Архитектура java database connectivity

JDBC Architecture

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

Figure 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.

Figure 2: Three-tier Architecture for Data Access.

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.

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JDBC Architecture

Java Database Connectivity (JDBC) is an API (Application Program Interface) or platform-independent interface which helps to connect java programs with various databases such as Oracle, My SQL, MS Access and SQL Server. It provides ways to query and update the database using Structured Query Language (SQL) update statements such as CREATE, DELETE, INSERT and UPDATE and query statements like SELECT. It is almost similar to ODBC (Open Database Connectivity) that was provided by Microsoft.

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To connect the java program or application with the database there are five steps to be followed:

1. Load the Driver: Driver helps to make a connection to the database hence driver must be loaded once in the program. This can be done by two methods:

• Class.forName(): By using this, the driver’s class file is loaded in the memory during run time. There is no need to create a new object. For example:

Class.forName("oracle.jdbc.driver.OracleDriver");

• DriverManager.registerDriver(): Here DriverManager is an inbuilt Java class where the register is its static member. By using this, the constructor of the driver class is called during compile time. In this new object is created. For example:

DriverManager.registerDriver(new oracle.jdbd.driver.OracleDriver());

2. Creating Connections: After the driver is loaded, the connection is set up. The connection object uses username, password, and URL to set up the connection. URL has a predefined format which contains database name, the driver used, IP address where the database is stored, Port number and the service provider. The connection can be set up by using the command:

Connection con = DriverManager.getConnection(URL, user, password);

3. Creating Statement: After establishing the connection, the user can interact with the database. The interfaces such as JDBC statement, PreparedStatement, CallableStatement provides methods that allow a user to send SQL statements and get data from the database. Command used to create statement is;

Statement stmt = con.createStatement();

4. Executing Query: The SQL query is executed to interact with the database. A query can be for updating/inserting in the database or for retrieving data. Statement interface provides two methods i.e. executeQuery() method to execute queries for retrieving data while executeUpdate() method to execute queries for updating or inserting. For Example:

int n = stmt.executeUpdate("DELETE TABLENAME"); if(n==1) System.out.println("Success"); else System.out.println("Failed");

5. Closing Connection: After executing our query, the data user wanted to update or retrieve has been done so now it’s time to close the established connection. The connection interface provides a method close() to close the connection. For example:

JDBC Architecture

JDBC supports two types of processing models for accessing database i.e. two-tier and three-tier.

1. Two-tier Architecture

This architecture helps java program or application to directly communicate with the database. It needs a JDBC driver to communicate with a specific database. Query or request is sent by the user to the database and results are received back by the user. The database may be present on the same machine or any remote machine connected via a network. This approach is called client-server architecture or configuration.

2. Three-tier Architecture

In this, there is no direct communication. Requests are sent to the middle tier i.e. HTML browser sends a request to java application which is then further sent to the database. Database processes the request and sends the result back to the middle tier which then communicates with the user. It increases the performance and simplifies the application deployment.

Components of JDBC Architecture

The components are explained below.

• Driver Manager: It is a class that contains a list of all drivers. When a connection request is received, it matches the request with the appropriate database driver using a protocol called communication sub-protocol. The driver that matches is used to establish a connection.
• Driver: It is an interface which controls the communication with the database server. DriverManager objects are used to perform communication.
• Connection: It is an interface which contains methods to contact a database.
• Statement: This interface creates an object to submit SQL queries or statements to the database.
• ResultSet: This contains the results retrieved after the execution of the SQL statements or queries.
• SQLException: Any errors that occur in database application are handled by this class.

Basic JDBC architectural diagram is shown below with the positioning of all components:

Interfaces

The java.sql package consists of many interfaces. Some popular interfaces are mentioned below:

• Driver Interface: This interface allows for multiple database drivers. DriverManager objects are created to communicate with the database. These objects are created by DriverManager.registerDriver();
• Connection Interface: Connection interface establishes the connection i.e. session between java program and the database. It has many methods like rollback(), close() etc.
• Statement Interface: This interface provides methods for the execution of the SQL queries. It provides factory methods to get a ResultSet object. Some methods of statement interface are executeQuery(), executeUpdate() etc.
• PreparedStatement Interface: This interface helps when the SQL queries need to implement many times. It accepts input parameters during runtime.
• CallableStatement Interface: This interface is used when stored procedures are to be accessed. It also accepts parameters during run time.
• ResultSet Interface: This interface helps to store the result returned after the execution of the SQL queries.

Types of JDBC drivers

There are four types of JDBC drivers:

1. Type-1 Driver or JDBC-ODBC Bridge

This driver acts as a bridge between JDBC and ODBC. It converts JDBC calls into ODBC calls and then sends the request to ODBC driver. It is easy to use but execution time is slow.

2. Type-2 Driver or Native API Partly Java Driver

This driver uses JNI (Java Native Interface) call on database specific native client API. It is comparatively faster than Type-1 driver but it requires native library and cost of application also increases.

3. Type-3 Driver or Network Protocol Driver

These drivers communicate to JDBC middleware server using proprietary network protocol. This middleware translates the network protocol to database specific calls. They are database independent. They can switch from one database to another but are slow due to many network calls.

4. Type-4 or Thin Driver

This driver is also called pure Java driver because they directly interact with the database. It neither requires any native library nor middleware server. It has better performance than other drivers but comparatively slow due to an increase in a number of network calls.

Conclusion

This article specifies the JDBC architecture, its interfaces and types of drivers to communicate or interact with the database.

Now a day’s databases are maintained in every sector hence updating them and retrieving data from them is necessary. So understanding the architecture would help to understand the basic JDBC concepts.

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