Spring Managed DI for Quartz Jobs With Dependencies

Problem Statement:

Quartz scheduler (v 2.1.3) triggers a job which has its own dependencies which needs to be managed using Spring (3.1.1.RELEASE+)

Solution:

The Job

public class HttpDealsDownloadJob implements Job {

// NO DEPENDENCIES HERE

  @Override

  public void execute(final JobExecutionContext context)

      throws JobExecutionException {

    final JobDataMap jdm = context.getJobDetail().getJobDataMap();
// EXTRACT YOUR DEPENDENCY FROM JOB DATA MAP

    final HttpFileDownloader delegate = (HttpFileDownloader) jdm

        .get("job.delegate");

    delegate.apply(context.getJobDetail().getJobDataMap().getWrappedMap());

  }

}

Spring Context

<bean id="mySchedulerFactoryBean"

class="org.springframework.scheduling.quartz.SchedulerFactoryBean">

<property name="configLocation" value="file:quartz.properties" />

<property name="jobFactory" ref="springBeanJobFactory" />

<property name="triggers">

<list>

<ref bean="myCronTriggerFactoryBean" />

</list>

</property>

</bean>

<bean id="springBeanJobFactory"

class="org.springframework.scheduling.quartz.SpringBeanJobFactory" />

<bean id="myCronTriggerFactoryBean"

class="org.springframework.scheduling.quartz.CronTriggerFactoryBean">

<property name="cronExpression" value="${my.cron.expression}" />

<property name="jobDetail" ref="myJobDetailFactoryBean" />

</bean>

<bean id="myJobDetailFactoryBean"

class="org.springframework.scheduling.quartz.JobDetailFactoryBean">

<property name="jobDataAsMap">

<map>

<entry key="source.url" value="${my.deals.url}" />

<entry key="job.delegate" value-ref="httpFileDownloader" />

</map>

</property>

<property name="jobClass"

value="org.zero.gb.acequia.scheduler.HttpDealsDownloadJob" />
<!-- INJECT APPLICATION CONTEXT -->

<property name="applicationContextJobDataKey" value="appicationContext" />

</bean>
<!-- THIS IS THE CLASS WHICH ACTUALLY DOES THE WORK -->

<bean id="httpFileDownloader" class="org.zero.acequia.integration.http.HttpFileDownloader">

             <!-- your dependencies here -->

     </bean>

Java: Memory leak

Around two years back, when I encountered an article mentioning memory leak in Java, it was little surprising for me and may be author knew about his audience and went ahead to provide one demo program. It surely made me aware of the issue and certain anti-patterns to avoid. Then, I encountered my very own first Java memory leak, and that I my skills are not adequate to handle them. Here, in the current case, when I first observed this phenomenon I went ahead and explicitly 'nulled' my references, which are other wise supposed to go out of scope any ways and hence eligible for garbage collection, but to my frustration this has only marginally helped as the changes have only reduced the rate of memory leak and has not eliminated it. Now I plan to work to work associated anti-patterns like that weak references or references to small living objects held by long living objects etc. Will keep you posted.

Failed to connect to remote VM. Connection refused. Connection refused: connect

A lot of time was wasted to resolve the above mentioned error, while I was trying to connect to a remote server using my eclipse IDE in debug mode. Here is the solution;

1. Compile your application using '-g' option. This will generate all the debugging related information, including local variables. By default, only line number and source file information is generated.
2. Launch a new Java Virtual Machine (VM) with the main class of the application to be debugged. For e.g. Launch a new Java Virtual Machine (VM) with the main class of the application to be debugged. For e.g. $> gt; java -Xdebug -Xnoagent -Xrunjdwp:transport=dt_socket, server=y, suspend=n, address=8000

Hope that helps.

Why slow?

Hmm.. so good that you are able to monitor response times of the application components but then how does that helps tuning the application... do not count activity.. show me the productivity.. so here I'm able to monitor my code and generate some couple of reports.. but then they didn't really helped me understand performance bottlenecks.. I would run them again and again to aggregate more reports!! No amount of diligence seemed to work.. imagine I was not able to find problems.. that reminds me of the adage 'bin mange moti mile aur mange mile na bheekh' ... I had understood there is sure shot knowledge gap from technical and business perspective... after all we are still far from creating tools which would scan and identify and fix code on their own. There are just so many options for every refactoring which one intends o make in the code.. one needs to weigh your options before making code change les it should fall under its own weight... Ok, I digressed because even while conducting my own research I chanced to read interesing articles which would give me a peek ino the future about gainfully utlizing concepts from autonomic computing to application monitoring as an aid to debugging applications... but 'Show me the results' was driving me crazy.. but then as the luck would have it a visit to the the local book shop helped me discover "Bitter Java" and as prophecized by "The Alchemist" when you one truly starts liking something the entire universe conspires to make it happen.. seemed so much true .. he "bitter ejb" chapter seems to have been written just for me a quick read with reports immediately helped me identify the 'chatty' interface between our application and the database.. the server frequent roundtrips are consuming far more time over the wire than conducting any productive work... steriotypically such problems occur when we make far more granular requests than is required or may be executing queries in loops... it helps to find initial symptoms of the problem at the macro level.. such an information can be suitably used in other low performing use cases.. bugs come and go, but I'm accumulating debugging skills ... I'm already feeling the need to study "Refactoring: Martin Fowler".. may be I should get back to reading.. more later

Tip: Sort a map by values

A handy tip to sort map by values.

//:~
package samples.core.java;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

public class SortMapByValueExample {
public static void main(String[] args) {
Map map = new TreeMap();
map.put("1", "100");
map.put("10", "50");
map.put("100", "40");
map.put("1000", "10000");

List keys = new ArrayList(map.keySet());
ByValueComparator bvc = new SortMapByValueExample().new ByValueComparator(
map);
Collections.sort(keys, bvc);
Iterator iterator = keys.iterator();
while (iterator.hasNext()) {
String key = (String) iterator.next();
System.out.println(key + "-" + map.get(key));
}
}

private class ByValueComparator implements Comparator {
private Map map;

public ByValueComparator(Map map) {
this.map = map;
}

public int compare(Object o1, Object o2) {
int integer = Integer.parseInt((String) this.map.get((String) o1));
int otherInteger = Integer.parseInt((String) this.map
.get((String) o2));
return -1
* (new Integer(integer)
.compareTo(new Integer(otherInteger)));
}
}
}

Performance monitoring - creating home grown utilities

One of my current focus area is performance engineering, which although is an umbrella concept in itself pretty much sums the need to achieve the non-funcional requirement defined for the software solution. You may find a neat introduction the concept here. As much as it is important from software engineering perspective, talking of it during design session is looked upon as 'over-engineering' and is grossly ignored saying 'It will be one nice problem to solve, but we are not there yet...' probably, I understand the product manager's need to hit the market ASAP.

As they say, 'Dates in the calendar are closer than they appear', we normally start receiving complaints in form of poor user experience, loss of revenue to the competition blah, blah.. so now we have the 'nice' problem actually waiting for us to solve. Frankly, to start with there are no straight answers or atleast I do not have one. What do we do now? Where do we start? Which are the ideal candidates for performance tuning exercise? Here, is what I would do to track the problem. Place an extremely light weight activity monitoring utility in production at all times because I deem it necessary to even capture the usage of the application by the real life users and not us software engineers enmasked as pseudo users [During one of my earlier assignments, the users of the application would simply close the browser window wih out logging out, because the application didn't contained his private data and just that the users didn' like to wait for the application to log out... resulting in numerous open sessions...]

There are plenty of open source and commercially available tools in the market, still if you feel the need to create a home grown solution for some reason, here is the simple idea that I'm working on now to collect metrics from different parts of the application performance and use it for the quantitative analysis of the application.

Provide a ThreadLocal storage to 'StatisticsCollector' which would provide probes to be kept at key parts of the application to record statistics, to start with I'm only collecting execution times. Create a new object each time a new thread is spawned and keep adding metrics for the components with their metrics at collection points and them to the tree data structure which represents the call hierarchy. Finally, once the response is committed for the thread persist the data and reset thread local variables. I have primarily identified following collection points viz. the servlet filter, servlet do*(), JSPs, transactions, cache hits, jdbc layer while they are less in number they can pretty much indicate the slowest moving layer in my application. This information will form the input o iterative process of profiling-tuning-monitoring to gain performance improvement upon completion of each cycle.