空指针异常

Question

java.lang.NullPointerException at com.opensymphony.xwork2.spring.SpringObjectFactory.getClassInstance(SpringObjectFactory.java:245) at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.verifyResultType(XmlConfigurationProvider.java:608) at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.addResultTypes(XmlConfigurationProvider.java:578) at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.addPackage(XmlConfigurationProvider.java:534) at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.loadPackages(XmlConfigurationProvider.java:295) at org.apache.struts2.config.StrutsXmlConfigurationProvider.loadPackages(StrutsXmlConfigurationProvider.java:112) at com.opensymphony.xwork2.config.impl.DefaultConfiguration.reloadContainer(DefaultConfiguration.java:264) at com.opensymphony.xwork2.config.ConfigurationManager.getConfiguration(ConfigurationManager.java:67) at org.apache.struts2.dispatcher.Dispatcher.getContainer(Dispatcher.java:967) at org.apache.struts2.dispatcher.Dispatcher.init_PreloadConfiguration(Dispatcher.java:435) at org.apache.struts2.dispatcher.Dispatcher.init(Dispatcher.java:479) at org.apache.struts2.dispatcher.ng.InitOperations.initDispatcher(InitOperations.java:74) at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.init(StrutsPrepareAndExecuteFilter.java:57) at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:285) at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:266) at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:108) at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4590) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5233) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:752) at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:728) at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734) at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1144) at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1878) at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745)八月 02, 2017 11:32:02 下午 org.apache.catalina.core.StandardContext filterStart严重: Exception starting filter [struts2]Class: com.opensymphony.xwork2.spring.SpringObjectFactoryFile: SpringObjectFactory.javaMethod: getClassInstance

Answer 1

兄弟，给你个建议，首先你要看报错信息中是否有你自定义的类或者借口，然后找到你的文件检查，空指针或许是传值到后台出现问题，你可以尝试debug运行，检查传值是否有问题

Answer 2

其实空指针异常是最容易避免的。首先你要明白为什么会空指针，空指针是你用null点了，然后会报空指针，比如：a.equals(b)，如果a是null则会出现空指针异常，为了避免这种情况，可以先验证a是否为null,也可以将可能出现null放在点号符号前面，可以避免空指针异常，这是个习惯，要是不养成好习惯，这个问题会困扰你的，知道了为什么，下次有意识的去避免就好，久而久之，就不会出现这种意外了。

Answer 3

不懂?

Answer 4

看不出来