Don't expose mutable arrays unnecessarily

Author: sebbASF

src/main/java/org/apache/commons/io/input/BOMInputStream.java

@@ -107,7 +107,7 @@ public class BOMInputStream extends ProxyInputStream {
      */
     public static class Builder extends AbstractStreamBuilder<BOMInputStream, Builder> {
 
-        static final ByteOrderMark[] DEFAULT = { ByteOrderMark.UTF_8 };
+        private static final ByteOrderMark[] DEFAULT = { ByteOrderMark.UTF_8 };
 
         private boolean include;
         private ByteOrderMark[] byteOrderMarks = DEFAULT;
@@ -140,13 +140,19 @@ public Builder setInclude(final boolean include) {
             return this;
         }
 
+        // for test access
+        static ByteOrderMark getDefaultBOM() {
+            return DEFAULT[0];
+        }
+
     }
 
     /**
      * Compares ByteOrderMark objects in descending length order.
      */
     private static final Comparator<ByteOrderMark> ByteOrderMarkLengthComparator = Comparator.comparing(ByteOrderMark::length).reversed();
 
+
     /**
      * Constructs a new {@link Builder}.
      *

src/test/java/org/apache/commons/io/input/BOMInputStreamTest.java

@@ -409,7 +409,7 @@ public void testNoBoms() throws Exception {
                 .setInclude(true)
                 .setByteOrderMarks((ByteOrderMark[]) null)
                 .get()) {
-            assertEquals(BOMInputStream.Builder.DEFAULT[0], bomInputStream.getBOM());
+            assertEquals(BOMInputStream.Builder.getDefaultBOM(), bomInputStream.getBOM());
         }
         assertThrows(IllegalArgumentException.class, () -> BOMInputStream.builder()
                 .setInputStream(createUtf8Input(data, true))