java spring boot db 연결시 java.lang.NullPointerException: null 발생할때

분영 아래와 같이 정상적으로 잘 연결한것 같지만 null  발생한다.

java Controller -> Service -> ServiceImpl -> DAO -> DAO.xml

ERROR org.apache.catalina.core.ContainerBase.[Tomcat].[localhost].[/].[dispatcherServlet] - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException: null
	at com.example.demo.web.UserController.postLogin(UserController.java:28) ~[main/:?]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_201]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_201]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_201]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_201]
	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.doPost(FrameworkServlet.java:909) ~[spring-webmvc-5.3.12.jar:5.3.12]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:681) ~[tomcat-embed-core-9.0.54.jar:4.0.FR]

해결

위 에러는 연결 부분을 확인을 해봐야 한다.

• Controller 에서 Service -> Service 사용하기 위해서는 @Autowired 사용.
• Service 에서 DAO
• DAO -> DAO.xml

   

@Autowired
 private UserService userService;

UserController.java

package com.example.demo.web;

import com.example.demo.common.Common;
import com.example.demo.domain.User;
import com.example.demo.service.UserService;
import groovy.util.logging.Slf4j;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpSession;
import java.util.HashMap;
import java.util.Map;

@Slf4j
@RestController
public class UserController extends Common {

    @Autowired
    private UserService userService;

    @PostMapping(value = "/login")
    public Map<String, Object> postLogin(@RequestBody User user, HttpSession session) {

        User signUser = userService.signIn(user.getUsername(), user.getPassword());

        log.info(signUser.getUsername());

        Map<String, Object> resultMap = new HashMap<>();
        resultMap.put("result", "ok");
        resultMap.put("authInfo", signUser );

        //session.setAttribute(">>>username", user.getUsername() );
        return resultMap;
    }
}