在Java中更改标准servlet构造函数
我有以下代码:在Java中更改标准servlet构造函数,java,servlets,web,java-server,Java,Servlets,Web,Java Server,我有以下代码: public BalleServlet() throws SAXException, IOException, ParserConfigurationException, ServletException { super(); ServletContext context = getServletContext(); InputSource xmlFile = new InputSource(context.getResourceAsStream("/WE
public BalleServlet() throws SAXException, IOException, ParserConfigurationException, ServletException {
super();
ServletContext context = getServletContext();
InputSource xmlFile = new InputSource(context.getResourceAsStream("/WEB-INF/balle.xml"));
xd = new XMLDoc(xmlFile);
// TODO Auto-generated constructor stub
}
我以前只有
public BalleServlet() throws SAXException, IOException, ParserConfigurationException, ServletException {
super();
}
这很好地发挥了作用
问题是getServletContext()似乎抛出了一个NullPointerException,我无法完全理解它为什么这样做。我看到许多其他人也在努力解决这个问题,但我还没有能够使用提供的解决方案。这是堆栈跟踪,顺便说一句:
java.lang.NullPointerException
at javax.servlet.GenericServlet.getServletContext(GenericServlet.java:125)
at Martin.Berntsen.BalleServlet.<init>(BalleServlet.java:36)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at java.lang.Class.newInstance0(Class.java:357)
at java.lang.Class.newInstance(Class.java:310)
at org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:138)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1144)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:865)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:136)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:695)
java.lang.NullPointerException
位于javax.servlet.GenericServlet.getServletContext(GenericServlet.java:125)
BalleServlet.(BalleServlet.java:36)
位于sun.reflect.NativeConstructorAccessorImpl.newInstance0(本机方法)
位于sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
在sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
位于java.lang.reflect.Constructor.newInstance(Constructor.java:513)
位于java.lang.Class.newInstance0(Class.java:357)
位于java.lang.Class.newInstance(Class.java:310)
位于org.apache.catalina.core.DefaultInstanceManager.newInstance(DefaultInstanceManager.java:138)
位于org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1144)
位于org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:865)
位于org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:136)
位于org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
位于org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
位于org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
位于org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
位于org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
位于org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
位于org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
位于org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
位于org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
位于org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
位于java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
位于java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
运行(Thread.java:695)
此代码修复了它:
public void init(ServletConfig config) throws ServletException {
super.init(config);
ServletContext context = getServletContext();
InputSource xmlFile = new InputSource(context.getResourceAsStream("/WEB-INF/balle.xml"));
try {
xd = new XMLDoc(xmlFile);
} catch (Exception e) {
System.out.println("Something wrong happened");
}
}
这是由重写init(ServletContext上下文)而不调用super.init(context)引起的。是否重写了init()函数?请使用
init
方法。这就是为什么。你能给我一个关于如何做的简短片段吗?