Java-如何编写包含给定集合变量的正则表达式的正则表达式

Question

I need to retrieve the numbers followed by some specific units such as 10 m, 5 km... from given web pages. Those specific units are keys of a map<String, Integer> . keySet() returns a comma separated list, like ["m", "km"...] . Is there a smart way to get the set as disjunction of the variables, like ["m"|"km"|...] so that I could use it in a regex such as:

"(\\d+)"+ " " +"myMap.keySet()......"

Answer 1

用管道将集合加入： "(\\\\d+)\\\\s*(" + StringUtils.join(myMap.keySet(), "|") + ")"

Answer 2

How about

myMap.keySet().toString().replaceAll(",\\s*", "|").replaceAll("^\\[|\\]$", "")
//                       ^                         ^
//                       |                         +remove [ at start and ] at end
//                       +replace `,` and spaces after it with |

instead

myMap.keySet()

Your code can look like this

String data = "1km is equal 1000 m, and 1  m is equal 100cm. 1 mango shouldnt be found";

Map<String, Integer> map = new HashMap<>();
map.put("m", 1);
map.put("km", 2);
map.put("cm", 3);

String regex = "\\d+\\s*("
        + map.keySet().toString()       //will create "[cm, m, km]"
            .replaceAll(",\\s*", "|")   //will change it to "[cm|m|km]"
            .replaceAll("^\\[|\\]$", "")//will change it to "cm|m|km"
        + ")\\b";                       
    // I added \\b - word boundary - to prevent matching `m` if it is at
    // start of some word like in 1 mango where it normally would match
    // (1 m)ango

Pattern p=Pattern.compile(regex);
Matcher m=p.matcher(data);
while(m.find()){
    System.out.println(m.group());
}

Answer 3

You can try this:

String p = "\\d+ (?:";
for (String key : yourMap.keySet())
   p += key + "|";
p = p.substring(0, p.length() - 1) + ")";