Help for writing custom rule using java?

[mihai3636]

Hello, everyone!

TL;DR

In the meanwhile I have found this question and the person who answered seems to answer lots of my questions:
#3463

I will try to use the info from that discussion tomorrow in order to create my rule, it looked really promising.

Until then, I let this here, maybe someone has some more useful advice for my lack of knowledge?

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I have read everything I could possibly read from the official documentation regarding rule creation. (here)
I have created my own custom rules using the XPath language.

BUT: I lack the knowledge that I need in order to complete the following steps:

I will give you some context in order to understand what I am working with:

I have a plain and simple java project and I added the pmd lib files to the external libraries.
In my main function, I execute the PMD on some input files in a programatic way, like in this tutorial.

Then I take the resulted json report and parse it with the goal of computing some statistics.

I did not use gradle or maven because I tried but I did not manage to make it work.

Now, I am trying to build a new custom rule using java because I want to add in the Violation message some variable.
For example: I want to build a rule similar with "TooManyMethods", but I will add into the Violation message the number of methods that were counted.

I understand the java code from those tutorial explaining how to build the rule, but I do now know:

• point 2, where do I write that java code before I compile it. Do I create a new project? Do I git pull from the pmd repo and add the code there?
• point 2, what does it mean "linking it to the PMD APIs".
• what does it mean to bundle it into a jar and add it to PMDs classpath. I mean, I know a JAR is like a pre-compiled piece of code, but that is all that I know regarding this matter.
• Let's say somehow I ever manage to write that custom rule, the only way to verify it is to do all these steps then run PMD and see the results? with XPath the testing was way faster.

Basically I do now understand how do I add my new java code to the already existing PMD code.

Honestly, at this point I do not even know what I don't know.

Could someone, please, give me some starting points regarding what I am trying to achieve? Thank you for reading all this.

[adangel]

You might also have a look at the examples here https://github.com/pmd/pmd-examples
This includes a maven example as well.

[mihai3636]

Hey, man! Just wanted to say thank you. I just used my first custom Java rule inside my project.

I went to your link and I used the maven example about generating a jar for the custom rule. It was so easy to use.
Now I can add anything I want inside the violation message, by using setMessage()

I will definitely look more into using maven, your link was an amazing starting point.

[Prapti08]

Hey,
I'm also working on some custom rules in java, but I'm not able to convert my logic into syntax. Is there anything like designer.bat for java rules where we can check our custom rules?
Because checking custom rules every time creating the jar and running those rules is quite a tedious process.Thanks in advance:)

[mihai3636]

Hey, I'm also working on some custom rules in java, but I'm not able to convert my logic into syntax. Is there anything like designer.bat for java rules where we can check our custom rules? Because checking custom rules every time creating the jar and running those rules is quite a tedious process.Thanks in advance:)

Hey there. If you use the maven example to generate the jar file for the custom rule, you will see there is an automated test example too. You basicaly write some code snippet and assert that your rule works. If it's not enough, I will get back to you with more details, tomorrow or Monday. It's Saturday night here and I write on phone.

[Prapti08]

Thanks a lot for your help . Can you also provide with resources

[mihai3636]

Thanks a lot for your help . Can you also provide with resources

Go to the java maven example: here
I assume you are already using that branch to create your java rules.

Now, you will find an xml file like in my screenshot. That is a test configuration for your custom rule.

You can change the < code> tag and the < expected> tags to be fit for your own custom rule.
If I am not answering your question or something is not clear, please ask again.

[Prapti08]

Yes, got it. Thank you :).
I just need one more help, I want to create a custom rule mentioned below-
If there is a try-catch block in the code, the very first statement after the catch block should be log.error("msg"); if its not there then pmd report should give a violation. I was able to write the rule using xpath but I'm not able to write this logic using java so that I can element more complex custom rules as we get a hold on nodes properly if we use java.
I'm referring this -https://javadoc.io/static/net.sourceforge.pmd/pmd-java/6.10.0/net/sourceforge/pmd/lang/java/ast/ASTCatchStatement.html
But the documentation is not that clear, Can you please explain to me what is your thought process behind writing custom rules in java?
I have been struggling with this for a long time.