Java Database Connectivity

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 and , as well as a few other classes elsewhere. Everything involved in JDBC is exported through module java.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). JDBC 4.1, is specified by a maintenance release 1 of JSR 221 and is included in Java SE 7. JDBC 4.2, is specified by a maintenance release 2 of JSR 221 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. ==Functionality==

Since JDBC is mostly a collection of interface definitions and specifications, it allows multiple implementations of these interfaces to exist and be used by the same application at runtime. The API provides a mechanism for dynamically loading the correct Java packages and registering them with the JDBC Driver Manager (). is used as a factory for creating JDBC connections. JDBC connections support creating and executing statements. JDBC connections support update statements such as SQL's Create (SQL)|, Insert (SQL)|, Update (SQL)| and Delete (SQL)|, or query statements such as Select (SQL)|. Additionally, stored procedures may be invoked through a JDBC connection. JDBC represents statements using one of the following classes: • – the is sent to the database server each and every time. In other words, the methods are executed using SQL statements to obtain a object containing the data. • – is a subinterface of the interface. 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. is used to execute pre-compiled SQL statements. Running pre-compiled statements increases statement execution efficiency and performance. The is often used for dynamic statement where some input parameters must be passed into the target database. The allows the dynamic query to vary depending on the query parameter. • – is a subinterface of the interface. It is used for executing stored procedures on the database. Both input and output parameters must be passed into the database for stored procedures. Update statements such as INSERT, UPDATE and DELETE return an update count indicating the number of rows affected in the database as an integer. 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 . 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 is used to create a JDBC . 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. import java.sql.Connection; import java.sql.DriverManager; Connection conn = DriverManager.getConnection( "jdbc:somejdbcvendor:other data needed by some jdbc vendor", "myLogin", "myPassword" ); try { // use the connection here } finally { try { // close the connection after we are done conn.close(); } catch (Throwable e) { // propagate the original exception, not the one caught here logger.warn("Could not close JDBC Connection", e); } } Starting from Java SE 7, one can use Java's try-with-resources statement to simplify the above code: import java.sql.Connection; import java.sql.DriverManager; try (Connection conn = DriverManager.getConnection( "jdbc:somejdbcvendor:other data needed by some jdbc vendor", "myLogin", "myPassword")) { // use the connection here } // conn.close() automatically called // the connection will automatically close after leaving the try block Once a connection is established, a can be created. import java.sql.Statement; try (Statement stmt = conn.createStatement()) { stmt.executeUpdate("INSERT INTO MyTable(name) VALUES ('my name')"); } Note that s, s, and s often tie up operating system resources such as sockets or file descriptors. In the case of s to remote database servers, further resources are tied up on the server, e.g. cursors for currently open s. 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. import java.sql.ResultSet; import java.sql.Statement; 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 The following code is an example of a PreparedStatement query which uses conn and class from the first example: import java.sql.PreparedStatement; import java.sql.ResultSet; 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()) { for (int i = 1; i If a database operation fails, JDBC raises an . 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 be translated into an application domain exception (an unchecked one) that eventually results in a transaction rollback and a notification to the user. The following code is an example of a database transaction: import java.sql.SQLException; boolean autoCommitDefault = conn.getAutoCommit(); try { conn.setAutoCommit(false); // Execute statements on conn here transactionally conn.commit(); } catch (SQLException 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 documentation. package org.wikipedia.examples; import java.sql.Connection; import java.sql.DriverManager; import java.sql.Statement; public class DatabaseExample { private static final String DB_URL = "jdbc:mysql://localhost/mydb"; public static void main(String[] args) { try { Class.forName("com.mysql.jdbc.Driver"); Connection conn = DriverManager.getConnection(DB_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 (SQLException e) { System.err.printf("A SQL error occurred: %s%n", e.getMessage()); } catch (Exception e) { System.err.println("An unknown error occurred."); e.printStackTrace(); } } } ==JDBC drivers==

JDBC drivers are client-side adapters (installed on the client machine, not on the server) that convert requests from Java programs to a protocol that the DBMS can understand. Types Commercial and free drivers provide connectivity to most relational-database servers. These drivers fall into one of the following types: • Type 1 that calls native code of the locally available ODBC driver. (Note: In JDBC 4.2, JDBC-ODBC bridge has been removed) • Type 2 that calls database vendor native library on a client side. This code then talks to database over the network. • Type 3, the pure-java driver that talks with the server-side middleware that then talks to the database. • Type 4, the pure-java driver that uses database native protocol. Note also a type called an internal JDBC driver - a driver embedded with JRE in Java-enabled SQL databases. It is used for Java stored procedures. This does not fit into the classification scheme above, although it would likely resemble either a type 2 or type 4 driver (depending on whether the database itself is implemented in Java or not). An example of this is the KPRB (Kernel Program Bundled) driver supplied with Oracle RDBMS. "jdbc:default:connection" offers a relatively standard way of making such a connection (at least the Oracle database and Apache Derby support it). However, in the case of an internal JDBC driver, the JDBC client actually runs as part of the database being accessed, and so can access data directly rather than through network protocols. Sources • Oracle provides a list of some JDBC drivers and vendors • Simba Technologies ships an SDK for building custom JDBC Drivers for any custom/proprietary relational data source • CData Software ships type 4 JDBC Drivers for various applications, databases, and Web APIs. • DataDirect Technologies provides a comprehensive suite of fast Type 4 JDBC drivers for all major database they advertise as Type 5 • IDS Software provides a Type 3 JDBC driver for concurrent access to all major databases. Supported features include resultset caching, SSL encryption, custom data source, dbShield • JDBaccess is a Java persistence library for MySQL and Oracle which defines major database access operations in an easy usable API above JDBC • JNetDirect provides a suite of fully Sun J2EE certified high-performance JDBC drivers. • JDBCR4 is a service program written by Scott Klement to allow access to JDBC from RPG on the IBM i. • HSQLDB is a RDBMS with a JDBC driver and is available under a BSD license. • SchemaCrawler is an open source API that leverages JDBC, and makes database metadata available as plain old Java objects (POJOs) ==See also==