Java(TM) Boutique - Building Web Applications Using Servlets and JSP

Tutorials : Building Web Applications Using Servlets and JSP :

From this step onwards the code is INDEPENDENT of the driver you are using

Statement stmt = con.createStatement();

At this point stmt object exists, but it does not have any SQL statement (query /update etc.) linked. To execute a Query we use the executeQuery method , similarly for an insert /update (and also any DDL statement) we use executeUpdate method.

String sql = "select USERID from USERTABLE where USERID ='guest' 
	and PASSWORD = 'guest' "; 
ResultSet rs = stmt.executeQuery(sql);

The query results are returned in a ResultSet object. A ResultSet object can be thought upon as a two dimensional array of objects. Every row in this array represents a single record selected from the table. The individual objects in one row correspond to the columns of the table.

The result set will contain all the rows selected from the table. We can go through individual rows using the "next()" method. Initially when the ResultSet is returned, the pointer or array index is before the first row. Every time you call next(), it will increment the pointer by 1 to point to the next row. If there is no next row to go to , next() will return false.

An example code to go through all the rows returned:

while (rs.next()) {
      // your processing logic
 }

The getXXX methods are used to retrieve a particular column value from the current row. To retrieve a String (database data types VARCHAR, CHAR and STRING depending on the DBMS and the driver) we use the getString() method. TheResultSet defines methods like getString for the major data types.

while (rs.next()) {
    String userId= rs.getString("USERID");
    String password = rs.getString("PASSWORD");
    }

One can also use the column number instead of name such as

String userId  = rs.getString(1);
String password  = rs.getString(2);

So far we covered the basic methods for accessing databases using JDBC. For advanced methods and method descriptions check out the JDBC API documentation.

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