Question

当我运行这个线程时，我得到了这个结果，我不知道为什么

FirstThread正在运行

加载栏页

线程“Thread-0”中的异常java.lang.NullPointerException at com.sctrcd.multidsdemo.integration.threads.FirstThread.run（FirstThread.java:29）

代码，

package com.sctrcd.multidsdemo.integration.threads;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Sort.Direction;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.support.AnnotationConfigContextLoader;
 import com.sctrcd.multidsdemo.domain.bar.Bar;
 import com.sctrcd.multidsdemo.integration.config.AppConfig;
 import com.sctrcd.multidsdemo.integration.repositories.bar.BarPagingAndSortingRepository;
 import com.sctrcd.multidsdemo.integration.repositories.bar.BarRepository;
@ContextConfiguration(classes =AppConfig.class,
loader=AnnotationConfigContextLoader.class)

public class FirstThread extends Thread {

@Autowired
BarPagingAndSortingRepository barPage;
  public void run() {
    System.out.println("FirstThread is running");
    System.out.println("Loading bar page");
    Page<Bar> bars=barPage.findAll(new PageRequest(0, 1, Direction.DESC, "id"));
    System.out.println("Bar page loaded");
    Bar bar=bars.getContent().get(0);
    System.out.println("Creating bar");
    System.out.println(bar.getId());
    System.out.println();
    //int a = 20;
    Thread.currentThread().interrupt();
    System.out.println("Interrupt");
  }
  public static void main(String args[]) {
    FirstThread thread=new FirstThread();
    thread.start();
  }
}

Answer 1

以调试模式运行程序并评估29行中的每个方法调用和变量。所以你会看到哪些是空的

由于此代码是从public static void main启动的 - 没有初始化任何Injection上下文，并且@Autowired注释不起作用，因此barPage为null。
在JUnit测试中，如果在Junit测试中有特殊的注释，它可以工作，它初始化了Spring上下文看看这里：http://www.springbyexample.org/examples/intro-to-ioc-creating-a-spring-application.html
始终考虑一条规则。豆类只能在另一个豆子中注射（自动装配）。你的测试用例不是bean

Answer 2

这是pagingAndSorting bean

package com.sctrcd.multidsdemo.integration.repositories.bar;

import org.springframework.data.repository.PagingAndSortingRepository;

import com.sctrcd.multidsdemo.domain.bar.Bar;

public interface BarPagingAndSortingRepository extends PagingAndSortingRepository<Bar, Integer> {

}

Answer 3

您的Main方法应该如此成功绑定到Spring上下文：

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
  public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");    
      BarPagingAndSortingRepository barPage = (BarPagingAndSortingRepository)  context.getBean("barPage");   
  }
}

线程java.lang.NullPointerException中的异常

3 个答案: