抛出IOException，由于某种原因，它是不可能捕获的 . 看看下面的代码 . 堆栈跟踪表示在调用“apply”-method时抛出IOException . 但是，异常不会被catch子句捕获 . 当我尝试捕获IOException时，Eclipse抱怨说：“IOException的无法访问的catch块 . 这个异常永远不会从try语句体中抛出”
为什么会这样？
码：
try {
action.apply();
}
catch (Exception e) {
System.out.println("Fail");
}
这是堆栈跟踪：
java.io.IOException: Unable to download JavaScript from 'somesite' (status 404).
at com.gargoylesoftware.htmlunit.html.HtmlPage.loadJavaScriptFromUrl(HtmlPage.java:1023)
at com.gargoylesoftware.htmlunit.html.HtmlPage.loadExternalJavaScriptFile(HtmlPage.java:967)
at com.gargoylesoftware.htmlunit.html.HtmlScript.executeScriptIfNeeded(HtmlScript.java:353)
at com.gargoylesoftware.htmlunit.html.HtmlScript$1.execute(HtmlScript.java:225)
at com.gargoylesoftware.htmlunit.html.HtmlScript.onAllChildrenAddedToPage(HtmlScript.java:235)
at com.gargoylesoftware.htmlunit.html.HTMLParser$HtmlUnitDOMBuilder.endElement(HTMLParser.java:718)
at org.apache.xerces.parsers.AbstractSAXParser.endElement(Unknown Source)
at com.gargoylesoftware.htmlunit.html.HTMLParser$HtmlUnitDOMBuilder.endElement(HTMLParser.java:676)
at org.cyberneko.html.HTMLTagBalancer.callEndElement(HTMLTagBalancer.java:1136)
at org.cyberneko.html.HTMLTagBalancer.endElement(HTMLTagBalancer.java:1038)
at org.cyberneko.html.filters.DefaultFilter.endElement(DefaultFilter.java:206)
at org.cyberneko.html.filters.NamespaceBinder.endElement(NamespaceBinder.java:329)
at org.cyberneko.html.HTMLScanner$ContentScanner.scanEndElement(HTMLScanner.java:2999)
at org.cyberneko.html.HTMLScanner$ContentScanner.scan(HTMLScanner.java:1991)
at org.cyberneko.html.HTMLScanner.scanDocument(HTMLScanner.java:895)
at org.cyberneko.html.HTMLConfiguration.parse(HTMLConfiguration.java:499)
at org.cyberneko.html.HTMLConfiguration.parse(HTMLConfiguration.java:452)
at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
at com.gargoylesoftware.htmlunit.html.HTMLParser$HtmlUnitDOMBuilder.parse(HTMLParser.java:896)
at com.gargoylesoftware.htmlunit.html.HTMLParser.parse(HTMLParser.java:350)
at com.gargoylesoftware.htmlunit.html.HTMLParser.parseHtml(HTMLParser.java:304)
at com.gargoylesoftware.htmlunit.DefaultPageCreator.createHtmlPage(DefaultPageCreator.java:134)
at com.gargoylesoftware.htmlunit.DefaultPageCreator.createPage(DefaultPageCreator.java:101)
at com.gargoylesoftware.htmlunit.WebClient.loadWebResponseInto(WebClient.java:420)
at com.gargoylesoftware.htmlunit.WebClient.getPage(WebClient.java:303)
at com.gargoylesoftware.htmlunit.WebClient.getPage(WebClient.java:360)
at org.openqa.selenium.htmlunit.HtmlUnitDriver.get(HtmlUnitDriver.java:228)
at org.openqa.selenium.htmlunit.HtmlUnitDriver.get(HtmlUnitDriver.java:216)
at org.openqa.selenium.internal.seleniumemulation.Open.handleSeleneseCommand(Open.java:36)
at org.openqa.selenium.internal.seleniumemulation.Open.handleSeleneseCommand(Open.java:22)
at org.openqa.selenium.internal.seleniumemulation.SeleneseCommand.apply(SeleneseCommand.java:33)
at Action.runSeleniumAction(Action.java:235)
at SessionDriver.runSession(SessionDriver.java:192)
at SessionDriver.run(SessionDriver.java:123)
4 回答
apply（）方法完全处理异常并且不重新抛出异常 . 如果确实如此，它将被标记为“public void apply（）throws IOException” .
编译器会对此发出警告，因为如果不这样做会导致错误处理不准确 .
是的，apply（）方法本身不会抛出该异常 . 应用方法（）中的其他内容是，并且某些东西打印完整的堆栈跟踪而不是您已经决定的“失败”消息在某种程度上更好 .
正如您在stacktrace中看到的那样，您的代码丢失了，因此您无法捕获异常 . 我的猜测是
SessionDriver.run()是从另一个线程调用的 .你试过Selenium-RC吗？它应该能够捕获这些错误并将它们传递给测试用例 .
您正在使用eclipse - 最简单的方法是获取异常源是在调试模式下运行应用程序并在
java.io.IOException上设置断点 . 因此，只要在正在运行的VM中的某处抛出此异常，eclipse就会停止应用程序并向您显示线程，类和代码行（如果可用） .