Reflection API, JDBC, Hibernate, RMI James Atlas July 22, 2008

Reflection API Examine or modify the runtime behavior Allows programatic access to Java internals Fields Methods Constructors Classes Access by name and argument type java.lang.reflect.* July 22, 2008 James Atlas - CISC370

Reflection API java.lang.Class java.lang.reflect.Constructor annotations modifiers constructors, methods, fields java.lang.reflect.Constructor newInstance(object..) July 22, 2008 James Atlas - CISC370

Reflection API java.lang.reflect.Field java.lang.reflect.Method annotations declaring class modifiers get(object) java.lang.reflect.Method invoke(object..) July 22, 2008 James Atlas - CISC370

JDBC: Java Database Connectivity Database-independent connectivity Connect to database Get information from database Update data in database Classes in java.sql.* package In Java, two steps Establish a connection with a database Execute queries, statements against database July 22, 2008 James Atlas - CISC370

JDBC: Creating a Connection Load the DB driver Classes/library used to connect to the database Specific to the type of database Load the class by name Class.forName("sun.jdbc.odbc.JdbcOdbcDriver”); Create the connection (see API for all ways) String url = ”jdbc:mysql://localhost:3306/masplasDB"; Connection con = DriverManager.getConnection(url, loginname, password); Need to close connection when done con.close() Type of DB Location of DB, port DB name July 22, 2008 James Atlas - CISC370

JDBC: Executing Queries: Statements Statement stmt = con.createStatement(); executeQuery(String query) Returns a ResultSet Iterate through ResultSet, row-by-row, getting results from each column stmt.executeQuery(“SELECT * FROM COFFEES”); executeUpdate(String query) to update table Returns an integer representing the number of affected rows or 0 for SQL statements that don’t execute anything July 22, 2008 James Atlas - CISC370

JDBC: Prepared Statements prepareStatement(String template) Compile SQL statement “templates” Reuse statement, passing in parameters Java handles formatting of Strings, etc. as parameters updateSales = con.prepareStatement( "UPDATE COFFEES SET SALES = ? WHERE COF_NAME LIKE ?"); Set parameters updateSales.setInt(1, 100); updateSales.setString(2, “French Roast”); Parameters July 22, 2008 James Atlas - CISC370

JDBC API Documentation: java.sql.* Limitations Statements, Connections, ResultSets, etc. are all Interfaces Driver/Library implements interfaces for its database Limitations Java doesn’t compile the SQL statements Exact syntax depends on DB Compile, run, verify queries outside of Java for your database Then copy and use in Java code July 22, 2008 James Atlas - CISC370

Hibernate “Hibernate's goal is to relieve the developer from 95 percent of common data persistence related programming tasks, compared to manual coding with SQL and the JDBC API” Object to relational mapping Integrated caching/pooling Transparent persistence Object-oriented query language (HQL) Very common in high-end business Java applications July 22, 2008 James Atlas - CISC370

Hibernate example: Event persistence We want to persist an Event object in a relational database Event has properties: ID (Long) Title (String) Date (Date) JavaBean pattern getProperty setProperty empty constructor July 22, 2008 James Atlas - CISC370

Hibernate example: mapping XML <?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="events.Event" table="EVENTS"> <id name="id" column="EVENT_ID"> <generator class="native"/> </id> <property name="date" type="timestamp" column="EVENT_DATE"/> <property name="title"/> </class> </hibernate-mapping> July 22, 2008 James Atlas - CISC370

Hibernate example: insert/select Session session = getSessionFactory().getCurrentSession(); Event theEvent = new Event(); theEvent.setTitle(title); theEvent.setDate(theDate); session.save(theEvent); select List events = session.createQuery("from Event").list(); for (int i = 0; i < events.size(); i++) { Event theEvent = (Event) events.get(i); System.out.println("Event: " + theEvent.getTitle() + " Time: " + theEvent.getDate()); } July 22, 2008 James Atlas - CISC370

Distributed Programming Two primary ways to communicate Message passing (servlets, web services) Remote method calls an object on one computer calls methods of an object on a different computer method call looks like a method call on a local object Remote Method Invocation (RMI) July 22, 2008 James Atlas - CISC370

Java RMI: Remote Method Invocation Lookup an object by name registry Naming service Client Object location Bind object to a name RMI Server Invoke methods on object “stubs” Appears as calling method on local objects Objects that implement java.rmi.Remote July 22, 2008 James Atlas - CISC370

Why Java RMI? Write distributed programs RMI automates a lot of process Does not require network programming, sockets Load class definitions for objects that are passed around July 22, 2008 James Atlas - CISC370

Example: Compute Engine Compute Engine runs on a high performance machine Clients submit compute intensive tasks and receive results July 22, 2008 James Atlas - CISC370

Example: Compute Engine Server java.rmi.Remote Task Compute +executeTask(Task<T>):T Pi Pi BigDecimal ComputePi ComputeEngine July 22, 2008 James Atlas - CISC370