Java Database Connectivity(JDBC)

What is JDBC?

Java Database Connectivity (JDBC) is an application programming interface (API) for the programming language Java, which defines how a client may access a database. It is a Java-based data access technology used for Java database connectivity. It is part of the Java Standard Edition platform, from Oracle Corporation. It provides methods to query and update data in a database and is oriented toward relational databases. A JDBC-to-ODBC bridge enables connections to any ODBC-accessible data source in the Java virtual machine (JVM) host environment.

History and implementation

Sun Microsystems released JDBC as part of Java Development Kit (JDK) 1.1 on February 19, 1997. Since then it has been part of the Java Platform, Standard Edition (Java SE).

The JDBC classes are contained in the Java package java.sql and javax.sql.

Starting with version 3.1, JDBC has been developed under the Java Community Process. JSR 54 specifies JDBC 3.0 (included in J2SE 1.4), JSR 114 specifies the JDBC Rowset additions, and JSR 221 is the specification of JDBC 4.0 (included in Java SE 6).[2]

JDBC 4.1, is specified by a maintenance release 1 of JSR 221[3] and is included in Java SE 7.

JDBC 4.2, is specified by a maintenance release 2 of JSR 221[5] and is included in Java SE 8.

The latest version, JDBC 4.3, is specified by a maintenance release 3 of JSR 221 and is included in Java SE 9.

What is a JDBC driver?

The JDBC API defines the Java interfaces and classes that programmers use to connect to databases and send queries. A JDBC driver implements these interfaces and classes for a particular DBMS vendor.

A Java program that uses the JDBC API loads the specified driver for a particular DBMS before it actually connects to a database. The JDBC DriverManager class then sends all JDBC API calls to the loaded driver.

There are four types of JDBC drivers:

• JDBC-ODBC bridge plus ODBC driver, also called Type 1 driver

Translates JDBC API calls into Microsoft ODBC calls that are then passed to the ODBC driver

The ODBC binary code must be loaded on every client computer that uses this type of driver.

ODBC is an acronym for Open Database Connectivity.

• Native-API, partly Java driver, also called Type 2 driver

Converts JDBC API calls into DBMS-specific client API calls

Like the bridge driver, this type of driver requires that some binary code is loaded on each client's computer.

• JDBC-Net, pure-Java driver, also called Type 3 driver

Sends JDBC API calls to a middle-tier server that translates the calls into the DBMS-specific network protocol

The translated calls are then sent to a particular DBMS.

• Native-protocol, pure-Java driver, also called Type 4 driver

Converts JDBC API calls directly into the DBMS-specific network protocol without a middle tier

This driver allows the client applications to connect directly to the database server.

Functionality

JDBC ('Java Database Connectivity) allows multiple implementations to exist and be used by the same application. The API provides a mechanism for dynamically loading the correct Java packages and registering them with the JDBC Driver Manager. The Driver Manager is used as a connection factory for creating JDBC connections.

JDBC connections support creating and executing statements. These may be update statements such as SQL's CREATE, INSERT, UPDATE, and DELETE, or they may be query statements such as SELECT. Additionally, stored procedures may be invoked through a JDBC connection. JDBC represents statements using one of the following classes:

• ?Statement – the statement is sent to the database server each and every time.
• ???PreparedStatement – the statement is cached and then the execution path is pre-determined on the database server allowing it to be executed multiple times in an efficient manner.
• ???CallableStatement – used for executing stored procedures on the database.

Update statements such as INSERT, UPDATE, and DELETE return an update count that indicates how many rows were affected in the database. These statements do not return any other information.

Query statements return a JDBC row result set. The row result set is used to walk over the result set. Individual columns in a row are retrieved either by name or by column number. There may be any number of rows in the result set. The row result set has metadata that describes the names of the columns and their types.

There is an extension to the basic JDBC API in the javax.sql.

JDBC connections are often managed via a connection pool rather than obtained directly from the driver.

Examples

When a Java application needs a database connection, one of the DriverManager.getConnection() methods are used to create a JDBC connection. The URL used is dependent upon the particular database and JDBC driver. It will always begin with the "jdbc:" protocol, but the rest is up to the particular vendor.

Connection conn = DriverManager.getConnection
     "jdbc:somejdbcvendor:other data needed by some jdbc vendor",
     "myLogin",
     "myPassword");
try {
     /* you use the connection here */
} finally {
    //It's important to close the connection when you are done with it
    try { 
        conn.close();
    } catch (Throwable e) { /* Propagate the original exception
                                instead of this one that you want just logged */ 
        logger.warn("Could not close JDBC Connection",e);
    }
}

try (Connection conn = DriverManager.getConnection
     "jdbc:somejdbcvendor:other data needed by some jdbc vendor",
     "myLogin",
     "myPassword")) {
     /* you use the connection here */
}  // the VM will take care of closing the connection        

Once a connection is established, a statement can be created.

try (Statement stmt = conn.createStatement()) 
    stmt.executeUpdate("INSERT INTO MyTable(name) VALUES ('my name')");
}        

Note that Connections, Statements, and ResultSets often tie up operating system resources such as sockets or file descriptors. In the case of Connections to remote database servers, further resources are tied up on the server, e.g., cursors for currently open ResultSets. It is vital to close() any JDBC object as soon as it has played its part; garbage collection should not be relied upon. The above try-with-resources construct is a code pattern that obviates this.

Data is retrieved from the database using a database query mechanism. The example below shows creating a statement and executing a query.

try (Statement stmt = conn.createStatement()
    ResultSet rs = stmt.executeQuery("SELECT * FROM MyTable")
) {
    while (rs.next()) {
        int numColumns = rs.getMetaData().getColumnCount();
        for (int i = 1; i <= numColumns; i++) {
           // Column numbers start at 1.
           // Also there are many methods on the result set to return
           //  the column as a particular type. Refer to the Sun documentation
           //  for the list of valid conversions.
           System.out.println( "COLUMN " + i + " = " + rs.getObject(i));
        }
    }
}        

An example of a PreparedStatement query, using conn and class from the first example.

try (PreparedStatement ps 
    conn.prepareStatement("SELECT i.*, j.* FROM Omega i, Zappa j WHERE i.name =?? AND j.num =??")
) {
    // In the SQL statement being prepared, each question mark is a placeholder
    // that must be replaced with a value you provide through a "set" method invocation.
    // The following two method calls replace the two placeholders; the first is
    // replaced by a string value, and the second by an integer value.
    ps.setString(1, "Poor Yorick");
    ps.setInt(2, 8008);

    // The ResultSet, rs, conveys the result of executing the SQL statement.
    // Each time you call rs.next(), an internal row pointer, or cursor,
    // is advanced to the next row of the result.  The cursor initially is
    // positioned before the first row.
    try (ResultSet rs = ps.executeQuery()) {
        while (rs.next()) {
            int numColumns = rs.getMetaData().getColumnCount();
            for (int i = 1; i <= numColumns; i++) {
                // Column numbers start at 1.
                // Also there are many methods on the result set to return
                // the column as a particular type. Refer to the Sun documentation
                // for the list of valid conversions.
                System.out.println("COLUMN " + i + " = " + rs.getObject(i));
            } // for
        } // while
    } // try
} // try        

If a database operation fails, JDBC raises an SQLException. There is typically very little one can do to recover from such an error, apart from logging it with as much detail as possible. It is recommended that the SQLException be translated into an application domain exception (an unchecked one) that eventually results in a transaction rollback and a notification to the user.

An example of a database transaction:

boolean autoCommitDefault = conn.getAutoCommit();
try {
    conn.setAutoCommit(false);

    /* You execute statements against conn here transactionally */

    conn.commit();
} catch (Throwable e) {
    try { conn.rollback(); } catch (Throwable e) { logger.warn("Could not rollback transaction", e); }
    throw e;
} finally {
    try { conn.setAutoCommit(autoCommitDefault); } catch (Throwable e) { logger.warn("Could not restore AutoCommit setting",e); }
}        

For an example of a CallableStatement (to call stored procedures in the database), see the JDBC API Guide documentation.

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;

public class Mydb1 {
   static String URL = "jdbc:mysql://localhost/mydb";

   public static void main(String[] args) {
      try {
        Class.forName("com.mysql.jdbc.Driver");

        Connection conn = DriverManager.getConnection(URL, "root", "root");
        Statement stmt = conn.createStatement();
      
        String sql = "INSERT INTO emp1 VALUES ('pctb5361', 'kiril', 'john', 968666668)";
        stmt.executeUpdate(sql);
           
        System.out.println("Inserted records into the table...");
      } catch (Exception e) {
        e.printStackTrace();
      }
   }
}