如何获取单词和等号以及等号和值之间的文本？

Question

I am learning regular expressions in Java (technically the Android API) and have come across a problem. I was originally using basic functionality of Java's String.matchAll(String expression, String occurence); but now I use Pattern and Matcher classes.

I followed this tutorial to learn the basics and it seemed pretty simple.

My Java regex is info(.*?)\\\\, and I have also tried this: (?<=\\\\binfo\\\\=).*?(?=\\\\=) .

For the first regex if I had a string "info i = 5," it would parse as "info = 5" . For the second one, if using the same string, I would get an exeption that there are no matches (InputMismatchException, I think).

My parsing code is:

//Produces "info i 5" rather than the desired "i"
public String parseStringAlias(String textToBeParsed)
{
    //Gets the value(or alias) located between the word info and the = sign
    Pattern p = Pattern.compile("info(.*?)\\=");
    Matcher m = p.matcher(textToBeParsed);

    //0 would be the first match
    return m.group(0);
}

//Returns InputMismatchException rather than the desired number between equals sign and comma
//If given out example of "info i = 5," should return 5
public String parseStringValue(String textToBeParsed)
{
    //Pattern fetches the value between the "=" and the ","
    Pattern p = Pattern.compile("(?<==).*?(?=\\,)");

    //Search for matches
    Matcher m = p.matcher(textToBeParsed);

    //0 would be the first match
    return m.group(0);
}

Answer 1

You have some issues with your regexps: you should escape only special regex characters like ( , ) , [ , etc. with \\\\ , not with // and not such chracters as , or = .

You do not match anything because you do not "run" the regex search.

Add m.find() before each return line, better, use it inside an if . And it looks like you are seeking .group(1) value with parseStringAlias method:

public static void main (String[] args) throws java.lang.Exception
{
    System.out.println(parseStringAlias("\"info i = 5,\""));
    System.out.println(parseStringValue("\"info i = 5,\""));
}
//Produces "info i 5" rather than the desired "i"
public static String parseStringAlias(String textToBeParsed)
{
    //Gets the value(or alias) located between the word info and the = sign
    Pattern p = Pattern.compile("info(.*?)="); // <- Note removed `//`
    Matcher m = p.matcher(textToBeParsed);
    //0 would be the first match
    if (m.find()) {                          // < - We "ran" the regex search
        return m.group(1);                   // <- Group 1 is accessed
    }
    return "";
}   

//Returns ImputMismatchException rather than the desired number between equals sign and comma
//If given out example of "info i = 5," should return 5
public static String parseStringValue(String textToBeParsed)
{
    //Pattern fetches the value between the "=" and the ","
    Pattern p = Pattern.compile("(?<==).*?(?=,)");          // <- Note removed `\\` and `//`
    //Search for matches
    Matcher m = p.matcher(textToBeParsed);
    //0 would be the first match
    if (m.find()) {                               // <- We "ran" the regex
        return m.group(0);                       // <- We access 0th group, the whole match
    }
    return "";
}

See IDEONE demo