我正在敲打为什么我的自定义taglib功能不起作用.该示例使用Math.cos和Math.sin.

这是班级：

package foo.tags;

public class Math {

public java.lang.Double cos(java.lang.Double value) {

return java.lang.Math.cos(value);

}

public java.lang.Double sin(java.lang.Double value) {

return java.lang.Math.sin(value);

}

}

这是.tld文件：

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"

version="2.0">

2.0

/WEB-INF/tags/math.tld

cos

foo.tags.Math

java.lang.Double cos(java.lang.Double)

sin

foo.tags.Math

java.lang.Double sin(java.lang.Double)

调用代码的重要摘要：

${math:sin(180)}

我在math：sin(180)的行上得到一个空指针异常.有谁看到我做错了什么？如果需要更多信息,请告诉我,但异常本身并不是非常有用.

编辑

这是堆栈跟踪：

Mar 17, 2013 2:27:14 PM org.apache.catalina.core.StandardWrapperValve invoke

SEVERE: Servlet.service() for servlet [Foo] in context with path [/Foo] threw exception [org.apache.jasper.JasperException: An exception occurred processing JSP page /WEB-INF/jsp/svg/clock1.jsp at line 10

[OTHER LINES REDACTED]

10: ${math:sin(180)}

[OTHER LINES REDACTED]

Stacktrace:] with root cause

java.lang.NullPointerException

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

at java.lang.reflect.Method.invoke(Unknown Source)

at org.apache.el.parser.AstFunction.getValue(AstFunction.java:112)

at org.apache.el.parser.AstMult.getValue(AstMult.java:39)

at org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:189)

at org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:985)

at org.apache.jsp.

at org.apache.jsp.

at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)

at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)

at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:684)

at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:593)

at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:530)

at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:954)

at org.apache.jsp.

at org.apache.jsp.

at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)

at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)

at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:684)

at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:471)

at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:402)

at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:329)

at org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:238)

at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:250)

at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1047)

at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:817)

at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)

at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644)

at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:560)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

at Foo.page.filter.SimulationProgressFilter.doFilter(SimulationProgressFilter.java:88)

at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237)

at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

at fOO.page.filter.CurrentSessionStateFilter.doFilter(CurrentSessionStateFilter.java:119)

at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237)

at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169)

at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)

at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)

at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:999)

at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:565)

at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:309)

at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)

at java.lang.Thread.run(Unknown Source)