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Convert special characters into decimal equivalents in java

Is there a java library to convert special characters into decimal equivalent?
example:
input: "©™®"
output: "& #169; & #8482; & #174;"(space after & is only for question purpose, if typed without a space decimal equivalent is converted to special character)
Thank you !

This can be simply achieved with String.format(). The representations are simply the character value as decimal, padded to 4 characters and wrapped in &#;
The only tricky part is deciding which characters are "special". Here I've assumed not digit, not whitespace and not alpha...
StringBuilder output = new StringBuilder();
String input = "Foo bar ©™® baz";
for (char each : input.toCharArray()) {
if (Character.isAlphabetic(each) || Character.isDigit(each) || Character.isWhitespace(each)) {
output.append(each);
} else {
output.append(String.format("&#%04d;", (int) each));
}
}
System.out.println(output.toString());

You just need to fetch the integer value of the character as mentioned in How do I get the decimal value of a unicode character in Java?.
As per Oracle Java doc
char: The char data type is a single 16-bit Unicode character. It has
a minimum value of '\u0000' (or 0) and a maximum value of '\uffff' (or
65,535 inclusive).
Assuming your characters fall within the character range, you can just get the decimal equivalent of each character from your string.
String text = "©™®";
char[] cArr = text.toCharArray();
for (char c : cArr)
{
int value = c; // get the decimal equivalent of the character
String result = "& #" + value; // append to some format string
System.out.println(result);
}
Output:
& #169
& #8482
& #174

Replace special characters in a string with their UTF-8 encoded character java?

I want to convert only the special characters to their UTF-8 equivalent character.
For example given a String: Abcds23#$_ss, it should get converted to Abcds23353695ss.
The following is how i did the above conversion:
The utf-8 in hexadecimal for # is 23 and in decimal is 35. The utf-8 in hexadecimal for $ is 24 and in decimal is 36. The utf-8 in hexadecimal for _ is 5f and in decimal is 95.
I know we have the String.replaceAll(String regex, String replacement) method. But I want to replace specific character with their specific UTF-8 equivalent.
How do I do the same in java?

I don't know how do you define "special characters", but this function should give you an idea:
public static String convert(String str)
{
StringBuilder buf = new StringBuilder();
for (int index = 0; index < str.length(); index++)
{
char ch = str.charAt(index);
if (Character.isLetterOrDigit(ch))
buf.append(ch);
else
buf.append(str.codePointAt(index));
}
return buf.toString();
}
#Test
public void test()
{
Assert.assertEquals("Abcds23353695ss", convert("Abcds23#$_ss"));
}

The following uses java 8 or above and checks whether a Unicode code point (symbol) is a letter or digit, pure ASCII (< 128) and otherwise output the Unicode code point as string of the numerical value.
static String convert(String str) {
int[] cps = str.codePoints()
.flatMap((cp) ->
Character.isLetterOrDigit(cp) && cp < 128
? IntStream.of(cp)
: String.valueOf(cp).codePoints())
.toArray();
return new String(cps, 0, cps.length);
}
String.codePoints() yields an IntStream, flatMap adds IntStreams in a single flattened stream, and toArray collects it in an array. So we can construct a new String from those code points. Entirely Unicode safe.
Conversion is not undoable without delimiters.
On Unicode:
Unicode numbers symbols, called code points, from 0 upwards, into the 3 byte range.
To be coded (formated) in bytes there exist UTF-8 (multi-byte), UTF-16LE and UTF-16BE (2byte-sequences) and UTF-32 (code points as-is more or less).
Java string constants in a .class file are in UTF-8. A String is composed of UTF-16BE chars. And String can give code points as above. So java by design uses Unicode for text.

How to convert hex string to octal string in java

I am converting a string into hexadecimal string and i want to convert that into octal string
I am doing it as follows
String s="I found the reason 2 days ago i was too bussy to update you.The problem was that the UDHL was missing. I should have added 06 at the beginning. it all works fine.For some reason I thought kannel adds this by itself (not very difficult...), but now I know it doesn't...";
String hex = String.format("%040x", new BigInteger(1, s.getBytes("UTF-8")));
Output is
4920666f756e642074686520726561736f6e203220646179732061676f20692077617320746f6f20627573737920746f2075706461746520796f752e5468652070726f626c656d20776173207468617420746865205544484c20776173206d697373696e672e20492073686f756c6420686176652061646465642030362061742074686520626567696e6e696e672e2020697420616c6c20776f726b732066696e652e466f7220736f6d6520726561736f6e20492074686f75676874206b616e6e656c2061646473207468697320627920697473656c6620286e6f74207665727920646966666963756c742e2e2e292c20627574206e6f772049206b6e6f7720697420646f65736e27742e2e2e
I need to convert hex to octal string. I tried like this
String octal = Integer.toOctalString(Integer.parseInt(hex,16));
But as expected it gave me number format exception as hex string have some characters in it.
I want to know how can i conver hex string to octal string.

As per the discussion in the comments, you want to convert each byte individually and convert them to octal:
String s = "My string to convert";
byte[] bytes = s.getBytes("UTF-8");
for (byte b : bytes) {
String octalValue = Integer.toString(b, 8);
// Do whatever
}

The problem is, that your input (String hex) is to big to be stored in a single integer.
3 hex digits correspond to 4 octal digits. So split your input string in chunks of three digits, use the conversion you already figured out, and concatenate the outputs.

Assign number on specific line to a variable

How do you assign an unknown substring (a Hex number) from a specific line in a txt file to a variable?
I've written the code to identify the necessary line and I've been told to use Regular Expressions (regex).
I don't know how to do that. Can it be done without regex?
This is an extract from an example txt file. I'm looking to get (and then compare Value(2) and Value(3)) but I need the Hex numbers first.
Default(2) = 0x00
Value(2) = 0xE0A64F36
Desc(2) = calculated from application
Address(2) = 0x60
Page(2) = Sensor
Name(3) = ROM CRC32
Type(3) = u32
Default(3) = 0x00
Value(3) = 0xE0A64F36
Desc(3) = fix CRC from ROM

Split by = and parse the hexadecimal number.
String s = "Value(2) = 0xE0A64F36";
String hex = s.split("=")[1].trim();
long l = Long.parseLong(hex.substring(2), 16);
// l == 3768995638

if you don't want to use regular expressions, you have to parse the string by the HEX pattern by yourself, such as getting the value part of the line (string after "=") and checking whether this part is in HEX format (starting with 0x and following characters are in 0-F) or using Integer.parseInt(String s, int radix) to try to parse it (catch the exception)

Assuming you have the strings already extracted and they are stored in 2 variables,
String value2 = "Value(2) = 0xE0A64F36";
String value3 = "Value(3) = 0xE0A64F36";
You can use substring and indexOf to get the actual value:
value2 = value2.substring(value2.indexOf("0x"));
value3 = value3.substring(value3.indexOf("0x"));
if (value2.compareToIgnoreCase(value3) == 0) {
// Do something here
}

You can do the extraction like this:
Pattern p = Pattern.compile("Value\\([23]\\) = (0x([0-9A-F]{8}))");
Matcher m = p.matcher(s);
while (m.find()) {
System.out.println(m.group(1));
System.out.println(Long.parseLong(m.group(2), 16));
}
Notice: if you want only to test if value(2) and value(3) are the same, you dont need to convert anything. You can only compare strings.

Java Char to its unicode hexadecimal string representation and vice-versa

I need to generate the hexadecimal code of Java characters into strings, and parse those strings again later. I found here that parsing can be performed as following:
char c = "\u041f".toCharArray()[0];
I was hoping for something more elegant like Integer.valueOf() for parsing.
How about generating the hexadecimal unicode properly?

This will generate a hex string representation of the char:
char ch = 'ö';
String hex = String.format("%04x", (int) ch);
And this will convert the hex string back into a char:
int hexToInt = Integer.parseInt(hex, 16);
char intToChar = (char)hexToInt;

After doing some deeper reading, the javadoc says the Character methods based on char parameters do not support all unicode values, but those taking code points (i.e., int) do.
Hence, I have been performing the following test:
int codePointCopyright = Integer.parseInt("00A9", 16);
System.out.println(Integer.toHexString(codePointCopyright));
System.out.println(Character.isValidCodePoint(codePointCopyright));
char[] toChars = Character.toChars(codePointCopyright);
System.out.println(toChars);
System.out.println();
int codePointAsian = Integer.parseInt("20011", 16);
System.out.println(Integer.toHexString(codePointAsian));
System.out.println(Character.isValidCodePoint(codePointAsian));
char[] toCharsAsian = Character.toChars(codePointAsian);
System.out.println(toCharsAsian);
and I am getting:
Therefore, I should not talk about char in my question, but rather about array of chars, since Unicode characters can be represented with more than one char. On the other side, an int covers it all.

On String level:
The following uses not char but int, say for Chinese, but is also adequate for chars.
int cp = "\u041f".codePointAt(0);
String s = new String(Character.toChars(cp));
On native2ascii level:
If you want to convert back and forth between \uXXXX and Unicode character, use from apache, commons-lang the StringEscapeUtils:
String t = StringEscapeUtils.escapeJava(s + "ö");
System.out.println(t);
On the command-line native2ascii can convert back and forth files between u-escaped and say UTF-8.