It seems that Files.newBufferedReader()
is more strict about UTF-8 than the naive alternative.
If I create a file with a single byte 128---so, not a valid UTF-8 character---it will happily be read if I construct an BufferedReader
on an InputStreamReader
on the result of Files.newInputStream()
, but with Files.newBufferedReader()
an exception is thrown.
This code
try (
InputStream in = Files.newInputStream(path);
Reader isReader = new InputStreamReader(in, "UTF-8");
Reader reader = new BufferedReader(isReader);
) {
System.out.println((char) reader.read());
}
try (
Reader reader = Files.newBufferedReader(path);
) {
System.out.println((char) reader.read());
}
has this result:
�
Exception in thread "main" java.nio.charset.MalformedInputException: Input length = 1
at java.nio.charset.CoderResult.throwException(CoderResult.java:281)
at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:339)
at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
at java.io.InputStreamReader.read(InputStreamReader.java:184)
at java.io.BufferedReader.fill(BufferedReader.java:161)
at java.io.BufferedReader.read(BufferedReader.java:182)
at TestUtf8.main(TestUtf8.java:28)
Is this documented? And is it possible to get the lenient behavior with Files.newBufferedReader()
?
The difference is in how the CharsetDecoder
used to decode the UTF-8 is constructed in the two cases.
For new InputStreamReader(in, "UTF-8")
the decoder is constructed using:
Charset cs = Charset.forName("UTF-8");
CharsetDecoder decoder = cs.newDecoder()
.onMalformedInput(CodingErrorAction.REPLACE)
.onUnmappableCharacter(CodingErrorAction.REPLACE);
This is explicitly specifying that invalid sequences are just replaced with the standard replacement character.
Files.newBufferedReader(path)
uses:
Charset cs = StandardCharsets.UTF_8;
CharsetDecoder decoder = cs.newDecoder();
In this case onMalformedInput
and onUnmappableCharacter
are not being called so you get the default action which is to throw the exception you are seeing.
There does not seem to be a way to change what Files.newBufferedReader
does. I didn't see anything documenting this while looking through the code.
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