如何在异步httpclient java 11中将多个异步get请求的响应写入单个文件？

问题描述

我可以像这样在Java 11中使用httpclient下载单个媒体文件

public class Httptest {
    
    private static HttpClient client = HttpClient.newBuilder().build();
            
    public static void main(String[] args) throws Exception {
        File fts = new File("P:/sample.ts");  //Destination of downloaded file
        fts.createNewFile();
        URI url = new URI("File url here"); //File Url
        
        HttpRequest request = HttpRequest.newBuilder()   //Creating HttpRequest using Builder class
                .GET()
                .uri(url)
                .build();
        Path file = Path.of("P:/samp.ts");
        //BodyHandlers class has methods to handle the response body
        // In this case,save it as a file (BodyHandlers.ofFile())
        HttpResponse<Path> response = client.send(request,BodyHandlers.ofFile(file)); 
    }
}

上面的代码段从URL下载.ts文件。并且已正确下载。

现在，我有网址列表List<URI> urls。我对网址列表进行了异步调用，并通过添加Executor service确保并发调用。 我受困的地方是如何将响应列表写入单个文件。

我到目前为止编写的代码：

public class httptest{
    
   // Concurrent requests are made in 4 threads
   private static ExecutorService executorService = Executors.newFixedThreadPool(4); 

   //HttpClient built along with executorservice
   private static HttpClient client = HttpClient.newBuilder() 
            .executor(executorService)
            .build();
    
   public static void main(String[] args) throws Exception{
        File fts = new File("P:/Spyder_directory/sample.ts");
        fts.createNewFile();
        List<URI> urls = Arrays.asList(
                         new URI("Url of file 1"),new URI("Url of file 2"),new URI("Url of file 3"),new URI("Url of file 4"),new URI("Url of file 5"));
        
        
        List<HttpRequest> requests = urls.stream()
                .map(HttpRequest::newBuilder)
                .map(requestBuilder -> requestBuilder.build())
                .collect(toList());
        Path file = Path.of("P:/Spyder_directory/sample.ts");
        List<CompletableFuture<HttpResponse<Path>>> results = requests.stream()
                .map(individual_req -> client.sendAsync(individual_req,BodyHandlers.ofFile(file)))
                .collect(Collectors.toList());
   }
}

在执行结束时创建的文件sample.ts没有所请求的响应。 如果您了解我的问题的要点，那么谁能为该问题提供替代解决方案。

解决方法

一种可能性是将HttpResponse.BodyHandlers.ofByteArrayConsumer与将字节写入文件的Consumer<Optional<byte[]>>一起使用。这样一来，您可以控制文件的打开方式，从而可以将其追加到现有文件中，而不必每次都创建一个新文件。

请注意，如果这样做，则不应使用sendAsync，因为请求将同时发送，因此也将同时接收到响应。如果您仍要同时发送请求，则需要缓冲响应并在将其记入文件时进行一些同步。