Spring Boot 数据访问与数据库集成指南

配置文件

在 application.properties 中指定数据源信息。注意时区和字符集设置，避免中文乱码或时间偏差。

# 服务器端口
server.port=8080

# 数据库连接信息
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

# JPA 配置
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

实体类定义

使用 JPA 注解映射表结构。这里以商品为例，主键采用自增策略。

import javax.persistence.*;

@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;

    // 构造方法
    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 和 Setter 方法省略，实际开发建议使用 Lombok
    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 +
                '}';
    }
}

仓库与控制器

继承 JpaRepository 即可获得基础 CRUD 能力，无需手动编写 SQL。自定义查询可通过方法名约定实现。

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);
}

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;
    }
}

开发测试：H2 内存数据库

对于单元测试或快速原型开发，H2 内存数据库是绝佳选择。它无需安装，启动即用，且支持控制台查看数据。

配置差异

只需替换 pom.xml 中的 H2 依赖，并修改 application.properties 中的 URL 即可。

<!-- H2 数据库依赖 -->
<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <scope>runtime</scope>
</dependency>

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

其余实体类和 Repository 接口可复用 MySQL 的配置，实现了环境无关性。

持久层框架：MyBatis 集成

当需要更精细地控制 SQL 语句，或者处理复杂的关联查询时，MyBatis 比 JPA 更具优势。

依赖与配置

引入 MyBatis Starter 后，需指定 Mapper XML 文件的位置。

<!-- MyBatis 依赖 -->
<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 接口与 XML

MyBatis 通过 XML 分离 SQL 与 Java 代码，便于维护。

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核心。Spring Boot 通过 @Transactional 注解轻松开启声明式事务。

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：readOnly = true 可以优化只读操作的性能。同时，确保 Service 层的调用由 Spring 容器代理，否则事务可能失效。

实战应用示例

在实际项目中，我们通常会整合上述组件构建完整的商品管理系统。以下是一个简化的完整链路示例，包含初始化数据和测试验证。

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));
    }
}

// 产品类
@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;
    }

    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 + '}';
    }
}

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

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

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

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

    @Transactional
    public void deleteProduct(Long id) {
        productRepository.deleteById(id);
    }

    @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;
    }
}

// 产品控制器
@RestController
@RequestMapping("/api/products")
public 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);
    }
}

运行测试后，访问 http://localhost:8080/api/products/top-selling?topN=3 将返回销量最高的前三款商品。这种分层架构不仅清晰，还便于后续扩展微服务或更换数据库。

结语

掌握 Spring Boot 的数据访问能力，关键在于理解不同持久层技术的适用场景。JPA 适合快速开发，MyBatis 适合复杂 SQL 优化，而事务管理则是保障数据安全的底线。希望本文的实战演示能帮助你在项目中从容应对各种数据集成需求。