Spring 引导将 CrudRepository 注入服务

Question

我很难将 CrudRepository 注入到使用 @Service 注释进行注释的服务中。我有两个包，一个 "core" 包含@Service 定义和可重用控制器定义的包。

我在x.y.application包中的主要应用如下：

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 );
    }

}

然后是控制器示例。

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> {
}

然后我的可重用控制器class

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 );
    }

}

然后是我的服务界面

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 );
}

最后是有问题的服务实现。

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()}

似乎任何spring注册的Component、Service、Resource都不能注入CrudRepository？但是，如果我不在 x.y.application 包中注释 CrudRepository，它会编译并注入 CrudRepository？

Answer 1

这可能是因为 CrudRepository 不是包扫描的一部分。因此 spring 无法为其注入代理实现。

Answer 2

要使依赖注入起作用，应用程序上下文必须知道创建特定 class 实例的方法。类其实例创建配方已知被称为 "beans"。您可以通过 XML 配置文件（旧学校）或注释（新学校）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 class 的实例实现此接口。

要以新的方式创建 bean 定义，您可以注释一个 class 或一个特定的方法，其中 return 特定 class 的实例与 @Bean 或包含它的任何其他元注释（@Service、@Controller 等）。

如果您打算使用 Spring 项目数据套件来自动生成存储库实现，您需要注释一个扩展核心 Spring 数据接口之一的接口（Repository、CrudRepository、PagingAndSortingRepository ) 带有 @Repository 注释，像这样

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

这为应用程序上下文提供了一个 bean 定义，并使其知道您希望为您生成存储库实现。

然后你可以注入 MyRepository 到服务 class.

我唯一的疑问是要在存储库类型定义中使用的通用类型。我希望存储库实现（您希望为您生成的那个）是特定于实体的而不是抽象的。

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