我面临空指针异常。你能帮我解释一下实际问题是什么以及我做错了什么吗?请原谅我的粗暴编码,因为我是初学者。
这是错误:
线程“main”中的异常java.lang.NullPointerException:无法调用“com.org.Controller.Controller.addFlight()”,因为“com.org.App.controller”为空 在 com.org.App.main(App.java:22)
这是课程:
应用程序
package com.org;
import com.org.Controller.Controller;
import org.springframework.beans.factory.annotation.Autowired;
import java.util.Scanner;
public class App {
@Autowired
public static Controller controller;
public static void main(String[] args) {
System.out.println("Hello, Welcome to AirGO Airline");
System.out.println("Please chose what you would like to do");
System.out.println("1.Add Flight:");
System.out.println("2.Search Flight");
Scanner scanner=new Scanner(System.in);
Integer userChoice= scanner.nextInt();
if (1==userChoice){
controller.addFlight();
} else if (2==userChoice) {
controller.showFlight();
}
System.out.println("Please Enter a Valid Input");
}
}
Controller //一个假的控制器类
package com.org.Controller;
import com.org.Config.AppConfig;
import com.org.Domain.Flight;
import com.org.Service.FlightServiceImpl;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import java.time.LocalDate;
public class Controller {
public void addFlight(){
ApplicationContext applicationContext= new AnnotationConfigApplicationContext(AppConfig.class);
FlightServiceImpl flightService= applicationContext.getBean(FlightServiceImpl.class);
Flight flight=new Flight();
flight.setAirlines("Indigo");
flight.setSource("India");
flight.setDestination("Japan");
flight.setFare(50456.54);
LocalDate date= LocalDate.now();
flight.setJourneyDate(date);
flight.setSeatCount(2);
flightService.addFlight(flight);
}
public void showFlight(){
ApplicationContext applicationContext= new AnnotationConfigApplicationContext(AppConfig.class);
FlightServiceImpl flightService= applicationContext.getBean(FlightServiceImpl.class);
LocalDate date= LocalDate.now();
}
}
服务
package com.org.Service;
import com.org.Domain.Flight;
import com.org.Repository.FlightRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class FlightServiceImpl implements FlightService{
@Autowired
FlightRepository flightRepository;
@Override
public void addFlight(Flight flight) {
try{
flightRepository.addFlight(flight);
}catch (Exception e){
System.out.println("Flight Insertion Unsuccessful, Cannot connect to Database....");
}
}
}
配置类
package com.org.Config;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan("com.org")
public class AppConfig {
//Beans AutoGenerated
}
域类
package com.org.Domain;
import java.time.LocalDate;
public class Flight {
private String flightId;
private String airlines;
private String source;
private String destination;
private double fare;
private LocalDate journeyDate;
private Integer seatCount;
public Flight() {
}
public String getFlightId() {
return flightId;
}
public void setFlightId(String flightId) {
this.flightId = flightId;
}
public String getAirlines() {
return airlines;
}
public void setAirlines(String airlines) {
this.airlines = airlines;
}
public String getSource() {
return source;
}
public void setSource(String source) {
this.source = source;
}
public String getDestination() {
return destination;
}
public void setDestination(String destination) {
this.destination = destination;
}
public double getFare() {
return fare;
}
public void setFare(double fare) {
this.fare = fare;
}
public LocalDate getJourneyDate() {
return journeyDate;
}
public void setJourneyDate(LocalDate journeyDate) {
this.journeyDate = journeyDate;
}
public Integer getSeatCount() {
return seatCount;
}
public void setSeatCount(Integer seatCount) {
this.seatCount = seatCount;
}
@Override
public String toString() {
return "Flight{" +
"flightId='" + flightId + '\'' +
", airlines='" + airlines + '\'' +
", source='" + source + '\'' +
", destination='" + destination + '\'' +
", fare=" + fare +
", journeyDate=" + journeyDate +
", seatCount=" + seatCount +
'}';
}
}
存储库
package com.org.Repository;
import com.org.Domain.Flight;
import org.springframework.stereotype.Repository;
import java.util.HashMap;
import java.util.Map;
@Repository
public class FlightRepositoryImpl implements FlightRepository{
private static Integer flightId = 1000;
@Override
public void addFlight(Flight flight) {
Map<Integer, Flight> database= new HashMap<Integer, Flight>();
flightId+=1;
database.put(flightId,flight);
System.out.println("Added flight details are: "+ flight.toString());
}
}
如下更新您的配置类。
package com.org.Config;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan("com.org")
public class AppConfig {
//Beans AutoGenerated
@Bean
public Controller controller() {
return new Controller();
}
}
但在理想的世界场景中。控制器类应使用
@RestController
或 @Controller
进行注释,并映射到正确的 http 端点映射。
希望这有帮助。