JavaTips

We can use Java.util.regex pakage to validate any form fields in server side
It is having two packages
1.java.util.regex.Matcher;
2.java.util.regex.Pattern; 


Example :
public class UsernameValidator{

      private Pattern pattern;
      private Matcher matcher;

      private static final String USERNAME_PATTERN = "^[a-z0-9_-]{3,15}$";

      public UsernameValidator(){
          pattern = Pattern.compile(USERNAME_PATTERN);
      }

      /**
       * Validate username with regular expression
       * @param username username for validation
       * @return true valid username, false invalid username
       */
      public boolean validate(final String username){

          matcher = pattern.matcher(username);
          return matcher.matches();

      }
}

This class validate the user name based on the pattern of regular expressions
this pattern will compile and initialize using constructor using compile method of the pattern class
then write a metod which validate your username and return true or false based on the the pattern
this method create the matcher object then this object will compare the using mateches method then return the boolean values

/***********************************************************JDBC ************************************************************************************/
/********************************connecting to database code ******************/
Class.forName("com.mysql.jdbc.Driver");
Connection conn = null;
conn = DriverManager.getConnection("jdbc:mysql://hostname:port/dbname","username", "password");
conn.close();
/********************************connecting to database code ******************/
/***********************************************************JDBC & Statement*********************************************************/
/********************************Create statement ******************/
The “Statement” interface is used to execute a simple SQL statement with no parameters. For create, insert, update or delete statement, uses “Statement.executeUpdate(sql)“; select query, uses “Statement.executeQuery(sql)“.

Statement statement = dbConnection.createStatement();
// execute create SQL stetement
statement.execute(createTableSQL);


Statement statement = dbConnection.createStatement();
// execute the insert SQL stetement
statement.executeUpdate(insertTableSQL);

Statement statement = dbConnection.createStatement();
// execute the update SQL stetement
statement.executeUpdate(updateTableSQL);

Statement statement = dbConnection.createStatement();
// execute the delete SQL stetement
statement.executeUpdate(deleteTableSQL);

String selectTableSQL = "SELECT USER_ID, USERNAME from DBUSER";
Statement statement = dbConnection.createStatement();
ResultSet rs = statement.executeQuery(selectTableSQL);
while (rs.next()) {
    String userid = rs.getString("USER_ID");
    String username = rs.getString("USERNAME");   
}
//batch update statement
dbConnection.setAutoCommit(false);

statement = dbConnection.createStatement();
statement.addBatch(insertTableSQL1);
statement.addBatch(insertTableSQL2);
statement.addBatch(insertTableSQL3);

statement.executeBatch();

dbConnection.commit();
/********************************Create statement ******************/
/********************************JDBC & PreparedStatement ******************/
The “PreparedStatement” interface is extended “Statement”, with extra feature to send a pre-compiled SQL statement with parameters. For create, insert, update or delete statement, uses “PreparedStatement.executeUpdate(sql)“; select query, uses “PreparedStatement.executeQuery(sql)“.

PreparedStatement preparedStatement = dbConnection.prepareStatement(createTableSQL);
// EXECUTE CREATE SQL stetement
preparedStatement.executeUpdate();
/************************************************************************************/
String insertTableSQL = "INSERT INTO DBUSER"
        + "(USER_ID, USERNAME, CREATED_BY, CREATED_DATE) VALUES"
        + "(?,?,?,?)";
PreparedStatement preparedStatement = dbConnection.prepareStatement(insertTableSQL);
preparedStatement.setInt(1, 11);
preparedStatement.setString(2, "guru");
preparedStatement.setString(3, "system");
preparedStatement.setTimestamp(4, getCurrentTimeStamp());
// execute insert SQL stetement
preparedStatement .executeUpdate();

String updateTableSQL = "UPDATE DBUSER SET USERNAME = ? WHERE USER_ID = ?";
PreparedStatement preparedStatement = dbConnection.prepareStatement(updateTableSQL);
preparedStatement.setString(1, "newValue");
preparedStatement.setInt(2, 1001);
// execute insert SQL stetement
preparedStatement .executeUpdate();

String deleteSQL = "DELETE DBUSER WHERE USER_ID = ?";
PreparedStatement preparedStatement = dbConnection.prepareStatement(deleteSQL);
preparedStatement.setInt(1, 1001);
// execute delete SQL stetement
preparedStatement.executeUpdate();

tring selectSQL = "SELECT USER_ID, USERNAME FROM DBUSER WHERE USER_ID = ?";
PreparedStatement preparedStatement = dbConnection.prepareStatement(selectSQL);
preparedStatement.setInt(1, 1001);
ResultSet rs = preparedStatement.executeQuery(selectSQL );
while (rs.next()) {
    String userid = rs.getString("USER_ID");
    String username = rs.getString("USERNAME");   
}

dbConnection.setAutoCommit(false);//commit trasaction manually

String insertTableSQL = "INSERT INTO DBUSER"
            + "(USER_ID, USERNAME, CREATED_BY, CREATED_DATE) VALUES"
            + "(?,?,?,?)";               
PreparedStatement = dbConnection.prepareStatement(insertTableSQL);

preparedStatement.setInt(1, 101);
preparedStatement.setString(2, "guru01");
preparedStatement.setString(3, "system");
preparedStatement.setTimestamp(4, getCurrentTimeStamp());
preparedStatement.addBatch();

preparedStatement.setInt(1, 102);
preparedStatement.setString(2, "guru102");
preparedStatement.setString(3, "system");
preparedStatement.setTimestamp(4, getCurrentTimeStamp());
preparedStatement.addBatch();
preparedStatement.executeBatch();

dbConnection.commit();

/********************************JDBC & PreparedStatement ******************/