Selenium：http://localhost:4444/wd/hub 返回 NullPointerException，我做错了什么

Question

假设：尝试在 C# 中通过此代码使用 RemoteWebDriver。

var url = new Uri("http://localhost:4444/wd/hub");
var wd = new RemoteWebDriver(url, DesiredCapabilities.Chrome());

上面的新 RemoteWebDriver 代码在超时之前不会响应...

更多详情

我已经使用 Selenium 服务器的这些参数启动了我的 Hub：

-jar "C:\SomeFolder\selenium-server-standalone-3.0.1.jar" -port 4444 -role hub

并使用这些参数注册了一个节点..

-jar "C:\SomeFolder\selenium-server-standalone-3.0.1.jar" -role node -hub http://localhost:4444/grid/register -port 9662 

调试

如果我在启动 Hub 后输入这个 URL，它表明有一个已注册的节点：

http://location:4444/grid/console

但是在启动 Hub 后输入这个 url 时

http://localhost:4444/wd/hub

浏览器显示这个指向 ExternalSessionKey.java 的 java (json) 堆栈跟踪

{"status":13,"value":{"class":"java.lang.NullPointerException","stackTrace":[{"fileName":"ExternalSessionKey.java","className":"org.openqa.grid.internal.ExternalSessionKey","methodName":"fromWebDriverRequest","lineNumber":77},{"fileName":"WebDriverRequest.java","className":"org.openqa.grid.web.servlet.handler.WebDriverRequest","methodName":"extractSession","lineNumber":62},{"fileName":"RequestHandler.java","className":"org.openqa.grid.web.servlet.handler.RequestHandler","methodName":"getSession","lineNumber":231},{"fileName":"RequestHandler.java","className":"org.openqa.grid.web.servlet.handler.RequestHandler","methodName":"process","lineNumber":118},{"fileName":"DriverServlet.java","className":"org.openqa.grid.web.servlet.DriverServlet","methodName":"process","lineNumber":83},{"fileName":"DriverServlet.java","className":"org.openqa.grid.web.servlet.DriverServlet","methodName":"doGet","lineNumber":61},{"fileName":"HttpServlet.java","className":"javax.servlet.http.HttpServlet","methodName":"service","lineNumber":687},{"fileName":"HttpServlet.java","className":"javax.servlet.http.HttpServlet","methodName":"service","lineNumber":790},{"fileName":"ServletHolder.java","className":"org.seleniumhq.jetty9.servlet.ServletHolder","methodName":"handle","lineNumber":808},{"fileName":"ServletHandler.java","className":"org.seleniumhq.jetty9.servlet.ServletHandler","methodName":"doHandle","lineNumber":587},{"fileName":"SessionHandler.java","className":"org.seleniumhq.jetty9.server.session.SessionHandler","methodName":"doHandle","lineNumber":221},{"fileName":"ContextHandler.java","className":"org.seleniumhq.jetty9.server.handler.ContextHandler","methodName":"doHandle","lineNumber":1127},{"fileName":"ServletHandler.java","className":"org.seleniumhq.jetty9.servlet.ServletHandler","methodName":"doScope","lineNumber":515},{"fileName":"SessionHandler.java","className":"org.seleniumhq.jetty9.server.session.SessionHandler","methodName":"doScope","lineNumber":185},{"fileName":"ContextHandler.java","className":"org.seleniumhq.jetty9.server.handler.ContextHandler","methodName":"doScope","lineNumber":1061},{"fileName":"ScopedHandler.java","className":"org.seleniumhq.jetty9.server.handler.ScopedHandler","methodName":"handle","lineNumber":141},{"fileName":"HandlerWrapper.java","className":"org.seleniumhq.jetty9.server.handler.HandlerWrapper","methodName":"handle","lineNumber":97},{"fileName":"Server.java","className":"org.seleniumhq.jetty9.server.Server","methodName":"handle","lineNumber":499},{"fileName":"HttpChannel.java","className":"org.seleniumhq.jetty9.server.HttpChannel","methodName":"handle","lineNumber":310},{"fileName":"HttpConnection.java","className":"org.seleniumhq.jetty9.server.HttpConnection","methodName":"onFillable","lineNumber":257},{"fileName":"AbstractConnection.java","className":"org.seleniumhq.jetty9.io.AbstractConnection$2","methodName":"run","lineNumber":540},{"fileName":"QueuedThreadPool.java","className":"org.seleniumhq.jetty9.util.thread.QueuedThreadPool","methodName":"runJob","lineNumber":635},{"fileName":"QueuedThreadPool.java","className":"org.seleniumhq.jetty9.util.thread.QueuedThreadPool$3","methodName":"run","lineNumber":555},{"className":"java.lang.Thread","methodName":"run","lineNumber":-1}]}}

任何人都可以为我解释堆栈跟踪，以及如何使其正常工作？

谢谢！

Answer 1

你没有错。

URL http://localhost:4444/wd/hub 的设计使其期望您的操作有一个 PAYLOAD。由于您没有提供所需的有效负载，您会看到 NullPointerException。

不应在浏览器中打开此 URL。它意味着通过 Http 操作使用符合 Selenium w3c spec 的适当有效负载来使用

Answer 2

问题的症状是此代码中的连接超时异常。

var url = new Uri("http://localhost:4444/wd/hub");
var wd = new RemoteWebDriver(url, DesiredCapabilities.Chrome());

根本原因

这是因为，在我的调试会话期间；我在此声明之前结束了程序：

wd.Quit();

因为我的集线器只配置了一个节点，所以之前的调试会话在集线器上仍然有一个孤立的会话。重新启动集线器解决了这个问题，但也可以根据需要配置任意数量的节点。

集线器逻辑的另一个错误是孤立节点没有在配置中设置的适当超时时间内被清理。这会导致孤立节点保持活动的时间比超时建议的时间长得多...查看配置选项以亲自查看。应该有一个不活动计时器，显示“如果 x 秒内没有活动”会终止会话。

一个解决方案

确保（至少）配置集线器以允许在调试解决方案时需要更多节点。