BAEL 7277 - Find Files by Extension in Specified Directory in Java (#15356)

* new module: libraries-7

* ready for review

libraries-6/README.md

@@ -17,4 +17,4 @@ Remember, for advanced libraries like [Jackson](/jackson) and [JUnit](/testing-m
 - [Using libphonenumber to Validate Phone Numbers](https://www.baeldung.com/java-libphonenumber)
 - [Apache Commons Collections vs Google Guava](https://www.baeldung.com/apache-commons-collections-vs-guava)
 - [Guide to Using ModelMapper](https://www.baeldung.com/java-modelmapper)
-- More articles [[<-- prev]](/libraries-5)
+- More articles [[<-- prev]](/libraries-5) [[next -->]](/libraries-7)

libraries-7/README.md

@@ -0,0 +1,11 @@
+## Libraries-7
+
+This module contains articles about various Java libraries. 
+These are small libraries that are relatively easy to use and do not require any separate module of their own.
+
+The code examples related to different libraries are each in their own module.
+
+Remember, for advanced libraries like [Jackson](/jackson) and [JUnit](/testing-modules) we already have separate modules. Please make sure to have a look at the existing modules in such cases.
+
+### Relevant articles
+- More articles [[<-- prev]](/libraries-6)

libraries-7/pom.xml

@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>libraries-7</artifactId>
+
+    <parent>
+        <artifactId>parent-modules</artifactId>
+        <groupId>com.baeldung</groupId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>commons-io</groupId>
+            <artifactId>commons-io</artifactId>
+            <version>${commons-io.version}</version>
+        </dependency>
+    </dependencies>
+
+</project>

libraries-7/src/main/java/com/baeldung/findfiles/FindFileApacheUtils.java

@@ -0,0 +1,29 @@
+package com.baeldung.findfiles;
+
+import java.io.File;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Iterator;
+
+import org.apache.commons.io.FileUtils;
+import org.apache.commons.io.filefilter.TrueFileFilter;
+import org.apache.commons.io.filefilter.WildcardFileFilter;
+
+public class FindFileApacheUtils {
+
+    private FindFileApacheUtils() {
+    }
+
+    public static Iterator<File> find(Path startPath, String extension) {
+        if (!Files.isDirectory(startPath)) {
+            throw new IllegalArgumentException("Provided path is not a directory: " + startPath);
+        }
+
+        if (!extension.startsWith("."))
+            extension = "." + extension;
+
+        return FileUtils.iterateFiles(startPath.toFile(), WildcardFileFilter.builder()
+            .setWildcards("*" + extension)
+            .get(), TrueFileFilter.INSTANCE);
+    }
+}

libraries-7/src/main/java/com/baeldung/findfiles/FindFileJava2Utils.java

@@ -0,0 +1,34 @@
+package com.baeldung.findfiles;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.List;
+
+public class FindFileJava2Utils {
+
+    private FindFileJava2Utils() {
+    }
+
+    public static List<File> find(File startPath, String extension) {
+        if (!startPath.isDirectory()) {
+            throw new IllegalArgumentException("Provided path is not a directory: " + startPath);
+        }
+
+        List<File> matches = new ArrayList<>();
+
+        File[] files = startPath.listFiles();
+        if (files == null)
+            return matches;
+
+        MatchExtensionPredicate filter = new MatchExtensionPredicate(extension);
+        for (File file : files) {
+            if (file.isDirectory()) {
+                matches.addAll(find(file, extension));
+            } else if (filter.test(file.toPath())) {
+                matches.add(file);
+            }
+        }
+
+        return matches;
+    }
+}

libraries-7/src/main/java/com/baeldung/findfiles/FindFileJava7Utils.java

@@ -0,0 +1,44 @@
+package com.baeldung.findfiles;
+
+import java.io.IOException;
+import java.nio.file.FileVisitResult;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.SimpleFileVisitor;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.util.ArrayList;
+import java.util.List;
+
+public class FindFileJava7Utils {
+
+    private FindFileJava7Utils() {
+    }
+
+    public static List<Path> find(Path startPath, String extension) throws IOException {
+        if (!Files.isDirectory(startPath)) {
+            throw new IllegalArgumentException("Provided path is not a directory: " + startPath);
+        }
+
+        final List<Path> matches = new ArrayList<>();
+        MatchExtensionPredicate filter = new MatchExtensionPredicate(extension);
+
+        Files.walkFileTree(startPath, new SimpleFileVisitor<Path>() {
+
+            @Override
+            public FileVisitResult visitFile(Path file, BasicFileAttributes attributes) {
+                if (filter.test(file)) {
+                    matches.add(file);
+                }
+
+                return FileVisitResult.CONTINUE;
+            }
+
+            @Override
+            public FileVisitResult visitFileFailed(Path file, IOException exc) {
+                return FileVisitResult.CONTINUE;
+            }
+        });
+
+        return matches;
+    }
+}

libraries-7/src/main/java/com/baeldung/findfiles/FindFileJava8Utils.java

@@ -0,0 +1,21 @@
+package com.baeldung.findfiles;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.function.Consumer;
+
+public class FindFileJava8Utils {
+
+    private FindFileJava8Utils() {
+    }
+
+    public static void find(Path startPath, String extension, Consumer<Path> consumer) throws IOException {
+        if (!Files.isDirectory(startPath)) {
+            throw new IllegalArgumentException("Provided path is not a directory: " + startPath);
+        }
+
+        MatchExtensionPredicate filter = new MatchExtensionPredicate(extension);
+        Files.walkFileTree(startPath, new SimpleFileConsumerVisitor(filter, consumer));
+    }
+}

libraries-7/src/main/java/com/baeldung/findfiles/MatchExtensionPredicate.java

@@ -0,0 +1,26 @@
+package com.baeldung.findfiles;
+
+import java.nio.file.Path;
+import java.util.function.Predicate;
+
+public class MatchExtensionPredicate implements Predicate<Path> {
+
+    private final String extension;
+
+    public MatchExtensionPredicate(String extension) {
+        if (!extension.startsWith("."))
+            extension = "." + extension;
+        this.extension = extension.toLowerCase();
+    }
+
+    @Override
+    public boolean test(Path path) {
+        if (path == null)
+            return false;
+
+        return path.getFileName()
+            .toString()
+            .toLowerCase()
+            .endsWith(extension);
+    }
+}

libraries-7/src/main/java/com/baeldung/findfiles/SimpleFileConsumerVisitor.java

@@ -0,0 +1,33 @@
+package com.baeldung.findfiles;
+
+import java.io.IOException;
+import java.nio.file.FileVisitResult;
+import java.nio.file.Path;
+import java.nio.file.SimpleFileVisitor;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+
+public class SimpleFileConsumerVisitor extends SimpleFileVisitor<Path> {
+
+    private final Predicate<Path> filter;
+    private final Consumer<Path> consumer;
+
+    public SimpleFileConsumerVisitor(MatchExtensionPredicate filter, Consumer<Path> consumer) {
+        this.filter = filter;
+        this.consumer = consumer;
+    }
+
+    @Override
+    public FileVisitResult visitFile(Path file, BasicFileAttributes attributes) {
+        if (filter.test(file))
+            consumer.accept(file);
+
+        return FileVisitResult.CONTINUE;
+    }
+
+    @Override
+    public FileVisitResult visitFileFailed(Path file, IOException exc) throws IOException {
+        return FileVisitResult.CONTINUE;
+    }
+}

libraries-7/src/test/java/com/baeldung/findfiles/FindFileUtilsIntegrationTest.java

@@ -0,0 +1,79 @@
+package com.baeldung.findfiles;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.apache.commons.io.FileUtils;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+public class FindFileUtilsIntegrationTest {
+
+    private static final String TEST_EXTENSION = ".test";
+    private static final String OTHER_EXTENSION = ".other";
+
+    private static final List<Path> TEST_FILES = new ArrayList<>();
+    private static final List<Path> OTHER_FILES = new ArrayList<>();
+
+    private static Path TEST_DIR;
+
+    @BeforeAll
+    static void setup() throws IOException {
+        TEST_DIR = Files.createTempDirectory(null);
+
+        final Path nestedDir = TEST_DIR.resolve("sub-dir");
+        Files.createDirectories(nestedDir);
+        
+        TEST_FILES.add(Files.createFile(TEST_DIR.resolve("a" + TEST_EXTENSION)));
+        OTHER_FILES.add(Files.createFile(TEST_DIR.resolve("a" + OTHER_EXTENSION)));
+
+        TEST_FILES.add(Files.createFile(nestedDir.resolve("b" + TEST_EXTENSION)));
+        OTHER_FILES.add(Files.createFile(nestedDir.resolve("b" + OTHER_EXTENSION)));
+    }
+
+    @AfterAll
+    static void cleanUp() {
+        FileUtils.deleteQuietly(TEST_DIR.toFile());
+    }
+
+    @Test
+    void whenFindFilesWithJava2_thenOnlyMatchingFilesFound() {
+        List<File> matches = FindFileJava2Utils.find(TEST_DIR.toFile(), TEST_EXTENSION);
+
+        assertEquals(TEST_FILES.size(), matches.size());
+    }
+
+    @Test
+    void whenFindFilesWithJava7_thenOnlyMatchingFilesFound() throws IOException {
+        List<Path> matches = FindFileJava7Utils.find(TEST_DIR, TEST_EXTENSION);
+
+        assertEquals(TEST_FILES.size(), matches.size());
+    }
+
+    @Test
+    void whenFindFilesWithJava8_thenOnlyMatchingFilesFound() throws IOException {
+        final AtomicInteger matches = new AtomicInteger(0);
+        FindFileJava8Utils.find(TEST_DIR, TEST_EXTENSION, path -> matches.incrementAndGet());
+
+        assertEquals(TEST_FILES.size(), matches.get());
+    }
+
+    @Test
+    void whenFindFilesWithApache_thenOnlyMatchingFilesFound() {
+        final AtomicInteger matches = new AtomicInteger(0);
+        Iterator<File> iterator = FindFileApacheUtils.find(TEST_DIR, TEST_EXTENSION);
+
+        iterator.forEachRemaining(file -> matches.incrementAndGet());
+
+        assertEquals(TEST_FILES.size(), matches.get());
+    }
+}

pom.xml

@@ -771,6 +771,7 @@
                 <module>libraries-4</module>
                 <module>libraries-5</module>
                 <module>libraries-6</module>
+                <module>libraries-7</module>
                 <module>libraries-ai</module>
                 <module>libraries-apache-commons-2</module>
                 <module>libraries-apache-commons-collections</module>
@@ -1021,6 +1022,7 @@
                 <module>libraries-4</module>
                 <module>libraries-5</module>
                 <module>libraries-6</module>
+                <module>libraries-7</module>
                 <module>libraries-ai</module>
                 <module>libraries-apache-commons-2</module>
                 <module>libraries-apache-commons-collections</module>