Java ThreadLocal and It's use

By

Have you ever wondered about accessing you HTTPServletRequest object (or any other contextual/scoped object) in a non web class? What I mean by non web class is any class that does not goes through a web request/response initialization life cycle. HttpServlet is a web class because web container initializes and provides the HttpServletRequest and HttpServletResponse objects.

Let’s say you have a POJO and you want to initialize few properties/variables of it from request object/parameters. Since the POJO is plain class it by default does not have access to the request object, then how to get access if current request Object? We have two options:

1.       Override the public constructor of POJO class to accept HttpServletRequest as an argument
e.g. public MyClass(HttpServletRequest request) { }

When we are forcing a class’s constructor to accept an Object, we always need to make sure that we are passing it and the class is tightly coupled with the underlying implementation. Also, we can not instantiate it without passing required arguments or null.

2.       Use the thread local capabilities of Java: Thread Local can be considered as a scope of access, like a request scope or session scope. It’s a thread scope. You can set any object in Thread Local and this object will be global and local to the specific thread which is accessing this object. Let’s take a look at the class that uses the thread local concept and then I’ll explain the code:

import java.util.LinkedList;
import javax.servlet.http.HttpServletRequest;

public abstract class RequestUtil {
private static ThreadLocal> threadLocalRequest =
new ThreadLocal>();

                public static void setRequest(HttpServletRequest request) {
                                LinkedList list =  threadLocalRequest.get();
                                if (list == null) {
                                                list = new LinkedList();
                                                threadLocalRequest.set(list);
                                }
                                list.addLast(request);
                }

                public static HttpServletRequest getRequest() {
                                LinkedList list =  threadLocalRequest.get();
                                if (list != null && list.size() > 0) {
                                                return list.getLast();
                                };
                                return null;
                }

                public static void clearRequest() {
                                LinkedList list = threadLocalRequest.get();
                                if (list != null && list.size() > 0) {
                                                list.removeLast();
                                };
                }
}


So what we are doing here is, we just created a simple class that has three static methods setRequest(),getRequest() and clearRequest() for setting, fetching and clearing request object from thread local scope. At the entry point of request (e.g. service or doGet or doPost method) we just need to call

RequestUtil.setRequest(request);

This will set the request object in thread local context/scope, and to access it from anywhere (any class) where we don’t have access to request object we just need to call:
       
RequestUtil.getRequest();

This call will always make sure that it returns the current request object in current thread.

If you explicitly want to clear the current request object from thread local scope just to make sure that it not accessible to any other then just call:

RequestUtil.clearRequest();
       
I hope this will help you to implement some useful piece of functionality in your application. You can refer the java doc for more information http://download.oracle.com/javase/1.4.2/docs/api/java/lang/ThreadLocal.html

Comments

Post a Comment

Popular posts from this blog

AEM, FORM Submission & Handling POST requests

By
In this article I’ll be specifically talking about how to handle POST request in AEM and what options we have. Please note that Adobe has added more security around handling POST request from AEM 6.x onwards to prevent CSRF attack. If you don’t configure AEM correctly, POST requests will not work even after using any of methods explained in this article.   You can read more about security configurations and restriction at: https://docs.adobe.com/docs/en/aem/6-1/develop/security/csrf-protection.html It is very common use cases to have external application POST some data to an AEM page (e.g. /content/en/home.html) or even submit a form (POST) to same URL. But, as you know that in AEM POST works differently and any POST call to AEM is intercepted by Sling’s POST servlet (org.apache.sling.servlets.post.impl.SlingPostServlet). In some cases org.apache.sling.servlets.post.impl. SlingPostServlet is very useful when you actually want to perform CURD (create, update, read a...
Read more

AEM - Query list of components and templates

By
Some time while migration or for auditing purposes we need to know where a particular component/template or any other resource have been used. Have you ever wondered about how to fetch a list of all the paths where a particular component or template is being used? I this short article I am going to show a quick way to write a utility with which you can get list if paths (actual resource nodes) where a targeted resource is being used. Here is the code snipped: public void getResourceListHelper(Resource parentResource , String targetSearchPropertyKey ,  String targetSearchPropertyValue , List components ) {      Resource childResource ; for (Iterator resourceChildrenIter = parentResource .listChildren(); resourceChildrenIter .hasNext();  getResourceListHelper ( childResource, targetSearchPropertyKey, targetSearchPropertyValue, components)) { childResource = (Resource) resourceChildrenIter .next(); ValueMap childProperties = (...
Read more

AEM 6.3 - Bundle Whitelisting - Deprecation of administrative authentication

By
Image
I stumbled on an issue when I was using neab with AEM 6.3. I created few neba ResourceModels and when I tried to access neba Model Registry, I got an error ( java.lang.IllegalStateException: org.apache.sling.api.resource.LoginException: Bundle org.eclipse.gemini.blueprint.extender is NOT whitelisted ): Image: neba Model Registry Menu Image: Error Screen NOTE: Neba team has already fixed it on their development branch and we don’t need to explicitly add whitelisting configuration for neba bundle. Here is the reason for error Originally the ResourceResolverFactory.getAdministrativeResourceResolver and SlingRepository.loginAdministrative methods have been defined to provide access to the resource tree and JCR Repository. These methods proved to be inappropriate because they allow for much too broad access. Consequently these methods are being deprecated and will be removed in future releases of the service implementations. The following methods are deprecat...
Read more

AEM as a Cloud Service (AEMaaCS) – Architecture Overview

By
Image
AEM as a Cloud Service (AEMaaCS) – Architecture Adobe Experience Manager (AEM) is one of the leading CMS from Adobe and is part of Adobe Experience Cloud (AEC). The Adobe Experience Manager (AEM) web content management offers a set of capabilities for creating, managing, delivering, and personalizing content across various digital marketing channels, including web, mobile, and email.  Before we dive into architecture of AEM as a Cloud Service (AEMaaCS) we need to understand why AEMaaCS is needed and how it is different as compared to classic AEM. To understand this, we’ll first look at: Evolution/history of AEM Challenges with traditional/classic AEM (the AEM that majority of us have used from last 10-12 years) Evolution/History of AEM The software was originally launched in early 2000 as Communiqué (CQ) by Day Software of Basel, Switzerland. After CQ 5.3 had been released, Day Software was acquired by Adobe Systems in 2010 then CQ became Adobe Experience Manager. ...
Read more