How to convert a byte array to a string, and string to a byte array with GWT?

问题

The String(byte[] bytes) constructor and String.getBytes() method are not implemented by GWT JRE emulation String class.

Does anybody know of an implementation? I do not want to use char[], But it seems like there is no other solution.

回答1:

If you create large arrays in Chrome, you might run into a Uncaught RangeError: Maximum call stack size exceeded exception. The code from LINEMAN78 can be modified to use a StringBuilder, which avoids this issue.

public static String getString(byte[] bytes, int bytesPerChar)
{
    if (bytes == null) throw new IllegalArgumentException("bytes cannot be null");
    if (bytesPerChar < 1) throw new IllegalArgumentException("bytesPerChar must be greater than 1");

    final int length = bytes.length / bytesPerChar;
    final StringBuilder retValue = new StringBuilder();

    for (int i = 0; i < length; i++)
    {
        char thisChar = 0;

        for (int j = 0; j < bytesPerChar; j++)
        {
            int shift = (bytesPerChar - 1 - j) * 8;
            thisChar |= (0x000000FF << shift) & (((int) bytes[i * bytesPerChar + j]) << shift);
        }

        retValue.append(thisChar);
    }

    return retValue.toString();
}

回答2:

The following code should work, just specify the number of bytes per character.

public class GwtPlayground implements EntryPoint
{
    static final Logger logger = Logger.getLogger("");

    @Override
    public void onModuleLoad()
    {
        VerticalPanel loggerArea = new VerticalPanel();
        logger.addHandler(new HasWidgetsLogHandler(loggerArea));
        RootPanel.get().add(loggerArea);

        String original = new String("A" + "\uffea" + "\u00f1" + "\u00fc" + "C");

        logger.info("original = " + original);
        byte[] utfBytes = getBytes(original, 2);

        String roundTrip = getString(utfBytes, 2);
        logger.info("roundTrip = " + roundTrip);
    }

    public static byte[] getBytes(String string, int bytesPerChar)
    {
        char[] chars = string.toCharArray();
        byte[] toReturn = new byte[chars.length * bytesPerChar];
        for (int i = 0; i < chars.length; i++)
        {
            for (int j = 0; j < bytesPerChar; j++)
                toReturn[i * bytesPerChar + j] = (byte) (chars[i] >>> (8 * (bytesPerChar - 1 - j)));
        }
        return toReturn;
    }

    public static String getString(byte[] bytes, int bytesPerChar)
    {
        char[] chars = new char[bytes.length / bytesPerChar];
        for (int i = 0; i < chars.length; i++)
        {
            for (int j = 0; j < bytesPerChar; j++)
            {
                int shift = (bytesPerChar - 1 - j) * 8;
                chars[i] |= (0x000000FF << shift) & (((int) bytes[i * bytesPerChar + j]) << shift);
            }
        }
        return new String(chars);
    }
}

As @Per Wiklander pointed out, this doesn't truely support UTF-8. Here is a true UTF-8 decoder ported from C here

private static class UTF8Decoder
{
    final byte[] the_input;
    int the_index, the_length;

    protected UTF8Decoder( byte[] bytes )
    {
        super();
        this.the_input = bytes;
        this.the_index = 0;
        this.the_length = bytes.length;
    }


    /*
    Get the next byte. It returns UTF8_END if there are no more bytes.
    */
    int get()
    {
        int c;
        c = the_input[the_index] & 0xFF;
        the_index += 1;
        return c;
    }


    /*
        Get the 6-bit payload of the next continuation byte.
        Return UTF8_ERROR if it is not a contination byte.
    */
    int cont()
    {
        int c = get();
        if( (c & 0xC0) == 0x80 )
            return (c & 0x3F);
        else
            throw new IllegalArgumentException( "Failed to pass strict UTF-8" );
    }

    CharSequence getStringUTF8()
    {
        StringBuilder sb = new StringBuilder( the_input.length ); // allocate a maximum size
        while( the_index < the_length )
        {
            int c; /* the first byte of the character */
            int r; /* the result */

            c = get();
            /*
                Zero continuation (0 to 127)
            */
            if( (c & 0x80) == 0 )
            {
                sb.append( (char) c );
            }
            /*
                One continuation (128 to 2047)
            */
            else if( (c & 0xE0) == 0xC0 )
            {
                int c1 = cont();
                if( c1 >= 0 )
                {
                    r = ((c & 0x1F) << 6) | c1;
                    if( r >= 128 )
                        sb.append( (char) r );
                    else
                        throw new IllegalArgumentException();
                }
            }
            /*
            Two continuation (2048 to 55295 and 57344 to 65535)
            */
            else if( (c & 0xF0) == 0xE0 )
            {
                int c1 = cont();
                int c2 = cont();
                if( (c1 | c2) >= 0 )
                {
                    r = ((c & 0x0F) << 12) | (c1 << 6) | c2;
                    if( r >= 2048 && (r < 55296 || r > 57343) )
                        sb.append( (char) r );
                    else
                        throw new IllegalArgumentException();
                }
            }
            /*
            Three continuation (65536 to 1114111)
            */
            else if( (c & 0xF8) == 0xF0 )
            {
                int c1 = cont();
                int c2 = cont();
                int c3 = cont();
                if( (c1 | c2 | c3) >= 0 )
                    sb.append( (char) ((((c & 0x0F) << 18) | (c1 << 12) | (c2 << 6) | c3) + 65536) ); // TODO this might not work as it is being cast to a char
            }
            else
                throw new IllegalArgumentException( "Failed strict UTF8 parsing" );
        }
        return sb;
    }
}

回答3:

Good question. I didn't realize it before.

as far as I know there is only 2 main method that convert byte array to String

1. You mentioned it
2. The fantastic way with java.io package that you can't use it on client-side

Here is mine implementation. I think it may be helpful to you

public static String convertByteArrayToString(byte[] byteArray) {
    String s = "";

    for (int i = 0; i < byteArray.length; i++) {
        s += (char) (byteArray[i]);
    }

    return s;
}

You can test it :

byte[] byteArray = new byte[] { 87, 79, 87, 46, 46, 46 };

System.out.println(convertByteArrayToString(byteArray));
System.out.println(new String(byteArray));

来源：https://stackoverflow.com/questions/4584998/how-to-convert-a-byte-array-to-a-string-and-string-to-a-byte-array-with-gwt