My scheduled job in spring boot is giving exception and returning null - spring

Question

I have written the code for scheduling jobs i.e simply adding data to database after every 5 seecs.Though the structure of code is correct but i am getting some exception.THe job is being scheduled after every 5 secs but nothing happens on database.
package com.example.schedule.service;
import com.example.schedule.dao.UserDao;
import com.example.schedule.model.User;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Service;
import java.util.Date;
import java.util.List;
import java.util.Random;
#Service
public class UserService {
private UserDao userdao;
#Scheduled(fixedRate = 5000)
public void add2DBjob(){
User user=new User();
user.setName("xadmin "+ new Random().nextInt(3774480));
userdao.save(user);
System.out.println("added object in database at : "+new Date().toString());
}
}
I have an User entity also with two properties name and id where id is primary key.
package com.example.schedule.model;
import lombok.*;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
#Entity
#Getter
#Setter
#ToString
#NoArgsConstructor
#AllArgsConstructor
public class User {
#Id
#GeneratedValue
private int id;
private String name;
}
I have application.properties file whose code I am attaching below
server.port=9090
spring.datasource.url=jdbc:mysql://localhost:3306/job
spring.datasource.username=root
spring.datasource.password=Ph#ne#121
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL8Dialect
I have a dao instance which extends jpa repository.
package com.example.schedule.dao;
import com.example.schedule.model.User;
import org.springframework.data.jpa.repository.JpaRepository;
public interface UserDao extends JpaRepository<User,Integer> {
}
After successful running of code though user table is formed in job database but i do not get any data .
Please see the image below for the error i get
Output of the job being scheduled after every 5 secs but giving null everytime
java.lang.NullPointerException: null
at com.example.schedule.service.UserService.add2DBjob(UserService.java:22) ~[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_282]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_282]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_282]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_282]
at org.springframework.scheduling.support.ScheduledMethodRunnable.run(ScheduledMethodRunnable.java:84) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:54) ~[spring-context-5.3.5.jar:5.3.5]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_282]
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [na:1.8.0_282]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_282]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [na:1.8.0_282]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_282]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_282]
at java.lang.Thread.run(Thread.java:748) [na:1.8.0_282]
2021-04-12 11:48:08.565 ERROR 23482 --- [ scheduling-1] o.s.s.s.TaskUtils$LoggingErrorHandler : Unexpected error occurred in scheduled task
java.lang.NullPointerException: null
at com.example.schedule.service.UserService.add2DBjob(UserService.java:22) ~[classes/:na]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_282]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_282]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_282]
at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_282]
at org.springframework.scheduling.support.ScheduledMethodRunnable.run(ScheduledMethodRunnable.java:84) ~[spring-context-5.3.5.jar:5.3.5]
at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:54) ~[spring-context-5.3.5.jar:5.3.5]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_282]
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [na:1.8.0_282]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_282]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [na:1.8.0_282]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_282]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_282]
at java.lang.Thread.run(Thread.java:748) [na:1.8.0_282]
please help me in finding what can be possible error in this?

Answer 1

You haven't initialized the userdao object in UserService class and that causes the problem. You need to autowire it.
#Autowired
private UserDao userdao;
or
private final UserDao userdao;
UserService(UserDao userdao){
this.userdao = userdao;
}
Also, check whether you have enabled scheduling in the configuration class. If not add #EnableScheduling annotation in the configuration class. You can also enable scheduling through XML configuration.