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Custom Checkstyle Rule Helper

Published: 12 Oct 2014

AbstractImportChecker.java simplifies the process of writing custom CheckStyle rules that examine class imports.

Note that Checkstyle contains a number of quite flexible built-in rules for managing imports, you should obviously use these if they meet your needs.

To implement your own custom import checker just sub-class AbstractImportChecker and provide an implementation for onImport():

public class ImportChecker extends AbstractImportChecker {
    @Override
    public void onImport(String packageName, String importName) {
        if (! isImportAllowedInPackage(packageName, importName)) {
            logError(String.format("Import %s not allowed in package %s", importName, packageName));
        }
    }
    
    private boolean isImportAllowedInPackage(String packageName, String importName) {
        return true; // custom logic here
    }
}

The DottedPath helper class can be used to check for sub-packages and package membership:

private boolean isImportAllowedInPackage(String packageName, String importName){
    DottedPath packagePath = new DottedPath(packageName);
    DottedPath importPath = new DottedPath(importName);
    
    return importPath.isChildOf(packagePath);
}

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