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

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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.serviceimport com.restfeel.entity.Blogimport org.springframework.data.mongodb.repository.MongoRepositoryimport org.springframework.data.mongodb.repository.Queryimport org.springframework.data.repository.query.Paraminterface BlogService : MongoRepository<Blog, String> {    @Query("{ 'title' : ?0 }")    fun findByTitle(@Param("title") title: String): Iterable<Blog>}package com.restfeel.controllerimport com.restfeel.service.BlogServiceimport com.restfeel.entity.Blogimport org.springframework.boot.autoconfigure.EnableAutoConfigurationimport org.springframework.context.annotation.ComponentScanimport org.springframework.stereotype.Controllerimport org.springframework.transaction.annotation.Propagationimport org.springframework.transaction.annotation.Transactionalimport org.springframework.ui.Modelimport org.springframework.web.bind.annotation.GetMappingimport org.springframework.web.bind.annotation.RequestParamimport org.springframework.web.bind.annotation.ResponseBodyimport 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.configimport com.mongodb.Mongoimport com.mongodb.MongoClientimport com.mongodb.MongoCredentialimport com.mongodb.ServerAddressimport org.springframework.beans.factory.annotation.Autowiredimport org.springframework.context.annotation.Beanimport org.springframework.context.annotation.Configurationimport org.springframework.core.env.Environmentimport org.springframework.data.mongodb.config.AbstractMongoConfigurationimport 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<String> {        return setOf("com.restfeel.dao", "com.restfeel.service")    }}

原理

比如说，有代码

@Autowiredprivate UserDao userDao;

其中UserDao来自

public interface UserDao extends CrudRepository<User, Long>

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。