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Graham Allan
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First example complete. A matcher that checks you're using method references by discovering the java source file from the class, scans the filesystem, and reads the source to check there's a :: before the method name. Phew.
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‎src/main/java/org/adoptopenjdk/lambda/tutorial/exercise4/Document.java‎

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import java.util.List;
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public final class Document {
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private final String title;
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private final List<Page> pages;
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public Document(List<Page> pages) {
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public Document(String title, List<Page> pages) {
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this.title = title;
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this.pages = Collections.unmodifiableList(new ArrayList<>(pages));
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}
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public String getPageContent(Integer pageNumber) {
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return this.pages.get(pageNumber).getContent();
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}
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public String getTitle() {
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return this.title;
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}
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public static final class Page {
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private final String content;
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‎src/test/java/org/adoptopenjdk/lambda/tutorial/Documents.java‎

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package org.adoptopenjdk.lambda.tutorial;
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/*
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* #%L
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* lambda-tutorial
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* %%
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* Copyright (C) 2013 Adopt OpenJDK
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* %%
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as
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* published by the Free Software Foundation, either version 2 of the
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* License, or (at your option) any later version.
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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. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public
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* License along with this program. If not, see
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* <http://www.gnu.org/licenses/gpl-2.0.html>.
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* #L%
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*/
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import org.adoptopenjdk.lambda.tutorial.exercise4.Document;
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import java.util.Arrays;
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import java.util.List;
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import static java.util.stream.Collectors.toList;
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public class Documents {
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/**
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* Return the titles from a list of documents.
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*/
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public static List<String> titlesOf(Document... documents) {
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return Arrays.stream(documents)
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.map(d -> d.getTitle())
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.collect(toList());
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}
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}

‎src/test/java/org/adoptopenjdk/lambda/tutorial/Exercise_4_Test.java‎

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@@ -22,8 +22,17 @@
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* #L%
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*/
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import org.adoptopenjdk.lambda.tutorial.exercise4.Document;
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import org.adoptopenjdk.lambda.tutorial.exercise4.Document.Page;
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import org.hamcrest.Matchers;
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import org.junit.Test;
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import java.util.Arrays;
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import java.util.function.Consumer;
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import static org.adoptopenjdk.lambda.tutorial.util.CodeUsesMethodReferencesMatcher.usesMethodReferences;
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import static org.hamcrest.MatcherAssert.assertThat;
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/**
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* Exercise 4 - Method References
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* <p>
@@ -109,6 +118,7 @@
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* </p>
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* <p>
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* <em>Constructor belonging to a particular class</em>
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* <br>
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* By now, we know how to use method references for static methods and instance methods, that leaves an odd case:
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* constructors.
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* <p>
@@ -134,5 +144,30 @@
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@SuppressWarnings("unchecked")
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public class Exercise_4_Test {
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/**
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* The <code>Documents</code> class has a method which transforms a list of <code>Document</code> into a list of
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* their titles. The implementation has already been filled out, but it uses a lambda, as in:
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* <code>.map(document -> document.getTitle())</code>
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* <br>
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* Instead of using a lambda, use a method reference instead.
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*
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* @see Documents#titlesOf(Document...)
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* @see Document#getTitle()
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*
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*/
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@Test
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public void getListOfDocumentTitlesUsingInstanceMethodReference() {
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Document expenses = new Document("My Expenses",
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Arrays.asList(new Page("LJC Open Conference ticket: £25"), new Page("Beer stipend: £100")));
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Document toDoList = new Document("My ToDo List",
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Arrays.asList(new Page("Build a todo app"), new Page("Pick up dry cleaning")));
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Document certificates = new Document("My Certificates",
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Arrays.asList(new Page("Oracle Certified Professional"), new Page("Swimming 10m")));
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assertThat(Documents.titlesOf(expenses, toDoList, certificates),
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Matchers.contains("My Expenses", "My ToDo List", "My Certificates"));
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assertThat(Documents.class, usesMethodReferences("getTitle"));
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}
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}

‎src/test/java/org/adoptopenjdk/lambda/tutorial/util/CodeUsesMethodReferencesMatcher.java‎

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package org.adoptopenjdk.lambda.tutorial.util;
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/*
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* #%L
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* lambda-tutorial
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* %%
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* Copyright (C) 2013 Adopt OpenJDK
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* %%
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as
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* published by the Free Software Foundation, either version 2 of the
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* License, or (at your option) any later version.
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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. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public
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* License along with this program. If not, see
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* <http://www.gnu.org/licenses/gpl-2.0.html>.
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* #L%
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*/
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import org.hamcrest.Description;
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import org.hamcrest.TypeSafeDiagnosingMatcher;
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import org.objectweb.asm.ClassReader;
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import org.objectweb.asm.ClassVisitor;
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import org.objectweb.asm.Opcodes;
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import java.io.File;
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import java.io.IOException;
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import java.nio.ByteBuffer;
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import java.nio.charset.StandardCharsets;
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import java.nio.file.Files;
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import java.nio.file.Path;
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import java.nio.file.Paths;
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import java.util.Arrays;
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import java.util.Optional;
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import static java.util.stream.Collectors.toList;
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public final class CodeUsesMethodReferencesMatcher extends TypeSafeDiagnosingMatcher<Class<?>> {
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private final String methodName;
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private CodeUsesMethodReferencesMatcher(String methodName) {
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this.methodName = methodName;
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}
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public static CodeUsesMethodReferencesMatcher usesMethodReferences(String methodName) {
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return new CodeUsesMethodReferencesMatcher(methodName);
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}
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@Override
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public void describeTo(Description description) {
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description.appendText("a source file using a method reference to invoke ").appendValue(methodName);
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}
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@Override
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protected boolean matchesSafely(Class<?> clazz, Description mismatchDescription) {
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try {
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Optional<String> sourceFileContent = getSourceContent(clazz);
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return sourceFileContent.map(c -> usesMethodReference(c, mismatchDescription)).orElseGet(() -> {
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mismatchDescription.appendText("could not read source file to discover if you used method references.");
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return false;
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});
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} catch (IOException e) {
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mismatchDescription.appendText("could not read source file to discover if you used method references.");
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mismatchDescription.appendValue(e);
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return false;
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}
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}
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private boolean usesMethodReference(String sourceCode, Description mismatchDescription) {
77+
if (sourceCode.contains("::"+methodName)) {
78+
return true;
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} else {
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mismatchDescription.appendText("source code did not use a method reference to invoke " + methodName + ". ");
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context(sourceCode, methodName, mismatchDescription);
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return false;
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}
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}
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private void context(String sourceCode, String methodName, Description mismatchDescription) {
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if (!sourceCode.contains(methodName)) {
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mismatchDescription.appendText("You did not appear to invoke the method at all.");
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} else {
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String[] lines = sourceCode.split("\\n");
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mismatchDescription.appendText("Actual invocations: ");
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mismatchDescription.appendValueList("[", ",", "]",
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Arrays.stream(lines).filter(l -> l.contains(methodName)).map(String::trim).collect(toList()));
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}
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}
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private Optional<String> getSourceContent(Class<?> clazz) throws IOException {
98+
String sourceFileName = getSourceFileName(clazz);
99+
Optional<File> sourceFile = findPathTo(sourceFileName);
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101+
return sourceFile.map(this::toContent);
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}
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private Optional<File> findPathTo(String sourceFileName) throws IOException {
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File cwd = new File(".");
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File rootOfProject = findRootOfProject(cwd);
107+
return findSourceFile(rootOfProject, sourceFileName);
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}
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private String toContent(File file) {
111+
try {
112+
byte[] encoded = Files.readAllBytes(Paths.get(file.toURI()));
113+
return StandardCharsets.UTF_8.decode(ByteBuffer.wrap(encoded)).toString();
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} catch (IOException e) {
115+
throw new RuntimeException("Could not read Java source file.", e);
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}
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}
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private Optional<File> findSourceFile(File rootOfProject, String sourceFileName) throws IOException {
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Path startingDir = Paths.get(rootOfProject.toURI());
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return Files.find(startingDir, 15, (path, attrs) -> path.endsWith(sourceFileName))
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.map(p -> new File(p.toUri()))
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.findFirst();
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}
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private File findRootOfProject(File cwd) {
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File[] pomFiles = cwd.listFiles((file, name) -> { return name.equals("pom.xml"); });
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if (pomFiles != null && pomFiles.length == 1) {
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return cwd;
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} else if (cwd.getParentFile() == null) {
131+
throw new RuntimeException("Couldn't find directory containing pom.xml. Last looked in: " + cwd.getAbsolutePath());
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} else {
133+
return findRootOfProject(cwd.getParentFile());
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}
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}
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private String getSourceFileName(Class<?> clazz) throws IOException {
138+
String resourceName = clazz.getName().replace(".", "/").concat(".class");
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ClassReader reader = new ClassReader(clazz.getClassLoader().getResourceAsStream(resourceName));
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SourceFileNameVisitor sourceFileNameVisitor = new SourceFileNameVisitor();
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reader.accept(sourceFileNameVisitor, 0);
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return sourceFileNameVisitor.getSourceFile();
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}
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private static final class SourceFileNameVisitor extends ClassVisitor {
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private String sourceFile = null;
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private boolean visitedYet = false;
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public SourceFileNameVisitor() {
153+
super(Opcodes.ASM5);
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}
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@Override
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public void visitSource(String source, String debug) {
158+
this.visitedYet = true;
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this.sourceFile = source;
160+
super.visitSource(source, debug);
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}
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public String getSourceFile() {
164+
if (!visitedYet) throw new IllegalStateException("Must visit a class before asking for source file");
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return this.sourceFile;
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}
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}
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}

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