Java HttpHandler 等待 CompletableFuture答案

【问题标题】：Java HttpHandler waiting for CompletableFutureJava HttpHandler 等待 CompletableFuture
【发布时间】：2021-07-01 20:38:33
【问题描述】：

我得到以下代码

public WebClient extends WebSocketClient{
...
    private StringBuilder response;
    
    public WebClient(StringBuilder response){
        this.response = response;
    }
    
    public void onMessage(ByteBuffer bytes
    
        CompletableFuture<Void> completableFuture  = CompletableFuture.
            supplyAsync(this::fsupplyAsync)
            .thenApply(this::fThenApply)
            }).exceptionally(t -> {
                return fexceptionally(t);
            }).thenAccept(x -> {
                fthenAccept(x);
            });

        completableFuture.get();
        this.setDone(true);
    
    }
    
...
}

public class handler implements HttpHandler { 
...

    public void handle(HttpExchange httpExchange) throws IOException {
        
        ByteBuffer message;
        ...
        StringBuilder response = new StringBuilder();
        
        WebClient client = new WebClient(response);
        
        client.send(message);
        
        while(!client.isDone()){
            Thread.sleep(2000);
        }
        
        httpExchange.getResponseHeaders().add("Access-Control-Allow-Origin", "*");
        final byte[] responseBytes = response.getBytes();
        httpExchange.sendResponseHeaders(200, responseBytes.length);
        outputStream.write(responseBytes);
    }
    
... 
}

我的想法是我打电话给另一个客户获取一些信息，等待他的响应，然后呈现已经接收和处理的数据。

但我正在寻找一种方法来避免需要 Thread.sleep 以避免系统中其他代码可能出现的问题。

在我将结果写入处理程序之前，是否有另一种方法可以等待 WebClient 中类似的未来调用的结果？

【问题讨论】：

标签： java websocket thread-safety httphandler

【解决方案1】：

我能够使用同步并等待我在客户端创建的对象来做到这一点。如您所见，我在客户端上的对象上调用同步并将其置于等待状态。然后在客户端完成后我调用 notifyall。

    public WebClient extends WebSocketClient{
...
    private StringBuilder response;

    Object waitUntlDone = new Object();

    
    public WebClient(StringBuilder response){
        this.response = response;
    }
    
    public void onMessage(ByteBuffer bytes
    
        CompletableFuture<Void> completableFuture  = CompletableFuture.
            supplyAsync(this::fsupplyAsync)
            .thenApply(this::fThenApply)
            }).exceptionally(t -> {
                return fexceptionally(t);
            }).thenAccept(x -> {
                fthenAccept(x);
            });

        completableFuture.get();
        this.setDone(true);
    
        synchronized (this.waitUntlDone){
            this.waitUntlDone.notifyAll();
        }
    }
    
...
}

public class handler implements HttpHandler { 
...

    public void handle(HttpExchange httpExchange) throws IOException {
        
        ByteBuffer message;
        ...
        StringBuilder response = new StringBuilder();
        
        WebClient client = new WebClient(response);
        
        client.send(message);
        
        synchronized (client.waitUntlDone){
            while (!client.isDone()) {
                client.waitUntlDone.wait(2000);
            }
        }
        
        httpExchange.getResponseHeaders().add("Access-Control-Allow-Origin", "*");
        final byte[] responseBytes = response.getBytes();
        httpExchange.sendResponseHeaders(200, responseBytes.length);
        outputStream.write(responseBytes);
    }
    
... 
}

【讨论】：