Question

I created a Java Servlet that get query result from mySQL database and print it in XML format.
the problem is that it takes a very long time, something about three minutes to print the xml result while in my PHP script it takes 5 seconds.

My Servlet relevant function is:
( run a query and return the xml in a String variable, then, print it to the page )

public String QueryResult(String query)
{
    String retStr;
    try {
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection ("jdbc:mysql://"+this.host+":"+this.port+"/"+this.db, this.user, this.pass);
        Statement stmt = conn.createStatement();
        ResultSet rset = stmt.executeQuery(query);
        ResultSetMetaData rsMetaData = rset.getMetaData();

        retStr = "<Result>\n";
        while (rset.next())
        {
            retStr += "\t<Item>\n";
            for (int i=1;i<=rsMetaData.getColumnCount();i++)
            {
                retStr += "\t\t<"+rsMetaData.getColumnName(i)+">"+ rset.getString(i) + "</"+rsMetaData.getColumnName(i)+">\n";
            }
            retStr += "\t</Item>\n";
        }
        retStr += "</Result>\n";
        stmt.close();
        conn.close();
    }
    catch(Exception e) 
    {
        return "<Result><Error>"+e.toString()+"</Error></Result>";
    }
    return retStr;
}

Answer 1

String Concatenation:

First of all, when speed matters, you do not want to concatenate strings the way you do. Each time you concatenate a String you are creating a new one.

Better use StringBuilder with a well planned capacity, as the default one won’t probably suit your need judging from the code snippet you show.

Also See:

String, StringBuffer, and StringBuilder

Why to use StringBuffer in Java instead of the string concatenation operator

XML:

XStream is a simple library to
serialize objects to XML and back
again.

Might not be related to your performance issue but might come in handy: XStream

“Performance” does figure in their features list.