记录一些遇见的bug——记录一个使用多线程异步调用openfeign时子线程丢失request请求头导致的空指针异常错误

Posted 2023-03-03 叶不修233

记录一些遇见的bug——记录一个使用多线程异步调用openfeign时子线程丢失request请求头导致的空指针异常错误

• • 1.出现问题的业务逻辑
  • 2.错误日志
  • 3.原因分析
  • 4.解决方案

1.出现问题的业务逻辑

List<MyData> demo()
    //异步往CompletableFuture中存数据
    List<CompletableFuture<MyData>> futures = new ArrayList<>();
    for (int i = 0; i < 10; i++) 
        //开启10个线程异步调用openfeign请求，往CompletableFuture中存方法返回的数据
        futures.add(this.loadData(args));
     
    //从CompletableFuture中取数据
    List<MyData> myDataList = new ArrayList<>();
    for (CompletableFuture<MyData> future : futures) 
        MyData myData = future.get();
        if (myData == null) 
            continue;
        
        myDataList.add(myData);
    
                    
    return myDataList;

                    
                    
CompletableFuture<MyData> loadData(String args)
    return CompletableFuture.supplyAsync(() -> 
        	//异步调用openfeign请求获取数据
            MyData myData = myGetDataClient.getData(args);
            return myData;
    );

2.错误日志

Caused by: java.lang.NullPointerException: null
	at com.flybees.config.FeignConfig.apply(FeignConfig.java:78)
	at feign.SynchronousMethodHandler.targetRequest(SynchronousMethodHandler.java:176)
	at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:101)
	at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:80)
	at feign.hystrix.HystrixInvocationHandler$1.run(HystrixInvocationHandler.java:109)
	at com.netflix.hystrix.HystrixCommand$2.call(HystrixCommand.java:302)
	at com.netflix.hystrix.HystrixCommand$2.call(HystrixCommand.java:298)
	at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:46)
	... 67 common frames omitted

3.原因分析

查看feign配置FeignConfig.java

获取request对象的请求头时报了空指针异常，意思就是主线程中的请求头并没有带过来

@Configuration
public class FeignConfig implements RequestInterceptor 

    @Override
    public void apply(RequestTemplate requestTemplate) 
        /*
         * 获取原线程的request对象的请求头中的token
         * RequestContextHolder.getRequestAttributes()：获取request原始的请求头对象
         * 接口类RequestAttributes不能使用，所以强转为ServletRequestAttributes类型
         */
        ServletRequestAttributes servletRequestAttributes =
            (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        //获取原Request对象
        HttpServletRequest request = servletRequestAttributes.getRequest();
        //把原request的请求头的所有参数都拿出来
        Enumeration<String> headerNames = request.getHeaderNames();
        while (headerNames.hasMoreElements()) 
            //获取每个请求头参数的名字
            String name = headerNames.nextElement();
            //获取值
            String value = request.getHeader(name);
            // 跳过 content-length,用于解决Caused by: feign.RetryableException: too many bytes written executing POST http://xx报错
            if (name.equalsIgnoreCase("content-length"))
                continue;
            
            //放到feign调用对象的request中去
            requestTemplate.header(name, value);
        
    

4.解决方案

在主线程里调用子线程时将request传递过去，并设置子线程的请求头

List<MyData> demo(String args)
    //异步往CompletableFuture中存数据
    List<CompletableFuture<MyData>> futures = new ArrayList<>();
    //获取当前线程（主线程）请求头对象(增)
    RequestAttributes requestAttributes = RequestContextHolder.currentRequestAttributes();
    for (int i = 0; i < 10; i++) 
        //开启10个线程异步调用openfeign请求，往CompletableFuture中存方法返回的数据（改）
        futures.add(this.loadData(args,requestAttributes);
     
    //从CompletableFuture中取数据
    List<MyData> myDataList = new ArrayList<>();
    for (CompletableFuture<MyData> future : futures) 
        MyData myData = future.get();
        if (myData == null) 
            continue;
        
        myDataList.add(myData);
    
                    
    return myDataList;

                    
                    
CompletableFuture<MyData> loadData(String args, RequestAttributes requestAttributes)
    return CompletableFuture.supplyAsync(() -> 
        try 
            //将主线程的request请求头传递到子线程，防止异步时发生子线程request请求头丢失的情况（改）
            RequestContextHolder.setRequestAttributes(requestAttributes);
            //在异步子线程中调用openfeign请求获取数据
            MyData myData = myGetDataClient.getData(args);
            return myData;
         finally 
            //清除子线程请求头信息(增)
            RequestContextHolder.resetRequestAttributes();
        
    );