Replacing Single Backslashes with Double Backslashes in Strings

When attempting to use replaceAll to convert a string like "\something\" into "\something\", developers often encounter errors. The common approach of using the replaceAll("\", "\\") method results in the exception "java.util.regex.PatternSyntaxException: Unexpected internal error near index 1". This occurs because the backslash () character is treated as both an escape character in strings and in regular expressions. To address this, escape the backslash in the regular expression by doubling it:

string.replaceAll("\\\\", "\\\\\\\\");

However, a regex is not always necessary here. Since we only want to perform a character-by-character replacement, String#replace() can be sufficient:

string.replace("\\", "\\\\");

Note that if the string is intended for use in a JavaScript context, it might be more suitable to use StringEscapeUtils#escapeEcmaScript() to cover a wider range of characters.