GsonBuilderUtils for programmatic Base64 serialization setup; common Base64Utils class adapts between Java 8 and Commons Codec

Issue: SPR-9488

spring-core/src/main/java/org/springframework/util/Base64Utils.java

@@ -0,0 +1,165 @@
+/*
+ * Copyright 2002-2014 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.util;
+
+import java.nio.charset.Charset;
+import java.util.Base64;
+
+/**
+ * A simple utility class for Base64 encoding and decoding.
+ *
+ * <p>Adapts to either Java 8's {@link java.util.Base64} class or Apache
+ * Commons Codec's {@link org.apache.commons.codec.binary.Base64} class.
+ * With neither Java 8 nor Commons Codec present, encode/decode calls
+ * will fail with an IllegalStateException.
+ *
+ * @author Juergen Hoeller
+ * @since 4.1
+ * @see java.util.Base64
+ * @see org.apache.commons.codec.binary.Base64
+ */
+public abstract class Base64Utils {
+
+	private static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
+
+
+	private static final Base64Delegate delegate;
+
+	static {
+		Base64Delegate delegateToUse = null;
+		// JDK 8's java.util.Base64 class present?
+		if (ClassUtils.isPresent("java.util.Base64", Base64Utils.class.getClassLoader())) {
+			delegateToUse = new JdkBase64Delegate();
+		}
+		// Apache Commons Codec present on the classpath?
+		else if (ClassUtils.isPresent("org.apache.commons.codec.binary.Base64", Base64Utils.class.getClassLoader())) {
+			delegateToUse = new CommonsCodecBase64Delegate();
+		}
+		delegate = delegateToUse;
+	}
+
+	/**
+	 * Assert that Byte64 encoding is actually supported.
+	 * @throws IllegalStateException if neither Java 8 nor Apache Commons Codec is present
+	 */
+	private static void assertSupported() {
+		Assert.state(delegate != null, "Neither Java 8 nor Apache Commons Codec found - Base64 encoding not supported");
+	}
+
+
+	/**
+	 * Base64-encode the given byte array.
+	 * @param src the original byte array (may be {@code null})
+	 * @return the encoded byte array (or {@code null} if the input was {@code null})
+	 * @throws IllegalStateException if Base64 encoding is not supported,
+	 * i.e. neither Java 8 nor Apache Commons Codec is present at runtime
+	 */
+	public static byte[] encode(byte[] src) {
+		assertSupported();
+		return delegate.encode(src);
+	}
+
+	/**
+	 * Base64-encode the given byte array to a String.
+	 * @param src the original byte array (may be {@code null})
+	 * @return the encoded byte array as a UTF-8 String
+	 * (or {@code null} if the input was {@code null})
+	 * @throws IllegalStateException if Base64 encoding is not supported,
+	 * i.e. neither Java 8 nor Apache Commons Codec is present at runtime
+	 */
+	public static String encodeToString(byte[] src) {
+		assertSupported();
+		if (src == null) {
+			return null;
+		}
+		if (src.length == 0) {
+			return "";
+		}
+		return new String(delegate.encode(src), DEFAULT_CHARSET);
+	}
+
+	/**
+	 * Base64-decode the given byte array.
+	 * @param src the encoded byte array (may be {@code null})
+	 * @return the original byte array (or {@code null} if the input was {@code null})
+	 * @throws IllegalStateException if Base64 encoding is not supported,
+	 * i.e. neither Java 8 nor Apache Commons Codec is present at runtime
+	 */
+	public static byte[] decode(byte[] src) {
+		assertSupported();
+		return delegate.decode(src);
+	}
+
+	/**
+	 * Base64-decode the given byte array from an UTF-8 String.
+	 * @param src the encoded UTF-8 String (may be {@code null})
+	 * @return the original byte array (or {@code null} if the input was {@code null})
+	 * @throws IllegalStateException if Base64 encoding is not supported,
+	 * i.e. neither Java 8 nor Apache Commons Codec is present at runtime
+	 */
+	public static byte[] decodeFromString(String src) {
+		assertSupported();
+		if (src == null) {
+			return null;
+		}
+		if (src.length() == 0) {
+			return new byte[0];
+		}
+		return delegate.decode(src.getBytes(DEFAULT_CHARSET));
+	}
+
+
+	private interface Base64Delegate {
+
+		byte[] encode(byte[] src);
+
+		byte[] decode(byte[] src);
+	}
+
+
+	private static class JdkBase64Delegate implements Base64Delegate {
+
+		public byte[] encode(byte[] src) {
+			if (src == null || src.length == 0) {
+				return src;
+			}
+			return Base64.getEncoder().encode(src);
+		}
+
+		public byte[] decode(byte[] src) {
+			if (src == null || src.length == 0) {
+				return src;
+			}
+			return Base64.getDecoder().decode(src);
+		}
+	}
+
+
+	private static class CommonsCodecBase64Delegate implements Base64Delegate {
+
+		private final org.apache.commons.codec.binary.Base64 base64 = new org.apache.commons.codec.binary.Base64();
+
+		public byte[] encode(byte[] src) {
+			return this.base64.encode(src);
+		}
+
+		public byte[] decode(byte[] src) {
+			return this.base64.decode(src);
+		}
+	}
+
+}