SpringBoot 上 JPA​​ 上的 NullPointerException

Question

我是 SpringBoot 的新手，我正在制作一個小的 CRUD。 當我嘗試發出 GET 請求以顯示我的 BD 中名為“soccer”的足球隊列表時，我收到以下錯誤消息：

java.lang.NullPointerException: Cannot invoke "com.balamcode.repo.EquipoRepo.findAll()" because "this.equiporepo" is null
at com.balamcode.servicio.EquipoServicio.findAll(EquipoServicio.java:22) ~[classes/:na]
at com.balamcode.rest.EquipoREST.getAllEquipos(EquipoREST.java:23) ~[classes/:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Method.java:567) ~[na:na]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-5.3.12.jar:5.3.12]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150) ~[spring-web-5.3.12.jar:5.3.12]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117) ~[spring-webmvc-5.3.12.jar:5.3.12]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.12.jar:5.3.12]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.12.jar:5.3.12]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.12.jar:5.3.12]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1067) ~[spring-webmvc-5.3.12.jar:5.3.12]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963) ~[spring-webmvc-5.3.12.jar:5.3.12]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.12.jar:5.3.12]
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.12.jar:5.3.12]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:655) ~[tomcat-embed-core-9.0.54.jar:4.0.FR]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.12.jar:5.3.12]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:764) ~[tomcat-embed-core-9.0.54.jar:4.0.FR]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.54.jar:9.0.54]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.12.jar:5.3.12]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.12.jar:5.3.12]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.12.jar:5.3.12]
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.12.jar:5.3.12]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:540) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:895) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1722) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.54.jar:9.0.54]
at java.base/java.lang.Thread.run(Thread.java:831) ~[na:na]

我的模型“Equipo”是：

package com.balamcode.modelos;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table (name = "equipo")
public class Equipo {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    private String nombre;
    
    public Equipo() {
        
    }
    
    public Equipo(String nombre) {
        super();
        this.nombre = nombre;
    }
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getNombre() {
        return nombre;
    }
    public void setNombre(String nombre) {
        this.nombre = nombre;
    }
    
    }

我的存儲庫“EquipoRepo”是

package com.balamcode.repo;

import org.springframework.data.jpa.repository.JpaRepository;

import com.balamcode.modelos.Jugador;

public interface JugadorRepo extends JpaRepository<Jugador, Integer>{

}

我的服務“EquipoServicio”是：

package com.balamcode.servicio;

import java.util.List;
import java.util.Optional;

import org.springframework.data.domain.Example;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Service;

import com.balamcode.modelos.Equipo;
import com.balamcode.repo.EquipoRepo;

@Service
public class EquipoServicio implements EquipoRepo{

    private EquipoRepo equiporepo;

    @Override
    public List<Equipo> findAll() {
        return equiporepo.findAll();
    }

    @Override
    public List<Equipo> findAll(Sort sort) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public List<Equipo> findAllById(Iterable<Integer> ids) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public <S extends Equipo> List<S> saveAll(Iterable<S> entities) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void flush() {
        // TODO Auto-generated method stub
        
    }

    @Override
    public <S extends Equipo> S saveAndFlush(S entity) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public <S extends Equipo> List<S> saveAllAndFlush(Iterable<S> entities) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public void deleteAllInBatch(Iterable<Equipo> entities) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void deleteAllByIdInBatch(Iterable<Integer> ids) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void deleteAllInBatch() {
        // TODO Auto-generated method stub
        
    }

    @Override
    public Equipo getOne(Integer id) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public Equipo getById(Integer id) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public <S extends Equipo> List<S> findAll(Example<S> example) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public <S extends Equipo> List<S> findAll(Example<S> example, Sort sort) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public Page<Equipo> findAll(Pageable pageable) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public <S extends Equipo> S save(S entity) {
        
        return equiporepo.save(entity);
    }

    @Override
    public Optional<Equipo> findById(Integer id) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public boolean existsById(Integer id) {
        // TODO Auto-generated method stub
        return false;
    }

    @Override
    public long count() {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public void deleteById(Integer id) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void delete(Equipo entity) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void deleteAllById(Iterable<? extends Integer> ids) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void deleteAll(Iterable<? extends Equipo> entities) {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void deleteAll() {
        // TODO Auto-generated method stub
        
    }

    @Override
    public <S extends Equipo> Optional<S> findOne(Example<S> example) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public <S extends Equipo> Page<S> findAll(Example<S> example, Pageable pageable) {
        // TODO Auto-generated method stub
        return null;
    }

    @Override
    public <S extends Equipo> long count(Example<S> example) {
        // TODO Auto-generated method stub
        return 0;
    }

    @Override
    public <S extends Equipo> boolean exists(Example<S> example) {
        // TODO Auto-generated method stub
        return false;
    }
}

我的名為“EquipoREST”的 REST 類是：

package com.balamcode.rest;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.balamcode.modelos.Equipo;
import com.balamcode.servicio.EquipoServicio;

@RestController
@RequestMapping("/equipo/")
public class EquipoREST {

    @Autowired
    private EquipoServicio equipoServicio;
    
    @GetMapping
    public ResponseEntity<List<Equipo>> getAllEquipos(){
        return ResponseEntity.ok(equipoServicio.findAll());
    }
}

Answer 1

嘗試在EquipoServicio添加@Autowired注釋。

@Autowired
private EquipoRepo equiporepo;

Answer 2

原因是您正在調用 null 對象的方法。 使用@Autowired 注釋來獲取一個對象。

@Autowired
private EquipoRepo equiporepo;

Answer 3

假設應用程序上下文是一個池。 有一些特定的方法可以將某些東西放入池中並從池中取出某些東西。

當您添加@Service ， @Repository ， @Bean你的類/方法，你把東西在游泳池。

public interface JugadorRepo extends JpaRepository<Jugador, Integer>{}

這里沒有@Repository 沒有問題，因為 JpaRepository 有它，而 JugadorRepo 擴展了 JpaRepository。

但是，如果您想使用池中的元素之一，則需要先獲取它。 您可以使用注入（構造函數、設置器）、@ @Autowired等。

@Autowired
private EquipoRepo equiporepo;

這可以解決您的問題。