JDBC

JDBC and Database Programming in Java:

JDBC and Database Programming in Java

Introduction :

Introduction Database Access in Java Find out any relevant background and interest of the audience SQL gurus? Visual Basic Database Forms?

Agenda:

Agenda Overview of Databases and Java Overview of JDBC JDBC APIs Other Database Techniques

Overview :

Overview TCP/IP java.net RMI JDBC CORBA Network OS

Vocabulary:

Vocabulary Glossary of terms Define the terms as used in this subject

Part I: Overview of Databases and Java:

Part I: Overview of Databases and Java

Databases in the Enterprise:

Databases in the Enterprise All corporate data stored in DB SQL standardizes format (sort of)

Why Java?:

Why Java? Write once, run anywhere Multiple client and server platforms Object-relational mapping databases optimized for searching/indexing objects optimized for engineering/flexibility Network independence Works across Internet Protocol Database independence Java can access any database vendor Ease of administration zero-install client

Database Architectures:

Database Architectures Two-tier Three-tier N-tier

Two-Tier Architecture:

Two-Tier Architecture Client connects directly to server e.g. HTTP, email Pro: simple client-side scripting offloads work onto the client Con: fat client inflexible

Three-Tier Architecture:

Three-Tier Architecture Application Server sits between client and database

Three-Tier Pros:

Three-Tier Pros flexible: can change one part without affecting others can connect to different databases without changing code specialization: presentation / business logic / data management can cache queries can implement proxies and firewalls

Three-Tier Cons:

Three-Tier Cons higher complexity higher maintenance lower network efficiency more parts to configure (and buy)

N-Tier Architecture:

N-Tier Architecture Design your application using as many “tiers” as you need Use Object-Oriented Design techniques Put the various components on whatever host makes sense Java allows N-Tier Architecture, especially with RMI and JDBC

Database Technologies:

Database Technologies Hierarchical obsolete (in a manner of speaking) any specialized file format can be called a hierarchical DB Relational (aka SQL) (RDBMS) row, column most popular Object-relational DB (ORDBMS) add inheritance, blobs to RDB NOT object-oriented -- “object” is mostly a marketing term Object-oriented DB (OODB) data stored as objects high-performance for OO data models

Relational Databases:

Relational Databases invented by Dr. E.F.Codd data stored in records which live in tables maps row (record) to column (field) in a single table “relation” (as in “relational”) means row to column (not table to table)

Joining Tables:

Joining Tables you can associate tables with one another allows data to nest allows arbitrarily complicated data structures not object-oriented

Join example:

Join example People name homeaddress workaddress Addresses id street state zip

SQL:

SQL Structured Query Language Standardized syntax for “querying” (accessing) a relational database Supposedly database-independent Actually, there are important variations from DB to DB

SQL Syntax:

SQL Syntax INSERT INTO table ( field1, field2 ) VALUES ( value1, value2 ) inserts a new record into the named table UPDATE table SET ( field1 = value1, field2 = value2 ) WHERE condition changes an existing record or records DELETE FROM table WHERE condition removes all records that match condition SELECT field1, field2 FROM table WHERE condition retrieves all records that match condition

Transactions:

Transactions 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

Part II: JDBC Overview:

Part II: JDBC Overview

JDBC Goals:

JDBC Goals SQL-Level 100% Pure Java Keep it simple High-performance Leverage existing database technology why reinvent the wheel? Use strong, static typing wherever possible Use multiple methods to express multiple functionality

JDBC Ancestry:

JDBC Ancestry X/OPEN ODBC JDBC

JDBC Architecture:

JDBC Architecture Application JDBC Driver 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

JDBC Drivers:

JDBC Drivers Type I: “Bridge” Type II: “Native” Type III: “Middleware” Type IV: “Pure”

JDBC Drivers (Fig.):

JDBC Drivers (Fig.) JDBC Type I “Bridge” Type II “Native” Type III “Middleware” Type IV “Pure” ODBC ODBC Driver CLI (.lib) Middleware Server

Type I Drivers:

Type I Drivers Use bridging technology Requires installation/configuration on client machines Not good for Web e.g. ODBC Bridge

Type II Drivers:

Type II Drivers Native API drivers Requires installation/configuration on client machines Used to leverage existing CLI libraries Usually not thread-safe Mostly obsolete now e.g. Intersolv Oracle Driver, WebLogic drivers

Type III Drivers:

Type III Drivers Calls middleware server, usually on database host Very flexible -- allows access to multiple databases using one driver Only need to download one driver But it’s another server application to install and maintain e.g. Symantec DBAnywhere

Type IV Drivers:

Type IV Drivers 100% Pure Java -- the Holy Grail Use Java networking libraries to talk directly to database engines Only disadvantage: need to download a new driver for each database engine e.g. Oracle, mSQL

JDBC Limitations:

JDBC Limitations No scrolling cursors No bookmarks

Related Technologies:

Related Technologies ODBC Requires configuration (odbc.ini) RDO, ADO Requires Win32 OODB e.g. ObjectStore from ODI JavaBlend maps objects to tables transparently (more or less)

Part III: JDBC APIs:

Part III: JDBC APIs

java.sql:

java.sql JDBC is implemented via classes in the java.sql package

Loading a Driver Directly:

Loading a Driver Directly Driver d = new foo.bar.MyDriver(); Connection c = d.connect(...); Not recommended, use DriverManager instead Useful if you know you want a particular driver

DriverManager:

DriverManager DriverManager tries all the drivers Uses the first one that works When a driver class is first loaded, it registers itself with the DriverManager Therefore, to register a driver, just load it!

Registering a Driver:

Registering a Driver statically load driver Class.forName(“foo.bar.MyDriver”); Connection c = DriverManager.getConnection(...); or use the jdbc.drivers system property

JDBC Object Classes:

JDBC Object Classes DriverManager Loads, chooses drivers Driver connects to actual database Connection a series of SQL statements to and from the DB Statement a single SQL statement ResultSet the records returned from a Statement

JDBC Class Usage:

JDBC Class Usage DriverManager Driver Connection Statement ResultSet

JDBC URLs:

JDBC URLs jdbc: subprotocol : source each driver has its own subprotocol each subprotocol has its own syntax for the source jdbc:odbc: DataSource e.g. jdbc:odbc:Northwind jdbc:msql:// host[:port]/database e.g. jdbc:msql://foo.nowhere.com:4333/accounting

DriverManager:

DriverManager Connection getConnection (String url, String user, String password) Connects to given JDBC URL with given user name and password Throws java.sql.SQLException returns a Connection object

Connection:

Connection A Connection represents a session with a specific database. Within the context of a Connection, SQL statements are executed and results are returned. Can have multiple connections to a database NB: Some drivers don’t support serialized connections Fortunately, most do (now) Also provides “metadata” -- information about the database, tables, and fields Also methods to deal with transactions

Obtaining a Connection:

Obtaining a Connection String url = "jdbc:odbc:Northwind"; try { Class.forName ("sun.jdbc.odbc.JdbcOdbcDriver"); Connection con = DriverManager.getConnection(url); } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (SQLException e) { e.printStackTrace(); }

Connection Methods:

Connection Methods Statement createStatement() returns a new Statement object PreparedStatement prepareStatement(String sql) returns a new PreparedStatement object CallableStatement prepareCall(String sql) returns a new CallableStatement object Why all these different kinds of statements? Optimization.

Statement:

Statement A Statement object is used for executing a static SQL statement and obtaining the results produced by it.

Statement Methods:

Statement Methods ResultSet executeQuery(String) Execute a SQL statement that returns a single ResultSet. int executeUpdate(String) Execute a SQL INSERT, UPDATE or DELETE statement. Returns the number of rows changed. boolean execute(String) Execute a SQL statement that may return multiple results. Why all these different kinds of queries? Optimization.

ResultSet:

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. you can’t rewind

ResultSet Methods:

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

ResultSet Methods:

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

ResultSet Methods:

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)

ResultSet Methods:

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)

isNull:

isNull 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)

Sample Database:

Sample Database Employee ID Last Name First Name 1 Davolio Nancy 2 Fuller Andrew 3 Leverling Janet 4 Peacock Margaret 5 Buchanan Steven

SELECT Example:

SELECT Example Connection con = DriverManager.getConnection(url, "alex", "8675309"); Statement st = con.createStatement(); ResultSet results = st.executeQuery("SELECT EmployeeID, LastName, FirstName FROM Employees");

SELECT Example (Cont.):

SELECT Example (Cont.) while (results.next()) { int id = results.getInt(1); String last = results.getString(2); String first = results.getString(3); System.out.println("" + id + ": " + first + " " + last); } st.close(); con.close();

Mapping Java Types to SQL Types:

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

Database Time:

Database Time Times in SQL are notoriously unstandard 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

Modifying the Database:

Modifying the Database use executeUpdate if the SQL contains “INSERT” or “UPDATE” Why isn’t it smart enough to parse the SQL? Optimization. executeUpdate returns the number of rows modified executeUpdate also used for “CREATE TABLE” etc. (DDL)

INSERT example:

INSERT example

Transaction Management:

Transaction Management Transactions are not explicitly opened and closed Instead, the connection has a state called AutoCommit mode if AutoCommit is true, then every statement is automatically committed default case: true

setAutoCommit:

setAutoCommit Connection.setAutoCommit(boolean) if AutoCommit is false, then every statement is added to an ongoing transaction you must explicitly commit or rollback the transaction using Connection.commit() and Connection.rollback()

Connection Managers:

Connection Managers Hint: for a large threaded database server, create a Connection Manager object It is responsible for maintaining a certain number of open connections to the database When your applications need a connection, they ask for one from the CM’s pool Why? Because opening and closing connections takes a long time Warning: the CM should always setAutoCommit(false) when a connection is returned

Optimized Statements:

Optimized Statements Prepared Statements SQL calls you make again and again allows driver to optimize (compile) queries created with Connection.prepareStatement() Stored Procedures written in DB-specific language stored inside database accesed with Connection.prepareCall()

JDBC Class Diagram:

JDBC Class Diagram Whoa!

Metadata:

Metadata Connection: DatabaseMetaData getMetaData() ResultSet: ResultSetMetaData getMetaData()

ResultSetMetaData:

ResultSetMetaData What's the number of columns in the ResultSet? What's a column's name? What's a column's SQL type? What's the column's normal max width in chars? What's the suggested column title for use in printouts and displays? What's a column's number of decimal digits? Does a column's case matter? Is the column a cash value? Will a write on the column definitely succeed? Can you put a NULL in this column? Is a column definitely not writable? Can the column be used in a where clause? Is the column a signed number? Is it possible for a write on the column to succeed? and so on...

DatabaseMetaData:

DatabaseMetaData What tables are available? What's our user name as known to the database? Is the database in read-only mode? If table correlation names are supported, are they restricted to be different from the names of the tables? and so on…

JavaBlend: Java to Relational Mapping:

JavaBlend: Java to Relational Mapping

JDBC 2.0:

JDBC 2.0 Scrollable result set Batch updates Advanced data types Blobs, objects, structured types Rowsets Persistent JavaBeans JNDI Connection Pooling Distributed transactions via JTS

Summary:

Summary State what has been learned Define ways to apply training Request feedback of training session

Where to get more information:

Where to get more information Other training sessions Reese, Database Programming with JDBC and Java (O’Reilly) http://java.sun.com/products/jdbc/ http://java.sun.com/products/java-blend/ http://www.purpletech.com/java/ (Author’s site)