Spring JPA-为什么当我的数据库中有数据时，我的findAll返回null？

时间：2020-02-01 22:00:14

标签： java mysql spring-data-jpa repository

我有一个要查询的实体的原始存储库。所讨论的实体是其他两个实体（两个外键）到另一列值的映射。 “中间表”是RoleMapSkill，使用表角色和技能的ID作为外键。当我在crud存储库中调用findAll方法时，我收到一个空指针（见下文）。

我知道数据库中有数据，但是由于某种原因它没有被返回。

请在下面查看我的实体类，存储库和控制器； 

java.lang.NullPointerException: null
    at main.SearchController.getRoleSkills(SearchController.java:52) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_241]
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_241]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[na:1.8.0_241]
    at java.lang.reflect.Method.invoke(Unknown Source) ~[na:1.8.0_241]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:888) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.2.RELEASE.jar:5.2.2.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1591) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [na:1.8.0_241]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [na:1.8.0_241]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.29.jar:9.0.29]
    at java.lang.Thread.run(Unknown Source) [na:1.8.0_241]

实体; 

package main;

import java.util.Set;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToMany;
import javax.persistence.OneToOne;

@Entity
public class RoleMapSkill {
    @Id
    private String mapId;
    @OneToOne
    Role role;
    @OneToOne
    Skill skill;

    private String rating;
//  
//  public RoleMapSkill(){
//      
//    }
    public RoleMapSkill(String Id, Role idRole, Skill idSkill, String rating){
        this.mapId=Id;
        this.role=idRole;
        this.skill=idSkill;
        this.rating=rating;
    }
    public String getIdRoleSkillRatings() {
        return mapId;
    }
    public void setIdRoleSkillRatings(String idRoleSkillRatings) {
        this.mapId = idRoleSkillRatings;
    }
    public Role getIdRole() {
        return role;
    }
    public void setIdRole(Role idRole) {
        this.role = idRole;
    }
    public Skill getIdSkill() {
        return skill;
    }
    public void setIdSkill(Skill idSkill) {
        this.skill = idSkill;
    }
    public String getRating() {
        return rating;
    }
    public void setRating(String rating) {
        this.rating = rating;
    }

}

回购; 

package main;

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

import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;

@Repository
public interface RoleMapSkillRepository extends CrudRepository<RoleMapSkill, Integer> {

    List<RoleMapSkill> findAll();
    @Query(value = "SELECT t FROM RoleMapSkill t RIGHT JOIN FETCH t.role where t.role = tester")            
    Optional<List<RoleMapSkill>> test(String tester);
//     Optional<List<RoleMapSkill>> findAllByroleIs(String roleId);


    }

控制器

package main;

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

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class SearchController {
      public EmployeeRepository employeeRepository;
      public RoleRepository roleRepository; 
      public SkillRepository skillRepository;   
      public RoleMapSkillRepository roleMapSkillRepository;

      @Autowired
        public void  employeeRepository(EmployeeRepository employeeRepository){
            this.employeeRepository = employeeRepository;
        }
      @Autowired
        public void  roleRepository(RoleRepository roleRepository){
            this.roleRepository = roleRepository;
        }
      @Autowired
        public void  skillRepository(SkillRepository skillRepository){
            this.skillRepository = skillRepository;
        }
//    @Autowired
//      public void  roleSkillRatingsRepository(roleSkillRatingsRepository roleSkillRatingsRepository){
//          this.roleSkillRatingsRepository = roleSkillRatingsRepository;
//      }


      @ResponseBody
        public List<Employee> getAllemployees() {
            System.out.println(employeeRepository.findAll());
            return employeeRepository.findAll();
        }

      @GetMapping("/test") 
      @ResponseBody
        public Map<String,Integer> getRoleSkills(String roleName) {
          //    List<Role> currentRole=roleRepository.findAll();
            Optional<Role> currentRole=roleRepository.findByroleNameIs("SWEM");
            String roleId=currentRole.get().getRoleId();
        //  Optional<List<RoleMapSkill>> skills = roleMapSkillRepository.test(roleId);
        //  List<RoleMapSkill> test=roleMapSkillRepository.findAll();
       //   System.out.print(test.get(0).getRating());
            List<RoleMapSkill> test=roleMapSkillRepository.findAll();
            System.out.print(test.get(0).getIdRoleSkillRatings());
            Optional<List<RoleMapSkill>> skills = roleMapSkillRepository.test(roleId);
            System.out.println(skills.get().get(0).getIdSkill());
//          System.out.print(currentRole.get(0).getRoleId());
//          System.out.print(currentRole.get(0).getRoleName());
//          System.out.print(currentRole.get(1).getRoleId());
//          System.out.print(currentRole.get(1).getRoleName());
        //  roleSkillRatingsRepository.findAllById(Integer.valueOf(currentRole.getIdRole()));
            return null;
        }
}

3 个答案:

答案 0 :(得分：0)

当人们仔细检查呈现的代码时，会发现RoleMapSkillRepository没有注入点（设置者）。因此，由于引用为NullPointerException，因此在findAll()上调用roleMapSkillRepository时会出现null。

为防止再次发生这种情况，我建议切换到基于构造函数的注入，并将所有注入的字段设置为final：

@Controller
public class SearchController {
     private final EmployeeRepository employeeRepository;
     private final RoleRepository roleRepository; 
     private final SkillRepository skillRepository;   
     private final RoleMapSkillRepository roleMapSkillRepository;

    @Inject
    public SearchController(
            final EmployeeRepository employeeRepository,
            final RoleRepository roleRepository,
            final SkillRepository skillRepository,
            RoleMapSkillRepository roleMapSkillRepository) {
        this.employeeRepository = employeeRepository;
        this.roleRepository = roleRepository;
        this.skillRepository = skillRepository;
        this.roleMapSkillRepository = roleMapSkillRepository;
    }
    ...
}

这样，如果未注入字段，则程序将无法编译。

评论您的代码：建议您使用JSR-330's @Inject-annotation。

答案 1 :(得分：0)

您必须从findAll()中删除RoleMapSkillRepository方法。因为它会停用默认值。扩展CrudRepository时，必须添加Entity对象和Entity对象的ID数据类型。您的RoleMapSkill实体ID数据类型为String。因此，您必须如下更改RoleMapSkillRepository：

@Repository
public interface RoleMapSkillRepository extends CrudRepository<RoleMapSkill, String> {

@Query(value = "SELECT t FROM RoleMapSkill t RIGHT JOIN FETCH t.role where t.role = tester")            
Optional<List<RoleMapSkill>> test(String tester);
//     Optional<List<RoleMapSkill>> findAllByroleIs(String roleId);
}

在控制器内部使用@Autowired注释，如下所示：

@Controller
public class SearchController {
    @Autowired
    public EmployeeRepository employeeRepository;
    @Autowired
    public RoleRepository roleRepository;
    @Autowired
    public SkillRepository skillRepository;
    @Autowired
    public RoleMapSkillRepository roleMapSkillRepository;

    //Rest of the code
}

答案 2 :(得分：0)

在从“可选”获取数据之前，请检查数据是否可用

可选<> 类 isPresent（）方法

if(currentRole.isPresent()){
   String roleId=currentRole.get().getRoleId();
}

List<RoleMapSkill> test=roleMapSkillRepository.findAll();
   if(test != null && !test.isEmpty()){
     System.out.print(test.get(0).getIdRoleSkillRatings());
   }


Optional<List<RoleMapSkill>> skills = roleMapSkillRepository.test(roleId);
   if(skills.isPresent() && !skills.get().isEmpty()){
     System.out.println(skills.get().get(0).getIdSkill());
   }
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