Your SlideShare is downloading. ×
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
ppt
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
882
On Slideshare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
50
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide
  • Lobs and DDL
  • Transcript

    • 1. JDBC – Java Database Connectivity Representation and Management of Data on the Internet
    • 2. Introduction to JDBC
      • JDBC is used for accessing databases from Java applications
      • Information is transferred from relations to objects and vice-versa
        • databases optimized for searching/indexing
        • objects optimized for engineering/flexibility
    • 3. JDBC Architecture Java Application JDBC Oracle DB2 Postgres Oracle Driver DB2 Driver Postgres Driver These are Java classes Network We will use this one…
    • 4. JDBC Architecture (cont.)
      • Java code calls JDBC library
      • JDBC loads a driver
      • Driver talks to a particular database
      • Can have more than one driver -> more than one database
      • Ideal: can change database engines without changing any application code
      Application JDBC Driver
    • 5. Seven Steps
      • Load the driver
      • Define the connection URL
      • Establish the connection
      • Create a Statement object stmt
      • Execute a query using stmt
      • Process the result
      • Close the connection
    • 6. Loading the Driver
      • We can register the Driver indirectly using the Java statement:
      • Class.forName(“oracle.jdbc.driver.OracleDriver");
      • Calling Class.forName causes the Driver class to be loaded
      • When this class is loaded, it automatically
        • creates an instance of itself
        • registers this instance with the DriverManager
    • 7. Another Option
      • Another option is to create an instance of the driver and register it with the Driver Manager:
        • Driver driver = new oracle.jdbc.OracleDriver();
        • DriverManager.registerDriver(driver);
    • 8. An Example
      • // A driver for imaginary1
      • Class.forName( "ORG.img.imgSQL1.imaginary1Driver" );
      • // A driver for imaginary2
      • Driver driver = new ORG.img.imgSQL2.imaginary2Driver();
      • DriverManager.registerDriver(driver);
      • //A driver for oracle
      • Class.forName( "oracle.jdbc.driver.OracleDriver" );     
      imaginary1 imaginary2 Registered Drivers Oracle
    • 9. Connecting to the Database
      • Every database is identified by a URL
      • Given a URL, DriverManager is asked to find the driver that can talk to the corresponding database
      • DriverManager tries all registered drivers, until a suitable one is found
    • 10. Connecting to the Database
      • Connection con = DriverManager.
      • getConnection( "jdbc.imaginaryDB1" );
      imaginary1 imaginary2 Registered Drivers Oracle    acceptsURL( “jdbc.imaginaryDB1” )? Read more in DriverManager API
    • 11. The URLs in CS
          • In CS, a URL has the following structure:
          • jdbc:oracle:thin:name/password@sol4:1521:stud
          • For example:
          • jdbc:oracle:thin:snoopy/snoopy@sol4:1521:stud
        • A complete example
      Your login Also, your login The machine on which our DBMS runs The standard port given to Oracle on sol4
    • 12. Interaction with the Database
      • We use Statement objects in order to
        • Extract data from the database
        • Update the database
      • Three different interfaces are used:
        • Statement , PreparedStatement , CallableStatement
      • All are interfaces, thus cannot be instantiated
      • They are created by the Connection
    • 13. Querying with Statement
      • The executeQuery method returns a ResultSet object representing the query result.
          • Will be discussed later…
      String queryStr = "SELECT * FROM Member " + "WHERE Lower(Name) = 'harry potter'" ; Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery(queryStr);
    • 14. Changing DB with Statement String deleteStr = “ DELETE FROM Member " + "WHERE Lower(Name) = ‘harry potter’" ; Statement stmt = con.createStatement(); int delnum = stmt.executeUpdate(deleteStr);
      • executeUpdate is used for data manipulation: insert, delete, update, create table, etc. (anything other than querying!)
      • executeUpdate returns the number of rows modified
    • 15. About Prepared Statements
      • Prepared Statements are used for queries that are executed many times
      • They are parsed (compiled) by the DBMS only once
      • Column values can be set after compilation
      • Instead of values, use ‘ ? ’
      • Hence, a Prepared Statement is statement that contains placeholders to be substituted later with actual values
    • 16. Querying with PreparedStatement String queryStr = &quot;SELECT * FROM Items &quot; + &quot;WHERE Name = ? and Cost < ? ” ; PreparedStatement pstmt = con.prepareStatement(queryStr); pstmt.setString(1, “t-shirt” ); pstmt.setInt(2, 1000); ResultSet rs = pstmt.executeQuery();
    • 17. Changing DB with PreparedStatement String deleteStr = “ DELETE FROM Items &quot; + &quot;WHERE Name = ? and Cost > ?” ; PreparedStatement pstmt = con.prepareStatement(deleteStr); pstmt.setString(1, “t-shirt” ); pstmt.setInt(2, 1000); int delnum = pstmt.executeUpdate();
    • 18. Statements vs. PreparedStatements: Be Careful!
      • Are these the same? What do they do?
      String val = “abc” ; PreparedStatement pstmt = con.prepareStatement( “select * from R where A=?” ); pstmt.setString(1, val); ResultSet rs = pstmt.executeQuery(); String val = “abc” ; Statement stmt = con.createStatement( ); ResultSet rs = stmt.executeQuery( “select * from R where A=” + val);
    • 19. Statements vs. PreparedStatements: Be Careful!
      • Will this work?
      • No!!! A ‘?’ can only be used to represent a column value
      • WHY?
      PreparedStatement pstmt = con.prepareStatement( “select * from ?” ); pstmt.setString(1, myFavoriteTableString);
    • 20. Timeout
      • Use setQueryTimeOut(int seconds) of Statement to set a timeout for the driver to wait for a statement to be completed
      • If the operation is not completed in the given time, an SQLException is thrown
      • What is it good for?
    • 21. ResultSet
      • A ResultSet provides access to a table of data generated by executing a Statement
      • Only one ResultSet per Statement can be open at once
      • The table rows are retrieved in sequence
        • A ResultSet maintains a cursor pointing to its current row of data
        • The 'next' method moves the cursor to the next row
    • 22. ResultSet Methods
      • boolean next()
        • activates the next row
        • the first call to next() activates the first row
        • returns false if there are no more rows
      • void close()
        • disposes of the ResultSet
        • allows you to re-use the Statement that created it
        • automatically called by most Statement methods
    • 23. ResultSet Methods
      • Type get Type (int columnIndex)
        • returns the given field as the given type
        • fields indexed starting at 1 (not 0)
      • Type get Type (String columnName)
        • same, but uses name of field
        • less efficient
      • int findColumn(String columnName)
        • looks up column index given column name
    • 24. ResultSet Methods
      • String getString(int columnIndex)
      • boolean getBoolean(int columnIndex)
      • byte getByte(int columnIndex)
      • short getShort(int columnIndex)
      • int getInt(int columnIndex)
      • long getLong(int columnIndex)
      • float getFloat(int columnIndex)
      • double getDouble(int columnIndex)
      • Date getDate(int columnIndex)
      • Time getTime(int columnIndex)
      • Timestamp getTimestamp(int columnIndex)
    • 25. ResultSet Methods
      • String getString(String columnName)
      • boolean getBoolean(String columnName)
      • byte getByte(String columnName)
      • short getShort(String columnName)
      • int getInt(String columnName)
      • long getLong(String columnName)
      • float getFloat(String columnName)
      • double getDouble(String columnName)
      • Date getDate(String columnName)
      • Time getTime(String columnName)
      • Timestamp getTimestamp(String columnName)
    • 26. ResultSet Example
      • Statement stmt = con.createStatement();
      • ResultSet rs = stmt.
      • executeQuery( &quot;select name,age from Employees&quot; );    
      • // Print the result
      • while (rs.next()) {  System.out.print(rs.getString(1) +  ”:“ );  System.out.println(rs.getShort( “age” )+ ”“ );
      • }
    • 27. Null Values
      • In SQL, NULL means the field is empty
      • Not the same as 0 or “”
      • In JDBC, you must explicitly ask if a field is null by calling ResultSet.isNull(column)
      • For example, getInt(column) will return 0 if the value is either 0 or null!!
    • 28. Null Values
      • When inserting null values into placeholders of Prepared Statements:
        • Use the method setNull(index, sqlType) for primitive types (e.g. INTEGER, REAL);
        • You may also use the setXXX(index, null ) for object types (e.g. STRING, DATE).
    • 29. ResultSet Meta-Data ResultSetMetaData rsmd = rs.getMetaData(); int numcols = rsmd.getColumnCount(); for (int i = 1 ; i <= numcols; i++) { System.out.print(rsmd.getColumnLabel(i)+ ” “ ); } A ResultSetMetaData is an object that can be used to get information about the properties of the columns in a ResultSet object. An example: write the columns of the result set Many more methods in the ResultSetMetaData API
    • 30. Mapping Java Types to SQL Types
      • SQL type Java Type
      • CHAR, VARCHAR, LONGVARCHAR String
      • NUMERIC, DECIMAL java.math.BigDecimal
      • BIT boolean
      • TINYINT byte
      • SMALLINT short
      • INTEGER int
      • BIGINT long
      • REAL float
      • FLOAT, DOUBLE double
      • BINARY, VARBINARY, LONGVARBINARY byte[]
      • DATE java.sql.Date
      • TIME java.sql.Time
      • TIMESTAMP java.sql.Timestamp
    • 31. More Information A detailed overview of type mapping and type conversion can be found at http://java.sun.com/j2se/1.3/docs/guide/jdbc/getstart/mapping.html
    • 32. Database Time
      • Times in SQL are notoriously non-standard
      • Java defines three classes to help
      • java.sql.Date
        • year, month, day
      • java.sql.Time
        • hours, minutes, seconds
      • java.sql.Timestamp
        • year, month, day, hours, minutes, seconds, nanoseconds
        • usually use this one
    • 33. Cleaning Up After Yourself
      • Remember to close the Connections, Statements, PreparedStatements and ResultSets
      con.close(); stmt.close(); pstmt.close(); rs.close()
    • 34. Dealing With Exceptions
      • An exception can have more exceptions in it.
      catch (SQLException e) { while (e != null) { System.out.println(e.getSQLState()); System.out.println(e.getMessage()); System.out.println(e.getErrorCode()); e = e.getNextException(); } }
    • 35. Advanced Topics
    • 36. LOBs: Large OBjects
      • Two types:
        • CLOB: Character large object (a lot of characters)
        • BLOB: Binary large object (a lot of bytes)
      • Actual data is not stored in the table with the CLOB/BLOB column. Only a pointer to the data is stored there
      • I will show how to use a BLOB; CLOBs are similar
    • 37. Retrieving a BLOB create table userImages( user varchar(50), image BLOB ); ResultSet rs = stmt.executeQuery( “select image from userImages” ); while (rs.next) { Blob b = rs.getBlob( “image” ); InputStream stream = b.getBinaryStream(); doSomething(stream); }
    • 38. Inserting a BLOB PreparedStatement pstmt = con.prepareStatement( “insert into userImages values(‘snoopy’, ?)” ); File file = new File( “snoopy.jpg” ); InputStream fin = new FileInputStream(file); pstmt.setBinaryStream (1, fin, file.length()); pstmt.executeUpdate();
    • 39. Transactions and JDBC
      • Transaction = more than one statement which must all succeed (or all fail) together
      • 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 = abort
    • 40. Example
      • 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?
    • 41. Transaction 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
    • 42. AutoCommit
      • If you set AutoCommit to false, you must explicitly commit or rollback the transaction using Connection.commit() and Connection.rollback()
      • In order to work with LOBs, you usually have to set AutoCommit to false, while retrieving the data
      • Note: DDL statements in a transaction may be ignored or may cause a commit to occur. The behavior is DBMS dependent
      setAutoCommit(boolean val)
    • 43. Fixed Example con.setAutoCommit(false); try { 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(); con.commit(); catch (Exception e) { con.rollback(); }
    • 44. Isolation Levels
      • How do different transactions interact? Do they see what another has written?
      • Possible problems:
        • Dirty Reads: a transaction may read uncommitted data
        • Unrepeatable Reads: two different results are seen when reading a tuple twice in the same transaction
        • Phantom Reads: tuples are added to a table between two readings of this table in a single transaction
    • 45. Isolation Levels JDBC defines four isolation modes : Yes No No Repeatable Read No No No Serializable Yes Yes No Read Commited Yes Yes Yes Read Uncommited Phantom Read Unrepeatable Read Dirty Read Level
    • 46. Isolation Levels
      • Set the transaction mode using setTransactionIsolation() of class Connection
      • Oracle only implements:
        • TRANSACTION_SERIALIZABLE
          • An exception may be thrown if serializability isn’t possible
        • TRANSACTION_READ_COMMITED
          • This is the default
    • 47. Level: READ_COMMITED
      • Transaction 1:
      • insert into A values(1)
      • insert into A values(2)
      • commit
      • Transaction 2:
      • select * from A
      • select * from A
      Table: A 1 2 Question: Is it possible for a transaction to see 1 in A, but not 2? Question: Is it possible for the 2 queries to give different answers for level SERIALIZABLE?

    ×