DispatcherServlet of Spring MVC - 10 things Java Developer should know

If you have worked with Spring MVC then you should know what is a DispatcherServlet? It's actually the heart of Spring MVC, precisely the C of MVC design pattern or Controller. Every single web request which is supposed to be processed by Spring MVC goes through DispatcherServlet. In general, its an implementation of Front Controller Pattern which provides a single point of entry in your application. It handles all incoming requests. It is also the bridge between Java and Spring and DispatcherServlet like any other Servlet is declared in the web.xml with a URL pattern enough to map every single web request to DispathcherServlert.

Java 8 - Sorting HashMap by values in ascending and descending order

In the last article, I have shown you how to sort a Map in Java 8 by keys and today, I'll teach you how to sort a Map by values using Java 8 features e.g. lambda expression, method reference, streams, and new methods added into the java.util.Comparator and Map.Entry classes. In order to sort any Map e.g. HashMap, Hashtable, LinkedHashMap, TreemMap, or even ConcurrentHashMap, you can first get set of entries by using the entrySet() method and then you can get the stream by calling the stream() method. The entrySet()  method returns a Set which inherit the stream() method from the java.util.Collection class. Once you got the stream, you can just call the sorted() method which can sort all Map.Entry objects available in Stream using a Comparator.

Difference between @RestController and @Controller Annotation in Spring MVC and REST

The @RestController annotation in Spring MVC is nothing but a combination of @Controller and @ResponseBody annotation. It was added into Spring 4.0 to make the development of RESTful Web Services in Spring framework easier. If you are familiar with the REST web services you know that the fundamental difference between a web application and a REST API is that the response from a web application is generally view (HTML + CSS + JavaScript) while REST API just return data in form of JSON or XML. This difference is also obvious in the @Controller and @RestController annotation. The job of @Controller is to create a Map of model object and find a view but @RestController simply return the object and object data is directly written into HTTP response as JSON or XML.

What does the InternalResourceViewResolver do in Spring MVC?

The InternalResourceViewResolver is an implementation of ViewResolver in Spring MVC framework which resolves logical view name e.g. "hello" to internal physical resources e.g. Servlet and JSP files e.g. jsp files placed under WEB-INF folder. It is a subclass of UrlBasedViewResolver, which uses "prefix" and "suffix" to convert a logical view name returned from Spring controller to map to actual, physical views. For example, if a user tries to access /home URL and HomeController returns "home" then DispatcherServlet will consult InternalResourceViewResolver and it will use prefix and suffix to find the actual physical view which is integral to a web application. For example, if prefix is "/WEB-INF/views/" and suffix is ".jsp" then "home" will be resolved to "/WEB-INF/home.jsp" by InternalResourceViewResolver.

How to Remove key value pairs or Entries from HashMap in Java 8

In the last article, I have shown how to remove key/value pairs from a map in Java based upon some conditions e.g. remove all entries where values are greater than 10$. I have told you that you must use the Iterator's remove() method for removing mapping while iteration to avoid ConcurrentModificationException, but that's not required anymore in Java 8. From JDK 8 onwards, you can selectively remove mapping without iterating over Map. The JDK 8 API has added several new methods to existing interfaces e.g. java.util.Collection, java.util.Map, Comparator etc because the interface can now contain concrete methods in form of static and default methods.

How to enable/disable an element using jQuery and JavaScript? Example

Sometimes we need to enable and disable input elements e.g. text box, radio buttons or checkbox, how can we do it dynamically without loading the page? Well, we can use JavaScript, particularly jQuery to do this. An element can be disabled in HTML by setting disable property to true and enabled again by setting disabled=false. By using jQuery, we can grab the element we want to enable or disable and change this property by using prop() or attr() function, depending upon which version of jQuery you are using. prop() function was added in jQuery 1.6 and its the standard way to deal with properties but attr() function does the same job for jQuery 1.5 and lower version so you can use attr() for the same purpose in jQuery version lower than 1.6.