001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2024 the original author or authors.
004//
005// This library is free software; you can redistribute it and/or
006// modify it under the terms of the GNU Lesser General Public
007// License as published by the Free Software Foundation; either
008// version 2.1 of the License, or (at your option) any later version.
009//
010// This library is distributed in the hope that it will be useful,
011// but WITHOUT ANY WARRANTY; without even the implied warranty of
012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
013// Lesser General Public License for more details.
014//
015// You should have received a copy of the GNU Lesser General Public
016// License along with this library; if not, write to the Free Software
017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
018///////////////////////////////////////////////////////////////////////////////////////////////
019
020package com.puppycrawl.tools.checkstyle.checks.imports;
021
022import java.util.HashSet;
023import java.util.Set;
024
025import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
026import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
027import com.puppycrawl.tools.checkstyle.api.DetailAST;
028import com.puppycrawl.tools.checkstyle.api.FullIdent;
029import com.puppycrawl.tools.checkstyle.api.TokenTypes;
030
031/**
032 * <p>
033 * Checks for redundant import statements. An import statement is
034 * considered redundant if:
035 * </p>
036 * <ul>
037 *   <li>It is a duplicate of another import. This is, when a class is imported
038 *   more than once.</li>
039 *   <li>The class non-statically imported is from the {@code java.lang}
040 *   package, e.g. importing {@code java.lang.String}.</li>
041 *   <li>The class non-statically imported is from the same package as the
042 *   current package.</li>
043 * </ul>
044 * <p>
045 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
046 * </p>
047 * <p>
048 * Violation Message Keys:
049 * </p>
050 * <ul>
051 * <li>
052 * {@code import.duplicate}
053 * </li>
054 * <li>
055 * {@code import.lang}
056 * </li>
057 * <li>
058 * {@code import.same}
059 * </li>
060 * </ul>
061 *
062 * @since 3.0
063 */
064@FileStatefulCheck
065public class RedundantImportCheck
066    extends AbstractCheck {
067
068    /**
069     * A key is pointing to the warning message text in "messages.properties"
070     * file.
071     */
072    public static final String MSG_LANG = "import.lang";
073
074    /**
075     * A key is pointing to the warning message text in "messages.properties"
076     * file.
077     */
078    public static final String MSG_SAME = "import.same";
079
080    /**
081     * A key is pointing to the warning message text in "messages.properties"
082     * file.
083     */
084    public static final String MSG_DUPLICATE = "import.duplicate";
085
086    /** Set of the imports. */
087    private final Set<FullIdent> imports = new HashSet<>();
088    /** Set of static imports. */
089    private final Set<FullIdent> staticImports = new HashSet<>();
090
091    /** Name of package in file. */
092    private String pkgName;
093
094    @Override
095    public void beginTree(DetailAST aRootAST) {
096        pkgName = null;
097        imports.clear();
098        staticImports.clear();
099    }
100
101    @Override
102    public int[] getDefaultTokens() {
103        return getRequiredTokens();
104    }
105
106    @Override
107    public int[] getAcceptableTokens() {
108        return getRequiredTokens();
109    }
110
111    @Override
112    public int[] getRequiredTokens() {
113        return new int[] {
114            TokenTypes.IMPORT, TokenTypes.STATIC_IMPORT, TokenTypes.PACKAGE_DEF,
115        };
116    }
117
118    @Override
119    public void visitToken(DetailAST ast) {
120        if (ast.getType() == TokenTypes.PACKAGE_DEF) {
121            pkgName = FullIdent.createFullIdent(
122                    ast.getLastChild().getPreviousSibling()).getText();
123        }
124        else if (ast.getType() == TokenTypes.IMPORT) {
125            final FullIdent imp = FullIdent.createFullIdentBelow(ast);
126            final String importText = imp.getText();
127            if (isFromPackage(importText, "java.lang")) {
128                log(ast, MSG_LANG, importText);
129            }
130            // imports from unnamed package are not allowed,
131            // so we are checking SAME rule only for named packages
132            else if (pkgName != null && isFromPackage(importText, pkgName)) {
133                log(ast, MSG_SAME, importText);
134            }
135            // Check for a duplicate import
136            imports.stream().filter(full -> importText.equals(full.getText()))
137                .forEach(full -> log(ast, MSG_DUPLICATE, full.getLineNo(), importText));
138
139            imports.add(imp);
140        }
141        else {
142            // Check for a duplicate static import
143            final FullIdent imp =
144                FullIdent.createFullIdent(
145                    ast.getLastChild().getPreviousSibling());
146            staticImports.stream().filter(full -> imp.getText().equals(full.getText()))
147                .forEach(full -> log(ast, MSG_DUPLICATE, full.getLineNo(), imp.getText()));
148
149            staticImports.add(imp);
150        }
151    }
152
153    /**
154     * Determines if an import statement is for types from a specified package.
155     *
156     * @param importName the import name
157     * @param pkg the package name
158     * @return whether from the package
159     */
160    private static boolean isFromPackage(String importName, String pkg) {
161        // imports from unnamed package are not allowed:
162        // https://docs.oracle.com/javase/specs/jls/se7/html/jls-7.html#jls-7.5
163        // So '.' must be present in member name and we are not checking for it
164        final int index = importName.lastIndexOf('.');
165        final String front = importName.substring(0, index);
166        return pkg.equals(front);
167    }
168
169}