Using Spring and Hibernate

8/3/2019 Using Spring and Hibernate

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Using Spring and Hibernate

Dave Elliman


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The overall architecture


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The enterprise view (Java)


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Revision - What is

Dependency Injection?

DI is all about wiring up objects or

plumbing if you prefer

It is about ensuring loose coupling and fitswell with design patterns

Design to an interface and then inject the

actual class at run time This is what inheritence is really for


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A Real World Example?

Web App

Stock Quotes Authenticator

Error Handler Logger Database

This example was originally created by Jim Weirich in Ruby on his blog.


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Remember the old way

public class WebApp{public WebApp(){

quotes = new StockQuotes();authenticator = new Authenticator();database = new Database();logger = new Logger();

errorHandler = new ErrorHandler();}

// More code here...

}


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What about the child

objects?

How does the StockQuotes find the Logger? How does the Authenticator find the

database?

Suppose you want to use a TestingLoggerinstead? Or a MockDatabase?


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Service Locator Interface

public interface ILocator

{

TObject Get();}


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Service Locator Example

public class MyLocator : ILocator{

protected Dictionary dict =new Dictionary();

public MyLocator(){dict.Add(typeof(ILogger), new Logger());dict.Add(typeof(IErrorHandler),

new ErrorHandler(this));dict.Add(typeof(IQuotes), new StockQuotes(this));

dict.Add(typeof(IDatabase), new Database(this));dict.Add(typeof(IAuthenticator),

new Authenticator(this));dict.Add(typeof(WebApp), new WebApp(this));

}

}


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StockQuotes with Locator

public class StockQuotes{public StockQuotes(ILocator locator)

{errorHandler =

locator.Get();logger = locator.Get();

}

// More code here...}


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Good things

Classes are decoupled from explicit

imlementation types Easy to externalise the configuration


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Dependency Injection

Containers

Gets rid of the dependency on the

ILocator

Object is no longer responsible for finding

its dependencies

The container does it for you


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Then what?

Write your objects the way you want Setup the container

Ask the container for objects

The container creates objects for you and

fulfills dependencies


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Setting Up the Container

(XML)


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Creating Objects

[Test]public void WebAppTest(){DIContainer container = GetContainer();

IStockQuotes quotes =container.Get();IAuthenticator auth =

container.Get();

Assert.IsNotNull( quotes.Logger );Assert.IsNotNull( auth.Logger );Assert.AreSame( quotes.Logger, auth.Logger );

}


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Existing Frameworks

Java Pico Container

Spring Framework

HiveMind

Ruby

Rico Copland

Python PyContainer

.NET Pico.NET

Spring.NET p&p Object Builder


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Spring with Persistence Layers


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Spring can act as the

Application


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A persistent POJO for Hibernate

package elc; public class Tutor { private String id; /// unique identifier private String surname; private String firstname; private Tutor(); /// default constructor public Tutor(String id, String surname, String firstname) { this.id = id; this.surname = surname; this.firstname = firstname); } public String getId() {return id; } public String getSurname() {return surname; }

public String getFirstname() {return firstname; } public void setId(String id) { this.id = id; } public void setSurname(String surname) { this.surname = surname; } public void setLogin(String firstname) { this.firstname = firstname; } }


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The Hibernate Session

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.cfg.Configuration;

... some code

Session = getSessionFactory().openSession();

Transaction tx = session.beginTransaction();

Tutor dave=new Tutor("dge","Elliman","Dave");

session.save(dave); tx.commit();

session.close();

... more code


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hibernate.cfg.xml

com.mysql.jdbc.Driver

jdbc:mysql://localhost/hibernatetutorial

root

10

true

org.hibernate.dialect.MySQLDialectupdate


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A I f d l


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An Intereface and a class to

define

public interface TutorDao {public void createTutor(final Tutor tutor);

public Tutor getTutor(final String id);

}

Also saveTutor(); deleteTutor() etc.

CRUD is now done with single lines of code. No

SQL needed


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Do you get the CONCEPTS?

You can look up the detail when you needit

ELC exam will test the concepts and not

the detail of xml configuration files of Javacode

You need to know that a configuration file

is needed and what it does, not the finedetail of its formatting


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Any Questions?

Im confused


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JEE and EJBs

Dave Elliman


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POJOs and POJIs

Plain Old Java Objects and Interfaces In the past EJBs were all rather different

and special and you could not test them

outside a container Now they are POJ you can


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Annotations

There has been a revolution in Server-sideJava and Tiger Jane 1.5: EJB

annotations

These are processed by a newtool called apt

You can write your own if you like


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The Concept

Entity bean

corresponds to a setof records in a

database

Session bean

handles business flow

(one per client unless

stateless, when may

be shared)


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Enterprise JavaBeans

Definition from OReillys EnterpriseJavaBeans bookAn Enterprise Java Bean is a standard server-

side component model Aha! Its a standard for building

MIDDLEWARE In multi-tiered solutions

The Context in Which EJBs


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The Context in Which EJBs

Are Used

EJB container

EJBeanEJB Object

clientEJB server

..

JT

S

JN

DI

secu

rity

EJB Home


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It All Works by RMI

Client

SkeletonStub Server-

Side

Compo

nent

Client-Side Network Middle Tier

invokes

return

results

connect to

remoteobject invoke

return

resultsreturn

results


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A Taxonomy of EJBs

EJB

Entity Session

Bean managed Container managed stateless stateful

Differences Between


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Differences Between

Beans

Entity Beans Represent persistent data

Long-livedSession Beans

Interact with clients

Model business Logic

Short-lived

Enterprise JavaBeans Container

Session Bean Entity Bean

Clients RDBMS


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Session Bean (Stateful)

Assigned to 1 client only Keeps info about a client

ie has attributes for clients state

Assigned to a client for lifetime

Non-persistent

Short-lived (client, timeout, server crash)


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Session Bean (Stateless)

Many clients can access it

Implements business logic

One bean can service multiple clients (fastand efficient)

Lifetime controlled by container

No state across methods

Each instance identical upon creation

Short-lived


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Insight Into Session Beans

EJB Server

Client Using

stateless

Session Beans

Clients Using

only Entity Beans


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Entity EJBs

Bean managed persistence (BMP) developer writes JDBC code and SQL

statements

Container managed persistence (CMP) Container generates methods to read and

write to the database dropped!

Takes necessary information from theDeployment Descriptor


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EJB Architecture Diagram

Client

Home

InterfaceHome

Stub

Remote

InterfaceEJB

Stub

EJB Server

EJB Container

Home Interface

EJBHome

Remote Interface

EJB Object

Bean Class


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A Stateless Session Bean

import javax.ejb.*;

/*** A stateless session bean requesting that a* remote busines interface be generated for it.*/@Stateless

@Remotepublic class HelloWorldBean {public String sayHello() {

return "Hello World!!!";}

}


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A Stateful Session Bean

import javax.ejb.*;

@Stateful

public class ShoppingCartBean implements ShoppingCart {

private String customer;

public void startToShop(String customer) {this.customer = customer;}

public void addToCart(Item item) {

System.out.println("Added item to cart... ");

}

@Remove

public void finishShopping() {

System.out.println("Shopping Done... ");

}}


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A Entity Java Bean

import javax.ejb.*;

@Entity

public class Order {

private Long id;

private int version;

private int itemId;

private int quantity;

private Customer cust;

@Id(generate=AUTO)

public Long getId() { return id; }

public void setId(Long id) { this.id = id; }

@Version

protected int getVersion() { return version; }

protected void setVersion(int version) { this.version = version; }

@Basic

public int getItemId() { return itemId; }

public void setItemId(int itemId) { this.itemId = itemId; }

@Basic

public int getQuantity() { return quantity; }public void setQuantity(int quantity) {

this.quantity = quantity;

}

@ManyToOne

public Customer getCustomer() { return cust; }

public setCustomer(Customer cust) { this.cust = cust; }

}


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Using Spring and Hibernate