Tag Archives: quick-tip

MongoDB Query Tip : Find All The Documents Where Array Length is Greater Than N

Suppose we have blog document in blogs collection as shown below.

> db.blogs.insert({author : "Shekhar Gulati","title":"Hello World","text":"Hello World!!","tags":["mongodb","openshift"]})
> db.blogs.insert({author : "Shekhar Gulati","title":"Hello World","text":"Hello World!!","tags":["mongodb","openshift","nosql"]})

Now you want to find out all those blogs which have more than 2 tags then query is shown below.

> db.blogs.find({$where : "this.tags.length > 2"}).pretty()
	"_id" : ObjectId("51011037bf779459a978f96f"),
	"author" : "Shekhar Gulati",
	"title" : "Hello World",
	"text" : "Hello World!!",
	"tags" : [

Spring Test Failing with A ServletContext is required to configure default servlet handling

If you are getting exception shown below in your Spring test

Caused by: java.lang.IllegalArgumentException: A ServletContext is required to configure default servlet handling
at org.springframework.util.Assert.notNull(Assert.java:112)
at org.springframework.web.servlet.config.annotation.DefaultServletHandlerConfigurer.(DefaultServletHandlerConfigurer.java:54)
at org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport.defaultServletHandlerMapping(WebMvcConfigurationSupport.java:330)
at org.springframework.web.servlet.config.annotation.DelegatingWebMvcConfiguration$$EnhancerByCGLIB$$c733f512.CGLIB$defaultServletHandlerMapping$22()
at org.springframework.web.servlet.config.annotation.DelegatingWebMvcConfiguration$$EnhancerByCGLIB$$c733f512$$FastClassByCGLIB$$b76778f9.invoke()
at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228)
at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:285)
at org.springframework.web.servlet.config.annotation.DelegatingWebMvcConfiguration$$EnhancerByCGLIB$$c733f512.defaultServletHandlerMapping()
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:160)

Then to fix this error migrate to Spring 3.2 release. Change the maven dependency as shown below


Quick Tip on Mockito — Mocking Iterator

Today I was writing unit test for a piece of code which required me to mock a iterator. My requirement was that I wanted to return true first time when hasNext() method and return false in the second iteration. It took me sometime to figure out how to write such a test case. My class for which I was writing test looks like as shown below.

import java.util.Iterator;

public class ResultFetcher {

	private ResultStore store;
	private ResultProcessor processor;

	public void fetchResults() {
		Iterator<String> iterator = store.resultIterator();
		while (iterator.hasNext()) {
			String result = iterator.next();

The unit test code is shown below. The important line in the test is Mockito.when(iterator.hasNext()).thenReturn(true,false); which will return true first time and false second time.

import java.util.Iterator;

import org.junit.Test;
import org.mockito.Mockito;

public class ResultFetcherTest {

public void testFetchResults() {
ResultFetcher fetcher = new ResultFetcher();

ResultStore store = Mockito.mock(ResultStore.class);
ResultProcessor processor = Mockito.mock(ResultProcessor.class);
fetcher.store = store;
fetcher.processor = processor;

Iteratoriterator = Mockito.mock(Iterator.class);


Logging JAXWS SOAP Request and Response using a Java Property

Today I was faced with the situation that I needed to log the SOAP requests and responses going in and out from a Java client. I just had the client jar no source code so I can’t any any log or change any other configuration. I needed to log the request and response because I was getting some weird exceptions which I was not able to understand. I got the hold of the SOAP request by passing a Java property

java -Dcom.sun.xml.internal.ws.transport.http.client.HttpTransportPipe.dump=true -jar client.jar

Fixing Exception — Entity manager has not been injected (is the Spring Aspects JAR configured as an AJC/AJDT aspects library?)

If you are working with Spring Roo and suddenly start getting exception “Entity manager has not been injected (is the Spring Aspects JAR configured as an AJC/AJDT aspects library?)” then make sure you have _Configurable.aj ITD in your project. This ITD makes the sure that your entity classes have all the required dependencies like EntityManager injected in them. Configurable ITD ¬†looks like as shown below

privileged aspect Movie_Roo_Configurable {

    declare @type: Movie: @Configurable;


Adding Third Party Jars To An OSGI Bundle

Few days back I was writing a Spring Roo add-on(an OSGI bundle) which required me to add some external 3rd party jars to the OSGI bundle pom.xml file. I am not very well verse with OSGI so it took me some time to figure out how to add 3rd party jars to an OSGI bundle. In this short blog post I am sharing the recipe to add third part jars.

The exception that you get when OSGI bundle is not able to find the dependency is like this.

org.osgi.framework.BundleException: Unresolved constraint com.shekhar.roo.addon [66]: Unable to resolve 66.0: missing requirement [66.0] package; (package=com.shekhar.utils)

To solve this error you need to add Embed-Dependency tag to your maven bundle plugin as shown below. The example shows that I need to add commons-io and utils jar to my OSGI bundle. To get more information about Embed-Dependency tag and maven bundle plugin please refer to the documentation.

		<Bundle-Copyright>Copyright Shekhar Gulati. All Rights Reserved.</Bundle-Copyright>

SCP command for Copying files from remote linux machine to local machine

I just faced a requirement that I needed to copy a zip file containing logs from a remote server to my local machine for some analysis.
I googled around and found at that you can use scp command to that for you.

scp -r <username of remote machine>:<remote location> <location of local directory>

scp -r shekhar@dev.xebia.com:/home/xebia/application/logs/logs-1-09-2011.zip /home/shekhar/tmp