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.design;
021
022import java.util.Objects;
023
024import com.puppycrawl.tools.checkstyle.StatelessCheck;
025import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
026import com.puppycrawl.tools.checkstyle.api.DetailAST;
027import com.puppycrawl.tools.checkstyle.api.TokenTypes;
028
029/**
030 * <div>
031 * Restricts throws statements to a specified count.
032 * Methods with "Override" or "java.lang.Override" annotation are skipped
033 * from validation as current class cannot change signature of these methods.
034 * </div>
035 *
036 * <p>
037 * Rationale:
038 * Exceptions form part of a method's interface. Declaring
039 * a method to throw too many differently rooted
040 * exceptions makes exception handling onerous and leads
041 * to poor programming practices such as writing code like
042 * {@code catch(Exception ex)}. 4 is the empirical value which is based
043 * on reports that we had for the ThrowsCountCheck over big projects
044 * such as OpenJDK. This check also forces developers to put exceptions
045 * into a hierarchy such that in the simplest
046 * case, only one type of exception need be checked for by
047 * a caller but any subclasses can be caught
048 * specifically if necessary. For more information on rules
049 * for the exceptions and their issues, see Effective Java:
050 * Programming Language Guide Second Edition
051 * by Joshua Bloch pages 264-273.
052 * </p>
053 *
054 * <p>
055 * <b>ignorePrivateMethods</b> - allows to skip private methods as they do
056 * not cause problems for other classes.
057 * </p>
058 * <ul>
059 * <li>
060 * Property {@code ignorePrivateMethods} - Allow private methods to be ignored.
061 * Type is {@code boolean}.
062 * Default value is {@code true}.
063 * </li>
064 * <li>
065 * Property {@code max} - Specify maximum allowed number of throws statements.
066 * Type is {@code int}.
067 * Default value is {@code 4}.
068 * </li>
069 * </ul>
070 *
071 * <p>
072 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
073 * </p>
074 *
075 * <p>
076 * Violation Message Keys:
077 * </p>
078 * <ul>
079 * <li>
080 * {@code throws.count}
081 * </li>
082 * </ul>
083 *
084 * @since 3.2
085 */
086@StatelessCheck
087public final class ThrowsCountCheck extends AbstractCheck {
088
089    /**
090     * A key is pointing to the warning message text in "messages.properties"
091     * file.
092     */
093    public static final String MSG_KEY = "throws.count";
094
095    /** Default value of max property. */
096    private static final int DEFAULT_MAX = 4;
097
098    /** Allow private methods to be ignored. */
099    private boolean ignorePrivateMethods = true;
100
101    /** Specify maximum allowed number of throws statements. */
102    private int max;
103
104    /** Creates new instance of the check. */
105    public ThrowsCountCheck() {
106        max = DEFAULT_MAX;
107    }
108
109    @Override
110    public int[] getDefaultTokens() {
111        return getRequiredTokens();
112    }
113
114    @Override
115    public int[] getRequiredTokens() {
116        return new int[] {
117            TokenTypes.LITERAL_THROWS,
118        };
119    }
120
121    @Override
122    public int[] getAcceptableTokens() {
123        return getRequiredTokens();
124    }
125
126    /**
127     * Setter to allow private methods to be ignored.
128     *
129     * @param ignorePrivateMethods whether private methods must be ignored.
130     * @since 6.7
131     */
132    public void setIgnorePrivateMethods(boolean ignorePrivateMethods) {
133        this.ignorePrivateMethods = ignorePrivateMethods;
134    }
135
136    /**
137     * Setter to specify maximum allowed number of throws statements.
138     *
139     * @param max maximum allowed throws statements.
140     * @since 3.2
141     */
142    public void setMax(int max) {
143        this.max = max;
144    }
145
146    @Override
147    public void visitToken(DetailAST ast) {
148        if (ast.getType() == TokenTypes.LITERAL_THROWS) {
149            visitLiteralThrows(ast);
150        }
151        else {
152            throw new IllegalStateException(ast.toString());
153        }
154    }
155
156    /**
157     * Checks number of throws statements.
158     *
159     * @param ast throws for check.
160     */
161    private void visitLiteralThrows(DetailAST ast) {
162        if ((!ignorePrivateMethods || !isInPrivateMethod(ast))
163                && !isOverriding(ast)) {
164            // Account for all the commas!
165            final int count = (ast.getChildCount() + 1) / 2;
166            if (count > max) {
167                log(ast, MSG_KEY, count, max);
168            }
169        }
170    }
171
172    /**
173     * Check if a method has annotation @Override.
174     *
175     * @param ast throws, which is being checked.
176     * @return true, if a method has annotation @Override.
177     */
178    private static boolean isOverriding(DetailAST ast) {
179        final DetailAST modifiers = ast.getParent().findFirstToken(TokenTypes.MODIFIERS);
180        boolean isOverriding = false;
181        DetailAST child = modifiers.getFirstChild();
182        while (child != null) {
183            if (child.getType() == TokenTypes.ANNOTATION
184                    && "Override".equals(getAnnotationName(child))) {
185                isOverriding = true;
186                break;
187            }
188            child = child.getNextSibling();
189        }
190        return isOverriding;
191    }
192
193    /**
194     * Gets name of an annotation.
195     *
196     * @param annotation to get name of.
197     * @return name of an annotation.
198     */
199    private static String getAnnotationName(DetailAST annotation) {
200        final DetailAST dotAst = annotation.findFirstToken(TokenTypes.DOT);
201        final DetailAST parent = Objects.requireNonNullElse(dotAst, annotation);
202        return parent.findFirstToken(TokenTypes.IDENT).getText();
203    }
204
205    /**
206     * Checks if method, which throws an exception is private.
207     *
208     * @param ast throws, which is being checked.
209     * @return true, if method, which throws an exception is private.
210     */
211    private static boolean isInPrivateMethod(DetailAST ast) {
212        final DetailAST methodModifiers = ast.getParent().findFirstToken(TokenTypes.MODIFIERS);
213        return methodModifiers.findFirstToken(TokenTypes.LITERAL_PRIVATE) != null;
214    }
215
216}