&nbsp;
Welcome to the Drools Tutorials,&nbsp;Drools is a business logic integration platform written in Java. Apart from the tutorials, we will also cover Interview Questions, Issues and How To&rsquo;s of Docker.
<h2 style="text-align: left;">Introduction of Drools</h2>
Drools is a Business Rules Management System (BRMS) solution. It provides a core <a class="zem_slink" title="Business rules engine" href="http://en.wikipedia.org/wiki/Business_rules_engine" target="_blank" rel="noopener wikipedia">Business Rules Engine</a> (BRE), a web authoring and rules management application (Drools Workbench) and an Eclipse IDE plugin for core development.
Drools is a <a class="zem_slink" title="Business logic" href="http://en.wikipedia.org/wiki/Business_logic" target="_blank" rel="noopener wikipedia">Business Logic</a> integration Platform (BLiP). It is written in Java. It is an open source project that is backed by JBoss and Red Hat, Inc. It extends and implements the Rete Pattern matching algorithm.
In layman&rsquo;s terms, Drools is a collection of tools that allow us to separate and reason over logic and data found within business processes. The two important keywords we need to notice are Logic and Data.
Drools is split into two main parts: Authoring and Runtime.
-Authoring: Authoring process involves the creation of Rules files (.DRL files).
-Runtime: It involves the creation of working memory and handling the activation.
<h3 style="text-align: left;">Authoring:</h3>
&nbsp;The Authoring process involves the creation Rules files (.DRL) which contain the rules which are fed into a parser. The parser checks for correctly syntax of the rules and produces an intermediate structure that "describes" the rules. This is then passed to the Package Builder which produces Packagesand undertakes any code generation and compilation that is necessary for the creation of the Package.
<h3 style="text-align: left;">Runtime:&nbsp;</h3>
Drools Runtime is required to instruct the editor to run the program with specific version of Drools jar. You can run your program/application with different Drools Runtime.
<h3 style="text-align: left;">Working Memory:</h3>
The <a href="https://en.wikipedia.org/wiki/Working_memory" target="_blank" rel="noopener">Working memory</a> is a key point of the Drools engine: it's here that Facts are inserted.
Facts are plain Java classes which rely on the <a class="zem_slink" title="JavaBeans" href="http://en.wikipedia.org/wiki/JavaBeans" target="_blank" rel="noopener wikipedia">Java Bean</a> pattern( your Java beans from your application). Facts are asserted into the Working Memory where they may then be modified or retracted.&nbsp;
When&nbsp;facts are asserted into the working memory, it will result in one or more rules being concurrently true and scheduled for execution by the Agenda - we start with a fact, it propagates and we end in a conclusion. This method of execution for a <a class="zem_slink" title="Production system" href="http://en.wikipedia.org/wiki/Production_system" target="_blank" rel="noopener wikipedia">Production Rule Systems</a> is called Forward Chaining.
<pre style="text-align: center;">Interested in mastering Drools Training? Enroll now for FREE demo on <a href="https://tekslate.com/drools-training" target="_blank" rel="noopener">Drools Training</a>.</pre>
<h2 style="text-align: left;">What is a Rule Engine?</h2>
Drools is <a href="https://tekslate.com/drools-rules-engine/">Rule Engine</a> or a Production Rule System that uses the rule-based approach to implement and Expert System. Expert Systems are knowledge-based systems that use knowledge representation to process acquired knowledge into a knowledge base that can be used for reasoning.
<h3 id="business-rules" style="text-align: left;">Business Rules</h3>
<div class="paragraph" style="text-align: justify;">Drools is a powerful hybrid reasoning system. It allows you to define your business logic using business rules in various formats (for example using decision tables etc.).</div>
<img class="aligncenter wp-image-19985" title="drools tutorials-Business Rules" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.636.png" alt="drools tutorials " width="581" height="399" />
<h3 id="wizards" style="text-align: left;">Wizards</h3>
<h4 id="getting-started" style="text-align: justify;">Getting started</h4>
The aim of the new project wizard is to set up an executable sample project to start using rules immediately. This will set up a basic structure, the classpath, sample rules and a test case to get you started. Supports selecting a Drools runtime for the Drools core dependencies.
<img class="aligncenter wp-image-19986" title="drools tutorials -wizard" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.637.png" alt="drools tutorials " width="468" height="445" />
<h3 id="debugging" style="text-align: left;">Debugging</h3>
<div class="sectionbody" style="text-align: justify;">
<div class="sect2">
<h4 id="debug-your-processes">Debug your processes</h4>
Debugging support to look at the current state of your session, including the data inserted in the working memory, the rules activated, etc. Supports breakpoints in the rules.</div>
</div>
<img class="aligncenter wp-image-19987" title="drools tutorials debugging" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.638.png" alt="drools tutorials " width="555" height="464" />
<h3 id="rules-repository" style="text-align: left;">Rules Repository</h3>
<div class="sectionbody">
<div class="sect2">
<h4 id="integration-using-git" style="text-align: justify;">Integration using Git</h4>
<div class="paragraph">
Integrate with the rules repository (as part of Guvnor, also known as the Kie Workbench or business central) using Git tooling.
<h3 style="text-align: left;">Drools Frequently Used Terms</h3>
<h4 style="text-align: justify;">Rules</h4>
The heart of the Rules Engine where you specify conditions (if &lsquo;a&rsquo; then &lsquo;b&rsquo;).
<h4 style="text-align: justify;">Facts</h4>
Facts are the data on which the rules will act upon. From Java perspective, Facts are the POJO (<a class="zem_slink" title="Plain Old Java Object" href="http://en.wikipedia.org/wiki/Plain_Old_Java_Object" target="_blank" rel="noopener wikipedia">Plain Old Java Object</a>).
<h4 style="text-align: justify;">Session</h4>
A Knowledge Session in Drools is the core component to fire the rules. It is the knowledge session that holds all the rules and other resources. A Knowledge Session is created from the KnowledgeBase.
For the rules engine to work, Facts are inserted into the session and when a condition is met, the subsequent rule gets fired. A Session is of two types:
-Stateless Knowledge Session
-Stateful Knowledge Session
<h4 style="text-align: justify;">Agenda</h4>
It&rsquo;s a logical concept. The agenda is the logical place where activations are waiting to be fired.
<h4 style="text-align: justify;">Activations</h4>
Activations are the then part of the rule. Activations are placed in the agenda where the appropriate rule is fired.
<h4 style="text-align: justify;">Main Drools Classes</h4>
The rules like &ldquo;Low Credit Score Rejection&rdquo; rule are contained in DRL files (files with the extension .drl) that comply with Drools native rule language syntax. To use the created rules in a Java application you must:
-Knowledge Builder: A knowledge builder is the class that knows how to load and process DRL files. The impact of parsing and building in memory objects from the DRL file happens at this point. An instance of a knowledge builder can be obtained from the KnowledgeBuilderFactory using the new KnowledgeBuilder() method
-Knowledge Package: A knowledge package is the result of processing a DRL file; a serializable object. The knowledge builder has a get Knowledge Packages() that returns a collection of knowledge packages.
-Knowledge Base: A knowledge base is where the knowledge packages are deployed to so that they can be used at runtime. The knowledge base is the object that will be used to create knowledge sessions. This knowledge base is a thread safe construct that serves as a factory of sessions.
-Knowledge Session: The knowledge session is the object used to interact with the rule engine. It is throught a session that you will make the rule engine aware of the facts (the data) that the rule engine will evaluate against the available rules. Inside the Rule Engine
<pre style="text-align: center;">Learn more about <a href="https://tekslate.com/drools-interview-questions/" target="_blank" rel="noopener">Drools Interview Questions</a> in this blog post.</pre>
Inside the rule engine, after you have inserted your facts into a knowledge session and invoked the session fireAllRules() method:
-Rules are matched against the facts in the knowledge session using the pattern matcher (Rete algorithm)
-The unordered list of activations (the Rules that apply based on the facts) is ordered internally (by a conflict resolver) in the session&rsquo;s agenda
-The first Rule in the agenda is the executed, possibly triggering steps 1 and 2 again
This loop is how a Rule Engine infers knowledge from existing facts using rules. You can see that a Rule Engine using pattern matching to reduce/transform the problem space to arrive at a set of facts that can be considered a solution to the problem at hand.
<h3 style="text-align: left;">Interacting with the Twitter API</h3>
One of the big decisions you&rsquo;ll face with implementing a rule-based system with Drools is how much Java to put in your rules. As with any other object-oriented application we want encapsulate complex behavior to make our rules more readable. There are also things that are much easily accomplished, tested and developed outside of the realm of the rules engine.
To deal with the interaction with Twitter I decided to use Twitter4J (http://yusuke.homeip.net/twitter4j), a Java library to interact with the Twitter API. Using Twitter4J I created a simple collection of static utility methods contained in the class TwitterUtils.java. Some of the available methods are:
-Double getTwitterInfluenceRatio(User user)
-Boolean hasSetProfileImage(User user)
-Double averageTweetsPerDay(User user)
-Boolean inactiveForTheLast(User user, Integer days)
-Integer followersInCommon(Twitter twitter, User target)
-Boolean isFollowing(Twitter twitter, String target)
Twitter4J provides the classes twitter4j.Twitter which represents the authenticated Twitter user and twitter4j.User which represents detailed information about a Twitter user.
<h2 style="text-align: left;">Conclusion</h2>
Rule engines can provide a Java developer with an environment in which logic and data are clearly separated. In the simple example used in this article it is easy to see how the DRL file becomes you laboratory of centralized knowledge about the problem at hand. Once the plumbing code is in place you can truly concentrate on the &ldquo;business logic&rdquo; in atomic, discrete, manageable chunks.
In this article we&rsquo;ve barely scratched the surface of the capabilities provided by Drools. Drools 5 is a complete offering that includes the rule engine (Drools Expert), a Business Rule Management System (Drools Guvnor), a process/workflow engine (Drools Flow) and an event processing/temporal reasoning engine (Drools Fusion).
For indepth understanding of Drools Tutorials click on
<ul>
<li style="text-align: justify;"><a href="https://tekslate.com/drools-rules-engine/" target="_blank" rel="noopener">Drools Rule Engine</a></li>
<li style="text-align: justify;"><a href="https://tekslate.com/drools-installation/" target="_blank" rel="noopener">Drools Installation</a></li>
<li style="text-align: justify;"><a href="https://tekslate.com/eclipse-plugin-drools/" target="_blank" rel="noopener">Eclipse plug-in Drools</a></li>
<li style="text-align: justify;"><a href="https://tekslate.com/drools-interview-questions/" target="_blank" rel="noopener">Drools Interview Questions</a></li>
</ul>
&nbsp;
</div>
</div>
</div>

Learn Drools With Free Online Tutorials

Drools Tutorials

drools-tutorials

Drools Interview Questions

drools-interview-questions

In this tutorial, we will go over Drools Installation step by step.
Drools&nbsp;enable an Eclipse-based IDE, however at its core, just&nbsp;<a class="zem_slink" title="Java version history" href="http://en.wikipedia.org/wiki/Java_version_history" target="_blank" rel="noopener wikipedia">Java 1.5</a> (<a class="zem_slink" title="Java Platform, Standard Edition" href="http://en.wikipedia.org/wiki/Java_Platform%2C_Standard_Edition" target="_blank" rel="noopener wikipedia">Java SE</a>) is required.
A simple way to begin&nbsp;is to download and install the Eclipse <a class="zem_slink" title="Plug-in (computing)" href="http://en.wikipedia.org/wiki/Plug-in_%28computing%29" target="_blank" rel="noopener wikipedia">plug-in</a>.&nbsp;It also requires the Eclipse GEF framework to be installed. This enables all the dependencies to create a new rule project usually. Installing the Eclipse plug-in requires just unzipping a file into Eclipse plug-in directory.
Use of the Eclipse plug-in is not necessarily required. Rule files are usually a textual input, and the IDE is another convenience. Rule engine can be integrated&nbsp;into various ways, and there is no "one size fits all".
Download and install Eclipse IDE.
Install the GEF Plugin for Eclipse:
<ul>
<li style="text-align: justify;">Run Eclipse IDE.</li>
<li style="text-align: justify;">Select Help &gt; Install New Software&hellip;.</li>
<li style="text-align: justify;">In the Work with: <a class="zem_slink" title="Combo box" href="http://en.wikipedia.org/wiki/Combo_box" target="_blank" rel="noopener wikipedia">combo box</a> type: http://download.eclipse.org/tools/gef/updates/releases/</li>
<li style="text-align: justify;">Select &ldquo;<a class="zem_slink" title="Graphical Editing Framework" href="http://en.wikipedia.org/wiki/Graphical_Editing_Framework" target="_blank" rel="noopener wikipedia">Graphical Editing Framework</a> GEF&rdquo;.</li>
<li style="text-align: justify;"><img class=" wp-image-19935 aligncenter" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.623.png" alt="Capture.623" width="621" height="481" /></li>
</ul>
<pre style="text-align: center;">At TekSlate, we offer resources that help you in learning various IT courses. We avail both written
 material and demo video tutorials. To gain in-depth knowledge and be on par with practical
 experience, then explore <a href="https://tekslate.com/drools-training" target="_blank" rel="noopener">Drools Training Videos</a>. </pre>
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<tr style="height: 39.0374px;">
<td style="width: 98.3494%; height: 39.0374px; text-align: center;">At TekSlate, we offer resources that help you in learning various IT courses. We avail both written material and demo video tutorials. To gain in-depth knowledge and be on par with practical experience, then explore <a href="https://tekslate.com/drools-training" target="_blank" rel="noopener">Drools Training</a>.</td>
</tr>
</tbody>
</table>
Install Drools:
<ul>
<li style="text-align: justify;">Select Help &gt; Install New Software&hellip;.</li>
<li style="text-align: justify;">In the Work with: combo box type: http://download.jboss.org/drools/release/6.1.0.Final/org.drools.updatesite/</li>
<li style="text-align: justify;">Select all.</li>
</ul>
<img class=" wp-image-19937 aligncenter" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.624.png" alt="Capture.624" width="596" height="463" />
Make sure the checkbox &ldquo;Contact all update sites during install to find required software&rdquo; is checked.
Create Drools Runtime:
<ul>
<li style="text-align: justify;">In Eclipse switch to the Drools perspective (upper right corner).</li>
<li style="text-align: justify;">Select File &gt; New &gt; Drools project.</li>
<li style="text-align: justify;">Choose a name and click &ldquo;Next&rdquo;.</li>
</ul>
<img class=" wp-image-19938 aligncenter" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.625.png" alt="Capture.625" width="558" height="532" />
Click &ldquo;Next&rdquo;.
<img class=" wp-image-19939 aligncenter" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.626.png" alt="Capture.626" width="578" height="548" />
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<tbody>
<tr style="height: 24.0374px;">
<td style="width: 98.3494%; text-align: center; height: 24.0374px;">Check out the top <a style="color: #236fa1;" href="https://tekslate.com/drools-interview-questions/" target="_blank" rel="noopener">Drools Interview Questions</a> now!</td>
</tr>
</tbody>
</table>
Click &ldquo;Configure Workspace Settings&hellip;&rdquo;.
<img class=" wp-image-19940 aligncenter" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.627.png" alt="Capture.627" width="557" height="529" />
Click &ldquo;Add&hellip;&rdquo;.
<img class=" wp-image-19941 aligncenter" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.628.png" alt="Capture.628" width="550" height="469" />
Click &ldquo;Create a new Drools 6 Runtime&hellip;&rdquo; and choose a directory to create the Drools Runtime.
<img class=" wp-image-19942 aligncenter" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.629.png" alt="Capture.629" width="535" height="264" />
Select the created Drools Runtime and click &ldquo;OK&rdquo;.
<img class=" wp-image-19943 aligncenter" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.630.png" alt="Capture.630" width="562" height="451" />
Enter a <code class="highlighter-rouge">GroupId</code>, an <code class="highlighter-rouge">ArtifactId</code>, and a <code class="highlighter-rouge">Version</code> for your project. You may choose arbitrary non-empty values. Afterwards, click &ldquo;Finish&rdquo; to create the project.
<img class=" wp-image-19944 aligncenter" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.6311.png" alt="Capture.631" width="560" height="525" />
<ul style="text-align: justify;">
<li>Open the class that contains the main method. It is located in the package <code class="highlighter-rouge">com.sample</code> and has the same name as the project.</li>
<li>To execute the project, <a class="zem_slink" title="Context menu" href="http://en.wikipedia.org/wiki/Context_menu" target="_blank" rel="noopener wikipedia">right-click</a> the editor and selectDebug As &gt; Drools Application. Observe the output. You can ignore the SLF4J warnings.</li>
</ul>
For an In-depth knowledge on Drools click on below:
<ul>
<li><a href="https://tekslate.com/drools-tutorials" target="_blank">Drools Tutorials</a></li>
<li><a href="https://tekslate.com/drools-rules-engine/" target="_blank" rel="noopener">Drools Rules Engine</a></li>
</ul>

How to install Drools?

Drools Installation

drools-installation

Drools is an <a class="zem_slink" title="Object-oriented programming" href="http://en.wikipedia.org/wiki/Object-oriented_programming" target="_blank" rel="noopener wikipedia">Object-Oriented</a> Rule Engine for Java. Drools is an augmented implementation of Forgy's Rete algorithm tailored for the Java language. Adapting Rete to an object-oriented interface allows for more natural expression of business rules with regards to business objects. More importantly, Drools provides for declarative logic programming and is flexible enough to match the semantics of your problem domain. The various parts that compose a rule may be extended to lend domain-specific sense to the rule.
<h2 style="text-align: justify;">Rule Engine</h2>
A rule engine may be viewed as a sophisticated if/then statement interpreter. The if/then statements that are interpreted are called rules.
The if portions of rules contain conditions such as account.getMoney() &lt; 0. The then portions of rules contain actions such as send Warning(account). if (account.getMoney() &lt; 0) send Warning(account); 
The inputs to a rule engine are a rule execution set and some data objects. The outputs from a rule engine are determined by the inputs and may include the original input data objects with possible modifications, new data objects, and side effects such as sendMail('Thank you for shopping').
<img class=" wp-image-19974 aligncenter" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/05/Capture.635.png" alt="Capture.635" width="640" height="315" />
Rules are stored in a <a class="zem_slink" title="Forward chaining" href="http://en.wikipedia.org/wiki/Forward_chaining" target="_blank" rel="noopener wikipedia">forward-chaining</a> rule engine, i.e. the engine implements an execution cycle that allows the action of one rule to cause the condition of other rules to become met. In this way, a cascade of rules may become activated and each rule action executed. Forward-chaining rule engines are suitable for problems that require drawing higher-level conclusions from simple input facts.
<pre style="text-align: center;">These core tutorials will help you to learn the Drools Rules Engine. For an in-depth understanding and practical
 experience, explore <a href="https://tekslate.com/drools-training" target="_blank" rel="noopener">Online Drools Training</a>.</pre>
So, here's how you could rewrite the above check as a rule:
global AccountManager manager;
rule "checkMoney" when $account : Account( money &lt; 0 ) then manager.warn($account); end
As you can see, a Rule file is based on two basic concepts:
Rules: declarative statements that govern the conduct of business processes. A rule consists of a condition and actions. The condition is evaluated, and if it evaluates to true, the rule engine initiates one or more actions.
Facts: are the data upon which rules operate. In our example, the available money are facts.
<h2 style="text-align: justify;">Using a Rule Engine</h2>
<a href="https://tekslate.com/drools-training">Rule systems</a> are capable of solving very, very hard problems, providing an explanation of how the solution was arrived at and why each "decision" along the way was made. Among the main benefit of a Rule engine can be mentioned:
Logic and Data Separation:&nbsp;Breaking your domain objects from business rules can lead to a mach easier to maintain application as it can shield from changes in the future, since the logic is all laid out in rules.
Speed and Scalability:&nbsp;Many times we apply "if" conditions that we didn't really need. The <a class="zem_slink" title="Rete algorithm" href="http://en.wikipedia.org/wiki/Rete_algorithm" target="_blank" rel="noopener wikipedia">Rete algorithm</a>, as implemented by Drools, replaces all of the if ... then statements with an optimized network.
Centralization of Knowledge:&nbsp;By using rules, you create a repository of knowledge (a knowledgebase) which can be considered as a <a class="zem_slink" title="Single Source of Truth" href="http://en.wikipedia.org/wiki/Single_Source_of_Truth" target="_blank" rel="noopener wikipedia">single point of truth</a>, for business policy (for instance) - ideally rules are so readable that they can also serve as documentation
Tool Integration:&nbsp;Writing rules means also to get accustomed with Rule language, validation and debugging. Eclipse provide an excellent tool to deliver and test your Rules.
Understandable Rules&nbsp;JBoss Drools:&nbsp;rules can make it easy to express solutions to difficult problems and consequently have those solutions verified (rules are much easier to read then code).Often, business users are more comfortable with expressing things that they know to be true, than to express things in an if...then format.
<h1 style="text-align: justify;">Advantages of Rule Engines</h1>
Turning to rules adds a set of advantages to your applications:
Greater flexibility: keeping your rules into a <a class="zem_slink" title="Knowledge base" href="http://en.wikipedia.org/wiki/Knowledge_base" target="_blank" rel="noopener wikipedia">Knowledge base</a> let you adapt easily your decisions when they are changing.
Easier to grasp: Rules are easier to understand than procedural code so they can be effectively used to bridge the gap between business analyst and developers.
Reduced complexity: When embedding lots of decision points to your procedural codes it can easily turn your application into a nightmare. On the other hand rules can handle much better increasing complexity because they use a consistent representation of business rules.
Reusability: By keeping rules are kept in one place leads to a greater reusability of your business rules. Also, traditional procedural code often impose unnecessary variations of base rules which are therefore more difficult to reuse in other contexts.
<pre style="text-align: center;">Learn more about <a href="https://tekslate.com/drools-interview-questions/" target="_blank" rel="noopener">Drools Interview Questions</a> in this blog post.</pre>
<div class="titlepage" style="text-align: justify;">
<div>
<div>
<h3 class="title">When should you use a Rule Engine?</h3>
</div>
</div>
</div>
The shortest answer to this is "when there is no satisfactory traditional programming approach to solve the problem.". Given that short answer, some more explanation is required. The reason why there is no "traditional" approach is possibly one of the following:
<div class="itemizedlist" style="text-align: justify;">
<ul>
<li>The problem is just too fiddle for traditional code.The problem may not be complex, but you can't see a non-fragile way of building a solution for it.</li>
<li>The problem is beyond any obvious algorithmic solution.It is a complex problem to solve, there are no obvious traditional solutions, or basically the problem isn't fully understood.</li>
<li>The logic changes oftenThe logic itself may even be simple but the rules change quite often. In many organizations software releases are few and far between and pluggable rules can help provide the "agility" that is needed and expected in a reasonably safe way.</li>
<li>Domain experts (or business analysts) are readily available, but are non-technical.Domain experts often possess a wealth of knowledge about business rules and processes. They typically are nontechnical, but can be very logical. Rules can allow them to express the logic in their own terms. Of course, they still have to think critically and be capable of logical thinking. Many people in nontechnical positions do not have training in formal logic, so be careful and work with them, as by codifying business knowledge in rules, you will often expose holes in the way the business rules and processes are currently understood.</li>
</ul>
</div>
If rules are a new technology for your project teams, the overhead in getting going must be factored in. It is not a trivial technology, but this document tries to make it easier to understand.
Typically in a modern OO application you would use a rule engine to contain key parts of your business logic,especially the really messy parts. This is an inversion of the OO concept of encapsulating all the logic inside your objects. This is not to say that you throw out OO practices, on the contrary in any real world application, business logic is just one part of the application. If you ever notice lots of conditional statements such as "if" and "switch", an overabundance of strategy patterns and other messy logic in your code that just doesn't feel right: that would be a place for rules. If there is some such logic and you keep coming back to fix it, either because you got it wrong, or the logic or your understanding changes: think about using rules. If you are faced with tough problems for which there are no algorithms or patterns: consider using rules.
Rules could be used embedded in your application or perhaps as a service. Often a rule engine works best as "stateful" component, being an integral part of an application. However, there have been successful cases of creating reusable rule services which are stateless.
For your organization it is important to decide about the process you will use for updating rules in systems that are in production. The options are many, but different organizations have different requirements. Frequently, rules maintenance is out of the control of the application vendors or project developers.
<h3 style="text-align: justify;">When not to use a Rule Engine?</h3>
As rule engines are dynamic (dynamic in the sense that the rules can be stored and managed and updated as data), they are often looked at as a solution to the problem of deploying software. (Most IT departments seem to exist for the purpose of preventing software being rolled out.) If this is the reason you wish to use a rule engine, be aware that rule engines work best when you are able to write declarative rules. As an alternative, you can consider data-driven designs (lookup tables), or script processing engines where the scripts are managed in a database and are able to be updated on the fly.
For an Indepth knowledge on Drools click on below:
<ul>
<li><a href="https://tekslate.com/drools-installation/" target="_blank" rel="noopener">Drools Installation</a></li>
</ul>
&nbsp;

What is a rule engine? What are the advantages of rule engine?

Drools Rules Engine

drools-rules-engine

Eclipse applications use a runtime based on a specification called OSGi. A software component in OSGi is called a bundle. An OSGi bundle is also always an Eclipse plug-in. Both terms can be used interchangeably. For example, a new plug-in can&nbsp;create new menu entries or toolbar entries.
-Java 1.5 (or higher) SE JDK
-Eclipse 4.2 (or any version) and the Drools plugin
As Drools is a BRMS (Business Rule Management System) written in Java, we will be covering how to add the desired plugins in this section. Considering maximum Java users use Eclipse, let&rsquo;s see how to add the Drools 5.x.0 plugin in Eclipse.
<h2 style="text-align: justify;">Download the Binaries</h2>
Download the binaries from the following link:
http://download.jboss.org/drools/release/5.3.0.Final/
After the download is complete, extract the files to your hard disk.
<h2 style="text-align: justify;">Install the Software</h2>
Launch Eclipse and go to help&rarr;install new software. Click on Add as shown in the following screenshot.
<img class="aligncenter wp-image-22374 size-full" title="Eclipse Plugin in Drools" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/07/Capture-60.png" alt="Eclipse Plugin in Drools" width="505" height="421" />
Thereafter, click on Local as shown here and select "&hellip;/binaries/org.drools.updatesite".
<img class="aligncenter wp-image-22375 size-full" title="Eclipse Plugin in Drools" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/07/Capture-61.png" alt="Eclipse Plugin in Drools" width="492" height="189" />
Select Drools and jBPM and click Next.
<img class="aligncenter wp-image-22376 size-full" title="Eclipse Plugin in Drools" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/07/Capture-62.png" alt="Eclipse Plugin in Drools" width="506" height="417" />
Again click Next. Thereafter, accept the terms and license agreement and click Finish.
<img class="aligncenter wp-image-22377 size-full" title="Eclipse Plugin in Drools" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/07/Capture-63.png" alt="Eclipse Plugin in Drools" width="501" height="420" />
Upon clicking Finish, the software installation starts:
<img class="aligncenter wp-image-22378 size-full" title="Eclipse Plugin in Drools" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/07/Capture-64.png" alt="Eclipse Plugin in Drools" width="503" height="275" />
Post successful installation, you will get the following dialog box:
<img class="aligncenter wp-image-22379 size-full" title="Eclipse Plugin in Drools" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/07/Capture-65.png" alt="Eclipse Plugin in Drools" width="506" height="145" />
Click on yes. Once Eclipse restarts, go to Windows &rarr; Preferences
<img class="aligncenter wp-image-22380 size-full" title="Eclipse Plugin in Drools" src="https://newtekslateassets.s3.us-west-2.amazonaws.com/wp-content/uploads/2016/07/Capture-66.png" alt="Eclipse Plugin in Drools" width="507" height="318" />
You can see <a href="https://tekslate.com/drools-training">Drools </a>under your preferences. Your Drools plugin installation is complete now.