Spring Boot多数据库场景下Controller注入异常及多库查询需求

我目前有MySQL加上4个NoSQL数据库，所有的数据库服务类都实现了CustomerService接口来完成CRUD操作。现在遇到了Spring依赖注入的异常——虽然加@Primary能解决单个实例注入的问题，但我的需求是同时从所有数据库中查询数据，而不是只使用某一个数据库。

相关代码 #

CustomerController类 #

@RestController
@RequestMapping("/customer")
public class CustomerController {
    @Autowired
    CustomerService customerService;
    public CustomerController(CustomerService customerService) {
        this.customerService = customerService;
    }
    @RequestMapping(value = "/{Id}", method = RequestMethod.POST)
    public ResponseEntity<Customer> create(@RequestBody CustomerData customerData) {
        customerService.create(customerData);
        return new ResponseEntity<Customer>(customerData, HttpStatus.CREATED);
    }
    @RequestMapping(value = "/{Id}", method = RequestMethod.GET)
    public ResponseEntity<Customer> read(@PathVariable("Id") String Id){
        Customer customer = (Customer)customerService.read(Id);
        if (customer == null){
            return new ResponseEntity<Customer>(HttpStatus.NOT_FOUND);
        }
        return new ResponseEntity<Customer>(customer, HttpStatus.OK);
    }
    @RequestMapping(method = RequestMethod.GET)
    public List<Customer> retrieveCustomers(){
        return customerService.retrieveAllCustomers();
    }
    @RequestMapping(value = "/{Id}", method = RequestMethod.PUT)
    public ResponseEntity<Customer> update(@PathVariable("Id") String Id, @RequestBody CustomerData customerData) {
        Customer currentCustomer = (Customer)customerService.read(Id);
        if(currentCustomer == null){
            return new ResponseEntity<Customer>(HttpStatus.NOT_FOUND);
        }
        currentCustomer.setName(customerData.getName());
        currentCustomer.setDistrict(customerData.getDistrict());
        currentCustomer.setDate(customerData.getDate());
        customerService.create(currentCustomer);
        return new ResponseEntity<Customer>(currentCustomer, HttpStatus.OK);
    }
    @RequestMapping(value = "/{Id}", method = RequestMethod.DELETE)
    public ResponseEntity<Void> delete(@PathVariable String Id){
        Customer customer = (Customer)customerService.read(Id);
        if (customer==null){
            return new ResponseEntity<Void>(HttpStatus.NOT_FOUND);
        }else {
            customerService.delete(Id);
            return new ResponseEntity<Void>(HttpStatus.GONE);
        }
    }
}

CustomerService接口 #

@Component
public interface CustomerService<E>{
    E create(Customer customer);
    E read(String id);
    List<E> retrieveAllCustomers();
    E update(String Id, Customer customer);
    //List<Order> retrieveAllOrders(String customerId);
    void delete(String id);
    void deleteAll();
}

MySQL-CustomerService类（其他NoSQL实现类结构类似） #

@Service("myCustomerService")
@Qualifier("myCustomerService")
@Profile(Profiles.MYSQL)
public class MyCustomerService implements CustomerService{
    @Autowired
    private MyCustomerRepository customerRepository;
    @Override
    public Customer create(Customer customer) {
        MyCustomer myCustomer = new MyCustomer(customer);
        customerRepository.save(myCustomer);
        return myCustomer;
    }
    @Override
    public Customer read(String id) {
        return customerRepository.findOne(id);
    }
    @Override
    public List<MyCustomer> retrieveAllCustomers() {
        return customerRepository.findAll();
    }
    @Override
    public Customer update(String id, Customer customerData) {
        MyCustomer customer = customerRepository.findOne(id);
        customer.copy(customerData);
        customerRepository.save(customer);
        return customer;
    }
    @Override
    public void delete(String id) {
        customerRepository.delete(id);
    }
    @Override
    public void deleteAll() {
        customerRepository.deleteAll();
    }
}

异常信息 #

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'customerController' defined in file [/demo/controller/CustomerController.class]: Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'demo.service.CustomerService' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}

application.yml配置 #

spring:
  datasource:
    url: jdbc:mysql://localhost/mydb
    username: root
    driver-class-name: com.mysql.jdbc.Driver
  data:
    mongodb:
      uri: mongodb://localhost:27017/MongoTest
    cassandra:
      keyspace-name: db_keyspace
      contact-points: localhost
      port: 9042
      schema-action: create_if_not_exists
    neo4j:
      uri: bolt://localhost:7474
      username: neo4j
      password: root
  jpa:
    properties:
      hibernate.show_sql: true
      hibernate.use_sql_comments: true
      hibernate.format_sql: true
      hibernate.dialect: org.hibernate.dialect.MySQL5Dialect
  mvc:
    view:
      prefix: /WEB-INF/jsp
      suffix: .jsp
logging:
  file: logback-spring.xml
  level: DEBUG

要实现同时从所有数据库查询数据，你需要修改CustomerController，让Spring注入所有CustomerService的实现类，而不是单个实例。具体步骤如下：

1. 修改Controller的依赖注入方式 #

把原来的单个CustomerService替换成List<CustomerService>或者Map<String, CustomerService>（Map的key就是每个Service的@Service注解里的名称，比如myCustomerService）。这样Spring会自动把所有实现了CustomerService的Bean都注入进来。

修改后的CustomerController示例：

@RestController
@RequestMapping("/customer")
public class CustomerController {
    // 注入所有CustomerService实现类
    private final List<CustomerService> customerServices;

    // 构造函数注入（推荐构造函数注入而非@Autowired）
    public CustomerController(List<CustomerService> customerServices) {
        this.customerServices = customerServices;
    }

    // 核心修改：合并所有数据库的客户数据
    @RequestMapping(method = RequestMethod.GET)
    public List<Customer> retrieveCustomers(){
        List<Customer> allCustomers = new ArrayList<>();
        // 遍历每个Service，查询各自数据库的客户数据并合并
        for (CustomerService service : customerServices) {
            allCustomers.addAll(service.retrieveAllCustomers());
        }
        return allCustomers;
    }

    // 可选：扩展create方法，将客户数据同步到所有数据库
    @RequestMapping(value = "/{Id}", method = RequestMethod.POST)
    public ResponseEntity<List<Customer>> create(@RequestBody CustomerData customerData) {
        List<Customer> createdCustomers = new ArrayList<>();
        for (CustomerService service : customerServices) {
            Customer created = service.create(customerData);
            createdCustomers.add(created);
        }
        return new ResponseEntity<>(createdCustomers, HttpStatus.CREATED);
    }

    // 同理，update、delete等方法也可以按需修改，实现多库同步操作
}

2. 确保所有Service实现类都被正确激活 #

每个NoSQL的Service实现类都要像MyCustomerService一样，加上@Service("xxxCustomerService")注解，确保Spring能扫描到并注册为Bean。如果使用了@Profile，需要在配置中激活所有需要的数据库Profile：

spring:
  profiles:
    active: mysql, mongo, cassandra, neo4j # 激活所有需要的数据库Profile

3. 处理泛型类型警告（可选） #

由于CustomerService是泛型接口，Spring可能会因为类型擦除抛出警告。如果所有实现类都返回Customer类型，可以将接口改为非泛型，或者注入时使用@Autowired配合@SuppressWarnings("rawtypes")来忽略警告，不影响功能正常运行。

这样修改后，你就能在retrieveCustomers方法中获取所有数据库的客户数据并合并，同时其他CRUD方法也可以按需扩展为操作所有数据库，完美解决不能用@Primary的问题。

内容的提问来源于stack exchange，提问作者heythere