Why does nullpointer crash?

Question

Java

Good day
Help me understand why nullpointer crashes when trying to register?
Send a POST request via postman.

{
    "username": "username",
    "password": 123123,
    "passwordConfirm": 123123
}

Really somewhere I do not appropriate?

2021-11-10 01:31:42.886 INFO 5753 --- [nio-8080-exec-2] ohhiQueryTranslatorFactoryInitiator : HHH000397: Using ASTQueryTranslatorFactory
Hibernate: select user0_.id as id1_1_, user0_.password as password2_1_, user0_.username as username3_1_ from t_user user0_ where user0_.username=?
2021-11-10 01:31:42.960 ERROR 5753 --- [nio-8080-exec-2] oaccC[.[.[/].[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.notes.service.UserService.saveUser(UserService.java:57) ~[classes/:na]
at com.example.notes.controllers.RegistrationController.addUser(RegistrationController.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:62) ~[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:566) ~[na:na]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java: 190) ~[spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
at org.springframework.web.servlet. mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation .RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:892) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal( RequestMappingHandlerAdapter.java:797) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
at org.springframework.web. servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1039) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942 ) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.8. RELEASE.jar:5.1.8.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:908) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet. java:882) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0 .21.jar:9.0.21]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
at org.apache .catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter. java:53) ~[tomcat-embed-websocket-9.0.21.jar:9.0.21]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
at org.apache.catalina.core.ApplicationFilterChain.doFilter( ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.21.jar:9.0.21]

RegistrationController

@PostMapping("/registration")
    public String addUser(@RequestBody UserDto userDto) {

        if (!userDto.getPassword().equals(userDto.getPasswordConfirm())) {
            return "Password not match";
        }

        if (!userService.saveUser(userDto)) {
            return "User already exists";
        }

        return "redirect:/";
    }

UserSercive

public boolean saveUser(UserDto userDto) {
        User user = userRepository.findByUsername(userDto.getUsername());
        if (user != null) {
            return false;
        }

        user.setRoles(Collections.singleton(new Role(1L, "ROLE_USER")));
        user.setUsername(userDto.getUsername());
        user.setPassword(bCryptPasswordEncoder.encode(userDto.getPassword()));
        userRepository.save(user);

        return true;
    }

Git link:
https://github.com/Akella058/notes_api

Answer 1

"The computer does not do what you wanted, but what you ordered it to"
Take a close look at the logic of your saveUser.
You are looking for a user by name. If it is found (user != null), then you return false.
And if not found (that is, user == null) then ... you call user.setRoles(...)
Of course, catching NPE.