Tag Archives: Java

Parallel Programming With Barrier Synchronization

Parallel Programming is an emerging computer science field that studies the opportunity of splitting data into small chucks and process them on multiple processors simultaneously which provides a faster execution time. Parallel programming is useful in sorting, image processing, network processing and may other memory intensive tasks.
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Injecting Spring Beans into Java Servlets

If you are working in a Java Web Application and you are using Spring IoC Container in your application, there is a chance that you might have to inject Spring Beans into a Java Servlet.

Since there is not a direct way to inject Spring Beans into a Java Servlet, you might try to lookup the Spring Beans from the Spring Context within your servlet and assign the dependencies which means that part of injection would no more be IoC and you would be looking for some concise way of doing this.
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Hibernate Logging

Through the years I’ve encountered a recurring requirement. Clients need to log changes to the database for auditing and legal purposes. To satisfy this requirement you could add logging to every save/update/delete call in your code. Or better yet, you could create an aspect that wraps these calls. While these would certainly work Hibernate provides a convenient interceptor.

In this article I will show you how to add a simple logger to Hibernate.
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Back to Basics: hashCode() & equals()

So we all know that if we implement equals() we must override hashCode() too. But why? The best explanation of this commandment can be found in Effective Java (2nd Edition) starting on page 45.


… Failure to do so will result in a violation of the general contract for Object.hashCode, which will
prevent your class from functioning properly in conjunction with all hash-based
collections, including HashMap, HashSet, and Hashtable. (Bloch, Effective Java, 2nd Ed.)

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Debugging memory leaks with VisualVM

At work I had run into a memory leak when scrolling through large result sets returned from Hibernate. I thought I had fixed it by performing a evict()/clear()/flush() in the HibernateTemplate that I was using but suddenly the leak was back. I was using VisualVm to monitor the heap so I started poking around to see if there was anything to help diagnose where the leak was.
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Would you start mocking me?

One of the primary principles of unit testing is to test a small piece of functionality in isolation. In order to achieve this, mock objects are often necessary. Historically using mocks could be quite painful. After using several mock frameworks, my favorite by far is Mockito.

Tutorial

In this tutorial we will walk through examples of the most common features of Mockito. My sample project can be downloaded here.

Interfaces and Implementation

Some mocking frameworks only supported mocking interfaces. As a result our projects became bloated with useless interfaces that were only used for testing.  Mockito creates mock objects with interfaces or classes.
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Rendering Global t:messages After Redirect

A common problem when working with JSF is getting global info messages  via <t:messages globalOnly="true"> or <f:messages globalOnly="true"> to display messages set in the previous request when you have a <redirect/> in your faces-config for a particular page You will not see your <t:messages> that are set on the previous page.

The Problem

For instance, say you have two pages – page1.xhtml and page2.xhtml. In your faces-config.xml, you will have 2 entries.

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Environment Specific Properties in Spring

On many occasions I want to be able to inject environment specific property values into my Spring managed beans. These may be things like web service endpoints, database URLs, etc. Values I know for each environment at build time, but I want to use the same WAR/EAR file in each environment. I would like to keep the actual values separate from the Spring config files themselves. And I would really like to manage a set of default values for each property, so that I do not need to specify a value for every property in every environment (ex. my credit card processing URL for dev, test, uat is the same, but for production it is different.)

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Replacing and Patching Java Application and Core classes

Why would you ever need that?

Say you get a jar file. After using the jar for a while you realise that there is a bug in a class in the jar file. Unfortunately you also find out that the jar is no longer supported and there is no way you will get a fix from the author (who is long gone fishing).

In order to solve this issue, you first need to get the source of the class. If you are lucky enough and the author did not obfuscate the class file you can decompile it with a decompiler (my favourite one is JD-GUI).

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Keep your dataTable clean with a custom popup

The basic idea is to output some data to a user in a table and allow them to take an action on each row individually. A fairly straightforward solution is to create a separate page to link to, passing the necessary row information along. If the action is simple enough, like a single checkbox, you could just embed the necessary component(s) in each row of the table. Too many components, however, can bloat the table and make the UI cumbersome to the user. Instead we can create a popup window to overlay our page, containing whatever components are needed, and activate it by a link embedded in our table. Passing the row information is a little trickier, but the result is a cleaner interface and a better user experience.
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