Problem of Statement and PreparedStatement

Question

hi
The PreparedStatement has a metod :
setNull(int parameterIndex, int sqlType)
I want make a class to simulate PreparedStatement.
String sql = "update tablename custname = ?,orderdate = ? where id = ?";
mySimulate = new mySimulate(sql);
mySimulate.setString(1,"myName");
mySimulate.setNull(2,null);
mySimulate.setInt(3,1);
Statement st = con.createStatement() ;
st.executeQuery(mySimulate.toString())
now i don't know how to simulate the method of setNull(),setObject(),setTime()

Answer 1

This isn't so easy because the SQL that gets returned will depend on the database you're using.
However, I would implement this by tokenising the original SQL string using '?' as a delimiter.
This would give you a list of SQL fragments.
You would then need another list of SQL values that gets populated when the setXXX methods are called. Finally you would interleave the two lists to form the finished string:
public class MySimulate
  protected static final SimpleDateFormat SQL_DATE_FORMAT = new SimpleDateFormat("dd/MM/yyyy"); // Or whatever format your database accepts
  protected static final String NULL = "NVL"; // Or whatever your database accepts for null value
  protected String[] clauses;
  protected String[] values;
  public MySimulate(String sql)
    StringTokenizer st = new StringTokenizer(sql, "?", false);
    clauses = new String[st.getTokenCount()];
    values = new String[clauses.length];
    for(int idx = 0; idx < clauses.length; idx++)
      clauses[idx] = st.nextToken();
  public void setString(int idx, String str)
    // Should replace all occurrences of ' with '' first!
    values[idx] = "'" + str + "'";
  public void setDate(int idx, Date date)
    values[idx] = SQL_DATE_FORMAT.format(date);
  public void setNull(int idx)
    values[idx] = NULL;
  public void setInt(int idx, int val)
    values[idx] = String.valueOf(val);
  public String toString()
    StringBuffer b = new StringBuffer();
    for(int idx = 0; idx < clauses.length; idx++)
      b.append(clauses[idx]);
      b.append(values[idx]);
    return b.toString();
}Something like that anyway.
You'll have to play around with how to format your dates, escaping quotes in string values etc. You might even want to make it configurable for different databases.
Hope it helps, though!