how to use Java to replace String?(regex)

Question

I hava one jsonString

String target = "[{"nickName":"andy","password":"wei","userword":"weitest32123"}]";

I wish to get

String target = "[{"nickName":"andy","password":"xxx","userword":"xxx"}]";

I want to use the java String method replaceall(regex,"xxx");

how do?

• Stephen C: 1) Your problem statement is ambiguous. You cannot unambiguously describe a transformation with a single example. Describe in words what you want the transformation to do. 2) You probably shouldn't do this using a regex. Parse the JSON, transform the data structure, and unparse to a new JSON string.
• Stephen C: (One reason why a regex may be the wrong solution is that the password or userword attributes could contain escaped quote characters. Or characters such as [, {, :, , etcetera. Or extra fields could be added or ... other things that would make the regex fragile.)
• Stephen C: I'm not sure, but I think that all three of the answers so far will fail if the userword or password contains an escaped quote. Or if the value of the nickname is "userword" or "password". This is the problem with using regexes for parsing. The edge-cases are tricky to deal with ...

Answer 1

Try this.

String input = "[{\"nickName\":\"andy\",\"password\":\"wei\",\"userword\":\"weitest32123\"}]";
String output = input.replaceAll("(?<=\"(pass|user)word\":\")[^\"]+", "xxx");
System.out.println(output);

output:

[{"nickName":"andy","password":"xxx","userword":"xxx"}]

Answer 2

You can do it with the Positive Lookbehind regexp regex101.com:

public static void main(String... args) {
 String str = "\"[{\"nickName\":\"andy\",\"password\":\"wei\",\"userword\":\"weitest32123\"}]\"";
 System.out.println(maskPassword(str)); // "[{"nickName":"andy","password":"xxx","userword":"xxx"}]"
}
public static String maskPassword(String str) {
 String regex = "(?<=\"(password|userword)\":)(\"[^\"]+\")";
 return str.replaceAll(regex, "\"xxx\"");
}

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P.S. I strongly recommend you not to do this with json string. This could follow a problem in the future. It's better to parse this json string into an object and then create json back with modification.

E.g. you can use a tool that I wrote gson-utils

Answer 3

This may seem like you're trying to parse some JSON. I'm not sure if casting it to object and then hiding values would be better approach.

But if you really need to do this way, this would be the solution

// You need this 2 imports
//import java.util.regex.Matcher;
//import java.util.regex.Pattern;
String text = "[{\"nickName\":\"andy\",\"password\":\"wei\",\"userword\":\"weitest32123\"}]";
Pattern pattern = Pattern.compile("\"(?<key>password|userword)\":\"(?<value>.*?)\"");
Matcher matcher = pattern.matcher(text);
String result = matcher.replaceAll("\"${key}\":\"xxx\"");

In Regex you need to specify all keys that you want to mask