how to generate a string from complex format similiar to regular expression? - expression

Question

We know String.format() can accept format with such style:
%[argument_index$][flags][width][.precision]conversion
which is well known as C printf() format, and introduced in java 1.5.
My task is, generating complex format including repeated or optional parameters.
For example, with the format:
select %1 from %2 where %3 and give %1->'*' %2->'users' %3->'age>20'
it returned:
select * from users where age>20
the format can be supported by Stirng.format().
However, I expect a format similar to:
select %1{, } from (%2(as %3)){,} (where %4 (and %5))?
when: %1->'*', %2->'users' %3->null, %3->'age>20'
it returned:
select * from users where age>20
when: %1->Stirng{'name','age'} , %2->'users' %3->'u', %4->'age>20', %5->null
it returned:
select name, age from users as u where age>20
when: %1->Stirng{'name','age'} , %2->'users' %3->'u', %4->null, %5->null
it returned:
select name, age from users as u
when: %1->Stirng{'name','age'} , %2->String{'users','order'} %3->{'u','o'}, %4->'age>20', %5->'u.id=o.userid'
it returned:
select name, age from users as u,orders as o where age>20 and u.id=o.userid
I think now you may understand my meanings. Are there a mature library to do such complex 'anti-regexp' work?

Answer 1

Maybe you are looking for a CustomFormatProvider?
class SqlFormatter:IFormatProvider, ICustomFormatter
{
public object GetFormat(Type formatType)
{
return this;
}
public string Format(string format, object arg, IFormatProvider formatProvider)
{
StringBuilder concat = new StringBuilder();
string[] formatParts = format.Split(':');
switch (formatParts[0])
{
case "sqlfield":
string sep = "";
if (formatParts.Length>1)
{
sep = formatParts[1];
}
string[] fields = (string[]) arg;
concat.Append(fields[0]);
for (int fieldIndex = 1; fieldIndex < fields.Length; fieldIndex++)
{
concat.Append(sep);
concat.Append(fields[fieldIndex]);
}
break;
case "sqltables":
concat.Append(arg.ToString());
break;
default:
break;
}
return concat.ToString();
}
}
Use it like this:
String sql = String.Format(
new SqlFormatter()
, "select {0:sqlfield:,} from {1:sqltables} "
, new string[]{"name","lname"}
, "person" );
Will give:
"select name,lname from person "
I'll leave the rest of the implementation (and robustness etc) to you...