使用selenium遇到java.lang.NoSuchMethodError: org.apache.xpath.XPathContext，排查

初试selenium webdriver，运行小程序，抛如下错误：

java.lang.NoSuchMethodError: org.apache.xpath.XPathContext.<init>(Z)V
     at org.apache.xpath.jaxp.XPathExpressionImpl.eval(XPathExpressionImpl.java:115)
     at org.apache.xpath.jaxp.XPathExpressionImpl.eval(XPathExpressionImpl.java:99)
     at org.apache.xpath.jaxp.XPathExpressionImpl.evaluate(XPathExpressionImpl.java:184)
     at org.openqa.selenium.firefox.internal.FileExtension.readIdFromInstallRdf(FileExtension.java:120)
     at org.openqa.selenium.firefox.internal.FileExtension.writeTo(FileExtension.java:60)
     at org.openqa.selenium.firefox.internal.ClasspathExtension.writeTo(ClasspathExtension.java:63)
     at org.openqa.selenium.firefox.FirefoxProfile.installExtensions(FirefoxProfile.java:416)
     at org.openqa.selenium.firefox.FirefoxProfile.layoutOnDisk(FirefoxProfile.java:394)
     at org.openqa.selenium.firefox.internal.NewProfileExtensionConnection.start(NewProfileExtensionConnection.java:89)
     at org.openqa.selenium.firefox.FirefoxDriver.startClient(FirefoxDriver.java:246)

google后检索到：https://code.google.com/p/selenium/issues/detail?id=2837

xalan.jar冲突导致，排除此包后ok.

注意下selenium的包引用，如果尝试用webdriver +java去运行用例，并不需要selenium-server这个jar包。根据官网文档，当使用Selenium-Grid将用例在多个机器或者虚拟机上执行， or 远程执行用例等情况才使用。

练习时可以直接引入 selenium-java 即可。如果是maven工程，直接在pom.xml中引入如下依赖即可（可在官网查询最新版本的）

<dependency>
  <groupId>org.seleniumhq.selenium</groupId>
  <artifactId>selenium-java</artifactId>
  <version>2.42.2</version>
</dependency>