBody Product product) {
        productService.addProduct(product);
    }

    @PutMapping("/{id}")
    public void updateProduct(@PathVariable Long id, @RequestBody Product product) {
        product.setId(id);
        productService.updateProduct(product);
    }

    @DeleteMapping("/{id}")
    public void deleteProduct(@PathVariable Long id) {
        productService.deleteProduct(id);
    }

    @GetMapping("/top-selling")
    public List<Product> getTopSellingProducts(@RequestParam int topN) {
        return productService.getTopSellingProducts(topN);
    }
}

运行应用后，访问 /api/products/top-selling?topN=3 即可看到销量最高的商品列表。这种分层设计不仅清晰，还便于后续维护和扩展。

总结

掌握 Spring Boot 的数据访问能力是后端开发的基础。无论是使用 JPA 的快速开发，还是 MyBatis 的精细控制，亦或是 H2 的便捷测试，理解其背后的原理和配置细节都能帮助你写出更健壮的代码。在实际选型时，根据团队习惯和项目复杂度决定即可。