Chapter 3.  Describe the JDBC API

3.1.  Identify the Java statements required to connect to a database using JDBC

[Note]

Before you process any SQL statement with JDBC, you need to establish a connection with the data source you want to use. A data source can be a DBMS, a legacy file system, or some other source of data with a corresponding JDBC driver.

Typically, a JDBC application connects to a target data source using one of two classes:

  • DriverManager: This fully implemented class connects an application to a data source, which is specified by a database URL. When this class first attempts to establish a connection, it automatically loads any JDBC 4.0 drivers found within the class path. Note that your application must manually load any JDBC drivers prior to version 4.0:

    // manually load JDBC driver class in JVM (before JDBC 4.0)
    try {
        Class.forName("oracle.jdbc.driver.OracleDriver");
    } catch(ClassNotFoundException e) {
        System.err.println("Error loading driver: " + e);
    }
    								

  • DataSource: This interface is preferred over DriverManager because it allows details about the underlying data source to be transparent to your application. A DataSource object's properties are set so that it represents a particular data source.

Specifying Database Connection URLs

A database connection URL is a string that your DBMS JDBC driver uses to connect to a database. It can contain information such as where to search for the database, the name of the database to connect to, and configuration properties. The exact syntax of a database connection URL is specified by your DBMS.

  • Java DB Database Connection URLs

    The following is the database connection URL syntax for Java DB:

    
    jdbc:derby:[subsubprotocol:][databaseName][;attribute=value]*
    
    								

    subsubprotocol specifies where Java DB should search for the database, either in a directory, in memory, in a class path, or in a JAR file. It is typically omitted.

    databaseName is the name of the database to connect to.

    attribute=value represents an optional, semicolon-separated list of attributes. These attributes enable you to instruct Java DB to perform various tasks (create database, encrypt database, etc.)

    The following database connection URL connects the user mikalai to sample database:

    jdbc:derby:sample;user=mikalai;password=secret111
    								

  • MySQL Connector/J Database URL

    The following is the database connection URL syntax for MySQL Connector/J:

    
    jdbc:mysql://[host][,failoverhost...][:port]/[database][?propertyName1][=propertyValue1][&propertyName2][=propertyValue2]...
    
    								

    host:port is the host name and port number of the computer hosting your database. If not specified, the default values of host and port are 127.0.0.1 and 3306, respectively.

    database is the name of the database to connect to. If not specified, a connection is made with no default database.

    failoverhost is the name of a standby database server (MySQL Connector/J supports failover).

    propertyName=propertyValue represents an optional, ampersand-separated list of properties. These attributes enable you to instruct MySQL Connector/J to perform various tasks.

Using the DriverManager Class

Connecting to your DBMS with the DriverManager class involves calling the method DriverManager.getConnection(...). The following method establishes a database connection:

public Connection getConnection() throws SQLException {
    Connection conn = null;

    Properties connectionProps = new Properties();
    connectionProps.put("user", userName);
    connectionProps.put("password", password);

    if (dbms.equals("mysql")) {
        conn = DriverManager.getConnection("jdbc:mysql://" + serverName + ":" + portNumber + "/" + dbName, connectionProps);
    } else if (dbms.equals("derby")) {
        conn = DriverManager.getConnection("jdbc:derby:" + dbName + ";create=true", connectionProps);
    }
    return conn;
}
					

The method DriverManager.getConnection(...) establishes a database connection. This method requires a database URL, which varies depending on your DBMS. The following are some examples of database URLs:

  • MySQL: jdbc:mysql://localhost:3306/testdb, where localhost is the name of the server hosting your database, 3306 is the port number, and testdb is the name of the database.

  • Java DB: jdbc:derby:testdb;create=true, where testdb is the name of the database to connect to, and create=true instructs the DBMS to create the database.

    NOTE: This URL establishes a database connection with the Java DB Embedded Driver. Java DB also includes a Network Client Driver, which uses a different URL syntax.

This method specifies the user name and password required to access the DBMS with a Properties object.

NOTE: In previous versions of JDBC, to obtain a connection, you first had to initialize your JDBC driver by calling the method Class.forName(...). This method required an object of type java.sql.Driver. Each JDBC driver contains one or more classes that implements the interface java.sql.Driver. See the documentation of your DBMS driver to obtain the name of the class that implements the interface java.sql.Driver. Any JDBC 4.0 drivers that are found in your class path are AUTOMATICALLY loaded. However, you must MANUALLY load any drivers prior to JDBC 4.0 with the method Class.forName(...).

The method above returns a java.sql.Connection object, which represents a connection with the DBMS or a specific database. Query the database through this object.

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