src/java.base/share/classes/java/nio/file/Files.java

@@ -41,11 +41,13 @@
 import java.nio.channels.FileChannel;
 import java.nio.channels.SeekableByteChannel;
 import java.nio.charset.Charset;
 import java.nio.charset.CharsetDecoder;
 import java.nio.charset.CharsetEncoder;
+import java.nio.charset.MalformedInputException;
 import java.nio.charset.StandardCharsets;
+import java.nio.charset.UnmappableCharacterException;
 import java.nio.file.attribute.BasicFileAttributeView;
 import java.nio.file.attribute.BasicFileAttributes;
 import java.nio.file.attribute.DosFileAttributes;   // javadoc
 import java.nio.file.attribute.FileAttribute;
 import java.nio.file.attribute.FileAttributeView;

@@ -3280,10 +3282,14 @@
 
         byte[] ba = readAllBytes(path);
         try {
             return JLA.newStringNoRepl(ba, cs);
         } catch (IllegalArgumentException e) {
+            Throwable cause = e.getCause();
+            if (cause != null && cause instanceof MalformedInputException) {
+                throw (MalformedInputException)cause;
+            }
             throw new IOException(e);
         }
     }
 
     /**

@@ -3636,10 +3642,14 @@
 
         try {
             byte[] bytes = JLA.getBytesNoRepl(String.valueOf(csq), cs);
             write(path, bytes, options);
         } catch (IllegalArgumentException e) {
+            Throwable cause = e.getCause();
+            if (cause != null && cause instanceof UnmappableCharacterException) {
+                throw (UnmappableCharacterException)cause;
+            }
             throw new IOException(e);
         }
 
         return path;
     }