如何强制 Vaadin 客户端引擎重试向服务器发送请求？

我目前正在试验 Vaadin Java 框架，我注意到客户端引擎不会重试向服务器发送请求。当移动互联网网络较弱或不一致时，最好继续重试发送请求而不是放弃。

有谁知道如何在 Vaadin 实现这一目标？

扩展 ApplicationConnection 并覆盖 doAjaxRequest 应该足以实现您想要做的事情。像这样的事情：

public class MyApplicationConnection extends ApplicationConnection {

    private final Logger logger = Logger
            .getLogger(MyApplicationConnection.class.getName());

    @Override
    protected void doAjaxRequest(final String uri, final JSONObject payload,
            final RequestCallback requestCallback) throws RequestException {
        // wrap the original request callback handle the retries
        RequestCallback myRequestCallback = new RequestCallback() {

            private int retries = 3;

            @Override
            public void onResponseReceived(Request request, Response response) {
                int status = response.getStatusCode();
                if (status / 100 == 2) { // 2xx Successful
                    requestCallback.onResponseReceived(request, response);
                } else {
                    handleError(request, response, null);
                }
            }

            @Override
            public void onError(Request request, Throwable exception) {
                handleError(request, null, exception);
            }

            private void handleError(Request request, Response response,
                    Throwable exception) {
                if (retries == 0) {
                    logger.info("Ajax request failed.");
                    if (response == null) {
                        requestCallback.onError(request, exception);
                    } else {
                        requestCallback.onResponseReceived(request, response);
                    }
                } else {
                    try {
                        logger.info("Ajax request failed, retrying " + retries
                                + " more times.");
                        retries--;
                        MyApplicationConnection.super.doAjaxRequest(uri,
                                payload, this);
                    } catch (RequestException e) {
                        // something went wrong in the ajax send() call, so no
                        // point in retrying
                        logger.warning("Sending Ajax request failed. Cause: "
                                + e.getMessage());
                        requestCallback.onError(request, exception);
                    }
                }
            }
        };
        super.doAjaxRequest(uri, payload, myRequestCallback);
    }
}

在您的 *.gwt.xml 文件中：

<replace-with class="com.example.client.MyApplicationConnection">
    <when-type-is class="com.vaadin.client.ApplicationConnection"/>
</replace-with>

您可能还想在handleError方法中添加一个Timer或其他东西，这样当网络中断时，请求将等待一段时间才能恢复。不过，这应该是相当微不足道的。