Map decodeBase64 to getMimeDecoder() to preserve URL-safe decoding (#133)

Apache's `Base64.decodeBase64` accepts both the standard (`+/`) and
URL-safe (`-_`) alphabets, whereas `java.util.Base64.getDecoder()` throws
`IllegalArgumentException` on URL-safe input. `getMimeDecoder()` is the
closest equivalent that handles both variants.

Fixes #132

Author: timtebeek

src/main/java/org/openrewrite/apache/commons/codec/ApacheBase64ToJavaBase64.java

@@ -60,7 +60,10 @@ public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, Execu
                 } else if (apacheEncode64.matches(mi)) {
                     templatePrefix = "Base64.getEncoder().encode(#{anyArray()})";
                 } else if (apacheDecode.matches(mi)) {
-                    templatePrefix = "Base64.getDecoder().decode(#{any(String)})";
+                    // Apache's `decodeBase64` accepts both the standard (`+/`) and URL-safe (`-_`) alphabets.
+                    // `getMimeDecoder()` is the closest `java.util.Base64` equivalent that decodes both variants,
+                    // whereas `getDecoder()` throws `IllegalArgumentException` on URL-safe input.
+                    templatePrefix = "Base64.getMimeDecoder().decode(#{any(String)})";
                 } else if (apacheEncode64UrlSafe.matches(mi)) {
                     templatePrefix = "Base64.getUrlEncoder().withoutPadding().encode(#{anyArray()})";
                 } else if (apacheEncode64UrlSafeString.matches(mi)) {

src/main/resources/META-INF/rewrite/examples.yml

@@ -45,10 +45,10 @@ examples:
 
       class Test {
           static byte[] decodeBytes(byte[] encodedBytes) {
-              return Base64.getDecoder().decode(encodedBytes);
+              return Base64.getMimeDecoder().decode(encodedBytes);
           }
           static byte[] decodeToBytes(String encodedString) {
-              return Base64.getDecoder().decode(encodedString);
+              return Base64.getMimeDecoder().decode(encodedString);
           }
           static String encodeToString(byte[] decodedByteArr) {
               return Base64.getEncoder().encodeToString(decodedByteArr);

src/test/java/org/openrewrite/apache/commons/codec/ApacheBase64ToJavaBase64Test.java

@@ -67,10 +67,10 @@ static String encodeBytesUrlSafeString(byte [] encodeBytes) {
 
               class Test {
                   static byte[] decodeBytes(byte[] encodedBytes) {
-                      return Base64.getDecoder().decode(encodedBytes);
+                      return Base64.getMimeDecoder().decode(encodedBytes);
                   }
                   static byte[] decodeToBytes(String encodedString) {
-                      return Base64.getDecoder().decode(encodedString);
+                      return Base64.getMimeDecoder().decode(encodedString);
                   }
                   static String encodeToString(byte[] decodedByteArr) {
                       return Base64.getEncoder().encodeToString(decodedByteArr);