![SQL Types/Java Types Mapping
SQL Type Java Type
CHAR String
VARCHAR String
LONGVARCHAR String
NUMERIC java.Math.BigDecimal
DECIMAL java.Math.BigDecimal
BIT boolean
TINYINT int
SMALLINT int
INTEGER int
BIGINT long
REAL float
FLOAT double
DOUBLE double
BINARY byte[]
VARBINARY byte[]
DATE java.sql.Date
TIME java.sql.Time
TIMESTAMP java.sql.Timestamp](https://image.slidesharecdn.com/jdbcconnectivity-150421214631-conversion-gate01/85/Jdbc-connectivity-23-320.jpg)
![• The PreparedStatement interface provides various methods to set
the value of the placeholders for the specific data types.
1. void setByte (int index , byte val) : Sets the java byte type value
for the parameter corresponding to index passed as a parameter.
2. void setBytes (int index , byte[] val) : Sets the Java byte type
array for the parameter corresponding to index passed as a
parameter.
3. void setBoolean (int index , boolean val) : Sets the Java boolean
type value for the parameter corresponding to index passed as a
parameter.
4. void setDouble (int index, double val) : Sets the Java double type
value value for the parameter corresponding to the index passed
as a parameter.](https://image.slidesharecdn.com/jdbcconnectivity-150421214631-conversion-gate01/85/Jdbc-connectivity-29-320.jpg)
Jdbc connectivity
- 1. JDBC - Java Database Connectivity The objectives of this chapter are: To describe the architecture of JDBC Driver Types JDBC Configuration To outline the classes in the java.sql package Executing SQL Statements sTo understand the use of JDBC
- 2. JDBC provides Java applications with access to most database systems via SQL The architecture and API closely resemble Microsoft's ODBC JDBC 1.0 was originally introduced into Java 1.1 JDBC 2.0 was added to Java 1.2 JDBC is based on SQL-92 JDBC classes are contained within the java.sql package There are few classes There are several interfaces What is JDBC?
- 3. 3 JDBC ArchitectureJDBC Architecture Java Application JDBC Oracle DB2 MySQL Oracle Driver DB2 Driver MySQL Driver Network We will use this one…
- 4. JDBC Architecture (cont.)JDBC Architecture (cont.) Application JDBC Driver • Java code calls JDBC library • JDBC loads a driver • Driver talks to a particular database • An application can work with several databases by using all corresponding drivers • Ideal: can change database engines without changing any application code (not always in practice)
- 5. Before APIs like JDBC and ODBC, database connectivity was tedious Each database vendor provided a function library for accessing their database The connectivity library was proprietary. If the database vendor changed for the application, the data access portions had to be rewritten If the application was poorly structured, rewriting its data access might involve rewriting the majority of the application The costs incurred generally meant that application developers were stuck with a particular database product for a given application Database Connectivity History
- 6. With JDBC, the application programmer uses the JDBC API The developer never uses any proprietary APIs • Any proprietary APIs are implemented by a JDBC driver • There are 4 types of JDBC Drivers JDBC Architecture Java Application JDBC API JDBC DriverManager JDBC Driver JDBC Driver
- 7. There are 4 types of JDBC Drivers Type 1 - JDBC-ODBC Bridge Type 2 - JDBC-Native Bridge Type 3 - JDBC-Net Bridge Type 4 - Direct JDBC Driver Type 1 only runs on platforms where ODBC is available ODBC must be configured separately Type 2 Drivers map between a proprietary Database API and the JDBC API Type 3 Drivers are used with middleware products Type 4 Drivers are written in Java In most cases, type 4 drivers are preferred JDBC Drivers Types
- 8. JDBC Classes DriverManager Manages JDBC Drivers Used to Obtain a connection to a Database • Types Defines constants which identify SQL types Date Used to Map between java.util.Date and the SQL DATE type • Time Used to Map between java.util.Date and the SQL TIME type TimeStamp Used to Map between java.util.Date and the SQL TIMESTAMP type
- 9. JDBC Interfaces Driver All JDBC Drivers must implement the Driver interface. Used to obtain a connection to a specific database type • Connection Represents a connection to a specific database Used for creating statements Used for managing database transactions Used for accessing stored procedures Used for creating callable statements Statement Used for executing SQL statements against the database
- 10. JDBC Interfaces ResultSet Represents the result of an SQL statement Provides methods for navigating through the resulting data • PreparedStatement Similar to a stored procedure An SQL statement (which can contain parameters) is compiled and stored in the database CallableStatement Used for executing stored procedures DatabaseMetaData Provides access to a database's system catalogue ResultSetMetaData Provides information about the data contained within a ResultSet
- 11. Using JDBC To execute a statement against a database, the following flow is observed Load the driver (Only performed once) Obtain a Connection to the database (Save for later use) Obtain a Statement object from the Connection Use the Statement object to execute SQL. Updates, inserts and deletes return Boolean. Selects return a ResultSet Navigate ResultSet, using data as required Close ResultSet Close Statement
- 12. Database URLs • When connecting to a database, you must specify the data source and you may need to specify additional parameters.For example, network protocol drivers may need a port, and ODBC drivers may need various attributes. • General Syntax : - jdbc:subprotocol name:other stuff • EX : jdbc:localhost:DB_NAME
- 13. Loading/Registering a Driver • The first step to develop a JDBC application is to load and register the required driver using the driver manager . • You can load and register a driver : 1. Programmatically : . Using the forName() method . Using the registerDriver () method 2. Manually: . By setting system property
- 14. Using the forName () Method • The forName() method is available in the java.lang.Class class. • The forName() method loads the JDBC driver and registers the driver with the driver manager. • The syntax to load a JDBC driver to access a database is : Class.forName (“driver_name”); • You can load the JDBC-ODBC Bridge driver using the following method call: Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver”);
- 15. Using the registerDriver () method • You can create an instance of the Driver class to load a JDBC driver. • The syntax to declare an instance of the Driver class is : Driver d = new <driver-name>; • You can use the following statement to crate an instance of the Driver class: Driver d = new sun.jdbc.odbc.JdbcOdbcDriver (); • Once you have created the Driver object ,call the registerDriver () method to register it with the DriverManager. • You can register the JDBC-ODBC Bridge driver using the following method call to registerDriver () method: DriverManager.registerDriver (d) ;
- 16. Setting System Property • Driver can also be loaded by setting system property for JDBC drivers. • You add the driver name to the jdbc.drivers system property to load a JDBC driver. • You use the –D command line option to set the system property on the command line. • The command to set the system property is : java –Djdbc.drivers=sun.jdbc.odbc.JdbcOdbcDriver Demo • In the preceding command , jdbc.drivers is the property name and sun.jdbc.odbc.JdbcOdbcDriver is the value that you need to set for the property. • After you load a driver , you need to establish the connection with a database.
- 17. Even a good API can have problems Loading drivers fits into this category The DriverManager is a singleton Each JDBC Driver is also a singleton When a JDBC Driver class is loaded, it must create an instance of itself and register that instance with the JDBC DriverManager How does one load a "class" into the Virtual machine? Use the static method Class.forName() Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); Loading Drivers
- 18. Connecting to a Database Once a Driver is loaded, a connection can be made to the database The connection is defined by URL The URL has the following form: jdbc:driver:databasename • Examples: jdbc:odbc:MyOdbcDatabase jdbc:postgres:WebsiteDatabase jdbc:oracle:CustomerInfo A connection is obtained in the following manner: Connection aConnection = DriverManager.getConnection("jdbc:odbc:myDatabase"); • Overloaded versions of the getConnection method allow the specification of a username and password for authentication with the database.
- 19. Executing SQL Statments • Managing Connections • Statements • Resultset • SQL Exceptions • Populating Database 19
- 20. Managing / Using a Connection The Connection interface defines many methods for managing and using a connection to the database public Statement createStatement() public PreparedStatement prepareStatement(String sql) public void setAutoCommit(boolean) public void commit() public void rollback() public void close() • The most commonly used method is createStatement() When an SQL statement is to be issued against the database, a Statement object must be created through the Connection
- 21. Statements The Statement interface defines two methods for executing SQL against the database public ResultSet executeQuery(String sql) public int executeUpdate(String sql) • executeQuery returns a ResultSet • All rows and columns which match the query are contained within the ResultSet • The developer navigates through the ResultSet and uses the data as required. • executeUpdate returns the number of rows changed by the update statement This is used for insert statements, update statements and delete statements
- 22. Result Set The ResultSet interface defines many navigation methods public boolean first() public boolean last() public boolean next() public boolean previous() The ResultSet interface also defines data access methods public int getInt(int columnNumber) -- Note: Columns are numbered public int getInt(String columnName)-- from 1 (not 0) public long getLong(int columnNumber) public long getLong(String columnName) public String getString(int columnNumber) public String getString(String columnName) There are MANY more methods. Check the API documentation for a complete list
- 23. SQL Types/Java Types Mapping SQL Type Java Type CHAR String VARCHAR String LONGVARCHAR String NUMERIC java.Math.BigDecimal DECIMAL java.Math.BigDecimal BIT boolean TINYINT int SMALLINT int INTEGER int BIGINT long REAL float FLOAT double DOUBLE double BINARY byte[] VARBINARY byte[] DATE java.sql.Date TIME java.sql.Time TIMESTAMP java.sql.Timestamp
- 24. Connection aConnection; try { Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); } catch(ClassNotFoundException x){ System.out.println("Cannot find driver class. Check CLASSPATH"); return; } try{ aConnection = DriverManager.getConnection("jdbc:odbc:MyDatabase", "Username", "Password"); } catch(SQLException x) { System.out.println("Exception connecting to database:" + x); return; } Example Code:
- 25. try{ Statement aStmt = aConnection.createStatement(); StringBuffer sb = new StringBuffer("SELECT Employee_id,Employee_Name"); sb.append(" FROM Employee WHERE EmployeeId>100"); ResultSet rs = aStmt.executeQuery(sb.toString()); while(rs.next()){ int employeeId = rs.getInt(1); String employeeName = rs.getString(2); System.out.println("Id:" + employeeId + "nName:" + employeeName); } rs.close(); aStmt.close(); } catch(SQLException x){ System.out.println("Exception while executing query:" + x); Example Code (continued):
- 26. PreparedStatement interface • The PreparedStatement objects accepts the runtime parameters. • The PreparedStatement interface is derived from the Statement interface and is available in the java.sql package. • The PreparedStatement objects are compiled and prepared only once by JDBC. • The future invocation of the PreparedStatement object does not recompile the SQL statements. • This helps in reducing the load on the database server and thus improving the performance of the application .
- 27. • The PreparedStatement interface inherits the following methods to execute SQL statement s from the Statement interface: 1. ResultSet executeQuery () : - Executes a SELECT statement and returns the result in a ResultSet object. 1. int executeUpdate(): Executes an SQL statement, INSERT , UPDATE , or DELETE and returns the count of the rows affected. 1. boolean execute () : Executes an SQL statement and returns a boolean value.
- 28. stat = con.prepareStatement(“SELECT * FROM authors WHERE au_id = ? ”) ; The SQL statement can contain ‘ ? ‘ symbol as placeholder that can be replaced by input parameters at runtime. Before executing the SQL statements specified in the PreparedStatement object , you must set the value of each ‘ ? ‘ parameter. stat.setString (1, “123”); ResultSet rs = stat.executeQuery ();
- 29. • The PreparedStatement interface provides various methods to set the value of the placeholders for the specific data types. 1. void setByte (int index , byte val) : Sets the java byte type value for the parameter corresponding to index passed as a parameter. 2. void setBytes (int index , byte[] val) : Sets the Java byte type array for the parameter corresponding to index passed as a parameter. 3. void setBoolean (int index , boolean val) : Sets the Java boolean type value for the parameter corresponding to index passed as a parameter. 4. void setDouble (int index, double val) : Sets the Java double type value value for the parameter corresponding to the index passed as a parameter.
- 30. 5. void setInt (int index , int val) : Sets the Java int type value for the parameter corresponding to index passed as a parameter. 6. void setLong(int index , long val) : Sets the Java long type value for the parameter corresponding to index passed as a parameter. 7. void setFloat (int index , float val) : Sets the Java float type value for the parameter corresponding to index passed as a parameter. 8. void setShort (int index , short val) : Sets the Java short type value for the parameter corresponding to index passed as a parameter. 9. void setString(int index , String val) : Sets the Java String type value for the parameter corresponding to index passed as a parameter.
- 31. Retrieving Rows String str = “SELECT * FROM titles WHERE au_id = ? ” ; PreparedStatement ps = con.prepareStatement(str) ; ps.setString(1 , “101”); ResultSet rs = ps.executeQuery ();
- 32. Inserting Rows String str = “ INSERT INTO authors (au_id , au_fname , au_lname) VALUES (? , ? , ? ) ” ; PreparedStatement ps = con.prepareStatement(str); ps.setString (1, “101”); ps.setString (2, “ABC”); ps.setString (3 , “XYZ”); int rt = ps.executeUpdate() ;
- 33. Updating & Deleting Row String str = “ UPDATE authors SET state = ? WHERE city = ? “ ; PreparedStatement ps = con.prepareStatement(str); ps.setString (1, “MH”); ps.setString (2, “Pune”); int rt = ps.executeUpdate() ; String str = “ DELETE FROM authors WHERE au_fname = ? “ ; PreparedStatement ps = con.prepareStatement(str); ps.setString (1, “PPPP”); int rt = ps.executeUpdate() ;
- 34. Scrollable ResultSet • Statement createStatement( int resultSetType, int resultSetConcurrency) • resultSetType: • ResultSet.TYPE_FORWARD_ONLY • -default; same as in JDBC 1.0 • -allows only forward movement of the cursor • -when rset.next() returns false, the data is no longer available and the result set is closed. • ResultSet.TYPE_SCROLL_INSENSITIVE • -backwards, forwards, random cursor movement. • -changes made in the database are not seen in the result set object in Java memory. • ResultSetTYPE_SCROLL_SENSITIVE • -backwards, forwards, random cursor movement. • -changes made in the database are seen in the result set object in Java memory. 34
- 35. Scrollable ResultSet (cont’d)Scrollable ResultSet (cont’d) • resultSetConcurrency: • ResultSet.CONCUR_READ_ONLY • This is the default (and same as in JDBC 1.0) and allows only data to be read from the database. • ResultSet.CONCUR_UPDATABLE • This option allows for the Java program to make changes to the database based on new methods and positioning ability of the cursor. • Example: • Statement stmt = conn.createStatement( ResultSet.TYPE_SCROLL_INSE NSITIVE, ResultSet.CONCUR_READ_ONLY); • ResultSetrset= stmt.executeQuery( “SHOW TABLES”); 35
- 36. Scrollable ResultSet (cont’d)Scrollable ResultSet (cont’d) public boolean absolute(int row) throws SQLException • -If the given row number is positive, this method moves the cursor to the given row number (with the first row numbered 1). • -If the row number is negative, the cursor moves to a relative position from the last row. • -If the row number is 0, an SQLException will be raised. public boolean relative(int row) throws SQLException • This method call moves the cursor a relative number of rows, either positive or negative. • An attempt to move beyond the last row (or before the first row) in the result set positions the cursor after the last row (or before the first row). public boolean first() throws SQLException public boolean last() throws SQLException public boolean previous() throws SQLException public boolean next() throws SQLException 36
- 37. Scrollable ResultSet (cont’d)Scrollable ResultSet (cont’d) public void beforeFirst() throws SQLException public void afterLast() throws SQLException public boolean isFirst() throws SQLException public boolean isLast() throws SQLException public boolean isAfterLast() throws SQLException public boolean isBeforeFirst() throws SQLException public int getRow() throws SQLException • getRow() method retrieves the current row number: The first row is number 1, the second number 2, and so on. 37
- 38. 38 Transactions and JDBCTransactions and JDBC • Transaction: more than one statement that must all succeed (or all fail) together - e.g., updating several tables due to customer purchase • If one fails, the system must reverse all previous actions • Also can’t leave DB in inconsistent state halfway through a transaction • COMMIT = complete transaction • ROLLBACK = cancel all actions
- 39. 39 ExampleExample • Suppose we want to transfer money from bank account 13 to account 72: PreparedStatement pstmt = con.prepareStatement("update BankAccount set amount = amount + ? where accountId = ?"); pstmt.setInt(1,-100); pstmt.setInt(2, 13); pstmt.executeUpdate(); pstmt.setInt(1, 100); pstmt.setInt(2, 72); pstmt.executeUpdate(); What happens if this update fails?
- 40. 40 Transaction ManagementTransaction Management • Transactions are not explicitly opened and closed • The connection has a state called AutoCommit mode • if AutoCommit is true, then every statement is automatically committed • if AutoCommit is false, then every statement is added to an ongoing transaction • Default: true
- 41. 41 AutoCommitAutoCommit • If you set AutoCommit to false, you must explicitly commit or rollback the transaction using Connection.commit() and Connection.rollback() • Note: DDL statements (e.g., creating/deleting tables) in a transaction may be ignored or may cause a commit to occur - The behavior is DBMS dependent setAutoCommit(boolean val)
Editor's Notes
- #42: Lobs and DDL