尝试使用springboot构建api时出现问题

Question

我正在尝试通过Spring Boot开发一个宁静的Web服务，但是却遇到了错误，并且尝试了不同的方法，但不知道问题出在哪里，也不知道如何解决。错误消息指向我的其余Controller类，但我不明白为什么。这是来自我的浏览器的错误跟踪：

There was an unexpected error (type=Internal Server Error, status=500).
No message available
java.lang.NullPointerException
    at com.dafe.spring.applogger.rest.UserLogRestController.findAll(UserLogRestController.java:28)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:893)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:798)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:94)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:367)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1639)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)

这里是错误跟踪所指向的RestController类。我将不胜感激。

package com.dafe.spring.applogger.rest;

import java.util.List;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.dafe.spring.applogger.dao.UserLogDAO;
import com.dafe.spring.applogger.entity.UserLog;

@RestController
@RequestMapping("/api")
public class UserLogRestController {

    private UserLogDAO userLogDao;

    //inject logDao using constructor injection

    public UserLogRestController(UserLogDAO theUserLogDao) {

    }

    //expose logs and return list of logs
    @GetMapping("/logs")
    public List<UserLog> findAll(){

        return userLogDao.findAll();

    }

}

这是我的Dao实现类：

package com.dafe.spring.applogger.dao;

import java.util.List;

import javax.persistence.EntityManager;

import org.hibernate.Session;
import org.hibernate.query.Query;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;

import com.dafe.spring.applogger.entity.UserLog;

@Repository
public class UserLogDaoHibernateImplementation implements UserLogDAO {


    //define field for entity manager
    private EntityManager entityManager;

    //set up constructor injection
    @Autowired
    public UserLogDaoHibernateImplementation(EntityManager theEntityManager) {

    entityManager= theEntityManager;
    }

    @Override
    @Transactional
    public List<UserLog> findAll() {

        //get the current hibernate session from entity manager
        Session currentSession = entityManager.unwrap(Session.class);


        //create a query
        Query <UserLog> theQuery = 
                currentSession.createQuery("from log", UserLog.class);

        //execute query and get result list

        List<UserLog> userLog = theQuery.getResultList();

        //return the results

        return userLog;
    }

} 

这是我的实体类

package com.dafe.spring.applogger.entity;

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

@Entity
@Table(name="log")
public class UserLog {

    //define field

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="id")
    private int id;

    @Column(name="user_id")
    private String userId;

    @Column(name="session_id")
    private String sessionId;


    //define constructors

    public UserLog() {

    }


    public UserLog(String userId, String sessionId) {
        this.userId = userId;
        this.sessionId = sessionId;
    }
    //define getters and setters


    public int getId() {
        return id;
    }


    public void setId(int id) {
        this.id = id;
    }


    public String getUserId() {
        return userId;
    }


    public void setUserId(String userId) {
        this.userId = userId;
    }


    public String getSessionId() {
        return sessionId;
    }


    public void setSessionId(String sessionId) {
        this.sessionId = sessionId;
    }


    @Override
    public String toString() {
        return "Log [id=" + id + ", userId=" + userId + ", sessionId=" + sessionId + "]";
    }


    //define toString


}

如果您能帮助我发现问题或提供解决方法，我将不胜感激。谢谢。

Answer 1

（轻松修复！；）您忘记了：

@Autowired //!! or similar

关于您：

private UserLogDAO userLogDao;

..或尊重//或者：

public UserLogRestController(/*@Autowired implicitely*/ UserLogDAO theUserLogDao) {
    userLogDao = theUserLogDao;
}

..在您的构造函数中。

Answer 2

我就知道了，谢谢您的贡献。在私有userLogDao上方使用了autowire注释后，即使这是一个有效的建议，它也无法正常工作，我在代码中发现了另一个错误，即我在GetMapping上使用了错误的相对路径。我使用“ / log”代替“ / userLog”。太激动了谢谢大家！