data processing

PowerPoint Presentation04e-BM/NS/HDCV/FSOFT v2/3
Lesson 6:
Database Programming
with Java
04e-BM/NS/HDCV/FSOFT v2/3
Course Objective
JDBC Basics
Statement
ResultSet
PreparedStatement
© FPT SOFTWARE – TRAINING MATERIAL – Internal use
Learning Approach
The following are strongly suggested for a better learning and understanding of this course:
Noting down the key concepts in the class
Analyze all the examples / code snippets provided
Study and understand the self study topics
Completion and submission of all the assignments, on time
Completion of the self review questions in the lab guide
Study and understand all the artifacts including the reference materials / e-learning / supplementary materials specified
Completion of the project (if application for this course) on time inclusive of individual and group activities
Taking part in the self assessment activities
Participation in the doubt clearing sessions
JDBC BASICS
Session 1
JDBC (Java DataBase Connectivity) provides a standard library for accessing relational databases
JDBC consists of two parts:
JDBC API, a purely Java-based API
JDBC Driver Manager,which communicates with vendor-specific drivers that perform the real communication with the database.
JDBC classes are in the java.sql package
Current JDBC version: 3.0
Vendor independent
Platform independent
Left side, Type 1: JDBC-ODBC Bridge plus ODBC Driver
This combination provides JDBC access via ODBC drivers. ODBC binary code -- and in many cases, database client code -- must be loaded on each client machine that uses a JDBC-ODBC Bridge. Sun provides a JDBC-ODBC Bridge driver, which is appropriate for experimental use and for situations in which no other driver is available.
Right side, Type 2: A native API partly Java technology-enabled driver
This type of driver converts JDBC calls into calls on the client API for Oracle, Sybase, Informix, DB2, or other DBMS. Note that, like the bridge driver, this style of driver requires that some binary code be loaded on each client machine.
Right side, Type 3: Pure Java Driver for Database Middleware
This style of driver translates JDBC calls into the middleware vendor's protocol, which is then translated to a DBMS protocol by a middleware server. The middleware provides connectivity to many different databases.
Left side, Type 4: Direct-to-Database Pure Java Driver
This style of driver converts JDBC calls into the network protocol used directly by DBMSs, allowing a direct call from the client machine to the DBMS server and providing a practical solution for intranet access.
1. Load the driver
3. Create a Statement object
4. Executing the Statement
6. Process the results.
7. Close the connection
Register with DriverManager
No need to register with DriverManager.
How to specify the Driver class.
Refer to the driver documentation.
Some examples.
Need username, password
Examples:
jdbc:oracle:thin:@localhost:1521:orcl
jdbc:mysql://127.0.0.1:3306/books
JDBC Statement Object
A Statement object is what sends your SQL statement to the DBMS
Create a Statement object and then execute it, supplying appropriate method with the SQL statement you want to send.
Statement stmt = con.createStatement();
For a SELECT statement, the method to use is executeQuery.
stmt.executeQuery( “SELECT * FROM XXX");
For statements that create or modify tables, the method to use is executeUpdate.
stmt.executeUpdate( "INSERT INTO XXX… “);
ResultSet object
A ResultSet object is a table of data representing a database result set, which is usually generated by executing a statement that queries the database.
You access the data in a ResultSet object through a cursor. This cursor is a pointer that points to one row of data in the ResultSet. Initially, the cursor is positioned before the first row.
ResultSet type
TYPE_FORWARD_ONLY: The result set cannot be scrolled; its cursor moves forward only, from before the first row to after the last row. The rows contained in the result set depend on how the underlying database generates the results. That is, it contains the rows that satisfy the query at either the time the query is executed or as the rows are retrieved.
TYPE_SCROLL_INSENSITIVE: The result can be scrolled; its cursor can move both forward and backward relative to the current position, and it can move to an absolute position. The result set is insensitive to changes made to the underlying data source while it is open. It contains the rows that satisfy the query at either the time the query is executed or as the rows are retrieved.
TYPE_SCROLL_SENSITIVE: The result can be scrolled; its cursor can move both forward and backward relative to the current position, and it can move to an absolute position. The result set reflects changes made to the underlying data source while the result set remains open.
The default ResultSet type is TYPE_FORWARD_ONLY.
ResultSet Concurrency
The concurrency of a ResultSet object determines what level of update functionality is supported.
There are two concurrency levels:
CONCUR_READ_ONLY: The ResultSet object cannot be updated using the ResultSet interface.
CONCUR_UPDATABLE: The ResultSet object can be updated using the ResultSet interface.
The default ResultSet concurrency is CONCUR_READ_ONLY.
Cursor Holdability
Calling the method Connection.commit can close the ResultSet objects that have been created during the current transaction. In some cases, however, this may not be the desired behavior. The ResultSet property holdability gives the application control over whether ResultSet objects (cursors) are closed when commit is called.
HOLD_CURSORS_OVER_COMMIT: ResultSet cursors are not closed; they are holdable: they are held open when the method commit is called. Holdable cursors might be ideal if your application uses mostly read-only ResultSet objects.
CLOSE_CURSORS_AT_COMMIT: ResultSet objects (cursors) are closed when the commit method is called. Closing cursors when this method is called can result in better performance for some applications.
The default cursor holdability varies depending on your DBMS.
ResultSet navigation
Moves the cursor froward one row from its current position.
previous()
Moves the cursor to the previous row in this ResultSet object.
first()
Moves the cursor to the first row in this ResultSet object.
last()
Moves the cursor to the last row in this ResultSet object.
beforeFirst()
Moves the cursor to the front of this ResultSet object, just before the first row. This method has no effect if the result set contains no rows.
afterLast()
Moves the cursor to the end of this ResultSet object, just after the last row. This method has no effect if the result set contains no rows.
getRow()
*
Note that the default sensitivity of a ResultSet is TYPE_FORWARD_ONLY, which means that it cannot be scrolled; you cannot call any of these methods that move the cursor, except next, if your ResultSet cannot be scrolled.
absolute(int row)
Moves the cursor to the given row number in this ResultSet object. If the row number is positive, the cursor moves to the given row number with respect to the beginning of the result set. The first row is row 1, the second is row 2, and so on. If the given row number is negative, the cursor moves to an absolute row position with respect to the end of the result set. For example, calling the method absolute(-1) positions the cursor on the last row; calling the method absolute(-2) moves the cursor to the next-to-last row, and so on.
relative(int rows)
*
Note that the default sensitivity of a ResultSet is TYPE_FORWARD_ONLY, which means that it cannot be scrolled; you cannot call any of these methods that move the cursor, except next, if your ResultSet cannot be scrolled.
The ResultSet interface declares getter methods (example: getBoolean, getLong, …) for retrieving column values from the current row.
You can retrieve values using either the index number of the column or the alias or name of the column.
The column index is usually more efficient. Columns are numbered from 1.
For maximum portability, result set columns within each row should be read in left-to-right order, and each column should be read only once.
With CONCUR_UPDATABLE ResultSet, you can update values using updateXXX() method.
You can update values using either the index number of the column or the name of the column.
However, none of these updater methods modifies the database; you must call the method ResultSet.updateRow to update the database.
Updating a row
Statement st = cn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE)
rs.first();
rs.updateInt(2,2345); //rs.update<Type>
rs.updateRow();
Statement st = cn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_UPDATABLE)
rs.first();
rs.update<Type>
rs.insertRow();
Step 1: Positioning the cursor
// Move the cursor to the last row of the result set
rs.last();
// Deleting the row from the result set
rs.deleteRow();
*
Note: Not all JDBD drivers support inserting new rows with the ResultSet interface. If you attempt to insert a new row and your JDBC driver database does not support this feature, a SQLFeatureNotSupportedException exception is thrown.
DisplayAuthors
Displays the data in a JTextArea
3
10
12 static String JDBC_DRIVER = "oracle.jdbc.driver.OracleDriver";
13 String DATABASE_URL = "jdbc:oracle:thin:@localhost:1521:orcl";
16 // and querying database
17 private Connection connection;
18 private Statement statement;
21 // results and displays results in window
22 public DisplayAuthors()
25
*
Line 5: Imports package java.sql, which contains classes and interfaces for the JDBC API.
27 try {
33 Class.forName( JDBC_DRIVER );
36 connection = DriverManager.getConnection( DATABASE_URL );
39 statement = connection.createStatement();
44
47 ResultSetMetaData metaData = resultSet.getMetaData();
48 int numberOfColumns = metaData.getColumnCount();
Line 33: Loads the class definition for the database driver.
Lines 36: Declare and initialize a Connection reference called connection.
Line 39: Invokes Connection method createStatement to obtain an object that implements interface Statement.
Line 43: Use the Statement object’s executeQuery method to execute a query that selects all the author information from table authors.
Line 47: Obtains the metadata for the ResultSet.
Line 48: Uses ResultSetMetaData method getColumnCount to retrieve the number of columns in the ResultSet.
51 results.append( metaData.getColumnName( i ) + "\t" );
52
58 results.append( resultSet.getObject( i ) + "\t" );
59
64 JTextArea textArea = new JTextArea( results.toString() );
65 Container container = getContentPane();
68
70 setVisible( true ); // display window
71
Line 51:Append the column names to the StringBuffer results.
Line 58:Append the data in each ResultSet row to the StringBuffer results.
Lines 64-70: Create the GUI that displays the StringBuffer results, set the size of the application window and show the application window.
75 catch ( SQLException sqlException ) {
76 JOptionPane.showMessageDialog( null, sqlException.getMessage(),
77 "Database Error", JOptionPane.ERROR_MESSAGE );
83 catch ( ClassNotFoundException classNotFound ) {
84 JOptionPane.showMessageDialog( null, classNotFound.getMessage(),
86
91 finally {
99 catch ( SQLException sqlException ) {
112 {
114 window.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
PreparedStatement Object
An object that represents a precompiled SQL statement.
PreparedStatement object is given an SQL statement when it is created. This SQL statement is sent to the DBMS right away, where it will be compiled.
When the PreparedStatement is executed, the DBMS can just run the PreparedStatement 's SQL statement without having to compile it first.
PreparedStatement objects are used more 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.
PreparedStatement Example
JDBC ADVANCED
Session 2
Handling SQLExceptions
When JDBC encounters an error during an interaction with a data source, it throws an instance of SQLException as opposed to Exception. The SQLException instance contains the following information:
A description of the error.
Retrieve the String object that contains this description by calling the method SQLException.getMessage.
A SQLState code.
These codes and their respective meanings have been standardized by ISO/ANSI and Open Group (X/Open), although some codes have been reserved for database vendors to define for themselves. This String object consists of five alphanumeric characters. Retrieve this code by calling the method SQLException.getSQLState.
An error code.
This is an integer value identifying the error that caused the SQLException instance to be thrown. Its value and meaning are implementation-specific and might be the actual error code returned by the underlying data source. Retrieve the error by calling the method SQLException.getErrorCode.
A cause.
A SQLException instance might have a causal relationship, which consists of one or more Throwable objects that caused the SQLException instance to be thrown. To navigate this chain of causes, recursively call the method SQLException.getCause until a null value is returned.
A reference to any chained exceptions.
If more than one error occurs, the exceptions are referenced through this chain. Retrieve these exceptions by calling the method SQLException.getNextException on the exception that was thrown.
Retrieving Exceptions
public static void printSQLException(SQLException ex) {
for (Throwable e : ex) {
if (e instanceof SQLException) {
Retrieving Exceptions
For example, if you execute a SQL statement but the table does not exist, the output will be similar to the following:
SQLState: 42Y55
Message: 'DROP TABLE' cannot be performed on ‘BOOKS.SAMPLEAUTHORS' because it does not exist.
Batch updates
A set of multiple update statements that is submitted to the database for processing as a batch
Statement, PreparedStatement and CallableStatement can be used to submit batch updates
Indivisible unit of work
Transaction
A transaction is a set of one or more statements that is executed as a unit, so either all of the statements are executed, or none of the statements is executed.
Transaction Processing
Start transaction
Disable auto-commit mode
The way to allow two or more statements to be grouped into a transaction is to disable the auto-commit mode.
con.setAutoCommit(false);
Commit
After the auto-commit mode is disabled, no SQL statements are committed until you call the method commit() explicitly. All statements executed after the previous call to the method commit() are included in the current transaction and committed together as a unit.
Enable auto-commit mode
Rollback transaction
If any error of abnormal case happened, you may want to aborts this transaction and restores values to what they were before the attempted update:
con.rollback()
Setting and Rolling Back to Savepoints
An SQL savepoint represents the state of data and schemas at a particular point in time within a unit of work.
To create a savepoint:
rollback(Savepoint savepoint)
RowSet
A JDBC RowSet object holds tabular data in a way that makes it more flexible and easier to use than a result set.
All RowSet objects are derived from the ResultSet interface and therefore share its capabilities. What makes JDBC RowSet objects special is that they add these new capabilities:
Function as JavaBeans Component
Add Scrollability or Updatability
Oracle has defined five RowSet interfaces for some of the more popular uses of a RowSet, and standard reference are available for these RowSet interfaces:
JdbcRowSet
CachedRowSet
WebRowSet
JoinRowSet
FilteredRowSet
Function as JavaBeans Component
All RowSet objects are JavaBeans components. This means that they have the following:
Properties
All RowSet objects have properties. A property is a field that has corresponding getter and setter methods.
JavaBeans Notification Mechanism
RowSet objects use the JavaBeans event model, in which registered components are notified when certain events occur. For all RowSet objects, three events trigger notifications:
A cursor movement
A change to the entire RowSet contents
The notification of an event goes to all listeners, components that have implemented the RowSetListener interface and have had themselves added to the RowSet object's list of components to be notified when any of the three events occurs.
Setting Up Listeners
A listener for a RowSet object is a component that implements the following methods from the RowSetListener interface:
cursorMoved: Defines what the listener will do, if anything, when the cursor in the RowSet object moves.
rowChanged: Defines what the listener will do, if anything, when one or more column values in a row have changed, a row has been inserted, or a row has been deleted.
rowSetChanged: Defines what the listener will do, if anything, when the RowSet object has been populated with new data.
An example of a component that might want to be a listener is a BarGraph object that graphs the data in a RowSet object. As the data changes, the BarGraph object can update itself to reflect the new data.
The following line of code means that every time the cursor for the crs objects moves, values in crs are changed, or crs as a whole gets new data, the BarGraph object bar will be notified:
crs.addRowSetListener(bar);
crs.removeRowSetListener(bar);
Add Scrollability or Updatability
Some DBMSs do not support result sets that can be scrolled (scrollable), and some do not support result sets that can be updated (updatable). If a driver for that DBMS does not add the ability to scroll or update result sets, you can use a RowSet object to do it.
A RowSet object is scrollable and updatable by default, so by populating a RowSet object with the contents of a result set, you can effectively make the result set scrollable and updatable.
A RowSet object is considered either connected or disconnected.
A connected RowSet object uses a JDBC driver to make a connection to a relational database and maintains that connection throughout its life span.
JdbcRowSet
A disconnected RowSet object makes a connection to a data source only to read in data from a ResultSet object or to write data back to the data source. After reading data from or writing data to its data source, the RowSet object disconnects from it, thus becoming "disconnected." During much of its life span, a disconnected RowSet object has no connection to its data source and operates independently.
CachedRowSet
WebRowSet
JoinRowSet
FilteredRowSet
Stored Procedures
A stored procedure is a group of SQL statements that form a logical unit and perform a particular task, and they are used to encapsulate a set of operations or queries to execute on a database server.
Stored procedures can be compiled and executed with different parameters and results, and they can have any combination of input, output, and input/output parameters.
String queryDrop = "DROP PROCEDURE IF EXISTS SHOW_AUTHORS";
String createProcedure =
Connection pool
*
Connection pool
Opening and maintaining a database connection for each user, is costly and wastes resources.
In connection pooling, after a connection is created, it is placed in the pool and it is used over again so that a new connection does not have to be established.
*
Connection pool
Connection pool
A new client #2 is assigned to a free connection
Connection pool
Client #1 is disconnected, and free a connection for use
Connection pool
A new client #3 is assigned to the free connection
You may write your own code
You may using Application server which supported connection pool (for ex: Tomcat, Jboss, Jetty, …)
You may using other libraries
*
Application server
</description>
<res-ref-name>
jdbc/EmployeeDB
</res-ref-name>
<res-type>
javax.sql.DataSource
</res-type>
<res-auth>
Container
</res-auth>
</resource-ref>
Tomcat configuration
The configuration properties for Tomcat's standard data source resource factory are as follows:
driverClassName - Fully qualified Java class name of the JDBC driver to be used.
username - Database username to be passed to our JDBC driver.
password - Database password to be passed to our JDBC driver.
url - Connection URL to be passed to our JDBC driver.
initialSize - The initial number of connections that will be created in the pool during pool initialization. Default: 0
maxActive - The maximum number of connections that can be allocated from this pool at the same time. Default: 8
minIdle - The minimum number of connections that will sit idle in this pool at the same time. Default: 0
maxIdle - The maximum number of connections that can sit idle in this pool at the same time. Default: 8
*
conn.close();
HSQL in-memory
SampleHSQL.jar
SampleHSQL.zip
MySQL
*
Guide to the student to using HSQL in-memory and MySQL at very basics. These files are in \Guide folder.
Summary
JDBC is an API specification developed by Sun Microsystems that defines a uniform interface for accessing different relational databases. The primary function of the JDBC API is to allow the developer to issue SQL statements and process the results in a consistent, database-independent manner.
A JDBC driver translates standard JDBC calls into a network protocol or client API call that facilitates communication with the database. This transla-tion provides JDBC applications with database independence.
The basic process of connecting to a database via JDBC goes like this: regis-ter the JDBC driver, establish a database connection, execute an SQL state-ment, process the results, close the database connection.
Summary(cont)
A prepared statement is an SQL statement that is precompiled by the data-base. Through precompilation, prepared statements improve the performance of SQL commands that are executed multiple times (given that the database supports prepared statements).
A transaction is a set of SQL statements that are grouped such that all state-ments are guaranteed to be executed or the entire operation will fail. If all statements execute successfully, the results are committed to the database; otherwise, all changes are rolled back.
A stored procedure is an SQL operation that is stored on the database server. Stored procedures are usually written in an SQL dialect that has been expanded to include conditional statements, looping constructs, and other procedural programming features.
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