Spring Boot Inject CrudRepository into Service

问题:

I am having difficulty injecting a CrudRepository into a service annotated with the @Service annotation. I have two packages one "core" package containing @Service definitions and reusable controller definitions.

My main application in the x.y.application package is as follows:

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 );
    }

}

Then an example 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> {
}

Then my re-usable controller 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 );
    }

}

Then my service 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 );
}

And finally the problematic implementation of service.

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 );*/
    }
}

The exception

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()}

It seems that any spring registered Component, Service, Resource cannot inject CrudRepository? However if i do not annotate the CrudRepository in the x.y.application package it compiles and the CrudRepository is injected?

回答1:

For dependency injection to work application context has to know a recipe for creating an instance of a specific class. Classes whose instance creation recipes are known are referred to as "beans". You can define beans either via XML configuration file (old school) or annotations (new school).

The error message you are receiving states that the application context does not have CrudRepository bean, i.e. it does not know how to create an instance of a class that implements this interface.

To create a bean definition in a new way you may annotate a class or a specific method which return instance of a specific class with @Bean or any other meta-annotation that includes it (@Service, @Controller, etc.).

If you intend to use Spring Data suite of projects to automate repository implementation generation, you need to annotate an interface which extends one of the core Spring Data interfaces (Repository, CrudRepository, PagingAndSortingRepository) with @Repository annotation like so

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

This provides a bean definition for the application context and makes it aware that you want the repository implementation to be generated for you.

Then you can inject MyRepository to the service class.

The only doubt I have is about the generic type to be used in repository type definition. I would expect the repository implementation (the one you want to be generated for you) to be entity-specific rather than abstract.

回答2:

This is probably because CrudRepository is not part of your package scan. And hence spring is unable to inject a proxy implementation for it.