[BAEL-11402] - Moved articles out of core-java (part 3)

core-java-io/src/main/java/com/baeldung/extension/Extension.java

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+package com.baeldung.extension;
+
+import com.google.common.io.Files;
+import org.apache.commons.io.FilenameUtils;
+
+import java.util.Optional;
+
+public class Extension {
+    //Instead of file name we can also specify full path of a file eg. /baeldung/com/demo/abc.java
+    public String getExtensionByApacheCommonLib(String filename) {
+        return FilenameUtils.getExtension(filename);
+    }
+
+    public Optional<String> getExtensionByStringHandling(String filename) {
+        return Optional.ofNullable(filename)
+                       .filter(f -> f.contains("."))
+                      .map(f -> f.substring(filename.lastIndexOf(".") + 1));
+    }
+
+    public String getExtensionByGuava(String filename) {
+        return Files.getFileExtension(filename);
+    }
+}

core-java-io/src/test/java/com/baeldung/extension/ExtensionUnitTest.java

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+package com.baeldung.extension;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.Optional;
+
+public class ExtensionUnitTest {
+    private Extension extension = new Extension();
+
+    @Test
+    public void getExtension_whenApacheCommonIO_thenExtensionIsTrue() {
+        String expectedExtension = "txt";
+        String actualExtension = extension.getExtensionByApacheCommonLib("jarvis.txt");
+        Assert.assertEquals(expectedExtension, actualExtension);
+    }
+
+    @Test
+    public void getExtension_whenStringHandle_thenExtensionIsTrue() {
+        String expectedExtension = "java";
+        Optional<String> actualExtension = extension.getExtensionByStringHandling("Demo.java");
+        Assert.assertEquals(expectedExtension, actualExtension.get());
+    }
+
+    @Test
+    public void getExtension_whenGuava_thenExtensionIsTrue() {
+        String expectedExtension = "class";
+        String actualExtension = extension.getExtensionByGuava("baeldung/Demo.class");
+        Assert.assertEquals(expectedExtension, actualExtension);
+    }
+}

core-java-io/src/test/java/com/baeldung/java/mimetype/MimeTypeUnitTest.java

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+package com.baeldung.java.mimetype;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.FileNameMap;
+import java.net.MalformedURLException;
+import java.net.URLConnection;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import javax.activation.MimetypesFileTypeMap;
+
+import org.apache.tika.Tika;
+import org.junit.Test;
+
+import net.sf.jmimemagic.Magic;
+import net.sf.jmimemagic.MagicException;
+import net.sf.jmimemagic.MagicMatch;
+import net.sf.jmimemagic.MagicMatchNotFoundException;
+import net.sf.jmimemagic.MagicParseException;
+
+/**
+ * Test class demonstrating various strategies to resolve MIME type of a file.
+ * @author tritty
+ *
+ */
+public class MimeTypeUnitTest {
+    /**
+     * Expected Ouput.
+     */
+    public static final String PNG_EXT = "image/png";
+
+    /**
+     * The location of the file.
+     */
+    public static final String FILE_LOC = "src/test/resources/product.png";
+
+    /**
+     * Test method, demonstrating usage in Java 7.
+     * 
+     * @throws IOException
+     */
+    @Test
+    public void whenUsingJava7_thenSuccess() throws IOException {
+        final Path path = new File(FILE_LOC).toPath();
+        final String mimeType = Files.probeContentType(path);
+        assertEquals(mimeType, PNG_EXT);
+    }
+
+    /**
+     * Test method demonstrating the usage of URLConnection to resolve MIME type.
+     * 
+     * @throws MalformedURLException
+     * @throws IOException
+     */
+    @Test
+    public void whenUsingGetContentType_thenSuccess() throws MalformedURLException, IOException {
+        final File file = new File(FILE_LOC);
+        final URLConnection connection = file.toURL()
+            .openConnection();
+        final String mimeType = connection.getContentType();
+        assertEquals(mimeType, PNG_EXT);
+    }
+
+    /**
+     * Test method demonstrating the usage of URLConnection to resolve MIME type.
+     * 
+     */
+    @Test
+    public void whenUsingGuessContentTypeFromName_thenSuccess() {
+        final File file = new File(FILE_LOC);
+        final String mimeType = URLConnection.guessContentTypeFromName(file.getName());
+        assertEquals(mimeType, PNG_EXT);
+    }
+
+    /**
+     * Test method demonstrating the usage of FileNameMap from URLConnection
+     * to resolve MIME type of a file.
+     * 
+     */
+    @Test
+    public void whenUsingGetFileNameMap_thenSuccess() {
+        final File file = new File(FILE_LOC);
+        final FileNameMap fileNameMap = URLConnection.getFileNameMap();
+        final String mimeType = fileNameMap.getContentTypeFor(file.getName());
+        assertEquals(mimeType, PNG_EXT);
+    }
+
+    /**
+     * Test method demonstrating the usage of MimeTypesFileTypeMap for resolution of 
+     * MIME type.
+     * 
+     */
+    @Test
+    public void whenUsingMimeTypesFileTypeMap_thenSuccess() {
+        final File file = new File(FILE_LOC);
+        final MimetypesFileTypeMap fileTypeMap = new MimetypesFileTypeMap();
+        final String mimeType = fileTypeMap.getContentType(file.getName());
+        assertEquals(mimeType, PNG_EXT);
+    }
+
+    /**
+     * Test method demonstrating usage of jMimeMagic.
+     * 
+     * @throws MagicParseException
+     * @throws MagicMatchNotFoundException
+     * @throws MagicException
+     */
+    @Test
+    public void whenUsingJmimeMagic_thenSuccess() throws MagicParseException, MagicMatchNotFoundException, MagicException {
+        final File file = new File(FILE_LOC);
+        final Magic magic = new Magic();
+        final MagicMatch match = magic.getMagicMatch(file, false);
+        assertEquals(match.getMimeType(), PNG_EXT);
+    }
+
+    /**
+     * Test method demonstrating usage of Apache Tika.
+     * 
+     * @throws IOException
+     */
+    @Test
+    public void whenUsingTika_thenSuccess() throws IOException {
+        final File file = new File(FILE_LOC);
+        final Tika tika = new Tika();
+        final String mimeType = tika.detect(file);
+        assertEquals(mimeType, PNG_EXT);
+    }
+}