2020-11-14 09:20:07 +00:00
<!DOCTYPE html>
< html >
< head >
< meta charset = "utf-8" >
< meta http-equiv = "X-UA-Compatible" content = "IE=edge" >
< meta name = "viewport" content = "width=device-width, initial-scale=1" >
< meta name = "description" content = "Writing your own PMD rules" >
< meta name = "keywords" content = "extendinguserdocsgetting_started, " >
< title > Introduction to writing PMD rules | PMD Source Code Analyzer< / title >
< link rel = "stylesheet" href = "css/syntax.css" >
< link rel = "stylesheet" type = "text/css" href = "https://maxcdn.bootstrapcdn.com/font-awesome/4.5.0/css/font-awesome.min.css" >
<!-- <link rel="stylesheet" type="text/css" href="css/bootstrap.min.css"> -->
< link rel = "stylesheet" href = "css/modern-business.css" >
< link rel = "stylesheet" href = "css/lavish-bootstrap.css" >
< link rel = "stylesheet" href = "css/customstyles.css" >
< link rel = "stylesheet" href = "css/theme-blue.css" >
< link rel = "stylesheet" href = "css/pmd-customstyles.css" >
< script src = "https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.4/jquery.min.js" > < / script >
< script src = "https://cdnjs.cloudflare.com/ajax/libs/jquery-cookie/1.4.1/jquery.cookie.min.js" > < / script >
< script src = "js/jquery.navgoco.min.js" > < / script >
< script src = "https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js" > < / script >
< script src = "https://cdnjs.cloudflare.com/ajax/libs/anchor-js/2.0.0/anchor.min.js" > < / script >
< script src = "js/toc.js" > < / script >
< script src = "js/customscripts.js" > < / script >
< link rel = "shortcut icon" href = "images/favicon.ico" type = "image/x-icon" >
< link rel = "icon" href = "images/favicon.ico" type = "image/x-icon" >
<!-- HTML5 Shim and Respond.js IE8 support of HTML5 elements and media queries -->
<!-- WARNING: Respond.js doesn't work if you view the page via file:// -->
<!-- [if lt IE 9]>
< script src = "https://oss.maxcdn.com/libs/html5shiv/3.7.0/html5shiv.js" > < / script >
< script src = "https://oss.maxcdn.com/libs/respond.js/1.4.2/respond.min.js" > < / script >
<![endif]-->
< link rel = "alternate" type = "application/rss+xml" title = "" href = "https://pmd.github.io/pmd/feed.xml" >
< script >
$(document).ready(function() {
// Initialize navgoco with default options
$("#mysidebar").navgoco({
caretHtml: '',
accordion: true,
openClass: 'active', // open
save: false, // leave false or nav highlighting doesn't work right
cookie: {
name: 'navgoco',
expires: false,
path: '/'
},
slide: {
duration: 400,
easing: 'swing'
}
});
$("#collapseAll").click(function(e) {
e.preventDefault();
$("#mysidebar").navgoco('toggle', false);
});
$("#expandAll").click(function(e) {
e.preventDefault();
$("#mysidebar").navgoco('toggle', true);
});
});
< / script >
< script >
$(function () {
$('[data-toggle="tooltip"]').tooltip()
})
< / script >
< script >
$(document).ready(function() {
$("#tg-sb-link").click(function() {
$("#tg-sb-sidebar").toggle();
$("#tg-sb-content").toggleClass('col-md-9');
$("#tg-sb-content").toggleClass('col-md-12');
$("#tg-sb-icon").toggleClass('fa-toggle-on');
$("#tg-sb-icon").toggleClass('fa-toggle-off');
});
});
< / script >
< / head >
< body >
<!-- Content is offset by the height of the topnav bar. -->
<!-- There's already a padding - top rule in modern - business.css, but it apparently doesn't work on Firefox 60 and Chrome 67 -->
< div id = "topbar-content-offset" >
<!-- Navigation -->
< nav class = "navbar navbar-inverse navbar-fixed-top" >
< div class = "container topnavlinks" >
< div class = "navbar-header" >
< button type = "button" class = "navbar-toggle" data-toggle = "collapse" data-target = "#bs-example-navbar-collapse-1" >
< span class = "sr-only" > Toggle navigation< / span >
< span class = "icon-bar" > < / span >
< span class = "icon-bar" > < / span >
< span class = "icon-bar" > < / span >
< / button >
< a class = "fa fa-home fa-lg navbar-brand" href = "index.html" > < span class = "projectTitle" > PMD Source Code Analyzer Project< / span > < / a >
< / div >
< div class = "collapse navbar-collapse" id = "bs-example-navbar-collapse-1" >
< ul class = "nav navbar-nav navbar-right" >
<!-- toggle sidebar button -->
< li > < a id = "tg-sb-link" href = "#" > < i id = "tg-sb-icon" class = "fa fa-toggle-on" > < / i > Nav< / a > < / li >
<!-- entries without drop - downs appear here -->
< li > < a href = "https://github.com/pmd/pmd/releases/latest" target = "_blank" > Download< / a > < / li >
< li > < a href = "https://github.com/pmd/pmd" target = "_blank" > Fork us on github< / a > < / li >
<!-- entries with drop - downs appear here -->
<!-- conditional logic to control which topnav appears for the audience defined in the configuration file. -->
<!-- comment out this block if you want to hide search -->
< li >
<!-- start search -->
< div id = "search-demo-container" >
< input type = "text" id = "search-input" placeholder = "search..." >
< ul id = "results-container" > < / ul >
< / div >
< script src = "js/jekyll-search.js" type = "text/javascript" > < / script >
< script type = "text/javascript" >
SimpleJekyllSearch.init({
searchInput: document.getElementById('search-input'),
resultsContainer: document.getElementById('results-container'),
dataSource: 'search.json',
searchResultTemplate: '< li > < a href = "{url}" title = "Introduction to writing PMD rules" > {title}< / a > < / li > ',
noResultsText: 'No results found.',
limit: 10,
fuzzy: true,
})
< / script >
<!-- end search -->
< / li >
< / ul >
< / div >
< / div >
<!-- /.container -->
< / nav >
<!-- Page Content -->
2022-02-25 09:51:51 +00:00
< div class = "container-toc-wrapper" >
< div class = "container" >
< div class = "col-lg-12" > < / div >
<!-- Content Row -->
< div class = "row" >
2020-11-14 09:20:07 +00:00
2022-02-25 09:51:51 +00:00
<!-- Sidebar Column -->
< div class = "col-md-3" id = "tg-sb-sidebar" >
2020-11-14 09:20:07 +00:00
< ul id = "mysidebar" class = "nav" >
2022-06-25 10:10:40 +00:00
< li class = "sidebarTitle" > PMD 6.48.0-SNAPSHOT< / li >
< div class = "sidebarTitleDate" > Release date: 30-July-2022< / div >
2020-11-14 09:20:07 +00:00
< li >
< a href = "#" > About< / a >
< ul >
< li > < a href = "index.html" > Home< / a > < / li >
< li > < a href = "pmd_release_notes.html" > Release notes< / a > < / li >
< li > < a href = "pmd_next_major_development.html" > PMD 7.0.0 development< / a > < / li >
< li > < a href = "pmd_about_help.html" > Getting help< / a > < / li >
< / ul >
< / li >
< li >
< a href = "#" > User Documentation< / a >
< ul >
< li > < a href = "pmd_userdocs_installation.html" > Installation and basic CLI usage< / a > < / li >
< li > < a href = "pmd_userdocs_making_rulesets.html" > Making rulesets< / a > < / li >
< li > < a href = "pmd_userdocs_configuring_rules.html" > Configuring rules< / a > < / li >
< li > < a href = "pmd_userdocs_best_practices.html" > Best practices< / a > < / li >
< li > < a href = "pmd_userdocs_suppressing_warnings.html" > Suppressing warnings< / a > < / li >
< li > < a href = "pmd_userdocs_incremental_analysis.html" > Incremental analysis< / a > < / li >
< li > < a href = "pmd_userdocs_cli_reference.html" > PMD CLI reference< / a > < / li >
< li > < a href = "pmd_userdocs_report_formats.html" > PMD Report formats< / a > < / li >
< li class = "subfolders" >
< a href = "#" > CPD reference< / a >
< ul >
< li > < a href = "pmd_userdocs_cpd.html" > Copy-paste detection< / a > < / li >
< li > < a href = "pmd_userdocs_cpd_report_formats.html" > CPD Report formats< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > Extending PMD< / a >
< ul >
< li class = "active" > < a href = "pmd_userdocs_extending_writing_rules_intro.html" > Introduction to writing rules< / a > < / li >
< li > < a href = "pmd_userdocs_extending_your_first_rule.html" > Your first rule< / a > < / li >
< li > < a href = "pmd_userdocs_extending_writing_xpath_rules.html" > XPath rules< / a > < / li >
< li > < a href = "pmd_userdocs_extending_writing_java_rules.html" > Java rules< / a > < / li >
< li > < a href = "pmd_userdocs_extending_designer_reference.html" > Rule designer reference< / a > < / li >
< li > < a href = "pmd_userdocs_extending_defining_properties.html" > Defining rule properties< / a > < / li >
< li > < a href = "pmd_userdocs_extending_metrics_howto.html" > Using and defining code metrics< / a > < / li >
< li > < a href = "pmd_userdocs_extending_rule_guidelines.html" > Rule guidelines< / a > < / li >
< li > < a href = "pmd_userdocs_extending_testing.html" > Testing your rules< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > Tools / Integrations< / a >
< ul >
< li > < a href = "pmd_userdocs_tools_maven.html" > Maven PMD Plugin< / a > < / li >
< li > < a href = "pmd_userdocs_tools_gradle.html" > Gradle< / a > < / li >
< li > < a href = "pmd_userdocs_tools_ant.html" > Ant< / a > < / li >
< li > < a href = "pmd_userdocs_tools_java_api.html" > PMD Java API< / a > < / li >
< li > < a href = "pmd_userdocs_tools_ci.html" > CI integrations< / a > < / li >
< li > < a href = "pmd_userdocs_tools.html" > Other Tools / Integrations< / a > < / li >
< / ul >
< / li >
< / ul >
< / li >
< li >
< a href = "#" > Rule Reference< / a >
< ul >
< li class = "subfolders" >
< a href = "#" > Apex Rules< / a >
< ul >
< li > < a href = "pmd_rules_apex.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_apex_bestpractices.html" > Best Practices< / a > < / li >
< li > < a href = "pmd_rules_apex_codestyle.html" > Code Style< / a > < / li >
< li > < a href = "pmd_rules_apex_design.html" > Design< / a > < / li >
< li > < a href = "pmd_rules_apex_documentation.html" > Documentation< / a > < / li >
< li > < a href = "pmd_rules_apex_errorprone.html" > Error Prone< / a > < / li >
< li > < a href = "pmd_rules_apex_performance.html" > Performance< / a > < / li >
< li > < a href = "pmd_rules_apex_security.html" > Security< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > Ecmascript Rules< / a >
< ul >
< li > < a href = "pmd_rules_ecmascript.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_ecmascript_bestpractices.html" > Best Practices< / a > < / li >
< li > < a href = "pmd_rules_ecmascript_codestyle.html" > Code Style< / a > < / li >
< li > < a href = "pmd_rules_ecmascript_errorprone.html" > Error Prone< / a > < / li >
< / ul >
< / li >
2022-04-28 13:34:56 +00:00
< li class = "subfolders" >
< a href = "#" > HTML Rules< / a >
< ul >
< li > < a href = "pmd_rules_html.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_html_bestpractices.html" > Best Practices< / a > < / li >
< / ul >
< / li >
2020-11-14 09:20:07 +00:00
< li class = "subfolders" >
< a href = "#" > Java Rules< / a >
< ul >
< li > < a href = "pmd_rules_java.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_java_bestpractices.html" > Best Practices< / a > < / li >
< li > < a href = "pmd_rules_java_codestyle.html" > Code Style< / a > < / li >
< li > < a href = "pmd_rules_java_design.html" > Design< / a > < / li >
< li > < a href = "pmd_rules_java_documentation.html" > Documentation< / a > < / li >
< li > < a href = "pmd_rules_java_errorprone.html" > Error Prone< / a > < / li >
< li > < a href = "pmd_rules_java_multithreading.html" > Multithreading< / a > < / li >
< li > < a href = "pmd_rules_java_performance.html" > Performance< / a > < / li >
< li > < a href = "pmd_rules_java_security.html" > Security< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > Java Server Pages Rules< / a >
< ul >
< li > < a href = "pmd_rules_jsp.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_jsp_bestpractices.html" > Best Practices< / a > < / li >
< li > < a href = "pmd_rules_jsp_codestyle.html" > Code Style< / a > < / li >
< li > < a href = "pmd_rules_jsp_design.html" > Design< / a > < / li >
< li > < a href = "pmd_rules_jsp_errorprone.html" > Error Prone< / a > < / li >
< li > < a href = "pmd_rules_jsp_security.html" > Security< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > Maven POM Rules< / a >
< ul >
< li > < a href = "pmd_rules_pom.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_pom_errorprone.html" > Error Prone< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > Modelica Rules< / a >
< ul >
< li > < a href = "pmd_rules_modelica.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_modelica_bestpractices.html" > Best Practices< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > PLSQL Rules< / a >
< ul >
< li > < a href = "pmd_rules_plsql.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_plsql_bestpractices.html" > Best Practices< / a > < / li >
< li > < a href = "pmd_rules_plsql_codestyle.html" > Code Style< / a > < / li >
< li > < a href = "pmd_rules_plsql_design.html" > Design< / a > < / li >
< li > < a href = "pmd_rules_plsql_errorprone.html" > Error Prone< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > Salesforce VisualForce Rules< / a >
< ul >
< li > < a href = "pmd_rules_vf.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_vf_security.html" > Security< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > VM Rules< / a >
< ul >
< li > < a href = "pmd_rules_vm.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_vm_bestpractices.html" > Best Practices< / a > < / li >
< li > < a href = "pmd_rules_vm_design.html" > Design< / a > < / li >
< li > < a href = "pmd_rules_vm_errorprone.html" > Error Prone< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > XML Rules< / a >
< ul >
< li > < a href = "pmd_rules_xml.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_xml_errorprone.html" > Error Prone< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > XSL Rules< / a >
< ul >
< li > < a href = "pmd_rules_xsl.html" > Index< / a > < / li >
< li > < a href = "pmd_rules_xsl_codestyle.html" > Code Style< / a > < / li >
< li > < a href = "pmd_rules_xsl_performance.html" > Performance< / a > < / li >
< / ul >
< / li >
< / ul >
< / li >
< li >
< a href = "#" > Language Specific Documentation< / a >
< ul >
< li > < a href = "pmd_languages_jsp.html" > JSP Support< / a > < / li >
2022-03-27 15:04:13 +00:00
< li class = "subfolders" >
< a href = "#" > Java Support< / a >
< ul >
< li > < a href = "pmd_languages_java.html" > Java Versions< / a > < / li >
< li > < a href = "pmd_java_metrics_index.html" > Java Code Metrics< / a > < / li >
< / ul >
< / li >
2020-11-14 09:20:07 +00:00
< li > < a href = "pmd_apex_metrics_index.html" > Apex code metrics< / a > < / li >
2021-03-26 08:22:23 +00:00
< li > < a href = "pmd_languages_plsql.html" > PLSQL< / a > < / li >
2021-10-29 17:50:40 +00:00
< li > < a href = "pmd_languages_visualforce.html" > Visualforce< / a > < / li >
2022-03-25 07:44:53 +00:00
< li > < a href = "pmd_languages_xml.html" > XML and XML dialects< / a > < / li >
2022-04-28 13:34:56 +00:00
< li > < a href = "pmd_languages_html.html" > HTML< / a > < / li >
2020-11-14 09:20:07 +00:00
< / ul >
< / li >
< li >
< a href = "#" > Developer Documentation< / a >
< ul >
< li > < a href = "pmd_devdocs_development.html" > Developer resources< / a > < / li >
< li > < a href = "pmd_devdocs_building.html" > Building PMD from source< / a > < / li >
< li > < a href = "https://github.com/pmd/pmd/blob/master/CONTRIBUTING.md" target = "_blank" > Contributing< / a > < / li >
< li > < a href = "pmd_devdocs_writing_documentation.html" > Writing documentation< / a > < / li >
< li > < a href = "pmd_devdocs_roadmap.html" > Roadmap< / a > < / li >
< li > < a href = "pmd_devdocs_how_pmd_works.html" > How PMD works< / a > < / li >
< li > < a href = "pmd_devdocs_pmdtester.html" > Pmdtester< / a > < / li >
< li > < a href = "pmd_devdocs_rule_deprecation_policy.html" > Rule Deprecation Policy< / a > < / li >
< li class = "subfolders" >
< a href = "#" > Major contributions< / a >
< ul >
2021-08-27 14:58:36 +00:00
< li > < a href = "pmd_devdocs_major_rule_guidelines.html" > Rule Guidelines< / a > < / li >
2020-11-14 09:20:07 +00:00
< li > < a href = "pmd_devdocs_major_adding_new_language.html" > Adding a new language< / a > < / li >
< li > < a href = "pmd_devdocs_major_adding_new_cpd_language.html" > Adding a new CPD language< / a > < / li >
< li > < a href = "pmd_devdocs_major_adding_new_metrics_framework.html" > Adding metrics support to a language< / a > < / li >
< / ul >
< / li >
< li class = "subfolders" >
< a href = "#" > Experimental features< / a >
< ul >
< li > < a href = "pmd_devdocs_experimental_ast_dump.html" > Creating (XML) dump of the AST< / a > < / li >
< / ul >
< / li >
< / ul >
< / li >
< li >
< a href = "#" > Project documentation< / a >
< ul >
< li class = "subfolders" >
< a href = "#" > Trivia about PMD< / a >
< ul >
< li > < a href = "pmd_projectdocs_trivia_news.html" > PMD in the press< / a > < / li >
< li > < a href = "pmd_projectdocs_trivia_products.html" > Products & books related to PMD< / a > < / li >
< li > < a href = "pmd_projectdocs_trivia_similarprojects.html" > Similar projects< / a > < / li >
< li > < a href = "pmd_projectdocs_trivia_meaning.html" > What does 'PMD' mean?< / a > < / li >
< / ul >
< / li >
< li > < a href = "pmd_projectdocs_faq.html" > FAQ< / a > < / li >
< li > < a href = "license.html" > License< / a > < / li >
< li > < a href = "pmd_projectdocs_credits.html" > Credits< / a > < / li >
< li > < a href = "pmd_release_notes_old.html" > Old release notes< / a > < / li >
< li class = "subfolders" >
< a href = "#" > Project management< / a >
< ul >
2021-04-23 20:35:51 +00:00
< li > < a href = "pmd_projectdocs_committers_infrastructure.html" > Infrastructure< / a > < / li >
2020-11-14 09:20:07 +00:00
< li > < a href = "pmd_projectdocs_committers_releasing.html" > Release process< / a > < / li >
< li > < a href = "pmd_projectdocs_committers_merging_pull_requests.html" > Merging pull requests< / a > < / li >
< li > < a href = "pmd_projectdocs_committers_main_landing_page.html" > Main Landing page< / a > < / li >
< / ul >
< / li >
< / ul >
< / li >
<!-- if you aren't using the accordion, uncomment this block:
< p class = "external" >
< a href = "#" id = "collapseAll" > Collapse All< / a > | < a href = "#" id = "expandAll" > Expand All< / a >
< / p >
-->
< / ul >
<!-- this highlights the active parent class in the navgoco sidebar. this is critical so that the parent expands when you're viewing a page. This must appear below the sidebar code above. Otherwise, if placed inside customscripts.js, the script runs before the sidebar code runs and the class never gets inserted. -->
< script > $ ( "li.active" ) . parents ( 'li' ) . toggleClass ( "active" ) ; < / script >
2022-02-25 09:51:51 +00:00
< / div >
2020-11-14 09:20:07 +00:00
2022-02-25 09:51:51 +00:00
<!-- Content Column -->
< div class = "col-md-9" id = "tg-sb-content" >
2022-03-24 11:42:13 +00:00
< header >
< div class = "row" >
< div class = "col-lg-12" >
< a href = "./" role = "button"
>< i class = "fa fa-home fa-lg" > < /i
>< / a >
» Introduction to writing PMD rules
< a
target="_blank"
href="https://github.com/pmd/pmd/blob/master/docs/pages/pmd/userdocs/extending/writing_rules_intro.md"
class="pull-right"
role="button"
>< i class = "fa fa-github fa-lg" > < / i > Edit on GitHub< /a
>
< / div >
< / div >
< hr / >
< / header >
< div class = "post-header" >
2020-11-14 09:20:07 +00:00
< h1 class = "post-title-main" > Introduction to writing PMD rules< / h1 >
< / div >
2022-03-24 11:42:13 +00:00
< div class = "post-content" data-github-edit-url = "https://github.com/pmd/pmd/blob/master/docs/pages/pmd/userdocs/extending/writing_rules_intro.md" >
2020-11-14 09:20:07 +00:00
< div class = "summary" > Writing your own PMD rules< / div >
2022-02-25 09:51:51 +00:00
< div id = "inline-toc" > <!-- empty, move TOC here when screen size too small --> < / div >
2020-11-14 09:20:07 +00:00
< p > PMD is a framework to perform code analysis. You can create your own rules to
check for patterns specific to your codebase, or the coding practices of your
team.< / p >
< h2 id = "how-rules-work-the-ast" > How rules work: the AST< / h2 >
< p > Before running rules, PMD parses the source file into a data structure called an
< strong > abstract syntax tree (AST)< / strong > . This tree represents the syntactic structure of the
code, and encodes syntactic relations between source code elements. For instance,
in Java, method declarations belong to a class: in the AST, the nodes representing
method declarations will be descendants of a node representing the declaration of
their enclosing class. This representation is thus much richer than the original
source code (which, for a program, is just a chain of characters), or the token
chain produced by a lexer (which is e.g. what Checkstyle works on). For example:< / p >
< table >
< colgroup >
< col width = "40%" / >
< col width = "70%" / >
< / colgroup >
< thead >
< tr class = "header" >
< th > Sample code (Java)< / th >
< th > AST< / th >
< / tr >
< / thead >
< tbody >
< tr >
< td >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "kd" > class< / span > < span class = "nc" > Foo< / span > < span class = "kd" > extends< / span > < span class = "nc" > Object< / span > < span class = "o" > {< / span >
< span class = "o" > }< / span >
< / code > < / pre > < / div > < / div >
< / td >
< td >
< div class = "language-java highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "err" > └─< / span > < span class = "nc" > CompilationUnit< / span >
< span class = "err" > └─< / span > < span class = "nc" > TypeDeclaration< / span >
< span class = "err" > └─< / span > < span class = "nc" > ClassOrInterfaceDeclaration< / span > < span class = "s" > "Foo"< / span >
< span class = "err" > ├─< / span > < span class = "nc" > ExtendsList< / span >
< span class = "err" > │< / span > < span class = "err" > └─< / span > < span class = "nc" > ClassOrInterfaceType< / span > < span class = "s" > "Object"< / span >
< span class = "err" > └─< / span > < span class = "nc" > ClassOrInterfaceBody< / span >
< / code > < / pre > < / div > < / div >
< / td >
< / tr >
< / tbody >
< / table >
< p > Conceptually, PMD rules work by < strong > matching a “pattern” against the AST< / strong > of a
file.
Rules explore the AST and find nodes that satisfy some conditions that are characteristic
of the specific thing the rule is trying to flag. Rules then report a violation on these nodes.< / p >
< h3 id = "discovering-the-ast" > Discovering the AST< / h3 >
2022-06-25 10:10:40 +00:00
< p > ASTs are represented by Java classes deriving from < a href = "https://docs.pmd-code.org/apidocs/pmd-core/6.48.0-SNAPSHOT/net/sourceforge/pmd/lang/ast/Node.html#" > < code > Node< / code > < / a > .
2020-11-14 09:20:07 +00:00
Each PMD language has its own set of such classes, and its own rules about how
these classes relate to one another, based on the grammar of the language. For
2022-06-25 10:10:40 +00:00
example, all Java AST nodes extend < a href = "https://docs.pmd-code.org/apidocs/pmd-java/6.48.0-SNAPSHOT/net/sourceforge/pmd/lang/java/ast/JavaNode.html#" > < code > JavaNode< / code > < / a > .< / p >
2020-11-14 09:20:07 +00:00
< p > The structure of the AST can be discovered through< / p >
< ul >
< li > the < a href = "pmd_userdocs_extending_designer_reference.html#ast-inspection" > Rule Designer< / a > < / li >
< li > the < a href = "pmd_devdocs_experimental_ast_dump.html" > AST dump feature< / a > < / li >
< / ul >
< h2 id = "writing-new-rules" > Writing new rules< / h2 >
< p > PMD supports two ways to define rules: using an < strong > XPath query< / strong > , or using a
< strong > Java visitor< / strong > . XPath rules are much easier to set up, since they’
directly in your ruleset XML, and are expressive enough for nearly any task.< / p >
< p > On the other hand, some parts of PMD’
accessing the usages of a declaration. And Java rules allow you to do some
complicated processing, to which an XPath rule couldn’ < / p >
< p > In the end, choosing one strategy or the other depends on the difficulty of what
your rule does. I’ < / p >
< h2 id = "xml-rule-definition" > XML rule definition< / h2 >
< p > New rules must be declared in a ruleset before they’
case for both XPath and Java rules. To do this, the < code class = "language-plaintext highlighter-rouge" > rule< / code > element is used, but
instead of mentioning the < code class = "language-plaintext highlighter-rouge" > ref< / code > attribute, it mentions the < code class = "language-plaintext highlighter-rouge" > class< / code > attribute,
with the implementation class of your rule.< / p >
< ul >
< li > < strong > For Java rules:< / strong > this is the class extending AbstractRule (transitively)< / li >
< li > < strong > For XPath rules:< / strong > this is < code class = "language-plaintext highlighter-rouge" > net.sourceforge.pmd.lang.rule.XPathRule< / code > < / li >
< / ul >
< p > Example:< / p >
< div class = "language-xml highlighter-rouge" > < div class = "highlight" > < pre class = "highlight" > < code > < span class = "nt" > < rule< / span > < span class = "na" > name=< / span > < span class = "s" > "MyJavaRule"< / span >
< span class = "na" > language=< / span > < span class = "s" > "java"< / span >
< span class = "na" > message=< / span > < span class = "s" > "Violation!"< / span >
< span class = "na" > class=< / span > < span class = "s" > "com.me.MyJavaRule"< / span > < span class = "nt" > > < / span >
< span class = "nt" > < description> < / span >
Description
< span class = "nt" > < /description> < / span >
< span class = "nt" > < priority> < / span > 3< span class = "nt" > < /priority> < / span >
< span class = "nt" > < /rule> < / span >
< / code > < / pre > < / div > < / div >
< div class = "alert alert-info" role = "alert" > < i class = "fa fa-info-circle" > < / i > < b > Note:< / b > In PMD 7, the < code class = "language-plaintext highlighter-rouge" > language< / code > attribute will be required on all < code class = "language-plaintext highlighter-rouge" > rule< / code >
elements that declare a new rule. Some base rule classes set the language implicitly in their
constructor, and so this is not required in all cases for the rule to work. But this
behavior will be discontinued in PMD 7, so missing < code class = "language-plaintext highlighter-rouge" > language< / code > attributes are
reported beginning with PMD 6.27.0 as a forward compatibility warning.< / div >
< h2 id = "resource-index" > Resource index< / h2 >
< p > To learn how to write a rule:< / p >
< ul >
< li > < a href = "pmd_userdocs_extending_your_first_rule.html" > Your First Rule< / a >
introduces the basic development process of a rule with a running example< / li >
< li > < a href = "pmd_userdocs_extending_writing_xpath_rules.html" > Writing XPath Rules< / a >
explains a bit more about XPath rules and our XPath API< / li >
< li > < a href = "pmd_userdocs_extending_writing_java_rules.html" > Writing Java Rules< / a >
describes how to write a rule in Java< / li >
< / ul >
< p > To go further:< / p >
< ul >
< li > < a href = "pmd_userdocs_extending_defining_properties.html" > Defining Properties< / a >
describes how to make your rules more configurable with rule properties< / li >
< li > < a href = "pmd_userdocs_extending_testing.html" > Testing your Rules< / a > introduces
our testing framework and how you can use it to safeguard the quality of
your rule< / li >
< / ul >
< div class = "tags" >
< b > Tags: < / b >
< a href = "tag_extending.html" class = "btn btn-default navbar-btn cursorNorm" role = "button" > extending< / a >
< a href = "tag_userdocs.html" class = "btn btn-default navbar-btn cursorNorm" role = "button" > userdocs< / a >
< a href = "tag_getting_started.html" class = "btn btn-default navbar-btn cursorNorm" role = "button" > getting_started< / a >
< / div >
< / div >
< footer >
2022-03-24 11:42:13 +00:00
< hr / >
< div >
This documentation is written in markdown. < br / >
If there is something missing or can be improved, edit this page on
github and create a PR:
< a
target="_blank"
href="https://github.com/pmd/pmd/blob/master/docs/pages/pmd/userdocs/extending/writing_rules_intro.md"
role="button"
>< i class = "fa fa-github fa-lg" > < / i > Edit on GitHub< /a
>
< / div >
< hr / >
< div class = "row" >
< div class = "col-lg-12 footer" >
© 2022 PMD Open Source Project. All rights
reserved. < br / >
< span > Page last updated:< / span >
2022-07-01 04:44:00 +00:00
February 2020 (6.22.0)< br / > Site last generated: Jul 1, 2022 < br / >
2022-03-24 11:42:13 +00:00
< p >
< img src = "images/pmd-logo-small.png" alt = "Company
logo"/>
< / p >
< / div >
< / div >
2020-11-14 09:20:07 +00:00
< / footer >
2022-02-25 09:51:51 +00:00
< / div >
<!-- /.row -->
2020-11-14 09:20:07 +00:00
< / div >
2022-02-25 09:51:51 +00:00
<!-- /.container -->
< / div >
<!-- Sticky TOC column -->
< div class = "toc-col" >
2022-03-24 11:42:13 +00:00
< div id = "toc" > < / div >
2020-11-14 09:20:07 +00:00
< / div >
2022-02-25 09:51:51 +00:00
<!-- /.toc - container - wrapper -->
2020-11-14 09:20:07 +00:00
< / div >
< / div >
< / body >
< / html >
