java - 嵌套异常是 java.util.concurrent.ExecutionException

Question

我是 Java 多线程新手，正在尝试使用 Callable 接口(interface)和 Future 类创建一个 Spring 项目。

我正在获取 dynamo 数据库中的所有记录，并且对于每条记录，我都会对外部服务进行多线程调用。

但我收到此错误:

nested exception is java.util.concurrent.ExecutionException: org.springframework.web.client.HttpServerErrorException: 500 null] with root cause

我的代码:

Controller :

@Autowired
public RestTemplate restTemplate;

@Autowired
public MyCallable myCallable;
@GetMapping("/myApp-multithread")
public String getQuoteOnSepThread() throws InterruptedException, ExecutionException {
    System.out.println("#################################################Multi Threaded Post Call######################");
    ExecutorService executor= Executors.newFixedThreadPool(10);
    List<Future<String>> myFutureList= new ArrayList<Future<String>>();
    long startTime=System.currentTimeMillis()/1000;

    Iterable<Customer> customerIterable=repo.findAll();
    List<Customer> customers=new ArrayList<Customer>();
    customerIterable.forEach(customers::add);


    for(Customer c:customers) {

        myCallable.sendCustomerToInterface(c);
        //System.out.println(c);
        Future<String> future= executor.submit(myCallable);
        myFutureList.add(future);

    }

    for(Future<String> fut:myFutureList) {
        fut.get();
    }
    executor.shutdown();

    long timeElapsed= (System.currentTimeMillis()/1000)-startTime;

    System.out.println("->>>>>>>>>>>>>>>Time Elapsed In Multi Threaded Post Call<<<<<<<<<<<<<<<-"+timeElapsed);
    return "Success";

}

MyCallable 类:

public class MyCallable implements Callable<String>{

@Autowired
public RestTemplate restTemplate;

//int index=-1;

Customer c= c= new Customer();;
public void sendCustomerToInterface(Customer cust) {

    c= cust;
}

@Override
public String call() throws Exception {

    System.out.println("Customer no"+ c.getId() +"On thread Number"+Thread.currentThread().getId());
    return restTemplate.postForObject("http://localhost:3000/save", c, String.class);

}

}

谁能帮我解决这个问题

编辑:

带有错误的完整堆栈跟踪:

org.springframework.web.client.HttpServerErrorException: 500 null at org.springframework.web.client.DefaultResponseErrorHandler.handleError(DefaultResponseErrorHandler.java:88) ~[spring-web-4.3.13.RELEASE.jar:4.3.13.RELEASE] at org.springframework.web.client.RestTemplate.handleResponse(RestTemplate.java:707) ~[spring-web-4.3.13.RELEASE.jar:4.3.13.RELEASE] at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:660) ~[spring-web-4.3.13.RELEASE.jar:4.3.13.RELEASE] at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:620) ~[spring-web-4.3.13.RELEASE.jar:4.3.13.RELEASE] at org.springframework.web.client.RestTemplate.postForObject(RestTemplate.java:387) ~[spring-web-4.3.13.RELEASE.jar:4.3.13.RELEASE] at com.OCADemoClient.OCADemoClient.MyCallable.call(MyCallable.java:32) ~[classes/:na] at com.OCADemoClient.OCADemoClient.MyCallable.call(MyCallable.java:1) ~[classes/:na] at java.util.concurrent.FutureTask.run(FutureTask.java:266) ~[na:1.8.0_181] at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) ~[na:1.8.0_181] at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) ~[na:1.8.0_181] at java.lang.Thread.run(Thread.java:748) [na:1.8.0_181]

Answer 1

根据JavaDoc :

Exception thrown when attempting to retrieve the result of a task that aborted by throwing an exception.

问题似乎是对于某些客户来说，调用

    restTemplate.postForObject("http://localhost:3000/save", c, String.class);

导致服务器错误，HTTP 响应代码为“500”

<小时/>

我在阅读您的评论后才注意到:

您只有一个 MyCallable 供所有客户共享。

这不起作用，因为您的 MyCallable 是一个有状态对象(它使用 void sendCustomerToInterface(Customer cust) 存储 Customer 且稍后需要在 call() 方法中检索此特定的 Customer)。

要使其正常工作，您可以像这样重写 MyCallable:

public class MyCallable implements Callable<String>{

    private RestTemplate restTemplate;
    private Customer c;

    public MyCallable(RestTemplate rt, Customer cust) {
        this.restTemplate = rt;
        this.c = cust;
    }

    @Override
    public String call() throws Exception {
        System.out.println("Customer no"+ c.getId() +"On thread Number"+Thread.currentThread().getId());
        return restTemplate.postForObject("http://localhost:3000/save", c, String.class);

    }
}

并在 Controller 中编写

for(Customer c:customers) {

    MyCallable myCallable = new MyCallable(restTemplate, c);
    //System.out.println(c);
    Future<String> future= executor.submit(myCallable);
    myFutureList.add(future);

}

<小时/>

顺便说一句，你的代码效率很低。您可以跳过生成客户列表，只需编写

for (Customer c: repo.findAll()) {
    //...
}