src/main/java/com/puppycrawl/tools/checkstyle/checks/imports/AvoidStarImportCheck.java

////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code for adherence to a set of rules.
// Copyright (C) 2001-2017 the original author or authors.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
////////////////////////////////////////////////////////////////////////////////

package com.puppycrawl.tools.checkstyle.checks.imports;

import java.util.ArrayList;
import java.util.List;

import com.puppycrawl.tools.checkstyle.StatelessCheck;
import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.FullIdent;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;

/**
 * <p>
 * Check that finds import statements that use the * notation.
 * </p>
 * <p>
 * Rationale: Importing all classes from a package or static
 * members from a class leads to tight coupling between packages
 * or classes and might lead to problems when a new version of a
 * library introduces name clashes.
 * </p>
 * <p>
 * An example of how to configure the check is:
 * </p>
 * <pre>
 * &lt;module name="AvoidStarImport"&gt;
 *   &lt;property name="excludes" value="java.io,java.net,java.lang.Math"/&gt;
 *   &lt;property name="allowClassImports" value="false"/&gt;
 *   &lt;property name="allowStaticMemberImports" value="false"/&gt;
 * &lt;/module&gt;
 * </pre>
 * The optional "excludes" property allows for certain packages like
 * java.io or java.net to be exempted from the rule. It also is used to
 * allow certain classes like java.lang.Math or java.io.File to be
 * excluded in order to support static member imports.
 *
 * <p>The optional "allowClassImports" when set to true, will allow starred
 * class imports but will not affect static member imports.
 *
 * <p>The optional "allowStaticMemberImports" when set to true will allow
 * starred static member imports but will not affect class imports.
 *
 * @author Oliver Burn
 * @author <a href="bschneider@vecna.com">Bill Schneider</a>
 * @author Travis Schneeberger
 */
@StatelessCheck
public class AvoidStarImportCheck
    extends AbstractCheck {

    /**
     * A key is pointing to the warning message text in "messages.properties"
     * file.
     */
    public static final String MSG_KEY = "import.avoidStar";

    /** Suffix for the star import. */
    private static final String STAR_IMPORT_SUFFIX = ".*";

    /** The packages/classes to exempt from this check. */
    private final List<String> excludes = new ArrayList<>();

    /** Whether to allow all class imports. */
    private boolean allowClassImports;

    /** Whether to allow all static member imports. */
    private boolean allowStaticMemberImports;

    @Override
    public int[] getDefaultTokens() {
        return new int[] {TokenTypes.IMPORT, TokenTypes.STATIC_IMPORT};
    }

    @Override
    public int[] getAcceptableTokens() {
        return new int[] {TokenTypes.IMPORT, TokenTypes.STATIC_IMPORT};
    }

    @Override
    public int[] getRequiredTokens() {
        // original implementation checks both IMPORT and STATIC_IMPORT tokens to avoid ".*" imports
        // however user can allow using "import" or "import static"
        // by configuring allowClassImports and allowStaticMemberImports
        // To avoid potential confusion when user specifies conflicting options on configuration
        // (see example below) we are adding both tokens to Required list
        //   <module name="AvoidStarImport">
        //      <property name="tokens" value="IMPORT"/>
        //      <property name="allowStaticMemberImports" value="false"/>
        //   </module>
        return new int[] {TokenTypes.IMPORT, TokenTypes.STATIC_IMPORT};
    }

    /**
     * Sets the list of packages or classes to be exempt from the check.
     * The excludes can contain a .* or not.
     * @param excludesParam a list of package names/fully-qualifies class names
     *     where star imports are ok.
     */
    public void setExcludes(String... excludesParam) {
        for (final String exclude : excludesParam) {
            if (exclude.endsWith(STAR_IMPORT_SUFFIX)) {
                excludes.add(exclude);
            }
            else {
                excludes.add(exclude + STAR_IMPORT_SUFFIX);
            }
        }
    }

    /**
     * Sets whether or not to allow all non-static class imports.
     * @param allow true to allow false to disallow
     */
    public void setAllowClassImports(boolean allow) {
        allowClassImports = allow;
    }

    /**
     * Sets whether or not to allow all static member imports.
     * @param allow true to allow false to disallow
     */
    public void setAllowStaticMemberImports(boolean allow) {
        allowStaticMemberImports = allow;
    }

    @Override
    public void visitToken(final DetailAST ast) {
        if (!allowClassImports && ast.getType() == TokenTypes.IMPORT) {
            final DetailAST startingDot = ast.getFirstChild();
            logsStarredImportViolation(startingDot);
        }
        else if (!allowStaticMemberImports
            && ast.getType() == TokenTypes.STATIC_IMPORT) {
            // must navigate past the static keyword
            final DetailAST startingDot = ast.getFirstChild().getNextSibling();
            logsStarredImportViolation(startingDot);
        }
    }

    /**
     * Gets the full import identifier.  If the import is a starred import and
     * it's not excluded then a violation is logged.
     * @param startingDot the starting dot for the import statement
     */
    private void logsStarredImportViolation(DetailAST startingDot) {
        final FullIdent name = FullIdent.createFullIdent(startingDot);
        final String importText = name.getText();
        if (importText.endsWith(STAR_IMPORT_SUFFIX) && !excludes.contains(importText)) {
            log(startingDot.getLineNo(), MSG_KEY, importText);
        }
    }

}