请教:是什么导致Unable to compile class for JSP

我的环境是:Apache 2.0.+Tomcat 5.0.27+ J2SDK 1.4.2,我运行http viewer例子的时候没有出现任何问题,但运行jspviewer例子的时候却出现没有找到javac compiler信息,具体如下:<BR>type Exception report
<br>
<P>message </P>
<P>description The server encountered an internal error () that prevented it from fulfilling this request.</P>
<P>exception </P>
<P>org.apache.jasper.JasperException: Unable to compile class for JSP<BR> org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:97)<BR> org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:346)<BR> org.apache.jasper.compiler.Compiler.generateClass(Compiler.java:414)<BR> org.apache.jasper.compiler.Compiler.compile(Compiler.java:472)<BR> org.apache.jasper.compiler.Compiler.compile(Compiler.java:451)<BR> org.apache.jasper.compiler.Compiler.compile(Compiler.java:439)<BR> org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:511)<BR> org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:295)<BR> org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)<BR> org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)<BR> javax.servlet.http.HttpServlet.service(HttpServlet.java:802)</P>
<P><BR>root cause </P>
<P>Unable to find a javac compiler;<BR>com.sun.tools.javac.Main is not on the classpath.<BR>Perhaps JAVA_HOME does not point to the JDK<BR> org.apache.tools.ant.taskdefs.compilers.CompilerAdapterFactory.getCompiler(CompilerAdapterFactory.java:106)<BR> org.apache.tools.ant.taskdefs.Javac.compile(Javac.java:935)<BR> org.apache.tools.ant.taskdefs.Javac.execute(Javac.java:764)<BR> org.apache.jasper.compiler.Compiler.generateClass(Compiler.java:382)<BR> org.apache.jasper.compiler.Compiler.compile(Compiler.java:472)<BR> org.apache.jasper.compiler.Compiler.compile(Compiler.java:451)<BR> org.apache.jasper.compiler.Compiler.compile(Compiler.java:439)<BR> org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:511)<BR> org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:295)<BR> org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)<BR> org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)<BR> javax.servlet.http.HttpServlet.service(HttpServlet.java:802)<BR>请教各位,该如何解决,谢谢!</P>