在使用dubbo时远程访问服务提供者的方法时出现空指针异常java.lang.NullPointerException

错误日志如下：

java.lang.NullPointerException
	at com.atguigu.service.UserService.hello(UserService.java:20)
	at com.atguigu.ConsumerUserApplicationTests.contextLoads(ConsumerUserApplicationTests.java:18)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
	at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
	at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:252)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
	at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:191)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
	at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:51)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)

分析：

• 想了很久，它报空指针说明方法没找到，没找到的原因是什么，我仔细检查了一遍，方法的提供者正常运行，
  
  

• 这边方法的使用着的基本配置也都是对的

#配置当前应用的名字
dubbo.application.name=consumer-user

#配置zookeeper地址，这里的zookeeper是在虚拟机中docker装的
dubbo.registry.address=zookeeper://192.168.88.132:2181

• 包括接口目录也是正确的，所以错误最终被定位在调用者上，也就是：

import jdk.nashorn.internal.ir.annotations.Reference;
import org.springframework.stereotype.Service;

/**
 * Created by CHEN on 2019/7/18.
 */
@Service
public class UserService {

    //  @Reference远程调用，通过全类名匹配的方式
    @Reference
    TicketService ticketService;


    public String hello(){

        String ticket = ticketService.getTicket();
        System.out.println(ticket);
        return ticket;
    }

}

• 仔细观察，发现流程没大问题，再看注解，@Service调用的时Spring包，这没问题，@Reference这里，调用的是JDK的包，瞬间就发现自己有点蠢，用Dubbo的注解竟然调JDK的包。。。

解决

• 方案很明确，把包换成Dubbo的包：

import com.alibaba.dubbo.config.annotation.Reference;

• 运行结果是：
  
  

• Dubbo+zookeeper的入门使用流程:
• https://www.jianshu.com/p/944284c80479