尝试使用 spring boot 构建 api 时出现问题
issue while trying to build an api with springboot
我正在尝试使用 spring 引导开发 restful Web 服务，但出现错误，我尝试了不同的方法，但不知道问题出在哪里，也不知道如何解决。错误消息指向我的休息控制器 class 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)
这是错误跟踪指向的 RestController class。我会很感激一些见解。
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 class:
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 class
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出路，我将不胜感激。谢谢。
（轻松修复！；）您忘记了：
@Autowired //!! or similar
在你的：
private UserLogDAO userLogDao;
..或respectivley/alternatively:
public UserLogRestController(/*@Autowired implicitely*/ UserLogDAO theUserLogDao) {
userLogDao = theUserLogDao;
}
..在你的构造函数中。
我刚收到，感谢您的贡献。在使用私有 userLogDao 上方的 autowire 注释后，即使这是一个有效的建议它也不起作用，我在我的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”。我很兴奋。谢谢大家！
我正在尝试使用 spring 引导开发 restful Web 服务，但出现错误，我尝试了不同的方法，但不知道问题出在哪里，也不知道如何解决。错误消息指向我的休息控制器 class 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)
这是错误跟踪指向的 RestController class。我会很感激一些见解。
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 class:
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 class
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出路，我将不胜感激。谢谢。
（轻松修复！；）您忘记了：
@Autowired //!! or similar
在你的：
private UserLogDAO userLogDao;
..或respectivley/alternatively:
public UserLogRestController(/*@Autowired implicitely*/ UserLogDAO theUserLogDao) {
userLogDao = theUserLogDao;
}
..在你的构造函数中。
我刚收到，感谢您的贡献。在使用私有 userLogDao 上方的 autowire 注释后，即使这是一个有效的建议它也不起作用，我在我的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”。我很兴奋。谢谢大家！