MalformedInputException: Character Encoding Error

Why This Happens

MalformedInputException occurs when reading text with the wrong character encoding. For example, reading a UTF-8 file as ISO-8859-1 may work but reading an ISO-8859-1 file as UTF-8 will fail because some byte sequences are invalid UTF-8.

The Problem

// File is encoded in ISO-8859-1 but read as UTF-8
String content = Files.readString(Path.of("data.txt")); // Defaults to UTF-8

The Fix

// Specify the correct charset
String content = Files.readString(Path.of("data.txt"), StandardCharsets.ISO_8859_1);

// Or handle errors gracefully:
CharsetDecoder decoder = StandardCharsets.UTF_8.newDecoder()
    .onMalformedInput(CodingErrorAction.REPLACE);

Step-by-Step Fix

1. 1

   Identify the encoding

   Determine the actual encoding of the file. Check for BOM markers, file metadata, or the source system's documentation.

2. 2

   Specify the correct charset

   Pass the correct Charset to file reading methods instead of relying on the default.

3. 3

   Handle encoding errors

   Use CodingErrorAction.REPLACE to substitute invalid characters, or CodingErrorAction.IGNORE to skip them.