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SONARJAVA-6100 : Implement rule S8450 - Use IO.readln() for console input instead of BufferedReader boilerplate (#5460)
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9 files changed

Lines changed: 267 additions & 2 deletions

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‎its/autoscan/src/test/java/org/sonar/java/it/AutoScanTest.java‎

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@@ -199,7 +199,7 @@ public void javaCheckTestSources() throws Exception {
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softly.assertThat(newDiffs).containsExactlyInAnyOrderElementsOf(knownDiffs.values());
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softly.assertThat(newTotal).isEqualTo(knownTotal);
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softly.assertThat(rulesCausingFPs).hasSize(10);
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softly.assertThat(rulesNotReporting).hasSize(17);
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softly.assertThat(rulesNotReporting).hasSize(18);
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/**
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* 4. Check total number of differences (FPs + FNs)

‎its/autoscan/src/test/resources/autoscan/autoscan-diff-by-rules.json‎

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"hasTruePositives": false,
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"falseNegatives": 0,
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"falsePositives": 0
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},
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{
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"ruleKey": "S8450",
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"hasTruePositives": false,
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"falseNegatives": 0,
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"falsePositives": 0
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}
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]

‎its/autoscan/src/test/resources/autoscan/diffs/diff_S8450.json‎

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{
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"ruleKey": "S8450",
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"hasTruePositives": false,
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"falseNegatives": 0,
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"falsePositives": 0
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}

‎java-checks-test-sources/default/src/main/files/non-compiling/checks/BufferedReaderBoilerplateCheckSample.java‎

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package checks;
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import java.io.BufferedReader;
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import java.io.IO;
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import java.io.InputStreamReader;
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.Reader;
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class BufferedReaderBoilerplateCheckSample {
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void noncompliantBasic() throws IOException {
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BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); // Noncompliant {{Use "IO.readln()" instead of this "BufferedReader" boilerplate.}}
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String line = reader.readLine();
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}
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void compliantBasic() throws IOException {
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String line = IO.readln();
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}
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void noncompliantWithPrompt() throws IOException {
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System.out.print("Enter text: ");
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BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); // Noncompliant
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String line = reader.readLine();
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}
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void noncompliantInTryCatch() {
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try {
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BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); // Noncompliant
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String line = reader.readLine();
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} catch (IOException ioe) {
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ioe.printStackTrace();
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}
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}
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void noncompliantInTryWithResources() throws IOException {
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try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) { // Noncompliant
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String line = reader.readLine();
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}
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}
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void noncompliantInlineUsage() throws IOException {
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String line = new BufferedReader(new InputStreamReader(System.in)).readLine(); // Noncompliant
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}
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void compliantWithFileStream(InputStream fileStream) throws IOException {
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BufferedReader reader = new BufferedReader(new InputStreamReader(fileStream)); // Compliant - not wrapping System.in
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String line = reader.readLine();
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}
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void compliantWithExistingReader(Reader existingReader) throws IOException {
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BufferedReader reader = new BufferedReader(existingReader); // Compliant - not wrapping System.in via InputStreamReader
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String line = reader.readLine();
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}
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void compliantNoSystemIn() throws IOException {
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InputStream other = new java.io.ByteArrayInputStream(new byte[0]);
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BufferedReader reader = new BufferedReader(new InputStreamReader(other)); // Compliant - not System.in
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String line = reader.readLine();
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}
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}

‎java-checks/src/main/java/org/sonar/java/checks/BufferedReaderBoilerplateCheck.java‎

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/*
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* SonarQube Java
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* Copyright (C) 2012-2025 SonarSource Sàrl
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* mailto:info AT sonarsource DOT com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the Sonar Source-Available License Version 1, as published by SonarSource SA.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the Sonar Source-Available License for more details.
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*
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* You should have received a copy of the Sonar Source-Available License
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* along with this program; if not, see https://sonarsource.com/license/ssal/
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*/
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package org.sonar.java.checks;
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import java.util.List;
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import org.sonar.check.Rule;
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import org.sonar.java.checks.methods.AbstractMethodDetection;
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import org.sonar.plugins.java.api.JavaVersion;
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import org.sonar.plugins.java.api.JavaVersionAwareVisitor;
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import org.sonar.plugins.java.api.semantic.MethodMatchers;
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import org.sonar.plugins.java.api.tree.ExpressionTree;
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import org.sonar.plugins.java.api.tree.MemberSelectExpressionTree;
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import org.sonar.plugins.java.api.tree.NewClassTree;
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import org.sonar.plugins.java.api.tree.Tree;
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@Rule(key = "S8450")
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public class BufferedReaderBoilerplateCheck extends AbstractMethodDetection implements JavaVersionAwareVisitor {
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private static final MethodMatchers BUFFERED_READER_CONSTRUCTOR = MethodMatchers.create()
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.ofTypes("java.io.BufferedReader")
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.constructor()
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.addParametersMatcher("java.io.Reader")
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.build();
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private static final MethodMatchers INPUT_STREAM_READER_CONSTRUCTOR = MethodMatchers.create()
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.ofTypes("java.io.InputStreamReader")
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.constructor()
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.addParametersMatcher("java.io.InputStream")
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.build();
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@Override
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public boolean isCompatibleWithJavaVersion(JavaVersion version) {
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return version.isJava25Compatible();
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}
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@Override
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public List<Tree.Kind> nodesToVisit() {
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return List.of(Tree.Kind.NEW_CLASS);
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}
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@Override
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protected MethodMatchers getMethodInvocationMatchers() {
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return BUFFERED_READER_CONSTRUCTOR;
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}
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@Override
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protected void onConstructorFound(NewClassTree newClassTree) {
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if (newClassTree.arguments().get(0) instanceof NewClassTree innerNewClass
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&& INPUT_STREAM_READER_CONSTRUCTOR.matches(innerNewClass)
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&& isSystemIn(innerNewClass.arguments().get(0))) {
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reportIssue(newClassTree, "Use \"IO.readln()\" instead of this \"BufferedReader\" boilerplate.");
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}
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}
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private static boolean isSystemIn(ExpressionTree expression) {
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return expression instanceof MemberSelectExpressionTree memberSelect
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&&"in".equals(memberSelect.identifier().name())
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&& memberSelect.expression().symbolType().is("java.lang.System");
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}
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}

‎java-checks/src/test/java/org/sonar/java/checks/BufferedReaderBoilerplateCheckTest.java‎

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/*
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* SonarQube Java
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* Copyright (C) 2012-2025 SonarSource Sàrl
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* mailto:info AT sonarsource DOT com
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the Sonar Source-Available License Version 1, as published by SonarSource SA.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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* See the Sonar Source-Available License for more details.
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*
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* You should have received a copy of the Sonar Source-Available License
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* along with this program; if not, see https://sonarsource.com/license/ssal/
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*/
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package org.sonar.java.checks;
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import org.junit.jupiter.api.Test;
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import org.sonar.java.checks.verifier.CheckVerifier;
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import static org.sonar.java.checks.verifier.TestUtils.nonCompilingTestSourcesPath;
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class BufferedReaderBoilerplateCheckTest {
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@Test
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void test() {
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CheckVerifier.newVerifier()
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.onFile(nonCompilingTestSourcesPath("checks/BufferedReaderBoilerplateCheckSample.java"))
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.withCheck(new BufferedReaderBoilerplateCheck())
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.withJavaVersion(25)
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.verifyIssues();
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}
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@Test
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void test_jav24() {
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CheckVerifier.newVerifier()
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.onFile(nonCompilingTestSourcesPath("checks/BufferedReaderBoilerplateCheckSample.java"))
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.withCheck(new BufferedReaderBoilerplateCheck())
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.withJavaVersion(24)
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.verifyNoIssues();
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}
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}

‎sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/S8450.html‎

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<p>The <code>java.io.IO</code> class provides simple methods for interactive console I/O. For standard console input, <code>IO.readln()</code> should
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be preferred over the traditional, more verbose <code>BufferedReader</code>.</p>
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<h2>Why is this an issue?</h2>
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<p>Traditionally, reading a line from the console required significant boilerplate code, involving <code>InputStreamReader</code>,
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<code>BufferedReader</code>, and explicit <code>IOException</code> handling. This pattern is not only verbose but also error-prone and harder to
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read.</p>
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<p>The modern <code>IO.readln()</code> method:</p>
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<ul>
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<li> Reduces boilerplate by providing a single-method call for reading lines. </li>
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<li> Eliminates the need for explicit checked exception handling for standard console input. </li>
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<li> Allows for an optional prompt string, combining the "print" and "read" steps into one cohesive operation. </li>
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<li> Avoids the resource management overhead (like <code>try-with-resources</code>) required for manual stream wrappers. </li>
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</ul>
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<h2>How to fix it</h2>
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<p>Replace manual stream wrapping of <code>System.in</code> with the static <code>IO.readln()</code> method. If you are using a version of Java where
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<code>IO</code> is automatically imported (such as in JShell or modern entry points), you can call <code>readln()</code> directly; otherwise, use
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<code>import static java.io.IO.readln;</code>.</p>
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<h3>Code examples</h3>
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<h4>Noncompliant code example</h4>
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<pre data-diff-id="1" data-diff-type="noncompliant">
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import java.io.BufferedReader;
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import java.io.InputStreamReader;
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import java.io.IOException;
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void main() {
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try {
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System.out.print("Enter text: ");
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BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
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String line = reader.readLine(); // Noncompliant: verbose boilerplate
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System.out.println(line);
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} catch (IOException ioe) {
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ioe.printStackTrace();
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}
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}
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</pre>
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<h4>Compliant solution</h4>
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<pre data-diff-id="1" data-diff-type="compliant">
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import static java.io.IO.readln;
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void main() {
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// Compliant: concise and readable console input
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String line = readln("Enter text: ");
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System.out.println(line);
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}
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</pre>
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<h2>Resources</h2>
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<h3>Documentation</h3>
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<ul>
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<li> <a href="https://openjdk.org/jeps/512">JEP 512: Compact Source Files and Instance Main Methods</a> </li>
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</ul>
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‎sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/S8450.json‎

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{
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"title": "Prefer \"IO.readln()\" over \"BufferedReader\" boilerplate",
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"type": "CODE_SMELL",
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"status": "ready",
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"remediation": {
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"func": "Constant\/Issue",
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"constantCost": "5min"
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},
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"tags": [
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"java25"
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],
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"defaultSeverity": "Minor",
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"ruleSpecification": "RSPEC-8450",
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"sqKey": "S8450",
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"scope": "All",
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"quickfix": "unknown",
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"code": {
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"impacts": {
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"MAINTAINABILITY": "LOW"
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},
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"attribute": "CONVENTIONAL"
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}
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}

‎sonar-java-plugin/src/main/resources/org/sonar/l10n/java/rules/java/Sonar_way_profile.json‎

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"S8432",
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"S8433",
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"S8444",
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"S8445"
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"S8445",
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"S8450"
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]
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}

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