Question

Can someone who understands JDBC write me a 15mins length worth of presentation on JDBC.

Answer 1

JDBC Introduction

Java has an API for working with databases, and this technology is known as JDBC. JDBC provides the developer with tools that allow clients to connect to databases, and send commands to the database. These commands are written in the Structured Query Language. However, JDBC can be used with any kind of data base. That is because JDBC abstracts common database functions into a set of common classes and methods.

Database-specific code is contained in a code library, commonly called a driver library. If there is a driver library for a database, you can use the JDBC API to send commands to the database and extract data from the database.

JDBC Product Components

• The JDBC API : The JDBC API provides programmatic access to relational data from the Java programming language. Using the JDBC API, applications can execute SQL statements, retrieve results, and propagate changes back to an underlying data source. The JDBC API can also interact with multiple data sources in a distributed, heterogeneous environment.
• The JDBC 4.0 API is divided into two packages: java.sql and javax.sql. Both packages are included in the Java SE and Java EE platforms.
• JDBC Driver Manager : The JDBC DriverManager class defines objects which can connect Java applications to a JDBC driver. DriverManager has traditionally been the backbone of the JDBC architecture. It is quite small and simple
• JDBC Test Suite : The JDBC driver test suite helps you to determine that JDBC drivers will run your program. These tests are not comprehensive or exhaustive, but they do exercise many of the important features in the JDBC API.
• JDBC-ODBC Bridge — The Java Software bridge provides JDBC access via ODBC drivers. Note that you need to load ODBC binary code onto each client machine that uses this driver. As a result, the ODBC driver is most appropriate on a corporate network where client installations are not a major problem, or for application server code written in Java in a three-tier architecture.

ODBC Vs JDBC

ODBC	JDBC
ODBC is written in C language.	JDBC is written in Java language.
ODBC is platform dependent. It is windows specific technology.	JDBC is platform independent. It runs on all OS.
Loads slow.	Loads fast.
ODBC is not thread safe.	JDBC is thread safe.
ODBC requires manual installation of ODBC driver manager and ODBC drivers.	No need to install JDBC drivers manually.They can be easily integrated in your java code.
Less secured.	Highly secured.

JDBC Architecture

Two-tier and Three-tier Processing Models
The JDBC API supports both two-tier and three-tier processing models for database access.

1: Two-tier Architecture for Data Access.

In the two-tier model, a Java applet or application talks directly to the data source. This requires a JDBC driver that can communicate with the particular data source being accessed. A user's commands are delivered to the database or other data source, and the results of those statements are sent back to the user. The data source may be located on another machine to which the user is connected via a network. This is referred to as a client/server configuration, with the user's machine as the client, and the machine housing the data source as the server. The network can be an intranet, which, for example, connects employees within a corporation, or it can be the Internet.

In the three-tier model, commands are sent to a "middle tier" of services, which then sends the commands to the data source. The data source processes the commands and sends the results back to the middle tier, which then sends them to the user. MIS directors find the three-tier model very attractive because the middle tier makes it possible to maintain control over access and the kinds of updates that can be made to corporate data. Another advantage is that it simplifies the deployment of applications. Finally, in many cases, the three-tier architecture can provide performance advantages.

2: Three-tier Architecture for Data Access.

Java appletor HTML bowser Client תLachine (GUI) HTTP, RML CORBA, or otber calls Application Server Tava) Server machine (business logic) JDBC DBMS-proprietary protocol Database server DBMS

Until recently, the middle tier has often been written in languages such as C or C++, which offer fast performance. However, with the introduction of optimizing compilers that translate Java bytecode into efficient machine-specific code and technologies such as Enterprise JavaBeans, the Java platform is fast becoming the standard platform for middle-tier development. This is a big plus, making it possible to take advantage of Java's robustness, multithreading, and security features.

With enterprises increasingly using the Java programming language for writing server code, the JDBC API is being used more and more in the middle tier of a three-tier architecture. Some of the features that make JDBC a server technology are its support for connection pooling, distributed transactions, and disconnected rowsets. The JDBC API is also what allows access to a data source from a Java middle tier.

Simple Example Code

public void connectToAndQueryDatabase(String username, String password) {

Connection con = DriverManager.getConnection(
"jdbc:myDriver:myDatabase",
username,
password);

Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("SELECT a, b, c FROM Table1");

while (rs.next()) {
int x = rs.getInt("a");
String s = rs.getString("b");
float f = rs.getFloat("c");
}
}

SQL Commands

SQL commands are divided into categories, the two main ones being Data Manipulation Language (DML) commands and Data Definition Language (DDL) commands. DML commands deal with data, either retrieving it or modifying it to keep it up-to-date. DDL commands create or change tables and other database objects such as views and indexes.

A list of the more common DML commands follows:

• SELECT : used to query and display data from a database. The SELECT statement specifies which columns to include in the result set. The vast majority of the SQL commands used in applications are SELECT statements.
• INSERT : adds new rows to a table. INSERT is used to populate a newly created table or to add a new row (or rows) to an already-existing table.
• DELETE : removes a specified row or set of rows from a table
• UPDATE : changes an existing value in a column or group of columns in a table

Result Sets and Cursors

The rows that satisfy the conditions of a query are called the result set. The number of rows returned in a result set can be zero, one, or many. A user can access the data in a result set one row at a time, and a cursor provides the means to do that. A cursor can be thought of as a pointer into a file that contains the rows of the result set, and that pointer has the ability to keep track of which row is currently being accessed. A cursor allows a user to process each row of a result set from top to bottom and consequently may be used for iterative processing. Most DBMSs create a cursor automatically when a result set is generated.

Earlier JDBC API versions added new capabilities for a result set's cursor, allowing it to move both forward and backward and also allowing it to move to a specified row or to a row whose position is relative to another row.

Transactions

A transaction is a set of one or more SQL statements that make up a logical unit of work. A transaction ends with either a commit or a rollback, depending on whether there are any problems with data consistency or data concurrency. The commit statement makes permanent the changes resulting from the SQL statements in the transaction, and the rollback statement undoes all changes resulting from the SQL statements in the transaction.

Stored Procedures

A stored procedure is a group of SQL statements that can be called by name. In other words, it is executable code, a mini-program, that performs a particular task that can be invoked the same way one can call a function or method. Traditionally, stored procedures have been written in a DBMS-specific programming language. The latest generation of database products allows stored procedures to be written using the Java programming language and the JDBC API. Stored procedures written in the Java programming language are bytecode portable between DBMSs. Once a stored procedure is written, it can be used and reused because a DBMS that supports stored procedures will, as its name implies, store it in the database.