Check if a String contains encoded characters

问题:

Hello I am looking for a way to detect if a string has being encoded

For example

    String name = "Hellä world";
    String encoded = new String(name.getBytes("utf-8"), "iso8859-1");

The output of this encoded variable is:

Hellä world

As you can see there is an A with grave and another symbol. Is there a way to check if the output contains encoded characters?

回答1:

Sounds like you want to check if a string that was decoded from bytes in latin1 could have been decoded in UTF-8, too. That's easy because illegal byte sequences are replaced by the character \ufffd:

String recoded = new String(encoded.getBytes("iso-8859-1"), "UTF-8");
return recoded.indexOf('\uFFFD') == -1; // No replacement character found

回答2:

Your question doesn't make sense. A java String is a list of characters. They don't have an encoding until you convert them into bytes, at which point you need to specify one (although you will see a lot of code that uses the platform default, which is what e.g. String.getBytes() with no argument does).

I suggest you read this http://kunststube.net/encoding/.

回答3:

String name = "Hellä world";
String encoded = new String(name.getBytes("utf-8"), "iso8859-1");

This code is just a character corruption bug. You take a UTF-16 string, transcode it to UTF-8, pretend it is ISO-8859-1 and transcode it back to UTF-16, resulting in incorrectly encoded characters.

回答4:

If I correctly understood your question, this code may help you. The function isEncoded check if its parameter could be encoded as ascii or if it contains non ascii-chars.

public boolean isEncoded(String text){

    Charset charset = Charset.forName("US-ASCII");
    String checked=new String(text.getBytes(charset),charset);
    return !checked.equals(text);

}

@Test
public void testAscii() throws Exception{
    Assert.assertFalse(isEncoded("Hello world"));
}


@Test
public void testNonAscii() throws Exception{
    Assert.assertTrue(isEncoded("Hellä world"));
}

You can also check for other charset changing charset var or moving it to a parameter.

回答5:

I'm not really sure what are you trying to do or what is your problem.

This line doesn't make any sense:

String encoded = new String(name.getBytes("utf-8"), "iso8859-1");

You are encoding your name into "UTF-8" and then trying to decode as "iso8859-1".

If you what to encode your name as "iso8859-1" just do name.getBytes("iso8859-1").

Please tell us what is the problem you encountered so that we can help more.

回答6:

You can check that your string is encoded or not by this code

public boolean isEncoded(String input) {

    char[] charArray = input.toCharArray();
    for (int i = 0, charArrayLength = charArray.length; i < charArrayLength; i++) {
        Character c = charArray[i];
        if (Character.getType(c) == Character.OTHER_LETTER)){
            return true;
        }
    }
    return false;
}