java.lang.NullPointerException org.apache.jsp.WEB_002dINF.pages.imagecheck.test_jsp._jspInit(test_jsp.java:22)的原因

HTTP Status 500 -
type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: java.lang.NullPointerException
	org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:538)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:370)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:238)
	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:250)
	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1047)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:817)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:669)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:574)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:70)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
root cause

java.lang.NullPointerException
	org.apache.jsp.WEB_002dINF.pages.imagecheck.test_jsp._jspInit(test_jsp.java:22)
	org.apache.jasper.runtime.HttpJspBase.init(HttpJspBase.java:52)
	org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:164)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:340)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:238)
	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:250)
	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1047)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:817)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:669)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:574)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:70)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.35 logs

　　

出現這個的原因是項目lib下面的jsp-api.jar和tomcat 下的jsp-api.jar有沖突導致的。因為項目里用到的library里包含了jsp-api.jar 和servlet-api.jar兩個包，然后通過myeclips發布的時候將會這兩個包復制到webroot/lib下去了，而tomcat的lib下面本來就有這兩個包，導致了沖突，這就是這個錯誤產生的主要原因。

解決方案是，編輯自定義user library,將user library設置為 system library,這樣在通過myeclips發布時就不會自動拷貝這兩個JAR包。

或者通過在tomcat_home/conf/catalina/下面加一個配置文件指定webroot來發布項目，避免不必要的自動拷貝.

以前都是用后一種方式發布的項目，今天突然測試一個代碼，然后偷懶用myeclipse上的發布按鈕發布到tomcat的webapps目錄下的發布方式。結果就出現了今天的這個問題，還奇怪的怎么好好的代碼就不好用了，整了好幾個小時，各種百思不得其解啊。整半天原來是JAR包沖突導致的。

上面是我百度的解決方法，我的解決方法很簡單，就直接的將我們項目中的jsp-api.jar和jsp-api去掉就可以了。