java - Spring Boot 将 CrudRepository 注入(inject)服务

Question

我在将 CrudRepository 注入(inject)使用 @Service 注释的服务时遇到困难。我有两个包，其中一个“核心”包包含 @Service 定义和可重用 Controller 定义。

我在x.y.application包中的主要应用程序如下:

package x.y.application;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.context.web.SpringBootServletInitializer;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.ImportResource;

@SpringBootApplication
@EnableAutoConfiguration
@ComponentScan({ "x.y.application", "x.y.core" })
public class Application  {

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

}

然后是一个示例 Controller 。

package x.y.application.controller;

import javax.inject.Inject;
import java.util.ArrayList;
import java.util.List;
import java.util.Iterator;

import x.y.application.model.User;
import x.y.core.controller.Controller;

import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import org.springframework.data.repository.CrudRepository;

@RestController
@RequestMapping("/test")
public class HelloController extends Controller<User> {
}

然后是我的可重用 Controller 类

package x.y.core.controller;

import javax.inject.Inject;
import java.util.ArrayList;
import java.util.List;
import java.util.Iterator;

import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.http.HttpStatus;
import org.springframework.data.repository.CrudRepository;
import org.springframework.dao.DataIntegrityViolationException;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.beans.factory.annotation.Autowired;

import x.y.core.service.Service;

public class Controller<T> {

    @Inject
    Service<T> service;

    @RequestMapping(value = "/index.json", method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_VALUE)
    public T create( @RequestBody T item ) throws Exception {
        return service.create( item );
    }

    @RequestMapping(value = "/{id}.json", method = RequestMethod.PUT, produces = MediaType.APPLICATION_JSON_VALUE)
    @ResponseStatus(value = HttpStatus.NO_CONTENT)
    public T update( @PathVariable Long id, @RequestBody T item ) throws Exception {
        return service.update( item );
    }

    @RequestMapping(value = "/{id}.json", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
    public T read( @PathVariable Long id ) throws Exception {
        return service.findOne( id );
    }

    @RequestMapping(value = "/index.json", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
    public List<T> readAll() throws Exception {
        return service.findAll();
    }

    @RequestMapping(value = "/{id}.json", method = RequestMethod.DELETE, produces = MediaType.APPLICATION_JSON_VALUE)
    @ResponseStatus(value = HttpStatus.NO_CONTENT)
    public void delete( @PathVariable Long id ) throws Exception {
        service.delete( id );
    }

}

然后是我的服务接口(interface)

package x.y.core.service;

import javax.inject.Inject;
import java.util.ArrayList;
import java.util.List;
import java.util.Iterator;
import java.lang.reflect.*;

import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.http.HttpStatus;
import org.springframework.data.repository.CrudRepository;
import org.springframework.dao.DataIntegrityViolationException;

public interface Service<T> {

    /**
     * create.
     * Creates a new entity in the database.
    */
    public T create( T item );

    /**
     * update.
     * Updates an existing entity in the database.
    */
    public T update( T item );

    public T findOne( Long id );

    public List<T> findAll();

    public void delete( Long id );
}

最后是服务的有问题的实现。

package x.y.core.service;

import javax.inject.Inject;
import java.util.ArrayList;
import java.util.List;
import java.util.Iterator;
import java.lang.reflect.*;

import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.http.HttpStatus;
import org.springframework.data.repository.CrudRepository;
import org.springframework.dao.DataIntegrityViolationException;
import org.springframework.beans.factory.annotation.Autowired;

@org.springframework.stereotype.Service
public class RepositoryService<T> implements Service<T> {

    @Inject //Throws exception
    CrudRepository<T,Long> repository;

    /**
     * create.
     * Creates a new entity in the database.
    */
    public T create( T item ) throws DataIntegrityViolationException {

        /*try {
            Field field = item.getClass().getDeclaredField( "id" );
            field.setAccessible( true );
            if( repository.exists( field.getLong( item ) ) ) {
                throw new DataIntegrityViolationException( "Entity object already exists." );
            }
        } catch ( Exception exception ) {
            throw new DataIntegrityViolationException( "Entity class does not contain Id attribute." );
        }

        return repository.save( item );*/ return item;
    }

    /**
     * update.
     * Updates an existing entity in the database.
    */
    public T update( T item ) throws DataIntegrityViolationException {

        /*try {
            Field field = item.getClass().getDeclaredField( "id" );
            field.setAccessible( true );
            if( !repository.exists( field.getLong( item ) ) ) {
                throw new DataIntegrityViolationException( "Entity object does not exists." );
            }
        } catch ( Exception exception ) {
            throw new DataIntegrityViolationException( "Entity class does not contain Id attribute." );
        }

        return repository.save( item );*/ return item;
    }

    public T findOne( Long id ) {
        /*if( !repository.exists( id ) ) {
            throw new DataIntegrityViolationException( "Item with id does not exists." );
        }
        return repository.findOne( id );*/ return null;
    }

    public List<T> findAll() {
       final List<T> resultList = new ArrayList<>();
       /*/ final Iterator<T> all    = repository.findAll().iterator();

        while( all.hasNext() ) {
            resultList.add( all.next() );
        }*/

        return resultList;
    }

    public void delete( Long id ) {
        /*if( !repository.exists( id ) ) {
            throw new DataIntegrityViolationException( "Item with id does not exists." );
        }
        repository.delete( id );*/
    }
}

异常

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.springframework.data.repository.CrudRepository] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@javax.inject.Inject()}

好像任何spring注册的Component、Service、Resource都无法注入(inject)CrudRepository？ 但是，如果我不在 x.y.application 包中注释 CrudRepository，它会编译并注入(inject) CrudRepository 吗？

Answer 1

为了使依赖注入(inject)发挥作用，应用程序上下文必须知道创建特定类实例的方法。实例创建配方已知的类称为“bean”。您可以通过 XML 配置文件(旧式)或注释(新式)来定义 bean。

您收到的错误消息表明应用程序上下文没有 CrudRepository bean，即它不知道如何创建实现此接口(interface)的类的实例。

要以新的方式创建 Bean 定义，您可以使用 @Bean 或任何其他包含它的元注释(>@Service、@Controller 等)。

如果您打算使用 Spring Data 项目套件来自动生成存储库实现，则需要使用 @Repository 像这样注释

@Repository
public interface MyRepository extends CrudRepository<Entity, Long> {
}

这为应用程序上下文提供了 bean 定义，并使其知道您希望为您生成存储库实现。

然后您可以将 MyRepository 注入(inject)到服务类中。

我唯一的疑问是关于存储库类型定义中使用的泛型类型。我希望存储库实现(您想要为您生成的存储库实现)是特定于实体的而不是抽象的。