使用速度，发生“ java.lang.NullPointerException”

Question

( version :velocity-1.7,commons-collections-3.2)

I use velocity to parse vm template,and set value in request scope ,show in jsp

My app work normaly a period of time , but When users access a period of time after, this jsp show error,cannot access

here is log :

Mar 8, 2013 11:40:54 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet spring threw exception
java.lang.NullPointerException
    at org.apache.commons.collections.ExtendedProperties.clearProperty(ExtendedProperties.java:797)
    at org.apache.commons.collections.ExtendedProperties.setProperty(ExtendedProperties.java:722)
    at org.apache.commons.collections.ExtendedProperties.combine(ExtendedProperties.java:783)
    at org.apache.velocity.runtime.RuntimeInstance.setProperties(RuntimeInstance.java:657)
    at org.apache.velocity.runtime.RuntimeInstance.init(RuntimeInstance.java:645)
    at org.apache.velocity.runtime.RuntimeSingleton.init(RuntimeSingleton.java:226)
    at org.apache.velocity.app.Velocity.init(Velocity.java:97)
    at com.feilong.tools.velocity.VelocityUtil.parseVMTemplateWithClasspathResourceLoader(VelocityUtil.java:67)
    at com.feilong.taglib.display.pager.PagerUtil.getPagerContent(PagerUtil.java:107)
    at com.feilong.taglib.display.pager.PagerTag.writeContent(PagerTag.java:48)
    at com.feilong.taglib.display.pager.PagerTag.writeContent(PagerTag.java:13)
    at com.feilong.taglib.base.AbstractCommonTag.doStartTag(AbstractCommonTag.java:19)
    at org.apache.jsp.pages.product.product_005flist_jsp._jspx_meth_feilongDisplay_005fpager_005f0(product_005flist_jsp.java:762)
    at org.apache.jsp.pages.product.product_005flist_jsp._jspx_meth_c_005fotherwise_005f1(product_005flist_jsp.java:433)
    at org.apache.jsp.pages.product.product_005flist_jsp._jspx_meth_c_005fchoose_005f1(product_005flist_jsp.java:243)
    at org.apache.jsp.pages.product.product_005flist_jsp._jspService(product_005flist_jsp.java:116)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

here is my util codes : (two public method:sometimes i use to parse vm template ,sometimes i use to parse string)

/**
 * VelocityUtil
 * 
 * @author feilong
  */
public final class VelocityUtil{

    private static String   RUNTIME_LOG_LOG4J_LOGGER        = "feilongVelocityLogger";

    private static String   RUNTIME_LOG_LOG4J_LOGGER_LEVEL  = "debug";

    public static String parseVMTemplateWithClasspathResourceLoader(String templateInClassPath,Map<String, Object> contextKeyValues){
        String resource_loader = "class";
        Properties properties = new Properties();
        properties.put(Velocity.RESOURCE_LOADER, resource_loader);
        properties.put(resource_loader + ".resource.loader.class", ClasspathResourceLoader.class.getName());
        properties.put(RuntimeConstants.RUNTIME_LOG_LOGSYSTEM_CLASS, Log4JLogChute.class.getName());
        properties.put(Log4JLogChute.RUNTIME_LOG_LOG4J_LOGGER, RUNTIME_LOG_LOG4J_LOGGER);
        properties.put(Log4JLogChute.RUNTIME_LOG_LOG4J_LOGGER_LEVEL, RUNTIME_LOG_LOG4J_LOGGER_LEVEL);
        properties.put(Velocity.INPUT_ENCODING, CharsetType.UTF8);
        properties.put(Velocity.OUTPUT_ENCODING, CharsetType.UTF8);

        Velocity.init(properties);
        return parseVMTemplateAfterInitVelocity(templateInClassPath, contextKeyValues);
    }


    public static String parseVMContentWithStringResourceLoader(String vmContent,Map<String, Object> contextKeyValues){
        String resource_loader = "string";
        Properties properties = new Properties();
        properties.put(Velocity.RESOURCE_LOADER, resource_loader);
        properties.put(resource_loader + ".resource.loader.class", StringResourceLoader.class.getName());
        properties.put(Velocity.INPUT_ENCODING, CharsetType.UTF8);
        properties.put(Velocity.OUTPUT_ENCODING, CharsetType.UTF8);

        Velocity.init(properties);

        String templateName = "feilongStringVelocity";
        StringResourceRepository stringResourceRepository = StringResourceLoader.getRepository();
        stringResourceRepository.putStringResource(templateName, vmContent);
        return parseVMTemplateAfterInitVelocity(templateName, contextKeyValues);
    }


    private static String parseVMTemplateAfterInitVelocity(String templateName,Map<String, Object> contextKeyValues){
        Template template = Velocity.getTemplate(templateName, CharsetType.UTF8);
        VelocityContext velocityContext = new VelocityContext();
        if (null != contextKeyValues){
            for (Map.Entry<String, Object> entry : contextKeyValues.entrySet()){
                velocityContext.put(entry.getKey(), entry.getValue());
            }
        }
        Writer writer = new StringWriter();
        template.merge(velocityContext, writer);
        try{
            writer.flush();
        }catch (IOException e){
            e.printStackTrace();
        }
        return writer.toString();
    }
}

Answer 1

If you are initializing Velocity every time you render the jsp (and it looks like you are from the code you posted) this could be the issue.

I've had this issue before and resolved it by initializing the VelocityEngine once and storing it for future use.

Taken from here (credit to 'Will Glass-Husain-2' from the Velocity forum on nabble.com):

Here's the general pattern. On app start up, initialize a VelocityEngine. Store it somewhere. Every time you need to process a template, get the template, create and populate a context, using the velocity engine merge the template (with the context).

In your code above, you could try moving the Velocity.init call to another method (called initialize, for example) which only gets called on first use of a method in your utils class. After initialize is called once, store that in a boolean and don't call initialize again.