Programming with Java

Transcription

1 Programming with Java Introduction to JDBC Instructor: Daniel J. Hood Northrop Grumman Corporation 1

2 Overview What is JDBC? JDBC Architecture JDBC API JDBC Drivers A JDBC Example Loading the Driver Opening/Closing a Connection Creating/Closing a Statement Getting a ResultSet Object-Relational Mapping Tools

3 What is JDBC Stands for Java DataBase Connectivity API consisting of Java classes, interfaces, exceptions and a specification which driver vendors adhere to java.sql javax.sql JDBC is Sun's attempt to create a platform neutral interface between various databases and the Java language Isolates program from database details For the most part you will use Interfaces defined in java.sql and javax.sql, and the vendor specified JDBC driver will provide classes which implement those interfaces So, if you are programming to an interface it should be trivial to change the underlying driver without breaking anything. 3

4 4 JDBC Architecture

5 JDBC API DriverManager Loads JDBC driver into JVM Used to obtain connections to a DataSource Connection Represents a connection with a DataSource Used to create Statement, PreparedStatement and CallableStatement objects. Statement Represents a static SQL statement. Can be used to retrieve ResultSet objects. PreparedStatement Higher performance alternative to Statement object, represents a precompiled SQL statement. 5

6 JDBC API (continued) CallableStatement Represents a stored procedure. Can be used to execute stored procedures in a RDBMS which supports them. ResultSet Represents a database result set generated by using a SELECT SQL statement. SQLException An exception class which encapsulates database base access errors. DataSource Abstracts a data source. This object can be used in place of DriverManager to efficiently obtain data source connections 6

7 JDBC Drivers Type 1 JDBC-ODBC bridge drivers Sits atop preexisting ODBC setup Type 2 Native-API partly Java drivers Uses native API as basis (wrapped via JNI) Type 3 Net-protocol All-Java drivers 100% Java Connect to another machine which talks to the DB in some fashion Type 4 Native-protocol All-Java drivers 100% Java Best solution when available 7

8 Obtaining a Driver for Your Database Each vendor must provide a JDBC driver to talk to their database Typically the JDBC driver is distributed as a jarfile that needs to be added to the classpath Various vendors JDBC Drivers MySQL Oracle dbc/ PostgreSQL Sybase R=Y&show=1265 MS Access JDBC-ODBC Driver

9 Loading the Driver The driver we are using will need to be registered with the JDBC DriverManager Typically done via loading the class directly Class.forName( com.oracle.jdbc.oracledriver ); This method may throw a ClassNotFoundException, so we must wrap it in a try/catch block try { Class.forName("com.mysql.jdbc.Driver"); catch (ClassNotFoundException e) { System.err.println("Failed to load the JDBC driver"); 9

10 JDBC URLs JDBC drivers use a JDBC URL to identify and connect to a given database Typically specify Driver name Machine to connect to Database name Username (typically optional) Password (typically optional) General format like so: jdbc:driver:databasename 10

11 Connecting to the Database To connect to the database we need to get a connection off of the DriverManager Connection conn = DriverManager.getConnection("url", "user", "password"); We should also take some care to close the connection when we are done with it to free up resources 11

12 Connecting to the Database (continued) Connection connection = null; try { Class.forName("com.mysql.jdbc.Driver"); connection = DriverManager.getConnection( "jdbc:mysql:// :3306/test","username","password"); catch (SQLException e) { e.printstacktrace(); catch (ClassNotFoundException e) { System.err.println("Failed to load the JDBC driver"); finally { if (connection!= null) { try { connection.close(); catch (SQLException e) { System.err.println("Failed to close the connection."); 12

13 Creating a Statement The next thing that we need to do is to create a SQL Statement to issue to the database There are 3 different types of statements that are supported Statement A basic SQL statement PreparedStatement A precompiled SQL statement CallableStatement Access to stored procedures Just like a connection, we should close the statement when we are done with it 13

14 Creating a Statement (continued) Connection connection = null; Statement statement = null; try { Class.forName("com.mysql.jdbc.Driver"); connection = DriverManager.getConnection( "jdbc:mysql:// :3306/test","username","password"); statement = connection.createstatement(); catch (SQLException e) { e.printstacktrace(); catch (ClassNotFoundException e) { System.err.println("Failed to load the JDBC driver"); // continued on next slide

15 Creating a Statement (continued) // continued from previous slide finally { if (statement!= null) { try { statement.close(); catch (SQLException e) { System.err.println("Failed to close the statement."); if (connection!= null) { try { connection.close(); catch (SQLException e) { System.err.println("Failed to close the connection.");

16 Obtaining a ResultSet We can get a ResultSet back which represents the results of our query A ResultSet is returned from executing a query statement.executequery("select * from people"); You can think of a result set as an iterator over a collection of results that you can walk through next() returns a boolean if there is more data and advances to the next item in the collection There are a lot of methods to get data out of the results set in the following format gettype(int colnum) gettype(string colname) i.e. String name = rs.getstring( first ); 16

17 Obtaining a ResultSet (continued) Connection connection = null; Statement statement = null; try { Class.forName("com.mysql.jdbc.Driver"); connection = DriverManager.getConnection( "jdbc:mysql:// :3306/test","username","password"); statement = connection.createstatement(); ResultSet results = statement.executequery("select * from people"); while (results!= null && results.next()) { System.out.println(results.getString("first") + " " + results.getstring("last") ); catch (SQLException e) { e.printstacktrace(); catch (ClassNotFoundException e) { System.err.println("Failed to load the JDBC driver"); // continued on next slide

18 Obtaining a ResultSet (continued) // continued from previous slide finally { if (statement!= null) { try { statement.close(); catch (SQLException e) { System.err.println("Failed to close the statement."); if (connection!= null) { try { connection.close(); catch (SQLException e) { System.err.println("Failed to close the connection.");

19 Execution For the following database table mysql> select * from people; first last John Doe Jane Smith rows in set (0.00 sec) Our code produces John Smith Jane Doe

20 Object-Relational Mapping Tools In recent years there has been a lot of work to reduce the complexity of manually writing the SQL code to map Java objects to a table in the database Tools like Hibernate ( provide a framework for persisting Plain Old Java Objects (POJOs) to a relational database Typically all you need to configure is the following: Where the database is and who to connect as What JDBC driver to use Which Java objects map to which tables Which members map to which columns This way you can write simple Java Bean classes and hand them off to a framework such as hibernate to persist them to the database The framework manages all SQL no SQL in your code 20