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