I. Java Prepared Statements
1. Généralités
Java JDBC Prepared statements are pre-compiled SQL statements. Precompiled SQL is useful if the same SQL is to be executed repeatedly, for example, in a loop. Prepared statements in java only save you time if you expect to execute the same SQL over again. Every java sql prepared statement is compiled at some point. To use a java preparedstatements, you must first create a object by calling the Connection.prepareStatement() method. JDBC PreparedStatements are useful especially in situations where you can use a for loop or while loop to set a parameter to a succession of values. If you want to execute a Statement object many times, it normally reduces execution time to use a PreparedStatement object instead.
The syntax is straightforward: just insert question marks for any parameters that you’ll be substituting before you send the SQL to the database. As with CallableStatements, you need to call close() to make sure database resources are freed as soon as possible. Below is a JDBC Program showing the use of jdbc prepared statements to insert data into tables using jdbc programming.
You need to supply values to be used in place of the question mark placeholders (if there are any) before you can execute a PreparedStatement object. You do this by calling one of the setXXX methods defined in the PreparedStatement class. There is a setXXX method for each primitive type declared in the Java programming language.
2. Exemple
PreparedStatement pstmt = con.prepareStatement(“update Orders set pname = ? where Prod_Id = ?”); pstmt.setInt(2, 100); pstmt.setString(1, “Bob”); pstmt.executeUpdate();
An important feature of a PreparedStatement object is that, unlike a Statement object, it is given an SQL statement when it is created. This SQL statement is sent to the DBMS right away, where it is compiled. As a result, the PreparedStatement object contains not just an SQL statement, but an SQL statement that has been precompiled. This means that when the PreparedStatement is executed, the DBMS can just run the PreparedStatement SQL statement without having to compile it first.
Using Prepared Statements in jdbc, objects can be used for SQL statements with no parameters, you probably use them most often for SQL statements that take parameters. The advantage of using SQL statements that take parameters is that you can use the same statement and supply it with different values each time you execute it.
For my website I am creating the following 2 tables (Employee, Orders) as a part of the JDBC tutorial.
Employee_ID is the primary key which forms a relation between the 2 tables
PreparedStatement pstmt = con.prepareStatement(“update Orders set pname = ? where Prod_Id = ?”); pstmt.setInt(2, 100); pstmt.setString(1, “Bob”); pstmt.executeUpdate();
An important feature of a PreparedStatement object is that, unlike a Statement object, it is given an SQL statement when it is created. This SQL statement is sent to the DBMS right away, where it is compiled. As a result, the PreparedStatement object contains not just an SQL statement, but an SQL statement that has been precompiled. This means that when the PreparedStatement is executed, the DBMS can just run the PreparedStatement SQL statement without having to compile it first.
Using Prepared Statements in jdbc, objects can be used for SQL statements with no parameters, you probably use them most often for SQL statements that take parameters. The advantage of using SQL statements that take parameters is that you can use the same statement and supply it with different values each time you execute it.
For my website I am creating the following 2 tables (Employee, Orders) as a part of the JDBC tutorial.
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import javax.swing.JOptionPane;
import java.sql.*;
public class JDBCProgram{
static String userid="scott", password = "tiger";
static String url = "jdbc:odbc:bob";
// String url = "jdbc:mySubprotocol:myDataSource"; ?
static Statement stmt;
static PreparedStatement pstmt;
static Connection con;
public static void main(String args[]){
JOptionPane.showMessageDialog(null,"JDBC Programming showing Updation of Table Data");
int choice = -1;
do{
choice = getChoice();
if (choice != 0){
getSelected(choice);
}
}
while ( choice != 0);
System.exit(0);
}
public static int getChoice()
{
String choice;
int ch;
choice = JOptionPane.showInputDialog(null,
"1. Create Employees Table\n"+
"2. Create Products Table\n"+
"3. Insert data into Employees Table\n"+
"4. Insert data into Orders Table\n"+
"5. Retrieve data for Employees Table\n"+
"6. Retrieve data for Orders Table\n"+
"7. Update Employees Table\n"+
"8. Update Employees Table Using a Prepared Statement\n"+
"9. Update many records of Orders Table Using a Prepared Statement\n"+
"10. List the name of employees who bought CD'sn"+
"0. Exit\n\n"+
"Enter your choice");
ch = Integer.parseInt(choice);
return ch;
}
public static void getSelected(int choice){
if(choice==1){
createEmployees();
}
if(choice==2){
createOrders();
}
if(choice==3){
insertEmployees();
}
if(choice==4){
insertOrders();
}
if(choice==5){
retrieveEmployees();
}
if(choice==6){
retrieveOrders();
}
if(choice==7){
updateEmployees();
}
if(choice==8){
updateEmployeesPrepared();
}
if(choice==9){
updateOrdersPrepared();
}
if(choice==10){
dynamicQuery();
}
}
public static Connection getConnection()
{
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
//Class.forName("myDriver.ClassName"); ?
} catch(java.lang.ClassNotFoundException e) {
System.err.print("ClassNotFoundException: ");
System.err.println(e.getMessage());
}
try {
con = DriverManager.getConnection(url,
userid, password);
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
return con;
}
/*CREATE TABLE Employees (
Employee_ID INTEGER,
Name VARCHAR(30)
);*/
public static void createEmployees()
{
Connection con = getConnection();
String createString;
createString = "create table Employees (" +
"Employee_ID INTEGER, " +
"Name VARCHAR(30))";
try {
stmt = con.createStatement();
stmt.executeUpdate(createString);
stmt.close();
con.close();
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
JOptionPane.showMessageDialog(null,"Employees Table Created");
}
/*CREATE TABLE Orders (
Prod_ID INTEGER,
ProductName VARCHAR(20),
Employee_ID INTEGER
);*/
public static void createOrders()
{
Connection con = getConnection();
String createString;
createString = "create table Orders (" +
"Prod_ID INTEGER, " +
"ProductName VARCHAR(20), "+
"Employee_ID INTEGER )";
try {
stmt = con.createStatement();
stmt.executeUpdate(createString);
stmt.close();
con.close();
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
JOptionPane.showMessageDialog(null,"Orders Table Created");
}
/*Employee_ID Name
6323 Hemanth
5768 Bob
1234 Shawn
5678 Michaels */
public static void insertEmployees()
{
Connection con = getConnection();
String insertString1, insertString2, insertString3, insertString4;
insertString1 = "insert into Employees values(6323, 'Hemanth')";
insertString2 = "insert into Employees values(5768, 'Bob')";
insertString3 = "insert into Employees values(1234, 'Shawn')";
insertString4 = "insert into Employees values(5678, 'Michaels')";
try {
stmt = con.createStatement();
stmt.executeUpdate(insertString1);
stmt.executeUpdate(insertString2);
stmt.executeUpdate(insertString3);
stmt.executeUpdate(insertString4);
stmt.close();
con.close();
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
JOptionPane.showMessageDialog(null,"Data Inserted into Employees Table");
}
/* Prod_ID ProductName Employee_ID
543 Belt 6323
432 Bottle 1234
876 Ring 5678
*/
public static void insertOrders()
{
Connection con = getConnection();
String insertString1, insertString2, insertString3, insertString4;
insertString1 = "insert into Orders values(543, 'Belt', 6323)";
insertString2 = "insert into Orders values(432, 'Bottle', 1234)";
insertString3 = "insert into Orders values(876, 'Ring', 5678)";
try {
stmt = con.createStatement();
stmt.executeUpdate(insertString1);
stmt.executeUpdate(insertString2);
stmt.executeUpdate(insertString3);
stmt.close();
con.close();
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
JOptionPane.showMessageDialog(null,"Data Inserted into Orders Table");
}
public static void retrieveEmployees(){
Connection con = getConnection();
String result = null;
String selectString;
selectString = "select * from Employees";
result ="Employee_ID\t\tName\n";
try {
stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(selectString);
while (rs.next()) {
int id = rs.getInt("Employee_ID");
String name = rs.getString("Name");
result+=id+"\t\t"+ name+"\n";
}
stmt.close();
con.close();
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
JOptionPane.showMessageDialog(null, result);
}
public static void retrieveOrders(){
Connection con = getConnection();
String result = null;
String selectString;
selectString = "select * from Orders";
result ="Prod_ID\t\tProductName\t\tEmployee_ID\n";
try {
stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(selectString);
while (rs.next()) {
int pr_id = rs.getInt("Prod_ID");
String prodName = rs.getString("ProductName");
int id = rs.getInt("Employee_ID");
result +=pr_id+"\t\t"+ prodName+"\t\t"+id+"\n";
}
stmt.close();
con.close();
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
JOptionPane.showMessageDialog(null, result);
}
public static void updateEmployees(){
Connection con = getConnection();
String updateString1;
updateString1 = "update Employees set name = 'hemanthbalaji'
where Employee_id = 6323";
try {
stmt = con.createStatement();
stmt.executeUpdate(updateString1);
stmt.close();
con.close();
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
JOptionPane.showMessageDialog(null,"Data Updated into Employees Table");
}
public static void updateEmployeesPrepared(){
Connection con = getConnection();
// create prepared statement
try {
pstmt = con.prepareStatement
("update Employees set name = ? where Employee_Id = ?");
pstmt.setString(1, "hemanthbob"); //Note index starts with 1
pstmt.setInt(2, 6323);
pstmt.executeUpdate();
pstmt.close();
con.close();
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
JOptionPane.showMessageDialog(null,"Data Updated into Employees Table");
}
public static void updateOrdersPrepared(){
int [] productIds = {543, 432, 876};
String [] productNames = {"cds", "dvds", "Espresso"};
int len = productNames.length;
Connection con = getConnection();
try {
pstmt = con.prepareStatement
("update Orders set productname = ? where Prod_Id = ?");
for(int i = 0; i < len; i++) {
pstmt.setInt(2, productIds[i]);
pstmt.setString(1, productNames[i]);
pstmt.executeUpdate();
}
pstmt.close();
con.close();
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
JOptionPane.showMessageDialog(null,"Data Updated into Orders Table");
}
public static void dynamicQuery(){
Connection con = getConnection();
String result = null;
String selectString;
selectString = "select Employees.name from Employees,
Orders where productname = 'cds' " +
"and Employees.employee_id = Orders.employee_id ";
result ="Name\n";
try {
stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(selectString);
while (rs.next()) {
String name = rs.getString("Name");
result+=name+"\n";
}
stmt.close();
con.close();
} catch(SQLException ex) {
System.err.println("SQLException: " + ex.getMessage());
}
JOptionPane.showMessageDialog(null, result);
}
}//End of class
