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| |
| ------ |
| Writing a custom rule |
| ------ |
| Brian Fox |
| ------ |
| Nov 2007 |
| ------ |
| |
| Writing a custom rule |
| |
| Custom rules are easy to make with the <<<maven-enforcer-rule-api>>>. These rules can then be invoked with the |
| {{{http://maven.apache.org/plugins/maven-enforcer-plugin/}maven-enforcer-plugin}}. |
| |
| Note: The files shown below may be downloaded here: {{{./custom-rule.zip}custom-rule.zip}} |
| |
| [[1]] First make a new jar project starting with the sample pom below: |
| |
| +---+ |
| <?xml version="1.0" encoding="UTF-8"?> |
| <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> |
| <modelVersion>4.0.0</modelVersion> |
| <groupId>custom-rule</groupId> |
| <artifactId>custom-rule-sample</artifactId> |
| <packaging>jar</packaging> |
| <version>1.0</version> |
| <name>My Custom Rule</name> |
| <description>This is my custom rule.</description> |
| <properties> |
| <api.version>1.0-beta-1</api.version> |
| <maven.version>2.0.9</maven.version> |
| </properties> |
| <build> |
| </build> |
| <dependencies> |
| <dependency> |
| <groupId>org.apache.maven.enforcer</groupId> |
| <artifactId>enforcer-api</artifactId> |
| <version>${api.version}</version> |
| </dependency> |
| <dependency> |
| <groupId>org.apache.maven</groupId> |
| <artifactId>maven-project</artifactId> |
| <version>${maven.version}</version> |
| </dependency> |
| <dependency> |
| <groupId>org.apache.maven</groupId> |
| <artifactId>maven-core</artifactId> |
| <version>${maven.version}</version> |
| </dependency> |
| <dependency> |
| <groupId>org.apache.maven</groupId> |
| <artifactId>maven-artifact</artifactId> |
| <version>${maven.version}</version> |
| </dependency> |
| <dependency> |
| <groupId>org.apache.maven</groupId> |
| <artifactId>maven-plugin-api</artifactId> |
| <version>${maven.version}</version> |
| </dependency> |
| <dependency> |
| <groupId>org.codehaus.plexus</groupId> |
| <artifactId>plexus-container-default</artifactId> |
| <version>1.0-alpha-9</version> |
| </dependency> |
| <dependency> |
| <groupId>junit</groupId> |
| <artifactId>junit</artifactId> |
| <version>3.8.1</version> |
| <scope>test</scope> |
| </dependency> |
| </dependencies> |
| </project> |
| +---+ |
| |
| [[2]] Create your rule class. The rule must implement the {{{./apidocs/index.html}EnforcerRule}} interface. |
| The rule can get access to components and the log via the {{{./apidocs/index.html}EnforcerRuleHelper}} interface. |
| If the rule succeeds, it should just simply return. If the rule fails, it should throw an {{{./apidocs/index.html}EnforcerRuleException}} with a descriptive message telling the user why the rule failed. |
| |
| There are several methods that must be implemented related to caching. |
| |
| Here's a sample class that shows how to access the helper methods and retrieve components by class name from the helper: |
| |
| +---+ |
| package org.apache.maven.enforcer.rule; |
| |
| import org.apache.maven.artifact.resolver.ArtifactResolver; |
| import org.apache.maven.enforcer.rule.api.EnforcerRule; |
| import org.apache.maven.enforcer.rule.api.EnforcerRuleException; |
| import org.apache.maven.enforcer.rule.api.EnforcerRuleHelper; |
| import org.apache.maven.execution.MavenSession; |
| import org.apache.maven.execution.RuntimeInformation; |
| import org.apache.maven.plugin.logging.Log; |
| import org.apache.maven.project.MavenProject; |
| import org.codehaus.plexus.component.configurator.expression.ExpressionEvaluationException; |
| import org.codehaus.plexus.component.repository.exception.ComponentLookupException; |
| |
| /** |
| * @author <a href="mailto:brianf@apache.org">Brian Fox</a> |
| */ |
| public class MyCustomRule |
| implements EnforcerRule |
| { |
| /** |
| * Simple param. This rule will fail if the value is true. |
| */ |
| private boolean shouldIfail = false; |
| |
| public void execute( EnforcerRuleHelper helper ) |
| throws EnforcerRuleException |
| { |
| Log log = helper.getLog(); |
| |
| try |
| { |
| // get the various expressions out of the helper. |
| MavenProject project = (MavenProject) helper.evaluate( "${project}" ); |
| MavenSession session = (MavenSession) helper.evaluate( "${session}" ); |
| String target = (String) helper.evaluate( "${project.build.directory}" ); |
| String artifactId = (String) helper.evaluate( "${project.artifactId}" ); |
| |
| // retrieveany component out of the session directly |
| ArtifactResolver resolver = (ArtifactResolver) helper.getComponent( ArtifactResolver.class ); |
| RuntimeInformation rti = (RuntimeInformation) helper.getComponent( RuntimeInformation.class ); |
| |
| log.info( "Retrieved Target Folder: " + target ); |
| log.info( "Retrieved ArtifactId: " +artifactId ); |
| log.info( "Retrieved Project: " + project ); |
| log.info( "Retrieved RuntimeInfo: " + rti ); |
| log.info( "Retrieved Session: " + session ); |
| log.info( "Retrieved Resolver: " + resolver ); |
| |
| if ( this.shouldIfail ) |
| { |
| throw new EnforcerRuleException( "Failing because my param said so." ); |
| } |
| } |
| catch ( ComponentLookupException e ) |
| { |
| throw new EnforcerRuleException( "Unable to lookup a component " + e.getLocalizedMessage(), e ); |
| } |
| catch ( ExpressionEvaluationException e ) |
| { |
| throw new EnforcerRuleException( "Unable to lookup an expression " + e.getLocalizedMessage(), e ); |
| } |
| } |
| |
| /** |
| * If your rule is cacheable, you must return a unique id when parameters or conditions |
| * change that would cause the result to be different. Multiple cached results are stored |
| * based on their id. |
| * |
| * The easiest way to do this is to return a hash computed from the values of your parameters. |
| * |
| * If your rule is not cacheable, then the result here is not important, you may return anything. |
| */ |
| public String getCacheId() |
| { |
| //no hash on boolean...only parameter so no hash is needed. |
| return ""+this.shouldIfail; |
| } |
| |
| /** |
| * This tells the system if the results are cacheable at all. Keep in mind that during |
| * forked builds and other things, a given rule may be executed more than once for the same |
| * project. This means that even things that change from project to project may still |
| * be cacheable in certain instances. |
| */ |
| public boolean isCacheable() |
| { |
| return false; |
| } |
| |
| /** |
| * If the rule is cacheable and the same id is found in the cache, the stored results |
| * are passed to this method to allow double checking of the results. Most of the time |
| * this can be done by generating unique ids, but sometimes the results of objects returned |
| * by the helper need to be queried. You may for example, store certain objects in your rule |
| * and then query them later. |
| */ |
| public boolean isResultValid( EnforcerRule arg0 ) |
| { |
| return false; |
| } |
| } |
| +---+ |
| |
| [[3]] Build and Install or Deploy your custom rule. |
| |
| [[4]] Add your custom-rule artifact as a dependency of the <<<maven-enforcer-plugin>>> in your build: |
| |
| +---+ |
| <project> |
| ... |
| <build> |
| <plugins> |
| <plugin> |
| <groupId>org.apache.maven.plugins</groupId> |
| <artifactId>maven-enforcer-plugin</artifactId> |
| <dependencies> |
| <dependency> |
| <groupId>custom-rule</groupId> |
| <artifactId>custom-rule-sample</artifactId> |
| <version>1.0</version> |
| </dependency> |
| </dependencies> |
| ... |
| </plugin> |
| </plugins> |
| </build> |
| ... |
| </project> |
| +---+ |
| |
| [[5]] Add your rule to the configuration section of the <<<maven-enforcer-plugin>>>. The name of your class will be the name of the rule, and |
| you must add an <<<implementation>>> hint that contains the fully qualified class name: |
| |
| +---+ |
| ... |
| <configuration> |
| <rules> |
| <myCustomRule implementation="org.apache.maven.enforcer.rule.MyCustomRule"> |
| <shouldIfail>true</shouldIfail> |
| </myCustomRule> |
| </rules> |
| </configuration> |
| ... |
| +---+ |
| |
| [[6]] That's it. The full plugin config may look like this: |
| |
| +---+ |
| <project> |
| ... |
| <build> |
| <plugins> |
| <plugin> |
| <groupId>org.apache.maven.plugins</groupId> |
| <artifactId>maven-enforcer-plugin</artifactId> |
| <version>1.0-beta-1</version> |
| <dependencies> |
| <dependency> |
| <groupId>custom-rule</groupId> |
| <artifactId>custom-rule-sample</artifactId> |
| <version>1.0</version> |
| </dependency> |
| </dependencies> |
| <executions> |
| <execution> |
| <id>enforce</id> |
| <configuration> |
| <rules> |
| <myCustomRule implementation="org.apache.maven.enforcer.rule.MyCustomRule"> |
| <shouldIfail>false</shouldIfail> |
| </myCustomRule> |
| </rules> |
| </configuration> |
| <goals> |
| <goal>enforce</goal> |
| </goals> |
| </execution> |
| </executions> |
| </plugin> |
| </plugins> |
| </build> |
| ... |
| </project> |
| +---+ |