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read unique char: 'あ' from json file in java

I am reading a JSON file in Java using this code:
String data = Files.readFile(jsonFile)
.trim()
.replaceAll("[^\\x00-\\x7F]", "")
.replaceAll("[\\p{Cntrl}&&[^\r\n\t]]", "")
.replaceAll("\\p{C}", "");
In my JSON file, there is a unique char: 'あ' (12354) that is interpreted to: "" (nothing) when reading the file.
How can I make this char show up in my variable "data"?
Due to answers I've got, I understand that the data is cleaned from high ASCII characters by adding replaceAll("[^\\x00-\\x7F]", ""). But what can I do if I want all high ASCII characters to be cleaned except this one 'あ'?

The character you want is the unicode character HIRAGANA LETTER A and has code U+3042.
You can simply add it to the list of valid characters:
...
.replaceAll("[^\\x00-\\x7F\\u3042]", "")
...

Filter Special Characters in Spring / Java

I'm using jsoup to get all text from websites.
Document doc = Jsoup.connect("URL").get();
String allText doc.text().toLowerCase();
Then I'm using Hibernate to persist the object that holds all text to a MySQL DB:
...
#Column(name="all_text")
#Lob
private String allText = null;
...
Everything is good so far. Only that sometimes I get a MySQL error when I try to save the object with allText:
java.sql.SQLException: Incorrect string value: '\xF0\x9F\x98\x8A s...' for column 'all_text' at row 1
Already looked this up and it's an encoding error. Probably have some special characters on their websites. I found a way to fix this by changing the encoding in the DB.
But my actual question is: what's the best way to filter and remove the special characters from the allText string and not persist them at all?
EDIT: To clarify, by special characters I mean Emoticons and all that stuff. Definitely anything that doesn't fit into UTF-8 encoding. I'm not concerned about ~ ^ etc...
Thanks in advance!

Just use regex:
allText.replaceAll("\\p{C}", "");
Don't forget to import java.util.regexPattern

Croatian character in Java standard output

I have a database with some cratian characters in it like Đ , in the database the character is stored correctly, when using a datatable in primefaces it also shows the character in the webpage just fine.
The problem is that when I send it to the out.println() the character Đ in the name is missing.
for (People p : people) {
System.out.println("p.getName());
}
I tried using String name2 = p.getName().getBytes("ISO-8859-2"); but it still not working

I assume you are using UTF-8 as default encoding on the Database and for Primefaces
Have also a look to this:
Display special characters using System.out.println

Java: Search in a wrong encoded String without modifying it

I have to find a user-defined String in a Document (using Java), which is stored in a database in a BLOB. When I search a String with special characters ("Umlaute", äöü etc.), it failes, meaning it does not return any positions at all. And I am not allowed to convert the document's content into UTF-8 (which would have fixed this problem but raised a new, even bigger one).
Some additional information:
The document's content is returned as String in "ISO-8859-1" (Latin1).
Here is an example, what a String could look like:
Die Erkenntnis, daà der Künstler Schutz braucht, ...
This is how it should look like:
Die Erkenntnis, daß der Künstler Schutz braucht, ...
If I am searching for Künstler it would fail to find it, because it looks for ü but only finds ü.
Is it possible to convert Künstler into Künstler so I can search for the wrong encoded version instead?
Note:
We are using the Hibernate Framework for Database access. The original Getter for the Document's Content returns a byte[]. The String is than returned by calling
new String(getContent(), "ISO-8859-1")
The problem here is, that I cannot change this to UTF-8, because it would then mess up the rest of our application which is based on a third party application that delivers data this way.

Okay, looks like I've found a way to mess up the encoding on purpose.
new String("Künstler".getBytes("UTF-8"), "ISO-8859-1")
By getting the Bytes of the String Künstler in UTF-8 and then creating a new String, telling Java that this is Latin1, it converts to Künstler. It's a hell of a hack but seems to work well.

Already answered by yourself.
An altoghether different approach:
If you can search the blob, you could search using
"SELECT .. FROM ... WHERE"
+ " ... LIKE '%" + key.replaceAll("\\P{Ascii}+", "%") + "%'"
This replaces non-ASCII sequences by the % wildcard: UTF-8 multibyte sequences are non-ASCII by design.

xmlhttp.setRequestHeader not working

this is my code
// assume var data has japanese characters
xmlhttp.open("POST","adminUpdate?&value="+data,true); // tried GET as well
xmlhttp.setRequestHeader("Content-Type", "text/plain;charset=UTF-8");
xmlhttp.send();
if I insert alert(data) then i can see japanese characters perfectly fine.
But on the server side (servlet class) when I add this code :
String query = request.getParameter("value");
system.out.println(query)
Now I see garbage value ??????
Ok so I added this line server side :
System.out.println("content type : "+ request.getContentType());
and I got this : text/plain;charset=UTF-8
So now my question is if the encoding is set correctly then why I cant see Japanese characters

One option is to send the query parameters as part of the request body and have the content type set to application/x-www-form-urlencoded.
Then, before getting the parameter, set the request's content character encoding
request.setCharacterEncoding("UTF-8");
String query = request.getParameter("value");
Note that wherever you're printing the query value has to be able to display UTF-8 encoded characters.