Fix NoClassDefFoundError on Android < 8.0

Author: vonox7

modules/cli-module/src/main/java/org/simplejavamail/internal/clisupport/CliSupport.java

@@ -7,7 +7,7 @@
 import org.simplejavamail.api.mailer.MailerFromSessionBuilder;
 import org.simplejavamail.api.mailer.MailerRegularBuilder;
 import org.simplejavamail.internal.clisupport.serialization.SerializationUtil;
-import org.simplejavamail.internal.util.MiscUtil;
+import org.simplejavamail.internal.util.FileUtil;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import picocli.CommandLine;
@@ -38,9 +38,9 @@ private static List<CliDeclaredOptionSpec> produceCliDeclaredOptionSpec() {
 			if (!CLI_DATAFILE.exists()) {
 				LOGGER.info("Initial cli.data not found, writing to (one time action): {}", CLI_DATAFILE);
 				List<CliDeclaredOptionSpec> declaredOptions = generateOptionsFromBuilderApi(RELEVANT_BUILDER_ROOT_API);
-				MiscUtil.writeFileBytes(CLI_DATAFILE, SerializationUtil.serialize(declaredOptions));
+				FileUtil.writeFileBytes(CLI_DATAFILE, SerializationUtil.serialize(declaredOptions));
 			}
-			return SerializationUtil.deserialize(MiscUtil.readFileBytes(CLI_DATAFILE));
+			return SerializationUtil.deserialize(FileUtil.readFileBytes(CLI_DATAFILE));
 		} catch (IOException e) {
 			throw new CliExecutionException(ERROR_INVOKING_BUILDER_API, e);
 		}

modules/cli-module/src/main/java/org/simplejavamail/internal/clisupport/therapijavadoc/TherapiJavadocHelper.java

@@ -17,7 +17,7 @@
 import org.jetbrains.annotations.TestOnly;
 import org.simplejavamail.internal.clisupport.CliDataLocator;
 import org.simplejavamail.internal.clisupport.serialization.SerializationUtil;
-import org.simplejavamail.internal.util.MiscUtil;
+import org.simplejavamail.internal.util.FileUtil;
 
 import java.io.File;
 import java.io.IOException;
@@ -48,7 +48,7 @@ public final class TherapiJavadocHelper {
 	private static Map<String, MethodJavadoc> loadTherapiCache() {
 		if (THERAPI_DATAFILE.exists()) {
 			try {
-				return SerializationUtil.deserialize(MiscUtil.readFileBytes(THERAPI_DATAFILE));
+				return SerializationUtil.deserialize(FileUtil.readFileBytes(THERAPI_DATAFILE));
 			} catch (IOException e) {
 				throw new RuntimeException(e);
 			}
@@ -60,7 +60,7 @@ private static Map<String, MethodJavadoc> loadTherapiCache() {
 	@TestOnly
 	public static void persistCache() {
 		try {
-			MiscUtil.writeFileBytes(THERAPI_DATAFILE, SerializationUtil.serialize(THERAPI_CACHE));
+			FileUtil.writeFileBytes(THERAPI_DATAFILE, SerializationUtil.serialize(THERAPI_CACHE));
 		} catch (IOException e) {
 			throw new RuntimeException(e);
 		}

modules/core-module/src/main/java/org/simplejavamail/internal/util/FileUtil.java

@@ -0,0 +1,36 @@
+package org.simplejavamail.internal.util;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.FileAlreadyExistsException;
+import java.nio.file.Files;
+
+import static java.lang.String.format;
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+// FileUtil uses java.nio.file, which is not available on Android < 8.0 and will throw there a NoClassDefFoundError.
+// See https://developer.android.com/reference/java/nio/file/package-summary.
+// Therefore, keep imports of java.nio.file.* inside this class.
+public class FileUtil {
+    public static String readFileContent(@NotNull final File file) throws IOException {
+        return new String(readFileBytes(file), UTF_8);
+    }
+
+    public static byte[] readFileBytes(@NotNull final File file) throws IOException {
+        if (!file.exists()) {
+            throw new IllegalArgumentException(format("File not found: %s", file));
+        }
+        return Files.readAllBytes(file.toPath());
+    }
+
+    public static void writeFileBytes(@NotNull final File file, final byte[] bytes) throws IOException {
+        try {
+            Files.createFile(file.toPath());
+        } catch (FileAlreadyExistsException e) {
+            // ignore
+        }
+        Files.write(file.toPath(), bytes);
+    }
+}

modules/core-module/src/main/java/org/simplejavamail/internal/util/MiscUtil.java

@@ -23,8 +23,6 @@
 import java.lang.reflect.Method;
 import java.net.URL;
 import java.nio.charset.Charset;
-import java.nio.file.FileAlreadyExistsException;
-import java.nio.file.Files;
 import java.util.AbstractMap;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -227,26 +225,6 @@ private static boolean containsNullableAnnotation(final Annotation[] annotations
 		return false;
 	}
 
-	public static String readFileContent(@NotNull final File file) throws IOException {
-		return new String(readFileBytes(file), UTF_8);
-	}
-
-	public static byte[] readFileBytes(@NotNull final File file) throws IOException {
-		if (!file.exists()) {
-			throw new IllegalArgumentException(format("File not found: %s", file));
-		}
-		return Files.readAllBytes(file.toPath());
-	}
-
-	public static void writeFileBytes(@NotNull final File file, final byte[] bytes) throws IOException {
-		try {
-			Files.createFile(file.toPath());
-		} catch (FileAlreadyExistsException e) {
-			// ignore
-		}
-		Files.write(file.toPath(), bytes);
-	}
-
 	@Nullable
 	public static DataSource tryResolveImageFileDataSourceFromDisk(final @Nullable String baseDir, final boolean allowOutsideBaseDir, final @NotNull String srcLocation) {
 		DataSource dataSource;

modules/simple-java-mail/src/main/java/org/simplejavamail/email/internal/EmailPopulatingBuilderImpl.java

@@ -16,6 +16,7 @@
 import org.simplejavamail.api.mailer.config.Pkcs12Config;
 import org.simplejavamail.email.EmailBuilder;
 import org.simplejavamail.internal.util.CertificationUtil;
+import org.simplejavamail.internal.util.FileUtil;
 import org.simplejavamail.internal.util.MiscUtil;
 import org.simplejavamail.internal.util.NamedDataSource;
 
@@ -642,7 +643,7 @@ public InternalEmailPopulatingBuilder withForward(@Nullable final MimeMessage em
 	@Cli.OptionNameOverride("withPlainTextFromFile")
 	public EmailPopulatingBuilder withPlainText(@NotNull final File textFile) {
 		try {
-			return withPlainText(MiscUtil.readFileContent(textFile));
+			return withPlainText(FileUtil.readFileContent(textFile));
 		} catch (IOException e) {
 			throw new EmailException(format(ERROR_READING_FROM_FILE, textFile), e);
 		}
@@ -664,7 +665,7 @@ public EmailPopulatingBuilder withPlainText(@Nullable final String text) {
 	@Cli.OptionNameOverride("prependTextFromFile")
 	public EmailPopulatingBuilder prependText(@NotNull final File textFile) {
 		try {
-			return prependText(MiscUtil.readFileContent(textFile));
+			return prependText(FileUtil.readFileContent(textFile));
 		} catch (IOException e) {
 			throw new EmailException(format(ERROR_READING_FROM_FILE, textFile), e);
 		}
@@ -686,7 +687,7 @@ public EmailPopulatingBuilder prependText(@NotNull final String text) {
 	@Cli.OptionNameOverride("appendTextFromFile")
 	public EmailPopulatingBuilder appendText(@NotNull final File textFile) {
 		try {
-			return appendText(MiscUtil.readFileContent(textFile));
+			return appendText(FileUtil.readFileContent(textFile));
 		} catch (IOException e) {
 			throw new EmailException(format(ERROR_READING_FROM_FILE, textFile), e);
 		}
@@ -708,7 +709,7 @@ public EmailPopulatingBuilder appendText(@NotNull final String text) {
 	@Cli.OptionNameOverride("withHTMLTextFromFile")
 	public EmailPopulatingBuilder withHTMLText(@NotNull final File textHTMLFile) {
 		try {
-			return withHTMLText(MiscUtil.readFileContent(textHTMLFile));
+			return withHTMLText(FileUtil.readFileContent(textHTMLFile));
 		} catch (IOException e) {
 			throw new EmailException(format(ERROR_READING_FROM_FILE, textHTMLFile), e);
 		}
@@ -730,7 +731,7 @@ public EmailPopulatingBuilder withHTMLText(@Nullable final String textHTML) {
 	@Cli.OptionNameOverride("prependTextHTMLFromFile")
 	public EmailPopulatingBuilder prependTextHTML(@NotNull final File textHTMLFile) {
 		try {
-			return prependTextHTML(MiscUtil.readFileContent(textHTMLFile));
+			return prependTextHTML(FileUtil.readFileContent(textHTMLFile));
 		} catch (IOException e) {
 			throw new EmailException(format(ERROR_READING_FROM_FILE, textHTMLFile), e);
 		}
@@ -752,7 +753,7 @@ public EmailPopulatingBuilder prependTextHTML(@NotNull final String textHTML) {
 	@Cli.OptionNameOverride("appendTextHTMLFromFile")
 	public EmailPopulatingBuilder appendTextHTML(@NotNull final File textHTMLFile) {
 		try {
-			return appendTextHTML(MiscUtil.readFileContent(textHTMLFile));
+			return appendTextHTML(FileUtil.readFileContent(textHTMLFile));
 		} catch (IOException e) {
 			throw new EmailException(format(ERROR_READING_FROM_FILE, textHTMLFile), e);
 		}

modules/simple-java-mail/src/test/java/org/simplejavamail/internal/util/MiscUtilTest.java

@@ -162,22 +162,22 @@ public void testCountMandatoryParameters() {
 	@Test
 	public void testReadFileContent()
 			throws IOException {
-		assertThatThrownBy(() -> MiscUtil.readFileContent(new File("moo")))
+		assertThatThrownBy(() -> FileUtil.readFileContent(new File("moo")))
 				.isInstanceOf(IllegalArgumentException.class)
 				.hasMessageContaining("File not found: moo");
 
-		assertThat(MiscUtil.readFileContent(new File("src/test/resources/ignore.properties")))
+		assertThat(FileUtil.readFileContent(new File("src/test/resources/ignore.properties")))
 				.contains("simplejavamail.defaults.bcc.address=moo");
 	}
 
 	@Test
 	public void testWriteFileContent()
 			throws IOException {
-		MiscUtil.writeFileBytes(new File("target/test.file"), "This is a test".getBytes());
+		FileUtil.writeFileBytes(new File("target/test.file"), "This is a test".getBytes());
 
-		assertThat(MiscUtil.readFileBytes(new File("target/test.file")))
+		assertThat(FileUtil.readFileBytes(new File("target/test.file")))
 				.isEqualTo("This is a test".getBytes());
-		assertThat(MiscUtil.readFileContent(new File("target/test.file")))
+		assertThat(FileUtil.readFileContent(new File("target/test.file")))
 				.isEqualTo("This is a test");
 	}