《Springboot极简教程》@EnableMongoRepositories路径配置：APPLICATION FAILED TO START: Parameter 0 of constructor...

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APPLICATION FAILED TO START

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Description:

Parameter 0 of constructor in com.restfeel.controller.BlogController required a bean of type 'com.restfeel.biz.BlogService' that could not be found.

Action:

Consider defining a bean of type 'com.restfeel.biz.BlogService' in your configuration.

:bootRun FAILED

FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':bootRun'.

代码

package com.restfeel.service

import com.restfeel.entity.Blog
import org.springframework.data.mongodb.repository.MongoRepository
import org.springframework.data.mongodb.repository.Query
import org.springframework.data.repository.query.Param

interface BlogService : MongoRepository {

    @Query("{ 'title' : ?0 }")
    fun findByTitle(@Param("title") title: String): Iterable

}




package com.restfeel.controller

import com.restfeel.service.BlogService
import com.restfeel.entity.Blog
import org.springframework.boot.autoconfigure.EnableAutoConfiguration
import org.springframework.context.annotation.ComponentScan
import org.springframework.stereotype.Controller
import org.springframework.transaction.annotation.Propagation
import org.springframework.transaction.annotation.Transactional
import org.springframework.ui.Model
import org.springframework.web.bind.annotation.GetMapping
import org.springframework.web.bind.annotation.RequestParam
import org.springframework.web.bind.annotation.ResponseBody
import java.util.*

/**
 * * 注意:
 *      这里要使用@Controller注解
 *      而不要使用@RestController
 *      否则return "index";只是返回字符串"index"， 不能跳转到index.html
 *
 *      @RestController is a stereotype annotation that combines @ResponseBody and @Controller.
 *      @RestController注解相当于@ResponseBody ＋ @Controller合在一起的作用。
 */

@Controller
@EnableAutoConfiguration
@ComponentScan
@Transactional(propagation = Propagation.REQUIRES_NEW)
class BlogController(val blogService: BlogService) {
    @GetMapping("/blogs.do")
    fun listAll(model: Model): String {
        val now = Date();
        blogService.save(Blog("SpringBoot极简教程", "XXX", "JasonChen", now, now, 0, now, "", 0))
        blogService.save(Blog("SpringBoot极简教程", "XXX", "BluceLi", now, now, 0, now, "", 0))
        blogService.save(Blog("SpringBoot极简教程", "XXX", "MichelleChen", now, now, 0, now, "", 0))

        val allblogs = blogService.findAll()
        model.addAttribute("blogs", allblogs)
        return "jsp/blog/list"
    }

    @GetMapping("/listblogs")
    @ResponseBody
    fun listblogs(model: Model) = blogService.findAll()

    @GetMapping("/findBlog")
    @ResponseBody
    fun findBlog(@RequestParam(value = "title") title: String) = blogService.findByTitle(title)

}

原因

@EnableMongoRepositories路径配置问题，AbstractMongoConfiguration扫描dao层包路径的配置要细心。

package com.restfeel.config

import com.mongodb.Mongo
import com.mongodb.MongoClient
import com.mongodb.MongoCredential
import com.mongodb.ServerAddress
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.core.env.Environment
import org.springframework.data.mongodb.config.AbstractMongoConfiguration
import org.springframework.data.mongodb.repository.config.EnableMongoRepositories

/**
 * Created by jack on 2017/3/29.
 */


@Configuration
@EnableMongoRepositories(*arrayOf("com.restfeel.dao", "com.???.???"))
class PersistenceConfig : AbstractMongoConfiguration() {

    @Autowired
    private val env: Environment? = null

    override fun getDatabaseName(): String {
        return env!!.getProperty("mongodb.name")
    }


    @Bean
    @Throws(Exception::class)
    override fun mongo(): Mongo {
        return MongoClient(listOf(ServerAddress(env!!.getProperty("mongodb.host"), env!!.getProperty("mongodb.port", Int::class.java))),
                listOf(MongoCredential
                        .createCredential(env!!.getProperty("mongodb.username"), env!!.getProperty("mongodb.name"),
                                env!!.getProperty("mongodb.password").toCharArray())))
    }

//    override fun getMappingBasePackage(): String {
//        return "com.restfiddle.dao"
//    }

    /**
     * 这地方是配置扫描继承Repository类的所有接口类的路径的，路径配置错误，bean就不会创建了。
     * 东海陈光剑 Jason Chen @蒋村花园如意苑 2017.3.30 01:41:35
     */
    override fun getMappingBasePackages(): Collection {
        return setOf("com.restfeel.dao", "com.restfeel.service")
    }
}

原理

比如说，有代码

@Autowired
private UserDao userDao;

其中UserDao来自

public interface UserDao extends CrudRepository

无论在哪儿也找不到这个Bean是在哪儿定义的，但是代码还能正常工作。@Autowired 默认找不到会报错，再不然就是null，不会创建bean。

我们正常会推测：这是 CrudRepository导致的， CrudRepository会自动创建一个Bean。事实如此，这个是spring data jpa的功能，它会扫描Repository的子类并实现它们。