Spring Boot注释自动接线的问题

Question

I have the following problem. I trying to start a Spring Boot application with the DB2 database with Hybernate. So i created a repository and used the @Autowired annotation to get some data from the DB. The problem is that when I run the application i receive the following error:

***************************
APPLICATION FAILED TO START
***************************

Description:

Field studenteRepository in com.ibm.snam.ai4legal.controller.HelloWorldController required a bean of type 'com.ibm.snam.ai4legal.repositories.StudenteRepository' that could not be found.


Action:

Consider defining a bean of type 'com.ibm.snam.ai4legal.repositories.StudenteRepository' in your configuration.

Here are the classes of the application

Application class:

package com.ibm.snam.ai4legal.application;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication(scanBasePackages = {"com.ibm"})
public class SBApplication {

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

Repository class:

package com.ibm.snam.ai4legal.repositories;

import org.springframework.data.repository.CrudRepository;

import com.ibm.snam.ai4legal.model.Studente;

public interface StudenteRepository extends CrudRepository<Studente, Integer>{

}

Model class:

package com.ibm.snam.ai4legal.model;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
@Entity
public class Studente{
    @Id
    @GeneratedValue
    private int id;
    private String nome;
    private String cognome;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getnome() {
        return nome;
    }
    public void setnome(String nome) {
        this.nome = nome;
    }
    public String getcognome() {
        return cognome;
    }
    public void setcognome(String cognome) {
        this.cognome = cognome;
    }
}

Controller class:

package com.ibm.snam.ai4legal.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.ModelAndView;

import com.ibm.snam.ai4legal.repositories.StudenteRepository;

@RestController
public class HelloWorldController {

    @Autowired
    StudenteRepository studenteRepository;

    @GetMapping(value = "/home")
    public ModelAndView helloworld() {

        ModelAndView hello = new ModelAndView("helloworld");
        return hello;
    }
}

and here the pom.xml file

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>projects</groupId>
    <artifactId>springwebapp</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <properties>
        <java.version>1.8</java.version>
        <failOnMissingWebXml>false</failOnMissingWebXml>
    </properties>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.3.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-actuator</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-jasper</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>com.ibm.db2.jcc</groupId>
            <artifactId>db2jcc4</artifactId>
            <version>4.26.14</version>
        </dependency>
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger2</artifactId>
            <version>2.6.1</version>
        </dependency>
        <dependency>
            <groupId>io.springfox</groupId>
            <artifactId>springfox-swagger-ui</artifactId>
            <version>2.6.1</version>
        </dependency>
    </dependencies>

<!--  <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>-->  

    <repositories>
        <repository>
            <id>repo</id>
            <url>file://${project.basedir}/lib</url>
        </repository>
    </repositories>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
    <packaging>war</packaging>
</project>

On the internet I found that I should insert <context:annotation-config/> in some configuration file but I have no idea in which file I have to put it. Someone can help?

Answer 1

You have to use @ComponentScan annotation. Try the below code.

@ComponentScan({"com.ibm.*"})
@SpringBootApplication
public class SBApplication {

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

Also mention @Repository annotation in StudenteRepository class.

Answer 2

Since you are using spring-boot-starter-data-jpa you need to provide the annotation @EnableJpaRepositories to tell springboot to autoconfigure everything.So you might want to use the auto configuration feature of springboot.The @EnableJpaRepositories annotation is not mandatory for auto configuring the spring-data-jpa but in some cases if spring component scan didn't recognize spring-data-jpa in classpath you will have to use this annotation to tell spring to autoconfigure it.

@EnableJpaRepositories will enabling auto configuration support for Spring Data JPA required to know the path of the JPA the repositories. By default, it will scan only the main application package and its sub packages for detecting the JPA repositories.So take care to put the main application class at the root package of your application .

@EnableJpaRepositories(basePackages ="com.ibm")
@SpringBootApplication(scanBasePackages = {"com.ibm"})
public class SBApplication {

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

Also, if your entity classes are not in the same package then you can use the @EntityScan annotation to specify the base packages. In your case you have not specifies the @Repository annotation on your interface which will tell spring-boot to create default implementations for your interface.If that annotation is not provided then spring will just ignore the interface and the bean creation will not happen.You won't be able to autowire it .So provide that and have methods declared in your interface and spring-bot will take care of the rest.

@Repository
public interface StudenteRepository extends CrudRepository<Studente, Integer>{

    //If to find a student record by the id attribute
    public Studente findById();
}

Answer 3

Either move SBApplication to com.ibm.snam.ai4legal package so it can benefit from default component scanning or add the following annotations to specify packages to be scanned for entities and repositories.

@SpringBootApplication(scanBasePackages = {"com.ibm"})
@EnableJpaRepositories(basePackages = {"com.ibm"})
@EntityScan(basePackages = {"com.ibm"})
public class SBApplication {

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