Add escape "\" in front of special character for a string

Question

I have a simple SQL query where I check whether the query matches any of the fields I have. I'm using LIKE statement for this. One of my field can have special characters and so does the search query. So I'm looking for a solution where I need to an escape "\" in front of the special character.

query = "hello+Search}query"

I need the above to change to

query = "hello\+Search\}query"

Is there a simple way of doing this other than searching for each special character separately and adding the "\". Because if I don't have the escape character I will get the error message

java.util.regex.PatternSyntaxException: Dangling meta character '+' near index 0

Thanks in advance

Langston

What context are you using it in? Why do you use it in a regex? Can you show the context where that error is happening (please edit the question). – Hamforrd

Also please add what database you are using. – Hamforrd

Answer 1

Decide which special characters you want to escape and just call

query.replace("}", "\\}")

You may keep all special characters you allow in some array then iterate it and replace the occurrences as exemplified. This method replaces all regex meta characters.

public String escapeMetaCharacters(String inputString){
    final String[] metaCharacters = {"\\","^","$","{","}","[","]","(",")",".","*","+","?","|","<",">","-","&","%"};

    for (int i = 0 ; i < metaCharacters.length ; i++){
        if(inputString.contains(metaCharacters[i])){
            inputString = inputString.replace(metaCharacters[i],"\\"+metaCharacters[i]);
        }
    }
    return inputString;
}

You could use it as query=escapeMetaCharacters(query); Don't think that any library you would find would do anything more than that. At best it defines a complete list of specialCharacters.

Plath

OP said "other than searching for each special character separately and adding the \". – Hamforrd

Indeed, but there is no better option. I recommend he just keeps track of all special characters he escapes. – Plath

You need to init outputString to inputString and not to an empty String, in case no special characters exists – Priapitis

Still need this kind of workaround in Java in 2018 :( – Hypochondria

Answer 2

There is actually a better way of doing this in a sleek manner.

String REGEX = "[\\[+\\]+:{}^~?\\\\/()><=\"!]";

StringUtils.replaceAll(inputString, REGEX, "\\\\$0");

Northington

This method is deprecated in newer versions of commons-lang3 ( my version is 3.12.0 ) – Lev

commons lang methods is just a null safe replacement for inbuilt string method String.replaceAll(). inputString.replaceAll(REGEX, "\\\\$0") would work too if you ensure inputString is not null. – Cochineal

Answer 3

You need to use \\ to introduce a \ into a string literal; that is you need to escape the \. (A single backslash is used to introduce special characters into a string: e.g. \t is a tab.)

query = "hello\\+Search\\}query" is what you need.

Guy

ok, but either way, I need a way to identify the location of the special character such as "+", so I would be able to add that value. My query looks like this "hello+Search}query" I need to find the special characters location to add the escape character. – Langston

Simply replace + with \\+, etc. – Guy

Or use a prepared statement. It should also be able to handle these special characters. – Monanthous

I need a generic method to identify all the special characters in my query, "+" was an example. So I was looking for a solution which is more elegant than looking for each special character and replace it. – Langston

@Tom: I agree. Sadly, the OP has not specified the database. – Guy

@Langston there isn't a more elegant solution. If you find a library/class that does that, inside you will find a function similar to what i provided. – Plath

Answer 4

I had to do same thing in javascript. I came up with below solution. I think it might help someone.

function escapeSpecialCharacters(s){
 let arr = s.split('');
 arr = arr.map(function(d){
         return d.replace(/[-\/\\^$*+?.()|[\]{}]/g, '\\'+d)
       });
 let reg = new RegExp(arr.join('')); 
 return reg;
}

let newstring = escapeSpecialCharacters("hello+Search}query");

Calabria

Answer 5

If you want to use Java 8+ and Streams, you could do something like:

private String escapeSpecialCharacters(String input) {
    List<String> specialCharacters = Lists.newArrayList("\\","^","$","{","}","[","]","(",")",".","*","+","?","|","<",">","-","&","%");
    return Arrays.stream(input.split("")).map((c) -> {
                if (specialCharacters.contains(c)) return "\\" + c;
                else return c;
    }).collect(Collectors.joining());
}

Chancre

Answer 6

The simple version ( without deprecated StringUtils.replaceAll ):

    String regex = "[\\[+\\]+:{}^~?\\\\/()><=\"!]";
    String query = "hello+Search}query";
    String replaceAll = query.replaceAll(regex, "\\\\$0");

Lev