Category: Computer Programming

Java & MySQL – Drop Database Example ”; Previous Next This chapter provides an example on how to drop an existing Database using JDBC application. Before executing the following example, make sure you have the following in place − To execute the following example you need to replace the username and password with your actual user name and password. Your MySQL is up and running. NOTE − This is a serious operation and you have to make a firm decision before proceeding to delete a database because everything you have in your database would be lost. Required Steps The following steps are required to create a new Database using JDBC application − Import the packages − Requires that you include the packages containing the JDBC classes needed for database programming. Most often, using import java.sql.* will suffice. Open a connection − Requires using the DriverManager.getConnection() method to create a Connection object, which represents a physical connection with a database server. Deleting a database does not require database name to be in your database URL. Following example would delete STUDENTS database. Execute a query − Requires using an object of type Statement for building and submitting an SQL statement to delete the database. Clean up the environment − try with resources automatically closes the resources. Sample Code Copy and paste the following example in TestApplication.java, compile and run as follows − import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.sql.Statement; public class TestApplication { static final String DB_URL = “jdbc:mysql://localhost/”; static final String USER = “guest”; static final String PASS = “guest123”; public static void main(String[] args) { // Open a connection try(Connection conn = DriverManager.getConnection(DB_URL, USER, PASS); Statement stmt = conn.createStatement(); ) { String sql = “DROP DATABASE STUDENTS”; stmt.executeUpdate(sql); System.out.println(“Database dropped successfully…”); } catch (SQLException e) { e.printStackTrace(); } } } Now let us compile the above example as follows − C:>javac TestApplication.java C:> When you run TestApplication, it produces the following result − C:>java TestApplication Database dropped successfully… C:> Print Page Previous Next Advertisements ”;

Java & MySQL – SavePoint ”; Previous Next The new JDBC 3.0 Savepoint interface gives you the additional transactional control. Most modern DBMS, support savepoints within their environments such as Oracle”s PL/SQL. When you set a savepoint you define a logical rollback point within a transaction. If an error occurs past a savepoint, you can use the rollback method to undo either all the changes or only the changes made after the savepoint. The Connection object has two new methods that help you manage savepoints − setSavepoint(String savepointName) − Defines a new savepoint. It also returns a Savepoint object. releaseSavepoint(Savepoint savepointName) − Deletes a savepoint. Notice that it requires a Savepoint object as a parameter. This object is usually a savepoint generated by the setSavepoint() method. There is one rollback (String savepointName) method, which rolls back work to the specified savepoint. The following example illustrates the use of a Savepoint object − try{ //Assume a valid connection object conn conn.setAutoCommit(false); Statement stmt = conn.createStatement(); //set a Savepoint Savepoint savepoint1 = conn.setSavepoint(“Savepoint1”); String SQL = “INSERT INTO Employees ” + “VALUES (106, 20, ”Rita”, ”Tez”)”; stmt.executeUpdate(SQL); //Submit a malformed SQL statement that breaks String SQL = “INSERTED IN Employees ” + “VALUES (107, 22, ”Sita”, ”Tez”)”; stmt.executeUpdate(SQL); // If there is no error, commit the changes. conn.commit(); }catch(SQLException se){ // If there is any error. conn.rollback(savepoint1); } In this case, none of the above INSERT statement would success and everything would be rolled back. Following is the example, which makes use of setSavepoint and rollback described. This sample code has been written based on the environment and database setup done in the previous chapters. Copy and paste the following example in TestApplication.java, compile and run as follows − import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Savepoint; import java.sql.Statement; public class TestApplication { static final String DB_URL = “jdbc:mysql://localhost/TUTORIALSPOINT”; static final String USER = “guest”; static final String PASS = “guest123”; static final String QUERY = “SELECT id, first, last, age FROM Employees”; static final String DELETE_QUERY = “DELETE FROM Employees WHERE ID = 8”; static final String DELETE_QUERY_1 = “DELETE FROM Employees WHERE ID = 9”; public static void printResultSet(ResultSet rs) throws SQLException{ // Ensure we start with first row rs.beforeFirst(); while(rs.next()){ // Display values System.out.print(“ID: ” + rs.getInt(“id”)); System.out.print(“, Age: ” + rs.getInt(“age”)); System.out.print(“, First: ” + rs.getString(“first”)); System.out.println(“, Last: ” + rs.getString(“last”)); } System.out.println(); } public static void main(String[] args) { // Open a connection try(Connection conn = DriverManager.getConnection(DB_URL, USER, PASS); Statement stmt = conn.createStatement( ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE); ) { conn.setAutoCommit(false); ResultSet rs = stmt.executeQuery(QUERY); System.out.println(“List result set for reference….”); printResultSet(rs); // delete row having ID = 8 // But save point before doing so. Savepoint savepoint1 = conn.setSavepoint(“ROWS_DELETED_1”); System.out.println(“Deleting row….”); stmt.executeUpdate(DELETE_QUERY); // Rollback the changes after save point 1. conn.rollback(savepoint1); // delete rows having ID = 9 // But save point before doing so. conn.setSavepoint(“ROWS_DELETED_2”); System.out.println(“Deleting row….”); stmt.executeUpdate(DELETE_QUERY_1); rs = stmt.executeQuery(QUERY); System.out.println(“List result set for reference….”); printResultSet(rs); // Clean-up environment rs.close(); } catch (SQLException e) { e.printStackTrace(); } } } Now, let us compile the above example as follows − C:>javac TestApplication.java C:> When you run TestApplication, it produces the following result − C:>java TestApplication List result set for reference…. ID: 1, Age: 23, First: Zara, Last: Ali ID: 2, Age: 30, First: Mahnaz, Last: Fatma ID: 3, Age: 35, First: Zaid, Last: Khan ID: 4, Age: 33, First: Sumit, Last: Mittal ID: 5, Age: 40, First: John, Last: Paul ID: 7, Age: 20, First: Sita, Last: Singh ID: 8, Age: 20, First: Rita, Last: Tez ID: 9, Age: 20, First: Sita, Last: Singh Deleting row…. Deleting row…. List result set for reference…. ID: 1, Age: 23, First: Zara, Last: Ali ID: 2, Age: 30, First: Mahnaz, Last: Fatma ID: 3, Age: 35, First: Zaid, Last: Khan ID: 4, Age: 33, First: Sumit, Last: Mittal ID: 5, Age: 40, First: John, Last: Paul ID: 7, Age: 20, First: Sita, Last: Singh ID: 8, Age: 20, First: Rita, Last: Tez C:> Print Page Previous Next Advertisements ”;

Java & MySQL – Commit & Rollback ”; Previous Next Once you are done with your changes and you want to commit the changes then call commit() method on connection object as follows − conn.commit( ); Otherwise, to roll back updates to the database made using the Connection named conn, use the following code − conn.rollback( ); The following example illustrates the use of a commit and rollback object − try{ //Assume a valid connection object conn conn.setAutoCommit(false); Statement stmt = conn.createStatement(); String SQL = “INSERT INTO Employees ” + “VALUES (106, 20, ”Rita”, ”Tez”)”; stmt.executeUpdate(SQL); //Submit a malformed SQL statement that breaks String SQL = “INSERTED IN Employees ” + “VALUES (107, 22, ”Sita”, ”Singh”)”; stmt.executeUpdate(SQL); // If there is no error. conn.commit(); }catch(SQLException se){ // If there is any error. conn.rollback(); } In this case, none of the above INSERT statement would success and everything would be rolled back. Following is the example, which makes use of commit and rollback described. This sample code has been written based on the environment and database setup done in the previous chapters. Copy and paste the following example in TestApplication.java, compile and run as follows − import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class TestApplication { static final String DB_URL = “jdbc:mysql://localhost/TUTORIALSPOINT”; static final String USER = “guest”; static final String PASS = “guest123”; static final String QUERY = “SELECT id, first, last, age FROM Employees”; static final String INSERT_QUERY = “INSERT INTO Employees (first, last, age) values(”Rita”, ”Tez”, 20)”; static final String INSERT_QUERY_2 = “INSERT INTO Employees (first, last, age) values(”Sita”, ”Singh”, 20)”; public static void printResultSet(ResultSet rs) throws SQLException{ // Ensure we start with first row rs.beforeFirst(); while(rs.next()){ // Display values System.out.print(“ID: ” + rs.getInt(“id”)); System.out.print(“, Age: ” + rs.getInt(“age”)); System.out.print(“, First: ” + rs.getString(“first”)); System.out.println(“, Last: ” + rs.getString(“last”)); } System.out.println(); } public static void main(String[] args) { Connection conn = null; Statement stmt = null; try{ // Open a connection System.out.println(“Connecting to database…”); conn = DriverManager.getConnection(DB_URL,USER,PASS); // Set auto commit as false. conn.setAutoCommit(false); // Execute a query to create statment with // required arguments for RS example. System.out.println(“Creating statement…”); stmt = conn.createStatement( ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE); // INSERT a row into Employees table System.out.println(“Inserting one row….”); stmt.executeUpdate(INSERT_QUERY); // INSERT one more row into Employees table stmt.executeUpdate(INSERT_QUERY_2); // Commit data here. System.out.println(“Commiting data here….”); conn.commit(); // Now list all the available records. String sql = “SELECT id, first, last, age FROM Employees”; ResultSet rs = stmt.executeQuery(sql); System.out.println(“List result set for reference….”); printResultSet(rs); // Clean-up environment rs.close(); stmt.close(); conn.close(); }catch(SQLException se){ se.printStackTrace(); // If there is an error then rollback the changes. System.out.println(“Rolling back data here….”); try{ if(conn!=null) conn.rollback(); }catch(SQLException se2){ se2.printStackTrace(); } }catch(Exception e){ e.printStackTrace(); }finally{ // finally block used to close resources try{ if(stmt!=null) stmt.close(); }catch(SQLException se2){ se2.printStackTrace(); } try{ if(conn!=null) conn.close(); }catch(SQLException se){ se.printStackTrace(); } } } } Now let us compile the above example as follows − C:>javac TestApplication.java C:> When you run TestApplication, it produces the following result − C:>java TestApplication Connecting to database… Creating statement… Inserting one row…. Commiting data here…. List result set for reference…. ID: 1, Age: 23, First: Zara, Last: Ali ID: 2, Age: 30, First: Mahnaz, Last: Fatma ID: 3, Age: 35, First: Zaid, Last: Khan ID: 4, Age: 33, First: Sumit, Last: Mittal ID: 5, Age: 40, First: John, Last: Paul ID: 6, Age: 20, First: Rita, Last: Tez ID: 7, Age: 20, First: Sita, Last: Singh C:> Print Page Previous Next Advertisements ”;

Java & MySQL – CallableStatement ”; Previous Next The CallableStatement interface is used to execute a call to a database stored procedure. Suppose, you need to execute the following stored procedure in TUTORIALSPOINT database − DELIMITER $$ DROP PROCEDURE IF EXISTS `TUTORIALSPOINT`.`getEmpName` $$ CREATE PROCEDURE `TUTORIALSPOINT`.`getEmpName` (IN EMP_ID INT, OUT EMP_FIRST VARCHAR(255)) BEGIN SELECT first INTO EMP_FIRST FROM Employees WHERE ID = EMP_ID; END $$ DELIMITER ; Three types of parameters exist: IN, OUT, and INOUT. The PreparedStatement object only uses the IN parameter. The CallableStatement object can use all the three. Here are the definitions of each − Parameter Description IN A parameter whose value is unknown when the SQL statement is created. You bind values to IN parameters with the setXXX() methods. OUT A parameter whose value is supplied by the SQL statement it returns. You retrieve values from theOUT parameters with the getXXX() methods. INOUT A parameter that provides both input and output values. You bind variables with the setXXX() methods and retrieve values with the getXXX() methods. The following code snippet shows how to employ the Connection.prepareCall() method to instantiate a CallableStatement object based on the preceding stored procedure − CallableStatement cstmt = null; try { String SQL = “{call getEmpName (?, ?)}”; cstmt = conn.prepareCall (SQL); . . . } catch (SQLException e) { . . . } finally { . . . } The String variable SQL, represents the stored procedure, with parameter placeholders. Using the CallableStatement objects is much like using the PreparedStatement objects. You must bind values to all the parameters before executing the statement, or you will receive an SQLException. If you have IN parameters, just follow the same rules and techniques that apply to a PreparedStatement object; use the setXXX() method that corresponds to the Java data type you are binding. When you use OUT and INOUT parameters you must employ an additional CallableStatement method, registerOutParameter(). The registerOutParameter() method binds the JDBC data type, to the data type that the stored procedure is expected to return. Once you call your stored procedure, you retrieve the value from the OUT parameter with the appropriate getXXX() method. This method casts the retrieved value of SQL type to a Java data type. Closing CallableStatement Object Just as you close other Statement object, for the same reason you should also close the CallableStatement object. A simple call to the close() method will do the job. If you close the Connection object first, it will close the CallableStatement object as well. However, you should always explicitly close the CallableStatement object to ensure proper cleanup. CallableStatement cstmt = null; try { String SQL = “{call getEmpName (?, ?)}”; cstmt = conn.prepareCall (SQL); . . . } catch (SQLException e) { . . . } finally { cstmt.close(); } We”re using try with resources which handles the resource closure automatically. Following example demonstrates all of the above said concepts. This code has been written based on the environment and database setup done in the previous chapter. Copy and paste the following example in TestApplication.java, compile and run as follows − import java.sql.CallableStatement; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; public class TestApplication { static final String DB_URL = “jdbc:mysql://localhost/TUTORIALSPOINT”; static final String USER = “guest”; static final String PASS = “guest123”; static final String QUERY = “{call getEmpName (?, ?)}”; public static void main(String[] args) { // Open a connection try(Connection conn = DriverManager.getConnection(DB_URL, USER, PASS); CallableStatement stmt = conn.prepareCall(QUERY); ) { // Bind values into the parameters. stmt.setInt(1, 102); // This would set ID // Because second parameter is OUT so register it stmt.registerOutParameter(2, java.sql.Types.VARCHAR); //Use execute method to run stored procedure. System.out.println(“Executing stored procedure…” ); stmt.execute(); //Retrieve employee name with getXXX method String empName = stmt.getString(2); System.out.println(“Emp Name with ID: 102 is ” + empName); } catch (SQLException e) { e.printStackTrace(); } } } Now let us compile the above example as follows − C:>javac TestApplication.java C:> When you run TestApplication, it produces the following result − C:>java TestApplication Executing stored procedure… Emp Name with ID: 102 is Zaid C:> JDBC SQL Escape Syntax The escape syntax gives you the flexibility to use database specific features unavailable to you by using standard JDBC methods and properties. The general SQL escape syntax format is as follows − {keyword ”parameters”} Here are the following escape sequences, which you would find very useful while performing the JDBC programming − d, t, ts Keywords They help identify date, time, and timestamp literals. As you know, no two DBMSs represent time and date the same way. This escape syntax tells the driver to render the date or time in the target database”s format. For Example − {d ”yyyy-mm-dd”} Where yyyy = year, mm = month; dd = date. Using this syntax {d ”2009-09-03”} is March 9, 2009. Here is a simple example showing how to INSERT date in a table − //Create a Statement object stmt = conn.createStatement(); //Insert data ==> ID, First Name, Last Name, DOB String sql=”INSERT INTO STUDENTS VALUES” + “(100,”Zara”,”Ali”, {d ”2001-12-16”})”; stmt.executeUpdate(sql); Similarly, you can use one of the following two syntaxes, either t or ts − {t ”hh:mm:ss”} Where hh = hour; mm = minute; ss = second. Using this syntax {t ”13:30:29”} is 1:30:29 PM. {ts ”yyyy-mm-dd hh:mm:ss”} This is combined syntax of the above two syntax for ”d” and ”t” to represent timestamp. escape Keyword This keyword identifies the escape character used in LIKE clauses. Useful when using the SQL wildcard %, which matches zero or more characters.