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

Question

The String(byte[] bytes) constructor String(byte[] bytes) and String.getBytes() not implemented using the GWT JRE emulation String class.

Does anyone know of an implementation? I do not want to use char[] , but there seems to be no other solution.

Answer 1

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 noted, this does not correctly support UTF-8. Here is a real 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; } } 

Answer 2

If you create large arrays in Chrome, you may encounter Throw RangeError exception: Maximum call stack size . The code from LINEMAN78 can be modified to use StringBuilder, which avoids this problem.

 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(); } 

Answer 3

Good question. I did not realize this before.

As far as I know, there are only 2 basic methods of converting a byte array to String

• You mentioned him
• A fantastic way with the java.io package that you cannot use on the client side

Here is my implementation. I think this may be useful for 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 check it out:

 byte[] byteArray = new byte[] { 87, 79, 87, 46, 46, 46 }; System.out.println(convertByteArrayToString(byteArray)); System.out.println(new String(byteArray));