【发布时间】：2020-02-27 16:31:06
【问题描述】：
当我使用 Java 8、Tomcat 8、Netbeans 8 运行 Web 应用程序时，它运行得非常好。使用 Netbeans 11 运行相同的应用程序，即使在 Netbeans 11 中仍然是 Java 8、Tomcat 8，也会出现以下错误。
这是 tomcat 错误日志。
Mar 05, 2020 9:30:40 AM org.apache.catalina.core.StandardContext filterStart
SEVERE: Exception starting filter DatabaseCheckFilter
java.lang.RuntimeException:
at filters.DatabaseCheckFilter.<init>(DatabaseCheckFilter.java:1)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at java.lang.Class.newInstance(Class.java:442)
at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:275)
at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:424)
at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:115)
at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4072)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4726)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:799)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:779)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:601)
at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:675)
at org.apache.catalina.startup.HostConfig.deployDescriptors(HostConfig.java:601)
at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:502)
at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1317)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:324)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:142)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1065)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:840)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1057)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:463)
at org.apache.catalina.core.StandardService.start(StandardService.java:525)
at org.apache.catalina.core.StandardServer.start(StandardServer.java:754)
at org.apache.catalina.startup.Catalina.start(Catalina.java:595)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:289)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:414)
类的代码是
package filters;
import dataaccesslayer.DatabaseCheck;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import utilities.exceptions.ExceptionLogger;
public class DatabaseCheckFilter implements Filter {
// The filter configuration object we are associated with. If
// this value is null, this filter instance is not currently
// configured.
private FilterConfig filterConfig = null;
public DatabaseCheckFilter() {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException {
boolean databaseError = false;
try {
DatabaseCheck check = new DatabaseCheck();
databaseError = check.Check(response);
if (databaseError == true) {
RequestDispatcher fd=request.getRequestDispatcher("/error/unavailable.jsp");
fd.forward(request,response);
}
else {
chain.doFilter(request, response);
}
} catch (Exception exception) {
ExceptionLogger.logException(exception);
}
}
public FilterConfig getFilterConfig() {
return (this.filterConfig);
}
public void setFilterConfig(FilterConfig filterConfig) {
this.filterConfig = filterConfig;
}
public void destroy() {
}
public void init(FilterConfig filterConfig) {
this.filterConfig = filterConfig;
}
}
web.xml 的摘录是
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
<filter>
<filter-name>UserInfoFilter</filter-name>
<filter-class>filters.UserInfoFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>UserInfoFilter</filter-name>
<url-pattern>/scheduler.jsp</url-pattern>
</filter-mapping>
<filter>
<filter-name>DatabaseCheckFilter</filter-name>
<filter-class>filters.DatabaseCheckFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>DatabaseCheckFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<servlet>
【问题讨论】：
-
您确定 stacktrace 不会以“Caused by:”继续，显示它失败的真正原因？ --- 另外，你能显示
DatabaseCheckFilter的代码吗？ -
如果没有
DatabaseCheckFilter类的来源，很难说什么，它看起来是你的一个，而不是一个内置的Java 类或一个来自常用库的类。我能想到的最好的猜测是这个类有一个类似于下面的catch块：catch (Exception e) { throw new RuntimeException(e.getMessage()); }，而这个catch块正在捕捉一个通常没有消息的NullPointerException。 -
我添加了完整的堆栈跟踪以及类和 web.xml 文件中的代码
-
请确保您没有将一些非常旧的 servlet-api.jar 与您的 .war 文件一起发送。更好的是：要么使用你最新的 tomcat 发行版中的 servlet-api.jar 来编译你的 web 应用程序，要么使用一些相对现代的版本。
-
我正在使用 Tomcat 8 中包含的 servlet-api.jar 文件