Replacing substring inside string not working? Java XML

Question

All,

I am storing SQL queries as XML for my java application to improve maintainability.

Parts of my query require parameterisation, therefore I have created identifiers that I can use to replace with values when I create my query string.

e.g.

WHERE CB.callback_date &gt;= TO_DATE('$LASTDATE$','DD/MM/YYYY')
  AND CB.callback_date &lt; TO_DATE('$FROMDATE$','DD/MM/YYYY')

I have a function in my application that will replace these substrings.

public static String xmlQueryPrep(String prep)
{

    //add dates to query
    prep.replace("'$LASTDATE$'", "'20/10/2013'");
    prep.replace("'$FROMDATE$'", "'18/10/2013'");
    prep.replace("&lt;", "<").replace("&gt;", ">");
    return prep;    
}

For some reason it is replacing the ASCII codes for < and > but it is not replacing my markup

Output

WHERE CB.callback_date >= TO_DATE('$LASTDATE$','DD/MM/YYYY')
  AND CB.callback_date < TO_DATE('$FROMDATE$','DD/MM/YYYY')

Why is it not replacing correctly?

It looks like you're using string operations to build SQL. Are you aware just how poor an idea that really is? If you can use a parameterized prepared query or a (correctly-designed) named query instead, you'll avoid a lot of trouble! (Note that this is true independent of what language you use to prepare the query.) — Donal Fellows
– Donal Fellows, Commented Oct 20, 2013 at 19:04

Alexis C. · Accepted Answer · 2013-10-20 15:06:14Z

7

Strings in Java are immutables.

An object is considered immutable if its state cannot change after it is constructed

If you take a look at the documentation, you will see that each method that is applied to a String to modify its content will return a new String.

You should do :

prep = prep.replace("'$LASTDATE$'", "'20/10/2013'");
prep = prep.replace("'$FROMDATE$'", "'18/10/2013'");
prep = prep.replace("&lt;", "<").replace("&gt;", ">");
return prep;

Or even better (method chaining):

return prep.replace("'$LASTDATE$'", "'20/10/2013'")
           .replace("'$FROMDATE$'", "'18/10/2013'")
           .replace("&lt;", "<")
           .replace("&gt;", ">");

edited Oct 20, 2013 at 15:06

answered Oct 20, 2013 at 14:54

Alexis C.

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4 Comments

Richard Tingle Over a year ago

In other words, string.replace(.....) returns a new string in which the replace operation has taken place, the old string is unaffected

tomaytotomato Over a year ago

Why is C++ different then with regards to strings?

Bohemian Over a year ago

Java is based on C/C++, but is s new/different language. There are many differences - thus is just one.

Donal Fellows Over a year ago

@serupticious Java's StringBuilder works a lot more like strings in C and C++, but it's (directly) used a lot less frequently.

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