Java Database Connectivity

JDBC, referred to as Java Database Connectivity, is a Java-based data access technology from Sun Microsystems, Inc. It is an API for the Java programming language that describes how a client can access a database. It provides mechanism for updating and querying data in a database. JDBC is oriented for relational databases. A JDBC-ODBC bridge allows connections to any ODBC-accessible data source in the JVM host environment.

The JDBC classes are comprised in the Java package java.sql and javax.sql. JDBC permits multiple implementations to be used by the same application. The API renders a method for dynamically importing the correct Java packages and registers them with the JDBC Driver Manager. The Driver Manager is utilized as a connection factory for creating JDBC connections.

JDBC connections support creation and execution of statements. These can be update statements such as SQL's, INSERT, CREATE, DELETE and UPDATE or they can be query statements for example, SELECT. In addition, stored procedures may be called down through a JDBC connection. JDBC interprets statements using one of the following classes:

Statement:

The statement is sent to the database server every time.

1.    PreparedStatement
It is  cached and the execution path is pre determined on the database server allow it to be executed multiple times efficiently.

2.    CallableStatement
they are employed for executing stored procedures on the database.

For example, in Update statements: UPDATE, DELETE and INSERT return an update count that shows number of rows were involved in the database. These statements do not give any other information.

Whereas Query statements returns a JDBC row result set. The row result set is utilized to move over the result set. Separate columns in a row are retrieved either by column number or name. There can be n number of rows in the result set. The row result set has metadata that shows the names of the columns and their types.

There is an extension to the primary JDBC API in the javax.sql.  JDBC connections are often handled through a connection pool rather than received directly from the driver.

SQL Language

SQL is referred as Structured Query Language. It is a programming language designed for managing data in relational database management systems known as RDBMS.

In an original manner, based upon relational algebra and tuple relational calculus. its scope includes query, delete, update,   data insert,  modification, schema creation and data access control.

SQL is often described as a declarative language, which includes procedural elements. SQL became a standard of the American National Standards Institute (ANSI) in 1986 and of the International Organization for Standards in 1987.

The SQL language is categorized into several language elements which are as following:

Clauses: They are constituent elements of statements and queries.

Expressions: They can produce either scalar values or tables comprising of columns and rows of data.

Predicates: They specify conditions that can be measured to SQL three-valued logic or Boolean truth values, which are then used to confine the effects of statements and queries or change the flow of program.

Queries: They retrieve the data based on specific standards. They are the most important element of SQL.

Statements: They may have a lasting effect on schemata and data or may control program flow, diagnostics, connections, transactions or sessions.

SQL statements also consider the semicolon (";") statement terminator. Though it is not required on every platform, it is described as a standard part of the SQL grammar.

JDBC drivers

JDBC drivers are client-side adapters that are installed on the client machine (not on the server). They convert requests from Java programs to a protocol that the DBMS can interpret.  There are free and commercial drivers available for most relational database servers. The drivers are categorized as following:

Type 1: It calls native code of the locally available ODBC driver.

Type 2: It calls database vendor native library on a client side. This code then communicates to database over network.

Type 3: The pure-java driver communicates with the server-side middleware that then communicates to database.

Type 4: The pure-java driver that utilizes database native protocol.

There is a driver embedded with JRE in Java-enabled SQL databases known as internal JDBC driver, used for Java stored procedure. The Java Database Connectivity API is the industry standard for database-independent connectivity between the Java programming language and a wide set of databases. It allows a call-level API for SQL-based database access.

JDBC technology permits user to use the Java programming language to exploit "Write Once, Run Anywhere" potentialities for applications that need access to enterprise data. With a JDBC technology enabled driver, user can connect all corporate data even in a heterogeneous environment.

Design Patterns

Design patterns lie in the domain of interconnections and modules. At a higher level there are architectural designs that are bigger in scope, usually define an overall pattern followed by an entire system. There are numerous design patterns, such as:

Algorithm scheme patterns dealing concerns related to high-level strategies defining how to use application features on a computing platform.

Computational design patterns dealing concerns in relation to identification of key computation.

Execution patterns that deal with concerns related to supporting application execution, including strategies in executing streams of building blocks to support task synchronization.

Implementation strategy patterns that deal with concerns related to enforcing source code to support

Program organization and the usual+ data structures particular to parallel programming.

Structural design patterns that deal with concerns related to high-level structures of applications being designed.

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