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This article shows you how to analyze the application of Drools rule engine technology in the ladder project, the content is concise and easy to understand, it will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

Application of Drools Rule engine Technology in Sky ladder Project

Today, I will mainly share with you the principle and rule configuration of Drools rule engine. Before the introduction, first of all, I would like to introduce the SQL evaluation and optimization project developed by our bank-- ladder system. Big data ladder system is an intelligent analysis SQL evaluation tool, which can not only improve script online efficiency and reduce personnel workload, but also extract code features according to various queries' computing power consumption, data security and code specification, and find code quality, safety, performance and other problems in time. Prevent the poor SQL from entering the production system, and provide effective guarantee for the stable and healthy operation of the system. The original intention of the elevator system design is that the user can evaluate the SQL statement according to the defined rules to avoid problems in the production environment. In the process of development, the ladder system can decouple the business logic from the hard coding, so as to modify the business logic without changing the code, do not re-code, and reduce the impact on other functions of the system. The elevator system is mainly composed of SQL syntax parsing and SQL evaluation. In the SQL evaluation stage, the Drools rule engine is used, which is a particularly important core part of the elevator system. Can the Drools rules engine take the lead? As it turns out, it did it!

Drools is an open source rule engine based on Java, which liberates complex and changeable rules from hard coding and stores them in files in the form of rule scripts, so that rule changes do not need to modify the code or restart the machine, so that the online environment can take effect immediately. The rule engine, developed from the reasoning engine, is a component embedded in the application, which separates business decisions from the application code and uses predefined semantic modules to write business decisions. It brings great convenience to programming by accepting data input, interpreting business rules, and making business decisions according to business rules.

What are the advantages of the Drools rule engine? As shown in figure 1 above, it can be seen intuitively that the Drools rules engine can separate and decouple business rules from business systems. At the same time, Drools can implement natural language description rule logic, which is easy for business people to understand. And can be visual rule customization, examination and approval, query and management. Effectively improve the maintainability of the code that implements complex logic. When the customer does not initially mention the need to take business logic into account, the rules can also be customized later, which, for developers, is in line with the organization's use of agile or iterative development processes.

Drools has so many advantages, so how does its basic working process be implemented? In the past, our general practice is to use an interface for business work, first of all, to pass in the parameters, and then to obtain the results of the implementation of the interface. Drools coincides with our previous practice in this respect. Drools also needs to pass in data for rule inspection, call external interfaces, and may need to obtain the results after rule execution. In Drools, this transfer data into the object is an ordinary JavaBean, a JavaBean inserted into the Working Memory (memory storage) after the object called Fact object, Fact object is not the original JavaBean object cloning, but the original JavaBean object reference, simple point, you can understand the Fact object as a bridge or channel for rules and application system data interaction. For the properties of the Fact object, we need to provide getter and setter methods. Through the getter and setter methods, we can easily operate on the Fact object.

After that, the Fact object matches all the rules in the current WorkingMemory and returns a FactHandler object. The FactHandler object is the reference of the Fact object inserted into the WorkingMemory. Through the FactHandler object, the corresponding Fact object can be deleted and modified by API.

Next, we introduce the configuration of Drools rule engine rule files. Drools rule engine configuration files support multiple formats, the most basic of which is * .drl file, of course, it can also be * .xml, or * .xls or * .xlsx. It looks very flexible, doesn't it! The format of the * .drl file is used in the ladder project.

The basic syntax of Drools can be divided into three parts: package path, reference and rule body; the simplest rule should include at least two parts: package path and rule body. A rule file can store multiple rules. in addition, user-defined functions, data objects, custom queries and other related objects that may be used in rules can be stored in the rule file. A simple rule file structure is shown in the following figure

In a rule body, the part between when and then is the conditional part. This section can contain 0 conditions. If the condition part is empty, the engine will automatically add an eval (true) condition, that is, the condition part returns true.

The result part is the content between then and end, which is executed only if all conditions are met in the conditional part, similar to the conditional statement in the Java program. In the results section, some macro functions or objects that can quickly operate on the current WorkingMemory, such as insert, update, modify and retract, can add, modify or delete Fact objects in the current WorkingMemory.

The basic working process and rule file configuration of the Drools rules engine are basically these. Then I simply implemented the API calling program of Drools by myself. First, I created a maven project. The related file directory and code are shown in the figure below.

This paper focuses on the introduction of kmodule.xml.

A kmodule can contain multiple kbase, each kbase has a name, you can take any string, but can not repeat the name. Then there is a packages, and you can see that the string in the packages is actually the name of the folder under the src/main/resources, or the package name. The rules engine will look for the rule definition file according to the package defined here. You can define multiple packages at the same time, separated by commas. There can be multiple ksession under each kbase, and only one is defined in this example.

Each ksession has a name, and the name can be any string, but it cannot be repeated. The name attribute in kbase and ksession cannot be duplicated globally. There are actually many other attributes in kbase and ksession, and each kbase can contain multiple ksession.

At run time, KieContainer creates the corresponding KieModule, KieBase, KieSession objects based on the kmodule.xml file. KieModule and KieBase are created only once, while KieSession may be created multiple times, because the creation cost of KieSession is very low, and KieSession contains run-time data, so it can be destroyed and created several times.

Final execution result of the project program (successful execution):

The above content is how to analyze the application of Drools rule engine technology in the ladder project. Have you learned the knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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