EJB3Struts

EJB 3

The EJB 3 provide an alternative to the CMP Entity Beans to access the database.

Unlike the previous ones, they are synchronized with the database only when decided by the program.

(See description in the WebLang page)

Book: D. Panda, R.Rahman, D Lane, “EJB3 in Action”,

Hamming.

Description in WebLang

ejb3 Country {

      package myPackage;

      relation <hasTowns 1:N isIn> Town;

      String name;

      int number;

      public Country create(String name, int number);

      public Country find(String name) {

            query = "select c from Country c where c.name=?"

      }

}

Use of an EJB3

javax.persistence.EntityManager em = ejb3_utility.Manager.open();

javax.persistence.EntityTransaction tx = em.getTransaction();

tx.begin();

 

    Country c = Country.create("Switzerland", 1291);

    c.setNumber(1291);   // will appear in the DB at the latest at the commit

 

  . . . Other calls to the EJBs in the same transaction . . .

 

tx.commit();     // or tx.rollback();

ejb3_utility.Manager.close();

Use of an EJB3

javax.persistence.EntityManager em = ejb3_utility.Manager.open();

javax.persistence.EntityTransaction tx = em.getTransaction();

tx.begin();

try {

    country = Country.find("Switzerland");

} catch (javax.ejb.FinderException fe) {

country = Country.create("Switzerland");

}

tx.commit();     // or tx.rollback();

ejb3_utility.Manager.close();

Use of an EJB3

javax.persistence.EntityManager em = ejb3_utility.Manager.open();

javax.persistence.EntityTransaction tx = em.getTransaction();

tx.begin();

em.remove(country);

tx.commit();     // or tx.rollback();

ejb3_utility.Manager.close();

EJB3: Expression of relationships in WebLang

indication in Xxxx in Yyyy methods available in Xxxx

<hasY 1:1 hasX> Yyyy no relation

<hasX 1:1 hasY> Xxxx

<hasX 1:1 target hasY>

Xxxx

Yyyy getHasY()

setHasY(yyyy)

(setHasY is made from the forward

relationship name with first letter

capitalized)

<hasY 1:1 target hasX>

Yyyy

no relation

<hasX 1:1 hasY> Xxxx

Yyyy getHasY()

setHasY(yyyy)

<hasY 1:N hasX> Yyyy no relation

<hasX N:1 hasY>

java.util.Collection y = getHasY()

setHasY(collection)

addHasY(yyyy), removeHasY(yyyy)

<hasY N:M hasX>

Yyyy

no relation

<hasX N:M hasY>

Xxxx

java.util.Collection y = getHasY()

setHasY(collection)

addHasY(yyyy), removeHasY(yyyy)

EJB3

Classes generated by WebLang

The files shown on the following slides are generated by the templates defined in the WebLang environment

EJB3: support functions, manager

public class Manager { // ThreadLocal object, always the same

static private EntityManagerFactory emf = null;

private EntityManager em = null;

private static ThreadLocal<Manager> threadManager =

new ThreadLocal<Manager>() {

protected synchronized Manager initialValue() { … }

};

public static EntityManager open() { .. Next slide … }

public static void set(EntityManager em) { … }

public static void close() { … }

}

EJB3: the manager is created by a factory

public static EntityManager open() { // main manager method, always the same

Manager manager = (Manager) threadManager.get();

if (manager.em == null) {

if (Manager.emf == null)

Manager.emf = Persistence.createEntityManagerFactory("TestEJB3");

manager.em = manager.emf.createEntityManager();

manager.em.setFlushMode(FlushModeType.COMMIT);

}

return (manager.em);

}

EJB3: support functions, primary key

// In the EJB class

private long id;

@Id

@GeneratedValue

public long getId() {

return id;

}

public void setId(long id) {

this.id = id;

}

EJB3: support functions, creation

/**

* @generated // used by the merger, if it is called

*/

public static Country create(String name,int number) {

Country entity = new Country();

entity.name = name;

entity.number = number;

javax.persistence.EntityManager em = ejb3_utility.Manager.open();

em.persist(entity);

return (entity);

}

EJB3: support functions, finding them/**

* @generated

*/

public static Country find(String name) throws Exception {

javax.persistence.EntityManager em = ejb3_utility.Manager.open();

Query query = em.createQuery("select c from Country c where c.name=?");

query.setParameter(1,name);

try {

Country result = (Country)query.getSingleResult();

return (result);

} catch (javax.persistence.NoResultException enf) {

throw new javax.ejb.FinderException(enf.getMessage());

} }

EJB3: support functions, relationships

@OneToMany(mappedBy="isIn")

public java.util.Collection<myPackage.Town> getHasTowns() {

return (hasTowns);

}

public void setHasTowns(java.util.Collection<myPackage.Town> hasTowns) {

if (hasTowns!=null) {

hasTowns.size(); // trick to avoid lazy initialisation

}

this.hasTowns = hasTowns;}

public void addHasTowns(myPackage.Town town) {

if (this.hasTowns == null)

this.hasTowns = new java.util.ArrayList<myPackage.Town>();

this.hasTowns.add(town);

town._setIsIn(this); // sets the reverse link

}

EJB3: the EJB is disconnected from the database between two calls

tx.begin();    client = Client.findByName("xxx");tx.commit();

. . . presentation layer (Struts) . . .

tx.begin(); // x is reattached to the transaction     x = em.merge(client);       

  for (Bill b: client.getHasBills() {        x.addHasBills(em.merge(b));    }tx.commit();

EJB3: lazy evaluation

tx.begin();    client = Client.findByName("xxx");    client.getHasBills().size(); // forces the collection to be loaded // prevents the lazy evaluationtx.commit();

// the collection may be handled outside the transaction// provided the lazy evaluation has been thwarted

EJB3: reattaching the beans to the DB

tx.begin();

// reattach x to the transaction     x = em.merge(client);       

// reintroduce the new copy into the session    request.getSession().setAttribute("client", x);  

// attach the member of the collection      for (Bill b: client.getHasBills() {        x.addHasBills(em.merge(b));    }tx.commit();

The EJB3 avoid the need of transferring data from the persistent object to the servlet Java beans

JET: Java Emitter Templates (Eclipse feature)

aaa

bbb ccc ddd

xxx

yyy1 yyy2 vvv zzz

aaa = xxx

bbb = yyy1, yyy2

ccc = vvv

ddd = zzz

JETJava Emitter Templates

Support derived from the JSP compiler to create templates in many different languages

WebLang page : http://ltiwww.epfl.ch/WebLang/Modules.html#modulestdm

JET: Eclipse templates, variable part<%@ jet package="ch.epfl.lti.codegen.weblang.template.java.client.rmi" imports="ch.epfl.lti.codegen.weblang.modules.java.client.rmi.* ch.epfl.lti.codegen.weblang.modules.java.base.*" class="GenRmiInterface“ %>

<% Rmi rmi = (Rmi)_argument[0]; String CLASSNAME = rmi.getNameFU(); %>

/* The interface of RMI method */<% if (rmi.getPackage() != null) {%>package <%=rmi.getPackage().toString() %>;<% }%>import java.rmi.Remote;

public interface <%=CLASSNAME%> extends Remote {<% for (String signature : rmi.getMethodSignature()) {%> public <%=signature%> throws Exception;<% }%>}

JET: Eclipse templates, constant part<%@ jet package="ch.epfl.lti.codegen.weblang.template.java.client.rmi" imports="ch.epfl.lti.codegen.weblang.modules.java.client.rmi.* ch.epfl.lti.codegen.weblang.modules.java.base.*" class="GenRmiInterface" skeleton="../generator.skeleton" %>

<% Rmi rmi = (Rmi)_argument[0]; String CLASSNAME = rmi.getNameFU(); %>

/* The interface of RMI method */<% if (rmi.getPackage() != null) {%>package <%=rmi.getPackage().toString() %>;<% }%>import java.rmi.Remote;

public interface <%=CLASSNAME%> extends Remote {<% for (String signature : rmi.getMethodSignature()) {%> public <%=signature%> throws Exception;<% }%>}

The templates defined in WebLang can easily be modified by the developer

// Handled by a modified template

@templatedir = myEjb3

ejb3 Country extends strutsfsm.StateForm {

package myPackage;

relation <hasTowns 1:N isIn> Town;

String name;

int number;

public Country create(String name, int number);

public Country find(String name) {

query = "select c from Country c where c.name=?"

} }

WebLang templates struts Supplier {

package store;

statemachine {

state state_0 > supply;

switch (sessionState) {

case state_s:

sessionState = state_0;

break;

case state_0: . . . }

@templatedir = zzzz

page supply {

country (Enter) {}

country.hasTowns[] {}

}

}

This page is handled by an updated template

Getting and compiling WebLang templates

Right-click the .cg file containing the @templatedir Get Templates folder _cg_resources with the templates corresponding to the module is created

Right-click the template you have modified Compile CG Template a new project is created to contain the templates (starts with “.” and is thus not always visible)

Use of the modified templates

When you have compiled a template, it will replace the standard one for all subsequent compilations of the .cg file, as long as you keep the @templatedir mark.

If you need extra parameters, you may enter a block like this one

parameters {

xxxx = "aa ss" "bbb" ccc;

mainHtml = "/start/Lotery.jsp";

}

Use of the extra parameters<% LinkedList sList = (LinkedList)_argument[0]; // within the html template // sList is the list of parameters defined in the .cg file

DataTree root = (DataTree)_argument[1]; // root of the tree created by the parser

LinkedList aList = root.getMainInstancesOfClass(html.Html.class); // available in every template for (Object o : aList) { HashMap hm = ((html.Html)o).getParameters(); // one hash map per module // with one key and one linkedList of String // for each line of parameters String name = ((html.Html)o).getName(); // get the name of the module } %>

// html is the package and Html.class is the class. Also exist servlet.Servlet, // struts.Struts// See the WebLang page