Question

我将SpringBoot用于我的Web应用程序，遇到以下错误：

上下文初始化期间遇到的异常-取消刷新尝试：org.springframework.beans.factory.BeanCreationException：在文件[D：\ Projects \ Java \ mydbexxcercise \ target \ classes \ com \中创建名称为'heroController'的bean时出错db \ controllers \ HeroController.class]：实例化bean失败；嵌套的异常是org.springframework.beans.BeanInstantiationException：无法实例化[com.db.controllers.HeroController]：构造方法抛出了异常；嵌套的异常是java.lang.NullPointerException。

这些是我的课程：

DBApp类（主类）：

package com.db.app;
import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.domain.EntityScan;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;

import org.springframework.data.jpa.repository.config.EnableJpaRepositories;

/*
* DAL - Data Access Layer
* BL - Business Layer
*
* */


@SpringBootApplication
@ComponentScan(basePackages = {"com.db.controllers","com.db.services"})
@EnableJpaRepositories(basePackages = "com.db.repositories")
@EntityScan(basePackages = "com.db.entities")
public class DBApp
{
    public enum PowerCatagory{SpecialPower,Weapon,Machines}
    private static ConfigurableApplicationContext appContext;
    public static void main(String[] args)
    {
        appContext = SpringApplication.run(DBApp.class,args);

    }

    public static ConfigurableApplicationContext getAppContext()
    {
        return appContext;
    }

}

HeroRepository类：

@Repository
public interface HeroRepository extends JpaRepository<Hero, Integer>
{


}

英雄实体类：

package com.db.entities;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
import com.db.app.DBApp;
import org.postgresql.geometric.PGpolygon;
import org.springframework.stereotype.Component;

@Entity
@Table(name="hero")
public class Hero
{

    public int getHid() {
        return hid;
    }

    public PGpolygon getArea() {
        return area;
    }

    public String getSpower() {
        return spower;
    }

    public String getFname() {
        return fname;
    }

    public String getLname() {
        return lname;
    }

    public DBApp.PowerCatagory getPc() {
        return pc;
    }

    public float getPower_level() {
        return power_level;
    }

    public float getLuck() {
        return luck;
    }

    @Id private int hid;//This is the table's primary key

    public void setHid(int hid) {
        this.hid = hid;
    }

    public void setArea(PGpolygon area) {
        this.area = area;
    }

    public void setSpower(String spower) {
        this.spower = spower;
    }

    public void setFname(String fname) {
        this.fname = fname;
    }

    public void setLname(String lname) {
        this.lname = lname;
    }

    public void setPc(DBApp.PowerCatagory pc) {
        this.pc = pc;
    }

    public void setPower_level(float power_level) {
        this.power_level = power_level;
    }

    public void setLuck(float luck) {
        this.luck = luck;
    }

    private PGpolygon area;
    private String spower;
    private String fname;
    private String lname;
    private DBApp.PowerCatagory pc;
    private float power_level;
    private float luck;

    public Hero(int hid, PGpolygon area, String spower, String fname, String lname, DBApp.PowerCatagory pc, float power_level, float luck) {
        this.hid = hid;
        this.area = area;
        this.spower = spower;
        this.fname = fname;
        this.lname = lname;
        this.pc = pc;
        this.power_level = power_level;
        this.luck = luck;
    }

}

HeroService类：

package com.db.services;
import com.db.entities.Hero;
import com.db.repositories.HeroRepository;
import com.db.app.DBApp;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;

@Service
public class HeroService
{
    private HeroRepository heroRepository = DBApp.getAppContext().getBean(HeroRepository.class);

    public List<Hero> getAllHeroes()
    {
        List<Hero> res = new ArrayList<>();
        heroRepository.findAll().forEach(res::add);
        return res;
    }

    public void addHero(Hero hero)
    {
        heroRepository.save(hero);
    }

    public Hero getHero(int id)
    {
        return heroRepository.findById(id).get();
    }

    public void updateHero(Hero hero)
    {
        heroRepository.save(hero);/*If a hero with the same id
        already exists in the DB then the save() function
        will automatically update that same tuple.*/
    }

    public void deleteHero(Hero hero)
    {
        heroRepository.delete(hero);
    }
}

HeroController类：

package com.db.controllers;
import com.db.app.DBApp;
import com.db.entities.Hero;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import com.db.services.HeroService;

import java.util.List;

@RestController
public class HeroController
{
    private HeroService heroService = DBApp.getAppContext().getBean(HeroService.class);

    @GetMapping("/hero")
    public List<Hero> getAllHeroes()
    {
        //System.out.println(heroService.getAllHeroes());
        return heroService.getAllHeroes();
    }

    @GetMapping("/")
    public String test()
    {
        //System.out.println(heroService.getAllHeroes());
        return "working!!!";
   }

}

pom.xml文件：

<?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>MyDBExcercise</groupId>
    <artifactId>mydbexxcercise</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-parent</artifactId>
        <version>2.1.4.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>com.aerospike</groupId>
            <artifactId>spring-data-aerospike</artifactId>
            <version>1.0.2.RELEASE</version>
        </dependency>


        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-jpa</artifactId>
            <version>2.1.6.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>javax.persistence</groupId>
            <artifactId>javax.persistence-api</artifactId>
            <version>2.2</version>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <version>42.2.5</version>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>5.4.2.Final</version>
        </dependency>

    </dependencies>



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


</project>

根据控制台，Spring无法初始化HeroController的原因是以下代码导致的异常：

private HeroService heroService = DBApp.getAppContext().getBean(HeroService.class);

我不知道为什么在这里抛出异常，所以我们将不胜感激。非常感谢您的宝贵时间

Answer 1

以下2处更改应解决此问题。无需从App Context获取bean。

@Service
public class HeroService {
    @Autowired
    private HeroRepository heroRepository;

＆

@RestController
public class HeroController {
    @Autowired
    private HeroService heroService;

＆pom.xml

<?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>
<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.1.4.RELEASE</version>
    <relativePath/> <!-- lookup parent from repository -->
</parent>

<groupId>MyDBExcercise</groupId>
<artifactId>mydbexxcercise</artifactId>
<version>0.0.1-SNAPSHOT</version>

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

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

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>

    <dependency>
        <groupId>com.aerospike</groupId>
        <artifactId>spring-data-aerospike</artifactId>
        <version>1.0.2.RELEASE</version>
    </dependency>


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

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-jpa</artifactId>
    </dependency>

    <dependency>
        <groupId>org.postgresql</groupId>
        <artifactId>postgresql</artifactId>
    </dependency>

</dependencies>

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

＆application.properties

spring.datasource.url=jdbc:postgresql://localhost:5432/postgres
spring.datasource.username=postgres
spring.datasource.password=*****
spring.jpa.properties.hibernate.jdbc.lob.non_contextual_creation=true

Answer 2

将您的DBApp移至com.db包中。
删除所有注释，但暗示@SpringBootApplication并自动检测其他注释
删除getAppContext方法。

有了这个，您的DBApp类应该看起来像这样。

package com.db;

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

@SpringBootApplication
public class DBApp {
    public enum PowerCatagory{SpecialPower,Weapon,Machines}

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

    }
}

现在在您的HeroService和HeroController中，您需要使用依赖注入。最佳实践是使用构造函数注入而不是字段注入。

@Service
public class HeroService {

  private final HeroRepository heroRepository;

  public HeroService(HeroRepository heroRepository) {
     this.heroRepository=heroRepository;
  }

HeroController

@RestController
public class HeroController {

  private final HeroService heroService;

  public HeroController(HeroService heroService) {
    this.heroService=heroService;
  }

注意：@Repository上的HeroRepository注释可以删除，因为它没有添加任何内容。

接下来，您的依赖关系变得一团糟，请使用专用的spring-boot-starters来获取正确和经过测试的版本。您不需要Hibernate / JPA依赖项（spring-boot-starter-data-jpa中包含了这些依赖项），而其他人则需要较新的版本。

<?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>MyDBExcercise</groupId>
    <artifactId>mydbexxcercise</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-parent</artifactId>
        <version>2.1.4.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>com.aerospike</groupId>
            <artifactId>spring-data-aerospike</artifactId>
            <version>2.0.1.RELEASE</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
        </dependency>

    </dependencies>

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

</project>

无法实例化类HeroController；构造函数抛出异常；嵌套的异常是java.lang.NullPointerException

2 个答案: