在portlet .jsp页面中，我连接一个applet，然后抛出异常

Question

In portlet's .jsp page I connect an applet, and after this it throws Exception Portlet system is Liferay

"'Name of portlet' is temporarily unavailable." shows on the page.

html/jsp code for applet:

<APPLET name="SignApplet" mayscript code="SignApplet.class" 
archive="<%=renderResponse.encodeURL(renderRequest.getContextPath() + "/lib/SignApplet.jar")%>, 
<%=renderResponse.encodeURL(renderRequest.getContextPath() + "/lib/crypto.tsp.jar")%>, 
<%=renderResponse.encodeURL(renderRequest.getContextPath() + "/lib/crypto.gammaprov.jar")%>"
height=500 width=500 style="display:none;">
    <PARAM NAME="file" VALUE="<%
    byte[] array = (byte[])session.getAttribute("downloadedFile");
    out.print(new String(array));
           %>" />
</APPLET>

jsp's name is LoadXLS. Here is log:

ApplicationDispatcher[/ExecutePortlet] PWC1231: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
    at java.lang.String.<init>(String.java:602)
    at org.apache.jsp.WEB_002dINF.jsp.LoadXLS_jsp._jspService(LoadXLS_jsp.java:232)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:403)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:492)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:378)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1539)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterChain.doFilter(InvokerFilterChain.java:72)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterChain.doFilter(InvokerFilterChain.java:113)
...

04:18:44,421 ERROR [PortletRequestDispatcherImpl:137] org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.JasperException: java.lang.NullPointerException
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:492)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:378)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1539)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterChain.doFilter(InvokerFilterChain.java:72)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterChain.doFilter(InvokerFilterChain.java:113)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilter.doFilter(InvokerFilter.java:70)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
    at org.apache.catalina.core.ApplicationDispatcher.doInvoke(ApplicationDispatcher.java:785)
...


04:18:44,421 ERROR [PortletServlet:97] javax.portlet.PortletException: org.apache.jasper.JasperException: java.lang.NullPointerException
javax.portlet.PortletException: org.apache.jasper.JasperException: java.lang.NullPointerException
    at com.liferay.portlet.PortletRequestDispatcherImpl.include(PortletRequestDispatcherImpl.java:139)
    at com.test.ExecutePortlet.doView(ExecutePortlet.java:249)
    at javax.portlet.GenericPortlet.doDispatch(GenericPortlet.java:328)
    at javax.portlet.GenericPortlet.render(GenericPortlet.java:233)
    at com.liferay.portlet.FilterChainImpl.doFilter(FilterChainImpl.java:100)
    at com.liferay.portal.kernel.portlet.PortletFilterUtil.doFilter(PortletFilterUtil.java:64)
    at com.liferay.portal.kernel.servlet.PortletServlet.service(PortletServlet.java:93)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1539)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
    at com.liferay.portal.kernel.servlet.filters.invoker.InvokerFilterChain.doFilter(InvokerFilterChain.java:72)
...


ApplicationDispatcher[/ExecutePortlet] PWC1231: Servlet.service() for servlet ExecutePortlet Servlet threw exception
javax.portlet.PortletException: org.apache.jasper.JasperException: java.lang.NullPointerException
    at com.liferay.portlet.PortletRequestDispatcherImpl.include(PortletRequestDispatcherImpl.java:139)
    at com.test.ExecutePortlet.doView(ExecutePortlet.java:249)
    at javax.portlet.GenericPortlet.doDispatch(GenericPortlet.java:328)
    at javax.portlet.GenericPortlet.render(GenericPortlet.java:233)
    at com.liferay.portlet.FilterChainImpl.doFilter(FilterChainImpl.java:100)
    at com.liferay.portal.kernel.portlet.PortletFilterUtil.doFilter(PortletFilterUtil.java:64)
    at com.liferay.portal.kernel.servlet.PortletServlet.service(PortletServlet.java:93)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1539)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
...

04:18:44,437 ERROR [render_portlet_jsp:154] java.lang.NullPointerException
    at java.lang.String.<init>(String.java:602)
    at org.apache.jsp.WEB_002dINF.jsp.LoadXLS_jsp._jspService(LoadXLS_jsp.java:232)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:111)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:403)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:492)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:378)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
...

Answer 1

From the stacktrace it seems you're using tomcat - a nice way to find the actual location of that NullpointerException in Tomcat is to go to the intermediary code that the JSP-Compiler generates, typically in tomcat's work folder - go to tomcat/work/Catalina/localhost/your-web-app-name/org/apache/jsp/... and locate the Java code generated from your JSP in there (from the stacktrace, it's named LoadXLS_jsp.java. ("Catalina/localhost" is the default folder - might be different in your setup)

The stacktrace says, that the NullpointerException occurs in line 232 ( at org.apache.jsp.WEB_002dINF.jsp.LoadXLS_jsp._jspService(LoadXLS_jsp.java:232) ) - while the whole file is machine-generated and not well readable, it should be quite simple to map it back to the original JSP.

My bet is - as dragon66 says in the comment to your question - session.getAttribute("downloadedFile") is null, thus the constructor that you use in out.print(new String(array)); gets a null value passed. The line at java.lang.String.<init>(String.java:602) tells you that the String constructor is where the NullpointerException is caused, but the next line - eg the calling method - tells you where the string constructor is called.