checking the first 3 characters of a string 1

[developerinlondon]

I need a way to check if the first 3 characters of a string equals something:
eg

            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            int i = -1;
            while (true) {
                i = rd.read(buffer, 0, buffer.length);
                if (i == -1) break;
                baos.write(buffer, 0, i);
            }
            /*
             if baos.toByteArray() begins with '\xFF\xFE\x3C' then 
             */
            xml_in = new String(baos.toByteArray(), "utf-16");
             /*
              else
               */
             xml_in = new String(baos.toByteArray());
            baos.close();

basically I need to manually check if the data i am reading is UTF-16, if it is then convert it from utf-16 format, otherwise use standard method.

any thoughts on how I could do this?

thanks in advance.

 

[sedj]

I would probably do something like :

ByteArrayOutputStream baos = new ByteArrayOutputStream();
int i = -1;
while (true) {
	i = rd.read(buffer, 0, buffer.length);
	if (i == -1) break;
	baos.write(buffer, 0, i);
}

byte[] byteData = baos.toByteArray();

if (checkData(byteData)) {
	xml_in = new String(byteData, "utf-16");
} else {
	xml_in = new String(baos.toByteArray());
}

baos.close();

where "checkData" is something along the lines of :

boolean checkData(byte[] data) throws IOException {
   if (data.length < 3) {
      throw new IOException("Checking job must have an array longer than 3 elements!");
   }
   
   if ((data[0] == '\xFF') && (data[1] == '\xFE') && (data[1] == '\x3C')) {
   	return true;
   } else {
   	return false;
   }
}

--------------------------------------------------
Free Database Connection Pooling Software

http://www.primrose.org.uk

 

[sedj]

xml_in = new String(baos.toByteArray());


should be :

xml_in = new String(byteData);


--------------------------------------------------
Free Database Connection Pooling Software

http://www.primrose.org.uk

 

[Diancecht]

Humm, maybe I'm wrong but ...

if you want to check what are you reading, wouldn't you need to check your input (rd) rather that the output?

Cheers,

Dian

 

[sedj]

Whether the incoming data is UTF-16 or not, you want to do something with the input - which is read into the ByteArrayOutputStream - so it seems OK to me ...

--------------------------------------------------
Free Database Connection Pooling Software

http://www.primrose.org.uk

 

[Diancecht]

Ouch, there's an else after that.

My mistake, sorry.

Just as a matter of curiosity, String class has a startsWith method.

Cheers,

Dian

 

[sedj]

Yes, but according to the encoding of the data, the OP wants to do different things with it - so it makes much more sense to analyse the byte array (seeing as you have to convert the BAOS to a byte[] to create the String anyhow ...

--------------------------------------------------
Free Database Connection Pooling Software

http://www.primrose.org.uk

 

[developerinlondon]

thanks for that sedj. just one small problem with it. I am getting the following -

    [javac]  if ((data[0] == '\xFF') && (data[1] == '\xFE')) {
    [javac]                           ^
    [javac] xxx.java:232: unclosed character literal
    [javac]  if ((data[0] == '\xFF') && (data[1] == '\xFE')) {
    [javac]                         ^
    [javac] xxx.java:232: unclosed character literal
    [javac]  if ((data[0] == '\xFF') && (data[1] == '\xFE')) {
    [javac]                              ^
    [javac] xxx.java:232: illegal escape character
    [javac]  if ((data[0] == '\xFF') && (data[1] == '\xFE')) {
    [javac]                                                  ^
    [javac] xxx.java:232: unclosed character literal
    [javac]  if ((data[0] == '\xFF') && (data[1] == '\xFE')) {
    [javac]                                                ^
    [javac] xxx.java:232: unclosed character literal
    [javac]  if ((data[0] == '\xFF') && (data[1] == '\xFE')) {
    [javac]                                                     ^
    [javac] xxx.java:237: ')' expected
    [javac]     }
    [javac]     ^

I tried changing it to 'and' but didnt help.

 

[sedj]

sorry, my bad :

if ((data[0] == 0xFF) && (data[1] == 0xFE) && (data[1] == 0x3C)) {

(if these are the true byte values you wish)

--------------------------------------------------
Free Database Connection Pooling Software

http://www.primrose.org.uk

 

[developerinlondon]

thanks for that.
actually I had to change my condition a bit since the data coming back in java is different then I had in other languages.
so it should be :
if ((data[0] == -1) && (data[1] == -2))
to check if a string is utf16.

 

[sedj]

Perhaps you should do :

if ((data[0] == ((byte)-1)) && (data[1] == ((byte)-2)))

because "-1" and "-2" are actually ints - bearing in mind that an int is 32 bits, and a byte is 8 bits - so a byte's int range is only from -127 to +127 ...

--------------------------------------------------
Free Database Connection Pooling Software

http://www.primrose.org.uk

 

[developerinlondon]

thanks.
I have a slightly different problem now. I need to check the String and see if its first 2 characters match something.

eg.

if (xml_in.StartsWith(0xFF + 0xFE)) {
   xml_in = new String(xml_in, "utf-16");
} else {
   xml_in = new String(xml_in);
}

any ideas how I could do this? (I may also need a way to check if they match -1 and -2 bytevalues depending on whether FF and FE works or not)