跟随《Spring实战第6版》用JDBC Template时遇依赖注入异常

学习《Spring实战第6版》第3章「使用JDBC Template存储数据」内容时，遇到如下异常：

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'jdbcIngredientRepository' defined in file [D:\Java Projects\taco-cloud\target\classes\tacos\data\JdbcIngredientRepository.class]: Unsatisfied dependency expressed through constructor parameter

相关代码 #

JdbcIngredientRepository #

package tacos.data;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
import java.util.Optional;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Repository;
import tacos.Ingredient;

@Repository
public class JdbcIngredientRepository implements IngredientRepository {
  private JdbcTemplate jdbcTemplate;
  @Autowired
  public JdbcIngredientRepository(JdbcTemplate jdbcTemplate) {
    this.jdbcTemplate = jdbcTemplate;
  }

  @Override
  public Iterable<Ingredient> findAll() {
    return jdbcTemplate.query(
        "select id, name, type from Ingredient",
        this::mapRowToIngredient);
  }

  @Override
  public Optional<Ingredient> findById(String id) {
    List<Ingredient> results = jdbcTemplate.query(
        "select id, name, type from Ingredient where id=?",
        this::mapRowToIngredient,
        id);
    return results.size() == 0 ?
            Optional.empty() :
            Optional.of(results.get(0));
  }

  @Override
  public Ingredient save(Ingredient ingredient) {
    jdbcTemplate.update(
        "insert into Ingredient (id, name, type) values (?, ?, ?)",
        ingredient.getId(),
        ingredient.getName(),
        ingredient.getType().toString());
    return ingredient;
  }

  private Ingredient mapRowToIngredient(ResultSet row, int rowNum)
      throws SQLException {
    return new Ingredient(
        row.getString("id"),
        row.getString("name"),
        Ingredient.Type.valueOf(row.getString("type")));
  }
}

IngredientRepository #

package tacos.data;

import java.util.Optional;

import tacos.Ingredient;

public interface IngredientRepository {
    Iterable<Ingredient> findAll();
    Optional<Ingredient> findById(String id);
    Ingredient save(Ingredient ingredient);
}

已尝试更换JDBC依赖、更新Maven项目，问题仍未解决，寻求帮助。

• 检查数据源配置：Spring容器无法创建JdbcTemplate实例，通常是因为缺少有效的数据源配置。确保application.properties或application.yml中配置了正确的数据库连接信息，示例：

  spring.datasource.url=jdbc:mysql://localhost:3306/taco_cloud?useSSL=false&serverTimezone=UTC
  spring.datasource.username=root
  spring.datasource.password=yourpassword
  spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
  

• 确认JDBC依赖完整性：除了Spring JDBC依赖，还需要引入对应数据库的驱动依赖。Maven依赖示例：

  <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-jdbc</artifactId>
  </dependency>
  <dependency>
      <groupId>com.mysql</groupId>
      <artifactId>mysql-connector-j</artifactId>
      <scope>runtime</scope>
  </dependency>
  

• 检查组件扫描范围：确保JdbcIngredientRepository所在的tacos.data包被Spring组件扫描覆盖。如果主启动类不在tacos根包下，需在启动类上添加@ComponentScan(basePackages = "tacos")指定扫描路径。
• 查看完整异常栈：原异常仅显示根因开头，完整异常栈会指明具体无法注入的依赖细节（比如JdbcTemplate创建失败的具体原因：数据源连接失败、驱动类找不到等），建议查看日志中完整的异常信息定位问题。

内容的提问来源于stack exchange，提问作者Pankaj