Java 7 Certification JDBC & Related Design Pattern

Java 7 CertificationJDBC & Related Design Pattern

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JDBC

• JDBC API provides a standard database – independent interface to interact with RDMSs.

• Typically, you use the JDBC API to connect to a database, query the data, and/or update data.

• Every database provides developers with 1. Standard SQL capabilities2. Extended SQL capabilities3. A proprietary programming languageto build database applications.


JDBC

• Therefore, if you want to process a set of rows in a database, you need to know the specific syntax for a specific database-dependent language.

• Using JDBC API relieves you of the effort to learn specific syntaxes for different databases.

• Using JDBC API you write a query using standard SQL and the Java API processes the result in a database-independent manner.


JDBC• Using JDBC API to access data in a database hides the

implementation differences that exist in different databases.

• It achieves the database transparency by defining most of its API using interfaces and letting the database vendors provide the implementations for those interfaces.

• The collection of implementation classes that is supplied by a vendor to interact with a specific database is called a ‘JDBC driver’.

• The ‘JDBC driver’ is used to connect to the RDMS.


JDBC

To connect to a database:1. Obtain the JDBC driver class files and add them

to the CLASSPATH environment variable.2. Register the JDBC driver with the

‘DriverManager’.3. Construct a connection URL.4. Use the static ‘getConnection()’ method of

‘DriverManager’ to establish a connection.


JDBC

• We will be working with the ‘APACHE DERBY’ database system which is included as part of the Java JDK.

• We will be including three jar files in our CLASSPATH.


JDBC

1. First set an environment variable called DERBY_HOME to the following:

C:\program files\java\jdk1.7.0_03\db\2. Add to the PATH: %DERBY_HOME%\bin3. Add to the CLASSPATH:

%DERBY_HOME%\LIB\DERBY.JAR; %DERBY_HOME%\LIB\DERBYTOOLS.JAR;%DERBY_HOME%\LIB\DERBYRUN.JAR;


JDBC• To connect to our APACHE DERBY database:// Register the JDBC driver classString driver="org.apache.derby.jdbc.EmbeddedDriver";Class.forName(driver); // set up the database name String dbName="jdbcDemoDB";// define the Derby connection URL to use String connectionURL = "jdbc:derby:" + dbName + ";create=true";// establish the connection to the database.conn = DriverManager.getConnection(connectionURL);


JDBC

JDBC connection project exercise.


JDBC

• You can execute different types of SQL statements using a JDBC driver.

• We use different JDBC ‘statement’ objects depending upon the kind of SQL statement.

• An instance of ‘java.sql.Statement’ interface represents a SQL statement in a java program.

• three interfaces to represent SQL statements:1. Statement2. Prepared Statement3. Callable Statement


JDBC

• If you have a SQL statement in the form of a string, you can use a ‘Statement’ object to execute it. These SQL statements are compiled each time they are executed.

• If you want to pre-compile a SQL statement once and execute it multiple times, use a ‘PreparedStatement’ object. It lets you specify a SQL statement in the form of a string that uses placeholders. You supply the values of the placeholders before executing the statement.

• Use a ‘CallableStatement’ object for a stored procedure or function in a database.


JDBC

• When you execute a SQL statement, the DBMS may return zero or more results. The results may include ‘update counts’, for example, the number of records affected in the database, or the results may include what are known as ‘result sets’, which consists of a group of records that have been retrieved from the database.


JDBC

• To execute a SQL statement using a ‘Statement’ object:

1. Get a connection object.Connection conn = … (get a Connection object)

2. Use the connection object to create a ‘Statement’ object:Statement stmt = conn.createStatement();


JDBC

3. Set up your SQL in a string:String sql = “update person set income=income*1.1”;

4. Execute the statement by calling one of the ‘execute’ methods of the ‘Statement’ object:

int rowsUpdated = stmt.executeUpdate(sql);5. Close the ‘Statement’ object to release resources:

stmt.close();6. Commit the transaction to the database:

conn.commit();


JDBC

• ‘Statement’ interface ‘execute()’ method is used to execute a SQL statement which does not return a value, such as ‘CREATE TABLE’.

• ‘executeUpdate()’ method is used for SQL that updates a database, as in ‘INSERT’, ‘UPDATE’ and ‘DELETE’ SQL statements. It returns the number of rows affected.

• ‘executeQuery()’ is used for SQL that produces a resultset, as in ‘SELECT’ SQL statements.


JDBC

• When you connect to a database the ‘auto-commit’ property for the ‘Connection’ object is set to ‘true’ by default. If a connection is in auto-commit mode, a SQL statement is committed automatically after its successful execution.

• If a ‘Connection’ is not in auto-commit mode, you must call the ‘commit()’ or ‘rollback()’ method of the ‘Connection’ object to commit or rollback the transaction.


JDBC• try {• Connection conn = get the connection…• conn.setAutoCommit(false);• Statement stmt = conn.createStatement();• String sql = “update person set

income=income*1.1”;• int rowsUpdated = stmt.executeUpdate(sql);• stmt.close();• conn.commit();• conn.close();• }• catch (SQLException e)• { conn.rollback(); e.printStackTrack(); conn.close();}


JDBC

JDBC database update exercise


JDBC

• The ‘PreparedStatement’ object pre-compiles the SQL statement and reuses the pre-compiled SQL statement if the statement in executed multiple times.

• A question mark (?) in a SQL string is a placeholder for an input parameter, whose value will be supplied before the statement is executed.


JDBCString sql = “insert into person” + “person_id,first_name,last_name,gender,”+ ”values (?,?,?,?,?,?)”;• Each of the ?s is a placeholder for a value. The first ? is

a placeholder for person_id, the second ? is for first_name, etc. The first placeholder is given an index of 1, the second placeholder is given an index of 2, etc.

Prepared Statement pstmt = conn.preparedStatement(sql);pstmt.setInt(1,801);


JDBCString sql = “insert into person” + “person_id,first_name,last_name,gender,”+ ”values (?,?,?,?,?,?)”;Connection conn = get a connection object…;Prepared Statement pstmt = conn.prepareStatement(sql);pstmt.setInt(1,801);pstmt.setString(2,”Tom”);pstmt.setString(3,”Baker”);pstmt.setString(4,”M”);java.sql.Date dob = java.sql.Date.valueOf(“1970-01-25”);pstmt.setDate(5,dob);pstmt.setDouble(6,45900);pstmt.executeUpdate();


JDBC

JDBC PreparedStatement Exercise


JDBC

• When you execute a query (a ‘SELECT’ statement) in a database, it returns the matching records in the form of a ‘ResultSet’.

• This is the data arranged in rows and columns.• The ‘SELECT’ statement determines the number of

rows and columns that are contained in a ‘ResultSet’.• The ‘Statement’ or ‘PreparedStatement’ or

‘CallableStatement’ object returns the result of a query as a ‘ResultSet’ object.


JDBC

• Scrollability• A ‘ResultSet’ can be forward-only or bi-

directional (move from row to row forwards or backwards).

• A bi-directional ‘ResultSet’ can be ‘update-sensitive’ or ‘update-insensitive’ (whether changes in the underlying database will be reflected in the ‘ResultSet’ while you are scrolling through its rows).


JDBC

• Concurrency• A ‘ResultSet’ may be ‘read-only’ or ‘updatable’.• Holdability• This property of a ‘ResultSet’ refers to its state

after a transaction which it is associated with, has been committed. The ‘ResultSet’ may be closed or kept open after commitment of the transaction.


JDBC

• You can get information about the properties of a ‘ResultSet’ supported by a JDBC driver by using methods of the ‘DatabaseMetaData’ interface.

• First we get a ‘DatabaseMetaData’ object as follows:

1. Connection conn = get a connection….2. DatabaseMetaData dmd =

conn.getMetaData();


JDBCboolean b1 = dmd.supportsResultSetType(TYPE_FORWARD_ONLY);boolean b2 = dmd.supportsResultSetType(TYPE_SCROLL_SENSITIVE);boolean b3 = dmd.supportsResultSetType(TYPE_SCROLL_INSENSITIVE);

boolean b4 = dmd.supportsResultSetConcurreny(TYPE_FORWARD_ONLY,CONCUR_READ_ONLY);boolean b5 = dmd.supportsResultSetConcurreny(TYPE_FORWARD_ONLY,CONCUR_UPDATABLE);boolean b6 = dmd.supportsResultSetConcurreny(TYPE_SCROLL_SENSITIVE,CONCUR_READ_ONLY);boolean b7 = dmd.supportsResultSetConcurreny(TYPE_SCROLL_SENSITIVE,CONCUR_UPDATABLE);boolean b6 = dmd.supportsResultSetConcurreny(TYPE_SCROLL_INSENSITIVE,CONCUR_READ_ONLY);boolean b7 = dmd.supportsResultSetConcurreny(TYPE_SCROLL_INSENSITIVE,CONCUR_UPDATABLE);

boolean b8 = dmd.supportsResultSetHoldability(HOLD_CURSORS_OVER_COMMIT);boolean b9 = dmd.supportsResultSetHoldability(CLOSE_CURSORS_AT_COMMIT);


JDBC

• Some additional ‘DatabaseMetaData’ methods:

String dbName = dmd.getDatabaseProductName();

String dbVersion = dmd.getDatabaseProductVersion();

String driverName = dmd.getDriverName();

String driverVersion = dmd.getDriverVersion();


JDBC

• JDBC DatabaseMetaData exercise


JDBC

• Typical way to get a forward-only ‘ResultSet’:

Connection conn = get a Connection object …Statement stmt = conn.getStatement();String sql = “select person_id, first_name,”+ “last_name,dob,income from person”;ResultSet rs = stmt.executeQuery(sql);

//now process the ‘ResultSet’ using the ‘rs’ variable.


JDBC

• The returned ‘ResultSet’ object from the ‘executeQuery()’ method is ready to be looped thru to get the associated data.

• At first, the row pointer(aka ‘cursor’) points to before the first row of the ‘ResultSet’.

• We must move the cursor to a valid row before accessing the column data for the row.

• The ‘next()’ method of the ‘ResultSet’ object is used to move the cursor to the next row.


JDBC

ResultSet rs = stmt.executeQuery(sql);While (rs.next()==true){

//process the current row in rs…}//done with the ResultSet rs.


JDBC

• A ‘ResultSet’ object lets you read the value of a column from its current row using one of the ‘getXXX()’ methods, where ‘XXX’ is the data type of the column.(e.g. ‘getInt()’, ‘getString()’)

• You must specify the index of column name in the ‘getXXX()’ method whose value you want to read.

int personID = rs.getInt(“person_id”);String firstName = rs.getString(2);


JDBCConnection conn = get a Connection object …Statement stmt = conn.getStatement();String sql = “select person_id, first_name,”+ “last_name,dob,income from person”;ResultSet rs = stmt.executeQuery(sql);while (rs.next()) {

int personID=rs.getInt(“person_id”);String firstName=rs.getString(“first_name”);String lastName = rs.getString(“last_name);java.sql.Date dob = rs.getDate(“dob”);double income = rs.getDouble(“income”);//do something with the retrieved values from the cols.

}


JDBCConnection conn = get a Connection object …Statement stmt = conn.getStatement();String sql = “select person_id, first_name,”+ “last_name,dob,income from person”;ResultSet rs = stmt.executeQuery(sql);while (rs.next()) {

int personID=rs.getInt(1);String firstName=rs.getString(2);String lastName = rs.getString(3);java.sql.Date dob = rs.getDate(4);double income = rs.getDouble(5);//do something with the retrieved values from the cols.

}


JDBC

• In a ‘ResultSet’ a column can have a null value. When a column has a null value a ‘getXXX()’ method returns the default value for the ‘XXX’ data type. For example, for numeric data types (int, double, byte) a ‘getXXX()’ method returns 0.

• If you want to know if the col value read was null, you need to call the ‘wasNull()’ method immediately after the ‘getXXX()’ call.


JDBC

ResultSet rs = get a ‘ResultSet’…java.sql.Date dob = rs.getDate(“dob”);If (rs.wasNull()) {

System.out.println(“dob is null”);}else {

System.out.println(“dob is:” + dob.toString());}


JDBC

JDBC ‘ResultSet’ exercise


JDBC

• To get a ‘ResultSet’ that scrolls forwards and backwards, we specify the scrollable property when you create a ‘Statement’ object, as follows:

Connection conn = get Connection object…Statement stmt = conn.getStatement(

ResultSet.TYPE_SCROLL_INSENSITIVE,

ResultSet.CONCUR_READ_ONLY);


JDBC

• When you specify scrollability in creating a ‘Statement’ object, if the JDBC driver does not support that type of scrollability, it will not generate an error. Rather, the driver will return a ‘ResultSet’ with a scrollability type that it does support.

• We can check the scrollability type of a returned ‘ResultSet’ object with method ‘getType()’.


JDBCResultSet rs = stmt.executeQuery(sql);

//determine the scrollability type of the ResultSetint cursorType = rs.getType();if (cursorType == ResultSet.TYPE_FORWARD_ONLY) { … }if (cursorType == ResultSet.TYPE_SCROLL_INSENSITIVE) { … }if (cursorType == ResultSet.TYPE_SCROLL_SENSITIVE) { … }

//determine the concurrency of the ResultSetint concurrency = rs.getConcurrency();if (concurrency == ResultSet.CONCUR_READ_ONLY) { … }if (concurrency == ResultSet.CONCUR_UPDATABLE) { … }


JDBC

• To determine the number of rows in the set - after retrieving the bi-directional ‘ResultSet’ object, call the ‘last()’ method to move the cursor to the last row of the set, then call the ‘getRow()’ method to get the row number of the last row, which will be the number of rows in the set.

• To process the ‘ResultSet’ after determining the number of rows, call ‘beforeFirst()’ to scroll the cursor before the first row and then loop thru.


JDBC

• Cursor movement methods://Movements relative to current cursor position:boolean next();boolean previous();boolean relative(int rows); // can move either direction

//Movements to absolute row numbersboolean first();boolean last();void beforeFirst();void afterLast();boolean absolute(int row);//positive row# - from beginning //negative row# - from end


JDBC

• Knowing current cursor positionboolean isBeforeFirst()boolean isFirst()boolean isLast()boolean isAfterLast()int getRow() //returns 0 if the cursor is positioned // before the first row, // after the last row, //or if the ResultSet is empty.


JDBC

• You can close a ‘ResultSet’ object by calling its ‘close()’ method.

rs.close();• Closing the ‘ResultSet’ frees the resources

associated with it.• When the ‘Statement’ object that produces

the ‘ResultSet’ object is closed, it automatically closes the ‘ResultSet’ object.


JDBC

JDBC bi-directional ResultSet exercise.


JDBC

• You can perform insert, update and delete actions using a ‘ResultSet’.

• The concurrency for the ‘ResultSet’ object must be ‘ResultSet.CONCUR_UPDATABLE’.

• There is an imaginary row in a ‘ResultSet’ that is called an ‘insert-row’.

• Think of this row as an empty new row which acts as a staging area for a new row to be inserted.


JDBC

• You position the cursor to the insert-row using the ‘ResultSet’ object’s ‘moveToInsertRow()’ method.

• When the cursor moves to the insert-row, it remembers its previous position.

• You can call the ‘moveToCurrentRow()’ method to move the cursor from the insert-row back to the previously current row.


JDBC

• Once the cursor is positioned at the insert-row, you need to set the values for the columns using one of the ‘updateXXX()’ methods of the ‘ResultSet’ object where ‘XXX’ is the type of the column.

• The first argument to ‘updateXXX()’ is either the column index of the column name, and the second argument is the value to be set.


JDBC

• Next we must send the changes to the database before our new row becomes part of our ‘ResultSet’ object.

• You can send the newly inserted row to the database by calling the ‘insertRow()’ method of the ‘ResultSet’ interface.

• If ‘auto-commit’ enabled for the ‘Connection’, the transaction will be committed immediately.

• Otherwise, ‘commit()’ the transaction to make the insert permanent (or ‘rollback()’ to cancel the transaction).


JDBCstmt=conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE);// Get the result set ResultSet rs = stmt.executeQuery(SQL);// Make sure our resultset is updatableint concurrency = rs.getConcurrency();if (concurrency != ResultSet.CONCUR_UPDATABLE) {System.out.println("JDBC driver does not " + "support updatable result set.");return;} // First insert a new row to the ResultSetrs.moveToInsertRow();rs.updateInt("person_id", 555);rs.updateString("first_name", "Richard");rs.updateString("last_name", "Castillo");rs.updateString("gender", "M");// Send the new row to the databasers.insertRow();


JDBC

To update an existing row in a ‘ResultSet’:• Move cursor to valid row of ‘ResultSet’.• Call an ‘updateXXX()’ method on a column.• Call the ‘updateRow()’ method to send the

changes to the database.• If ‘auto-commit’ enabled, changes sent to

database immediately.• Otherwise, you commit the changes.


JDBCstmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE);// Get the result set ResultSet rs = stmt.executeQuery(SQL);// Make sure our resultset is updatableint concurrency = rs.getConcurrency();if (concurrency != ResultSet.CONCUR_UPDATABLE) {System.out.println("JDBC driver does not " + "support updatable result set.");return;}// Give everyone a raisewhile (rs.next()) { double oldIncome = rs.getDouble("income"); double newIncome = 0.0; If (rs.wasNull()) { // The person with no income starts at 10000.00 oldIncome = 10000.00; newIncome = oldIncome;} else {// Increase income newIncome = oldIncome + oldIncome * (raise / 100.0);} // Update the income column for current row to newIncome rs.updateDouble("income", newIncome); // Send the changes to the database before we scroll to next row rs.updateRow();}


JDBC

To delete a row from a ‘ResultSet’:• Position the cursor at a valid row.• Call the ‘deleteRow()’ method of the

‘ResultSet’ object.• If ‘auto-commit’ is enabled, row will be

permanently deleted from the database.• Otherwise, commit the transaction, or cancel

the delete by rolling back the transaction.


JDBC

JDBC ResultSet Update Exercise


JDBC

• The interface ‘RowSet’ from the ‘javax.sql’ package is a wrapper for ‘ResultSet’ and inherits from the ‘ResultSet’ interface.

• A ‘RowSet’ allows for simpler JDBC programming. You need not deal directly with ‘Connection’ and ‘Statement’ objects, all you need to work with is the ‘RowSet’ object.


JDBC

• A ‘ResultSet’ is not serializable, where as a ‘RowSet’ is serializable.

• A ‘ResultSet’ object is always connected to a database, whereas a ‘RowSet’ object need not be connected to a data source at all times. It can connect to a database when required, e.g. when retrieving/updating data in the database.

• A ‘RowSet’ object is by default scrollable and updatable.


JDBC

• The ‘javax.sql.RowSet’ package defines five interfaces which inherit from the ‘RowSet’ interface, which itself inherits from the ‘ResultSet’ interface.

• Therefore, all the methods of the ‘ResultSet’ interface are available in these five types of rowsets.

• Typically, database vendors provide implementation classes for the five types of rowsets.


JDBC

The five types of rowsets are:

• JdbcRowSet• CachedRowSet• WebRowSet• FilteredRowSet• JoinRowSet


JDBC

• The ‘javax.sql.rowset.RowSetFactory’ interface lets you create the different types of ‘RowSet’ objects.

• To get an instance of ‘RowSetFactory’ we use the static ‘newFactory()’ method of the ‘javax.sql.RowSetProvider’ class.

• The ‘RowSetFactory’ interface has five methods to create the five types of rowsets.

• They are named ‘createXXXRowset()’ where XXX could be ’Jdbc’,‘Cached’, ‘Web’,‘Filtered’, and ’Join’.


JDBCtry { RowSetFactory rsf = RowSetProvider.newFactory();

JdbcRowSet jrs = rsf.createJdbcRowSet();

//… work with the JdbcRowSet…

}catch (SQLException e){ e.printStackTrace();}


JDBC

• A ‘RowSet’ object will need to connect to a data source to retrieve and update data.

• A ‘RowSet’ will use a JDBC driver to connect to a database. Set the connection properties as follows:

RowSet rs = … get a RowSet object …;Rs.setUrl = “jdbc:derby:jdbcDemoDb”;Rs.setUsername = “user”;Rs.setPassword = “password”;

• You don’t need to establish connection to the database, the ‘RowSet’ object will take care of it.


JDBC

• When you work with a ‘RowSet’ you need not worry about ‘Statement’, ‘PreparedStatement’ etc. objects.

• However you must specify a command that will generate the result set for the ‘RowSet’ object.

• The command would be in the form of a SQL statement in a string.

• You can use a ‘?’ as a placeholder for any parameter to be passed to the command at runtime.

• To set the parameter at runtime, use one of the ‘setXXX()’ methods of the ‘RowSet’ interface.


JDBC

RowSet rs = … get a RowSet object …

String sql=“select person_id,first_name”+ “last_name from person”;

rs.setCommand(sql);


JDBC

RowSet rs = … get a RowSet object …String sql=“select person_id,first_name”+ “last_name from person”+ “where income between ? and ?”;rs.setDouble(1,20000.0);rs.setDouble(2,40000.0);rs.setCommand(sql);


JDBC

To populate a ‘RowSet’ object with data by executing its command, you call its ‘execute()’ method:

rs.execute();

After the ‘execute()’ method is executed, the ‘RowSet’ object has data in it, and you need to scroll to a row to read/update its column value.


JDBC

• A ‘RowSet’ inherits all cursor movement methods from the ‘ResultSet’ interface.

• By default, all ‘RowSet’ objects are bi-directional scrollable and updateable.

rs.execute();while (rs.next()) { int personID = rs.getInt(“person_id”); String firstname=rs.getString(“first_name”);}


JDBC

• Updating data in a ‘RowSet’ is similar to updating data in a ‘ResultSet’ object.

• To update a columns value, you need to move the cursor to a row and use one of the ‘updateXXX()’ methods to set the new value for the column.

• Then you call the ‘updateRow()’ method of the ‘RowSet’ object.


JDBC

• To insert a new row, move the cursor to the insert-row by calling ‘moveToInsertRow()’ method of the ‘RowSet’.

• Set the column values in the insert-row by using the ‘updateXXX()’ methods of ‘RowSet’.

• Then call ‘insertRow()’ method of ‘RowSet’ to insert the row into the ‘RowSet’.


JDBC

• To delete a row, move the cursor to the row you want to delete and call the ‘deleteRow()’ method of the ‘RowSet’.


JDBC

How and when the changes to a ‘RowSet’ are actually propagated to the database depends on the type of ‘RowSet’.


JDBC

The five types of rowsets are:

• JdbcRowSet• CachedRowSet• WebRowSet• FilteredRowSet• JoinRowSet


JDBC

• A ‘JdbcRowSet’ is also called a ‘connected-rowset’ because it always maintains a database connection.

• As a ‘ResultSet’ object always maintains a database connection so does the ‘JdbcRowSet’

• The ‘setAutoCommit()’ method enables or disables auto-commit mode.

• Methods ‘commit()’ and ‘rollback()’ allow you to commit or rollback changes to data.


JDBC

• Updating data using a ‘JdbcRowSet’ object is similar to updating for a ‘ResultSet’.

• All methods will be called on the ‘JdbcRowSet’ instead of the ‘ResultSet’ object.

• You must call the ‘updateRow()’ method of the ‘JdbcRowSet’ after updating the column value(s) and before you scroll to another row.

• Use the ‘JdbcRowSet’ object’s ‘commit()’ or ‘rollback()’ methods to commit or rollback.


JDBC

JdbcRowSet Update exercise


JDBC

• A ‘CachedRowSet’ is also called a ‘disconnected rowset’. It keeps the database connection open only for the duration it needs to interact with the database.

• It retrieves all data generated by the command and caches it in memory.

• A ‘CachedRowSet’ is always serializable, scrollable, and updateable.


JDBC

• Methods to populate a ‘CachedRowSet’ object:

void execute() void execute(Connection conn)void populate(ResultSet data)void populate (ResultSet rs, int startRow)

• All of the above throw ‘SQLException’


JDBC• If you have set the database connection properties for a

‘CachedRowSet’ you can use the ‘execute()’ method with no parameters.

• Another version of the ‘execute()’ method accepts a ‘Connection’ object which will be used to populate the ‘CachedRowSet’ with data.

• The ‘populate()’ method will populate the ‘CachedRowSet’ with data from the ‘ResultSet’ object passed in.

• Another version of the ‘populate()’ method accepts a starting row number of the ‘ResultSet’


JDBC

• You can obtain the number of rows in a ‘CachedRowSet’ using its ‘size()’ method.

• Since a ‘CachedRowSet’ caches all its rows in memory, it can provide you a count of rows at any time.

int rowCount = myCachedRowSet.size();• Retrieving rows from a database for a

‘CachedRowSet’ is similar to that for ‘JdbcRowSet’, except for the additional ‘size()’ method of ‘CachedRowSet’.


JDBC

CachedRowSet exercise


JDBC

• ‘CachedRowSet’ provides a feature called ‘paging’ to allow you to retrieve rows in chunks.

• Use the ‘setPageSize(int size)’ method to set the pagesize.

• Use the ‘nextPage()’ method to get subsequent pages, and use the ‘previousPage()’ method to get prior pages.

• Both methods return ‘true’ if there are more pages to retrieve, otherwise they return ‘false’.

• Use an outer loop to retrieve pages, and an inner loop to retrieve rows of the page.


JDBCString sqlCommand = "select person_id, first_name, last_name from person";cachedRs.setCommand(sqlCommand);cachedRs.setPageSize(4); // Set page size cachedRs.execute();int pageCounter = 1;// Retrieve and print person records one page at a timedo { System.out.println("Page #" + pageCounter + " (Row Count=" + cachedRs.size() +")"); // Loop and Print the records in the current page // Increment the page count by 1 pageCounter++; } while (cachedRs.nextPage());


JDBC

• You can update data in a ‘CachedRowSet’ and save the changes back to the database.

• Use ‘updateRow()’, ‘insertRow()’, ‘deleteRow()’ methods as with ‘JdbcRowSet’ but in this case these methods DO NOT send the changes to the database.

• Send changes to the database by calling the ‘acceptChanges()’ method.


JDBC

• ‘WebRowSet’ inherits from ‘CachedRowSet’ and adds capabilities to read data from an XML doct and write data to an XML doct.

• User ‘readXML()’ to read XML data into a ‘WebRowSet, and ‘writeXML’ to export XML data from a ‘WebRowSet’.


JDBCWebRowSet wrs = … get a web rowset with data …;

//Create a StringWriter object to hold the exported XMLjava.io.StringWriter sw = new java.io.StringWriter();

//Write the XML representation of wrs into swwrs.writeXML(sw);

//Get the String object from swString webRsXML = sw.toString();

• String webRsXML contains the XML representation of the wrs object.


JDBC

Importing XML into a ‘WebRowSet’:

//Create a StringReader object from an XML StringJava.io.StringReader sr = new java.io.StringReader(webRsXML);

//Create an empty WebRowSet objectRowSetFactory rsf = RowSetProvider.newFactory();WebRowSet newWebRs = rsf.createWebRowSet();

// Import the XML content into the new WebRowSetnewWebRs.readXML(sr);


JDBC

WebRowSetXml exercise


JDBC

• ‘FilteredRowSet’ inherits from ‘WebRowSet’ and provides filtering capabilities for a rowset.

• You view the rows based on a set of criteria which is called a ‘filter’.

• Setting a ‘filter’ to the rowset does not delete rows from the rowset, rather, you only access those rows that satisfy the ‘filter’ criteria.

• You can reset the ‘filter’ to view all rows.• A ‘filter’ is an object of a class that implements the

‘javax.sql.rowset.Predicate’ interface.


JDBC

• ‘JoinRowSet’ inherits from ‘WebRowSet’.• It provides the ability to combine (or join) two or more

disconnected rowsets into one.• You retrieve data in multiple rowsets, using

‘CachedRowSet’, ‘WebRowSet’ or ‘FilteredRowSet’.• Create and empty ‘JoinRowSet’.• Add all rowsets to the ‘JoinRowSet’ by calling its

‘addRowSet()’ method.• You may specify the ‘JOIN’ columns in a rowset when

you add a rowset to the ‘JoinRowSet’.


JDBCcachedRs1 = ... get a CachedRowSet …cachedRs2 = ... get a second CachedRowSet …String sqlCommand1 = "select person_id, first_name from person " + "where person_id in (101, 102)";String sqlCommand2 = "select person_id, last_name from person " + "where person_id in (101, 102)";cachedRs1.setCommand(sqlCommand1);cachedRs2.setCommand(sqlCommand2);cachedRs1.execute();cachedRs2.execute();// Create a JoinRowSet for cachedRs1 and cachedRs2 joinRs = … get a JoinRowSet object …// Add rowsets to the join rowset - join them based on the person_id columnjoinRs.addRowSet(cachedRs1, "person_id");joinRs.addRowSet(cachedRs2, "person_id");


JDBC

• A database transaction consists of one or more changes as a unit of work.

• A ‘savepoint’ in a transaction is like a marker that marks a point in a transaction so that, if needed, the transaction can be undone (rolled back) up to that point.


JDBCConnection conn = … get a Connection object …Statement stmt = conn.createStatement();stmt.execute(“insert into person…”); // insert 1stmt.execute(“insert into person…”); // insert 2stmt.execute(“insert into person…”); // insert 3stmt.execute(“insert into person…”); // insert 4stmt.execute(“insert into person…”); // insert 5• At this point we either commit the transaction, which will

insert all five records in the ‘person’ table:conn.commit();• Or we rollback the transaction so that no inserts will occur.conn.rollback();


JDBC

• A ‘savepoint’ will let you set a marker in between any of the ‘INSERT’ statements.

• To mark a ‘savepoint’, call the ‘setSavepoint()’ method of a ‘Connection’ object.

• The ‘setSavepoint()’ method returns a ‘Savepoint’ object which is your marker, and which you must keep for future use.


JDBCConnection conn = … get a Connection object …Statement stmt = conn.createStatement();stmt.execute(“insert into person…”); // insert 1Savepoint sp1 = conn.setSavepoint();// savepoint 1stmt.execute(“insert into person…”); // insert 2Savepoint sp2 = conn.setSavepoint();// savepoint 2stmt.execute(“insert into person…”); // insert 3Savepoint sp3 = conn.setSavepoint();// savepoint 3stmt.execute(“insert into person…”); // insert 4Savepoint sp4 = conn.setSavepoint();// savepoint 4stmt.execute(“insert into person…”); // insert 5Savepoint sp5 = conn.setSavepoint();// savepoint 5


JDBC

• We can use another version of the ‘rollback()’ method of the ‘Connection’ object, which accepts a ‘Savepoint’ object.

• To undo all the changes which were made after savepoint 4:

conn.rollback(sp4);• To undo all changes made after savepoint 2:

conn.rollback(sp2);


JDBC

• Once you rollback to a particular ‘savepoint’, all savepoints which were created after the given ‘savepoint’ will be released, and you cannot refer to them again.

• You can also release a ‘savepoint’ explicitly by calling the ‘releaseSavepoint(Savepoint sp)’ method of a ‘Connection’ object.

• After a partial rollback, remember to ‘commit()’ the remaining portions of the transaction.


JDBCThe purpose of the DAO pattern is to hide the persistence mechanism of an application from its application logic. In other words, to turn this sequence of calls

application logic --> persistence mechanism

into this

application logic --> DAO's --> persistence mechanism

The advantage of this abstraction is that you can change the persistence mechanism without affecting the application logic. All you need to change is the DAO layer which, if designed properly, is a lot easier to do than changing all the application logic.


JDBC• In OOP, a useful and important design principle is

“separation of concerns.” The DAO design pattern helps you comply with this design principle. If you are not using DAO, then your business logic will be exposed to the concrete implementation details of the persistence mechanisms - an undesirable state of affairs. Use of the DAO design pattern ensures that you separate your core logic from your persistence mechanism.

• If your database environment changes, all you need to change is the DAO layer, which is a lot easier to do than changing all the application logic.


JDBC

//Student.java{…. Fields, getters, setters….}

// StudentDAO.java public interface StudentDAO { public void insertStudent( Student student); public Student findStudent( int id); public void deleteStudent( int id);}


JDBC

// RDBMSDAO.java public class RDBMSDAO implements StudentDAO{ public void insertStudent( Student student){ // insertStudent implementation } public Student findStudent( int id){ // findStudent implementation return Student; } public void deleteStudent( int id) { // deleteStudent implementation }}


JDBC

// Main.java public class Main{ public static void main( String[] args) { Student student = new Student( ... ); StudentDAO studentDAO = new RDBMSDAO(); studentDAO.insertStudent(student); }}


JDBC// OODBMSDAO.java public class OODBMSDAO implements StudentDAO{ public void insertStudent( Student student){ // insertStudent implementation } public Student findStudent( int id){ // findStudent implementation return Student; } public void deleteStudent( int id) { // deleteStudent implementation }}


JDBC

// Main.java public class Main{ public static void main( String[] args) { Student student = new Student( ... ); StudentDAO studentDAO = new OODBMSDAO(); studentDAO.insertStudent(student); }}


JDBC

• The ‘DAO Design Pattern’ fits nicely with the ‘Factory Design Pattern’, and both techniques are often used together.

• Let us first gain an understanding of the ‘Factory Design Pattern’, and then we will examine how to use it in combination with the ‘DAO Design Pattern’.


JDBC

• In real life, factories are manufacturing units that produce multiple instances of a product. For instance, a car factory produces cars. The main responsibility of the car factory is to keep producing cars of the required type and model.

• In the software environment, you can implement a factory that returns the required type of object(s) on demand in OOP. In this case, the factory decides which classes to instantiate.


JDBC

public interface Shape { public void drawTheShape(); public void colorTheShape(); }


JDBCpublic class Circle implements Shape { private int xPos, yPos;private int radius;public Circle( int x, int y, int r) {xPos = x;yPos = y;radius = r;}public void drawTheShape() { implementation here }public void colorTheShape() { implementation here }}


JDBC

public class Rectangle implements Shape {private int length, height;public Rectangle( int l, int h){length = l;height = h;}public void drawTheShape(){ implementation code} public void colorTheShape(){ implementation code } }


JDBC

public class ShapeFactory {public static Shape getShape( String shapeType){switch( shapeType) {case "Circle": return new Circle( 10, 10,20);case "Rectangle": return new Rectangle(10,20);}


JDBC

public class Test {public static void main( String[] args) {String shapeType=“Circle”;Shape shape = ShapeFactory.getShape(shapeType);shape.drawTheShape();shape.colorTheShape();}}


JDBC• You define a ‘Shape’ interface, which defines two public

methods, ‘drawTheShape()’ and ‘colorTheShape()’.• Classes ‘Circle’ and ‘Rectangle’ implement this interface and

provide implementation of interface methods.• The ‘factory’ class ‘ShapeFactory’ has a ‘getShape()’ method

which, based upon the requested type of shape, creates a new instance of the appropriate ‘Shape’ class.

• From the main() method of the ‘Test’ class, you supply a String which indicates which type of ‘Shape’ you want. The main() method then calls the getShape() method of ShapeFactory class. The getShape() method creates and returns a new instance based on the requested type.


JDBC

• We will now look at the combination of the ‘DAO Design Pattern’ with the ‘Factory Design Pattern’.

• Recall that the purpose of the DAO pattern is to hide the persistence mechanism of an application from its application logic.

• The advantage of this abstraction is that you can change the persistence mechanism without affecting the application logic. All you need to change is the DAO layer which, if designed properly, is a lot easier to do than changing all the application logic.


JDBC

//Student.java{…. Fields, getters, setters….}

// StudentDAO.java public interface StudentDAO { public void insertStudent( Student student); public Student findStudent( int id); public void deleteStudent( int id);}


JDBC

// RDBMSDAO.java public class RDBMSDAO implements StudentDAO{ public void insertStudent( Student student){ // insertStudent implementation } public Student findStudent( int id){ // findStudent implementation return Student; } public void deleteStudent( int id) { // deleteStudent implementation }}


JDBC// OODBMSDAO.java public class OODBMSDAO implements StudentDAO{ public void insertStudent( Student student){ // insertStudent implementation } public Student findStudent( int id){ // findStudent implementation return Student; } public void deleteStudent( int id) { // deleteStudent implementation }}


JDBC

• So now we have two ‘StudentDAO’ implementations – RDBMSDAO and OODBMSDAO.

• We will define a ‘Factory’ (using the ‘Factory Design Pattern’), which will have the capability to produce each type of DAO object.


JDBC

public class DAOFactory {public static StudentDAO getStudentDAO(String type){switch( type){case “RDBMS”: return new RDBMSDAO();Case “OODBMS”: return new OODBMSDAO();}}


JDBC

• Now we will use our ‘factory’ to persist an instance of a ‘Student’.

• First we will instantiate a new ‘Student’.• Then we will use our factory to get a

‘StudentDAO’ of type ‘RDBMSDAO’. • Then we will use our ‘StudentDAO’ object to

persist our ‘Student’ object.


JDBC

public class Test {public static void main( String[] args) {Student s1 = new Student(…);StudentDAO DAO = DAOFactory.getStudentDAO("RDBMS");DAO.insertStudent( s1);}}

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Java 7 Certification JDBC & Related Design Pattern

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