JDBC - Statement Object Example
Following is the example, which makes use of the following three queries along with the opening and closing statement −
boolean execute(String SQL) : Returns a boolean value of true if a ResultSet object can be retrieved; otherwise, it returns false. Use this method to execute SQL DDL statements or when you need to use the truly dynamic SQL.
int executeUpdate(String SQL): Returns the number of rows affected by the execution of the SQL statement. Use this method to execute SQL statements, for which you expect to get a number of rows affected - for example, an INSERT, UPDATE, or DELETE statement.
ResultSet executeQuery(String SQL): Returns a ResultSet object. Use this method when you expect to get a result set, as you would with a SELECT statement.
This sample code has been written based on the environment and database setup done in the previous chapters.
Copy and past the following example in JDBCExample.java, compile and run as follows −
//STEP 1. Import required packages import java.sql.*; public class JDBCExample { // JDBC driver name and database URL static final String JDBC_DRIVER = "com.mysql.jdbc.Driver"; static final String DB_URL = "jdbc:mysql://localhost/EMP"; // Database credentials static final String USER = "username"; static final String PASS = "password"; public static void main(String[] args) { Connection conn = null; Statement stmt = null; try{ //STEP 2: Register JDBC driver Class.forName("com.mysql.jdbc.Driver"); //STEP 3: Open a connection System.out.println("Connecting to database..."); conn = DriverManager.getConnection(DB_URL,USER,PASS); //STEP 4: Execute a query System.out.println("Creating statement..."); stmt = conn.createStatement(); String sql = "UPDATE Employees set age=30 WHERE id=103"; // Let us check if it returns a true Result Set or not. Boolean ret = stmt.execute(sql); System.out.println("Return value is : " + ret.toString() ); // Let us update age of the record with ID = 103; int rows = stmt.executeUpdate(sql); System.out.println("Rows impacted : " + rows ); // Let us select all the records and display them. sql = "SELECT id, first, last, age FROM Employees"; ResultSet rs = stmt.executeQuery(sql); //STEP 5: Extract data from result set while(rs.next()){ //Retrieve by column name int id = rs.getInt("id"); int age = rs.getInt("age"); String first = rs.getString("first"); String last = rs.getString("last"); //Display values System.out.print("ID: " + id); System.out.print(", Age: " + age); System.out.print(", First: " + first); System.out.println(", Last: " + last); } //STEP 6: Clean-up environment rs.close(); stmt.close(); conn.close(); }catch(SQLException se){ //Handle errors for JDBC se.printStackTrace(); }catch(Exception e){ //Handle errors for Class.forName e.printStackTrace(); }finally{ //finally block used to close resources try{ if(stmt!=null) stmt.close(); }catch(SQLException se2){ }// nothing we can do try{ if(conn!=null) conn.close(); }catch(SQLException se){ se.printStackTrace(); }//end finally try }//end try System.out.println("Goodbye!"); }//end main }//end JDBCExample
Now let us compile the above example as follows −
C:\>javac JDBCExample.java C:\>
When you run JDBCExample, it produces the following result −
C:\>java JDBCExample Connecting to database... Creating statement... Return value is : false Rows impacted : 1 ID: 100, Age: 18, First: Zara, Last: Ali ID: 101, Age: 25, First: Mahnaz, Last: Fatma ID: 102, Age: 30, First: Zaid, Last: Khan ID: 103, Age: 30, First: Sumit, Last: Mittal Goodbye! C:\>