基于特殊字符的子字符串

Question

I have to fetch the tablename and columnnames from a sql. For this I had split from clause data based on space and stored all the elements in a list, But now some of the columns having method calling or some other validations.

For ex some of columns :

• max(TableName1.ColumnName1) --> TableName1.ColumnName1
• concat('Q',TableName2.ColumnName2)} --> TableName2.ColumnName2
• left(convert(varchar(90),TableName3.ColumnName3),1)}) --> TableName3.ColumnName3

Now I validate strings which are having .
Here I had only hint ie ( . ) based on this I have to get right and left strings upto/before special characters.

Might get special characters like , ( )

Answer 1

import java.util.*;
import java.text.*;
import java.util.regex.*;

public class Parser {

    private static Pattern p = Pattern.compile("(?![\\(\\,])([^\\(\\)\\,]*\\.[^\\(\\)\\,]+)(?=[\\)\\,])");

    private static String getColumnName(String s) {
        Matcher m = p.matcher(s);
        while(m.find()) {
            return m.group(1);
        }
        return "";
    }

     public static void main(String []args) {
        String s1= "max(TableName1.ColumnName1)";
        System.out.println(getColumnName(s1));

        String s2= "concat('Q',TableName2.ColumnName2)}";
        System.out.println(getColumnName(s2));

        String s3= "left(convert(varchar(90),TableName3.ColumnName3),1)})";
        System.out.println(getColumnName(s3));
     }
}

Output:

TableName1.ColumnName1                                                                                                                                                                                                                
TableName2.ColumnName2                                                                                                                                                                                                                
TableName3.ColumnName3  

Answer 2

You can use a regular expression like [(),{}] to split the array into tokens, and then just select the token with the "." sign in it. For example:

public static String getColumnName (String input) {
    if (StringUtils.isEmpty(input)) return input;
    String[] tokens = input.split("[(),{}]");
    for (String token: tokens) {
      if (token.contains(".")) return token;
    }
    return input;
}
public static void main(String args[]) throws Exception {
    //The two tokens will be "max", "TableName1.ColumnName1".
    String test1 = "max(TableName1.ColumnName1)";

    //The three tokens will be "concat", "Q" and "TableName2.ColumnName2".
    String test2 = "concat('Q',TableName2.ColumnName2)}";

    //The six tokens will be "left", "convert", "varchar", 
    //"90", "", "1" and "TableName3.ColumnName3".
    String test3 = "left(convert(varchar(90),TableName3.ColumnName3),1)})";

    System.out.println(getColumnName(test1));
    System.out.println(getColumnName(test2));
    System.out.println(getColumnName(test3));
}

The print out will give you:

TableName1.ColumnName1
TableName2.ColumnName2
TableName3.ColumnName3