@Autowired注解中的空指针异常

Question

我知道还有很多资源已经回答了这个问题。但是，仍然有一些已解决的问题并出现 NULL Pointer Exception Application.java 文件

package com.shubham.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import com.shubham.demo.producer.ProducerMain;

@SpringBootApplication
public class DemoApplication {
    
    
    @Autowired 
    private static ProducerMain producerMain; 
    
    public ProducerMain getProducerMain() {
        return producerMain;
    }
    public void setProducerMain(ProducerMain producerMain) {
        DemoApplication.producerMain = producerMain;
    }
    
    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
        producerMain.StartProducer();   // ---> Getting Null Pointer Exception 
    }

}

Producer.Main class

package com.shubham.demo.producer;

@Configurable 
@Component 
public class ProducerMain {
    
    public ProducerMain() {
        super();
    }
    public void StartProducer() {
        System.out.println("Started the Producer");
    }
    
}

Answer 1

您得到空指针是因为您用@Autowired 注释的字段是静态字段。 Spring 不支持自动装配静态字段。

尝试将 @Autowired 添加到您的 setter 方法而不是字段。

private static ProducerMain producerMain; 

public ProducerMain getProducerMain() {
    return producerMain;
}
@Autowired 
public void setProducerMain(ProducerMain producerMain) {
    DemoApplication.producerMain = producerMain;
}

@Autowired注解中的空指针异常

Null Pointer Exception in @Autowired Annotation

spring

inversion-of-control

spring-boot