Презентация 7. Java databases and JDBC 2. JDBC Database Access JDBC онлайн

Содержание слайда: 7. Databases and JDBC 2. JDBC Database Access

Содержание слайда: JDBC Basics The JDBC API is a Java API that can access any kind of tabular data, especially data stored in a Relational Database JDBC Product Components The JDBC API  JDBC Driver Manager  JDBC Test Suite  JDBC-ODBC Bridge 

Содержание слайда: Eclipse & Derby Projects Eclipse: New -> Java Project Fill project name and click next Click “Add External JARs” button in the libraries tab Find derby.jar (usually in Program Files \ Java\jdk1.7.0_xx\db\lib folder) and click Open button Click Finish button

Содержание слайда: Processing SQL Statements with JDBC Establishing a connection Create a statement Execute the query Process the ResultSet object Close the connection

Содержание слайда: Basic Example I package app; import java.sql.*; public class E721JDBCBasics { public static void main(String[] args) { try{ // jdbc statements body (see next slide) } catch(SQLException ex){ System.out.println("Error " + ex.getMessage()); } } }

Содержание слайда: Basic Example II Connection con = DriverManager.getConnection ("jdbc:derby:C:\\VMO\\Курсы\\Projects\\CM"); Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery( "SELECT name, charge FROM merchant"); while (rs.next()){ String nm = rs.getString("name"); double p = rs.getDouble(2); System.out.println(nm + " " + p); } con.close(); See 721JDBCBasics project for the full text

Содержание слайда: Processing SQL Statements with JDBC Establishing a connection Create a statement Execute the query Process the ResultSet object Close the connection

Содержание слайда: Establishing a connection. A JDBC application connects to a target data source using one of two classes: DriverManager - connects an application to a data source, specified by a database URL DataSource - allows details about the underlying data source to be transparent to your application

Содержание слайда: Connection example public static Connection getConnection() throws IOException, SQLException{ Connection conn = null; Properties props = new Properties(); InputStreamReader in = new InputStreamReader(new FileInputStream("appProperties.txt"), "UTF-8"); props.load(in); in.close(); String connString = props.getProperty("DBConnectionString"); conn = DriverManager.getConnection(connString); return conn; } See 722JDBCConnection project for the full text

Содержание слайда: Processing SQL Statements with JDBC Establishing a connection Create a statement Execute the query Process the ResultSet object Close the connection

Содержание слайда: Creating Statements Kinds of statements: Statement - simple SQL statements with no parameters PreparedStatement (extends Statement) - precompiling SQL statements that might contain input parameters CallableStatement (extends PreparedStatement) - used to execute stored procedures that may contain both input and output parameters

Содержание слайда: Insert New Customer Example I Connection con = getConnection(); String sql = "INSERT INTO customer (name, address, "; sql += " email, ccNo, ccType, maturity) values("; sql += " 'Clar Nelis', 'Vosselaar st. 19, Trnaut, Belgium', "; sql += " 'Clar@adw.com', '11345694671231', "; sql += " 'MasterCard', '2014-07-31') "; Statement stmt = con.createStatement(); stmt.executeUpdate(sql); con.close(); See 723SimpleInsert project for the full text

Содержание слайда: Prepared Statements Usually reduces execution time (the DBMS can just run the PreparedStatement SQL statement without having to compile it first) Used most often for SQL statements that take parameters. You can use the same statement and supply it with different values each time you execute it

Содержание слайда: Insert New Customer Example II public void addCustomer(String name, String address, String email, String ccNo, String ccType, java.sql.Date dt) throws SQLException, IOException{ Connection con = getConnection(); String sql = "INSERT INTO customer (name, address, "; sql += " email, ccNo, ccType, maturity) values(?,?,?,?,?,?) "; PreparedStatement stmt = con.prepareStatement(sql); stmt.setString(1, name); stmt.setString(2, address); stmt.setString(3, email); stmt.setString(4, ccNo); stmt.setString(5, ccType); stmt.setDate(6, dt); stmt.executeUpdate(); con.close(); } See 724PreparedInsert project for the full text

Содержание слайда: SQL Date From GregorianCalendar: GregorianCalendar c = new GregorianCalendar(2012, 03, 31); java.util.Date dt = c.getTime(); java.sql.Date dt1 = new java.sql.Date(dt.getTime()); From LocalDate: LocalDate dt1 = LocalDate.of(2015, 2, 15); Instant instant = dt1.atStartOfDay(ZoneId.systemDefault()).toInstant(); java.sql.Date dt = new java.sql.Date(java.util.Date.from(instant).getTime());

Содержание слайда: Processing SQL Statements with JDBC Establishing a connection Create a statement Execute the query Process the ResultSet object Close the connection

Содержание слайда: Executing Queries executeQuery: Returns one ResultSet object executeUpdate: Returns an integer representing the number of rows affected by the SQL statement execute: Returns true if the first object that the query returns is a ResultSet object

Содержание слайда: Exercise: Get Merchant’s Total Show total for a merchant which id is given in the first command string parameter.

Содержание слайда: Exercise: Get Merchant’s Total See 725Query project for the full text.

Содержание слайда: Processing SQL Statements with JDBC Establishing a connection Create a statement Execute the query Process the ResultSet object Close the connection

Содержание слайда: Processing ResultSet Objects You access the data in a ResultSet object through a cursor Note that this cursor is not a database cursor This cursor is a pointer that points to one row of data in the ResultSet object Initially, the cursor is positioned before the first row You call various methods defined in the ResultSet object to move the cursor

Содержание слайда: Exercise: List of Merchants Create an application to display list of merchants: Create a Merchant class with fields necessary for saving merchant’s data and getStringForPrint method for displaying these data Create getMerchants method for filling list of merchants from a corresponding data table Process this list of merchants to display it on the system console

Содержание слайда: Exercise: List of Merchants See 726MerchList project for the full text.

Содержание слайда: Processing SQL Statements with JDBC Establishing a connection Create a statement Execute the query Process the ResultSet object Close the connection

Содержание слайда: Closing Connections Call the method Statement.close to immediately release the resources it is using. When you call this method, its ResultSet objects are closed finally { if (stmt != null) { stmt.close(); } }

Содержание слайда: Closing Connections in Java 7 Use a try-with-resources statement to automatically close Connection, Statement, and ResultSet objects try (Statement stmt = con.createStatement()) { // ... }

Содержание слайда: Three-tired application

Содержание слайда: Handling SQLExceptions The SQLException contains the following information A description of the error - getMessage() A SQLState standard code – getSQLState() An error code (DB specific) – getErrorCode() A cause (Throwable objects that caused the SQLException instance to be thrown) – getCause() A reference to any chained exceptions – getNextException()

Содержание слайда: Data Tier Separation of concerns principle: business and presentation tiers should not know anything about database structure SQLexceptions should be processed within data tier

Содержание слайда: Exercise: Add Payment Create a method to add new payment info to the database

Содержание слайда: Exercise: Add Payment See 727AddPayment project for the full text.

Содержание слайда: Transactions These statements should take effect only together: // Insert new record into PAYMENT table // Update corresponding record in MERCHANT table The way to be sure that either both actions occur or neither action occurs is to use a transaction

Содержание слайда: Using Transactions public static void addPayment(Connection conn, java.util.Date dt, int customerId, int merchantId, String goods, double total) throws SQLException{ conn.setAutoCommit(false); double charge = getCharge(conn, merchantId); if (charge < 0.0) return; // Insert new record into PAYMENT table // Update corresponding record in MERCHANT table conn.commit(); }

Содержание слайда: Rollback Method Calling the method rollback terminates a transaction and returns any values that were modified to their previous values. If you are trying to execute one or more statements in a transaction and get a SQLException, call the method rollback to end the transaction and start the transaction all over again.

Содержание слайда: Exercise: Get Income Report Create a report about CM system’s income got from each merchant.

Содержание слайда: Exercise: Get Income Report See 728MerchantCharge project for the full text.

Содержание слайда: Object-Relational Mapping SQL DBMS can only store and manipulate scalar values such as integers and strings organized within tables Data management tasks in object-oriented programming are typically implemented by manipulating objects that are almost always non-scalar values The problem is translating the logical representation of the objects into an atomized form that is capable of being stored on the database

Содержание слайда: ORM Advantages&Disadvantages Advantage: often reduces the amount of code that needs to be written Disadvantage: performance problem

Содержание слайда: Some Java ORM Systems Hibernate, open source ORM framework, widely used MyBatis, formerly named iBATIS, has .NET port Cayenne, Apache, open source for Java Athena Framework, open source Java ORM Carbonado, open source framework, backed by Berkeley DB or JDBC EclipseLink, Eclipse persistence platform TopLink by Oracle QuickDB ORM, open source ORM framework (GNU LGPL)

Содержание слайда: Manuals http://docs.oracle.com/javase/tutorial/jdbc/index.html