JDK17 Http Request 异步处理 源码刨析

为什么可以异步？

#调用起始源码
// 3. 发送异步请求并处理响应
CompletableFuture future = client.sendAsync(
request,
HttpResponse.BodyHandlers.ofString() // 响应体转为字符串
).thenApply(response -> {
// 状态码检查（非200系列抛出异常）
if (response.statusCode() < 200 || response.statusCode() >= 300) {
throw new RuntimeException(“HTTP错误: " + response.statusCode());
}
return response;
}).thenApply(HttpResponse::body) // 提取响应体3
.thenAccept(body -> {
// 4. 打印响应结果（截取前100字符示例）
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
System.out.println(”\n▼ 响应内容 (前100字符):\n"
+ body.substring(0, Math.min(100, body.length())) + “…”);
}).exceptionally(e -> {
// 5. 异常处理（提取根本原因）
Throwable root = e;
while (root.getCause() != null) root = root.getCause();
System.err.println("❌ 请求失败: " + root.getMessage());
return null;
});

#client.sendAsync

public CompletableFuture<T> whenComplete(
    BiConsumer<? super T, ? super Throwable> action) {
    return uniWhenCompleteStage(null, action);
}

@Override
public CompletableFuture<HttpResponse>
sendAsync(HttpRequest userRequest, BodyHandler responseHandler)
{
return sendAsync(userRequest, responseHandler, null);
}

@Override
public <T> CompletableFuture<HttpResponse<T>>
sendAsync(HttpRequest userRequest,
          BodyHandler<T> responseHandler,
          PushPromiseHandler<T> pushPromiseHandler) {
    return sendAsync(userRequest, responseHandler, pushPromiseHandler, delegatingExecutor.delegate);
}

#关键在这里
@SuppressWarnings(“removal”)
private CompletableFuture<HttpResponse>
sendAsync(HttpRequest userRequest,
BodyHandler responseHandler,
PushPromiseHandler pushPromiseHandler,
Executor exchangeExecutor) {

    Objects.requireNonNull(userRequest);
    Objects.requireNonNull(responseHandler);



        MultiExchange<T> mex = new MultiExchange<>(userRequest,
                                                        requestImpl,
                                                        this,
                                                        responseHandler,
                                                        pushPromiseHandler,
                                                        acc);
        CompletableFuture<HttpResponse<T>> res =
                mex.responseAsync(executor).whenComplete((b,t) -> unreference());
        if (DEBUGELAPSED) {
            res = res.whenComplete(
                    (b,t) -> debugCompleted("ClientImpl (async)", start, userRequest));
        }