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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. Hibernate example: mapping XML
<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"
<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

13. 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

14. 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

15. 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

16. 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

17. 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

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