替换Java中的某些固定字符串

Question

I have a string query which looks like this

{"query":{"bool":{"should":[{"terms":{"user.id":[#users_to_follow],"minimum_match":1}},{"terms":{"tweets":[#keywords_to_track],"minimum_match":1}}]}},"filter":{"range":{"publishedDate":{"from":#Unix_timestamp}}},"size":#sizelength}"

I am trying to replace certain strings in the query with another string using:

query.replace("#users_to_follow",usersToFollow);
query.replace("#keywords_to_track", keyworsToTrack);
query.replace("#Unix_timestamp","1325930428000" );
query.replace("#sizelength",Integer.toString(SMLApplicationProperties.ES_RESULTSET_SIZE));

However when I run this thing, it does not actually replace the given strings from query.

Answer 1

You need to understand that String class is immutable. Any operation on String returns a new String. You need to assign it back to query variable:

query = query.replace("#users_to_follow",usersToFollow); 
query = query.replace("#keywords_to_track", keyworsToTrack); 
query = query.replace("#Unix_timestamp","1325930428000" ); 
query = query.replace("#sizelength",Integer.toString(SMLApplicationProperties.ES_RESULTSET_SIZE));

Answer 2

You need to get the result of the replace operation :

query = query.replace("#users_to_follow",usersToFollow);

That's because query.replace doesn't change the string you pass, it builds and returns a new one (string in java are immutable).

Answer 3

您可以优化（并非所有人都接受）：

String query = query.replace("#users_to_follow",usersToFollow).replace("#keywords_to_track", keyworsToTrack).replace("#Unix_timestamp","1325930428000" ).replace("#sizelength",Integer.toString(SMLApplicationProperties.ES_RESULTSET_SIZE));