Exploring EJB3 With JBoss Application Server Part 6.2

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1 By Swaminathan Bhaskar 01/24/2009 Exploring EJB3 With JBoss Application Server Part 6.2 In this part, we will continue to explore Entity Beans Using Java Persistence API (JPA). Thus far, we have seen examples that explored various aspects of persisting a single entity using JPA. In the following paragraphs, we will be looking at the various types of entity relationships, namely, one-to-one, many-to-one, one-to-many, and many-to-many. Let us explore the one-to-one entity relationship. There could be two types of one-to-one relationships Unidirectional or Bidirectional. The relationship between any Customer and their Address is one-toone unidirectional relationship because a business usually looks up the Address given a Customer and not vice versa. The following diagram illustrates the relationship: Before we proceed with the example, we need to setup the two tables in the MySQL database testdb as follows: CREATE TABLE ADDRESS_TBL ( ADDR_ID INTEGER AUTO_INCREMENT, ADDRESS VARCHAR(50) NOT NULL, ZIP VARCHAR(10) NOT NULL, PRIMARY KEY PK_ADDR_ID(ADDR_ID) ); CREATE TABLE CUSTOMER_TBL ( CUST_ID INTEGER AUTO_INCREMENT, NAME VARCHAR(50) NOT NULL, CUST_ADDR_ID INTEGER, PRIMARY KEY PK_CUST_ID(CUST_ID), CONSTRAINT CUST_ADDR_FK FOREIGN KEY (CUST_ADDR_ID) REFERENCES ADDRESS_TBL(ADDR_ID) ); The following code shows the Address Entity Bean: Name: Bhaskar S

2 package custaddr.common; public class Address implements java.io.serializable { private static final long serialversionuid = private int id; private String address; private String zip; public int getid() { return id; public void setid(int id) { this.id = id; public String getaddress() { return address; public void setaddress(string arg) { address = arg; public String getzip() { return zip; public void setzip(string arg) { zip = arg; The Address entity uses auto generated primary key column (ADDR_ID). The following code shows the Customer Entity Bean: Name: Bhaskar S package custaddr.common; public class Customer implements java.io.serializable { private static final long serialversionuid = private int id; private String name;

3 private Address address; public int getid() { return id; public void setid(int id) { this.id = id; public String getname() { return name; public void setname(string n) { name = n; public Address getaddress() { return address; public void setaddress(address arg) { address = arg; The Customer entity is more interesting than the Address entity. The Customer entity uses auto generated primary key column (CUST_ID). annotation indicates that the Customer entity is related to the Address entity via the join column CUST_ADDR_ID. If we look at the table CUSTOMER_TBL we see that the column CUST_ADDR_ID references the column ADDR_ID on the table ADDRESS_TBL as a foreign key. annotation captures this relationship and indicates the join column. annotation indicates the one-to-one relationship between the Customer and the Address entity. The cascade attribute indicates that any data operation performed on the Customer entity also needs to be performed on the related Address entity. We will see the impact of this attribute in a following paragraphs when we look at the CustAddrBean Stateless Session Bean. The following code shows the Remote interface for CustAddr: Name: Bhaskar S package custaddr.remote; import javax.ejb.remote; import public interface CustAddr { public Customer getcustomer(int id); public void addcustomeraddress(string name, String address, String zip);

4 The CustAddr interface allows us to add a new Customer and its related Address or lookup an existing Customer and its related Address. The following shows the code for CustAddrBean stateless session bean: Name: Bhaskar S package custaddr.ejb; import custaddr.common.customer; import custaddr.common.address; import custaddr.remote.custaddr; import javax.ejb.stateless; import javax.persistence.entitymanager; import public class CustAddrBean implements CustAddr private EntityManager public Customer getcustomer(int id) { Customer cust = null; cust = _emgr.find(customer.class, id); if (cust!= null) { System.out.println("-> Customer<Query>: Id = " + cust.getid() + ", Name = " + cust.getname() + ", Address = " + cust.getaddress().getaddress()); return public void addcustomeraddress(string name, String address, String zip) { Address addr = new Address(); addr.setaddress(address); addr.setzip(zip); Customer cust = new Customer(); cust.setname(name); cust.setaddress(addr); // _emgr.persist(addr); // Need this if Customer does not use (cascade={cascadetype.all) _emgr.persist(cust); System.out.println("-> Customer<Insert>: Id = " + cust.getid() + ", Name = " + name); If we do not use the cascade attribute with annotation, then we will have to explicitly persist the Address entity before persisting the Customer entity. See the highlighted comment line. Failing to do so will cause the following exception: Caused by: java.lang.illegalstateexception: org.hibernate.transientobjectexception: object references an unsaved transient instance - save the transient instance before flushing: custaddr.common.customer.address -> custaddr.common.address By using the cascade attribute with annotation, persisting the Customer implicitly persists the related Address entity.

5 The following shows the code for a standalone client that is accessing the CustAddrBean stateless session bean through the remote interface CustAddr: Name: Bhaskar S package custaddr.client; import custaddr.remote.custaddr; import custaddr.common.address; import custaddr.common.customer; import java.io.bufferedreader; import java.io.inputstreamreader; import javax.naming.context; import javax.naming.initialcontext; public class CustAddrClient { public static void main(string[] args) { try { BufferedReader input = new BufferedReader(new InputStreamReader(System.in)); Context ctx = new InitialContext(); CustAddr custaddr = (CustAddr) ctx.lookup("custaddr/remote"); boolean exit = false; while (! exit) { System.out.println("1. Get Customer Information"); System.out.println("2. New Customer Information"); System.out.println("3. Quit"); String choice = input.readline(); if (choice.equals("1")) { System.out.print("Id: "); String idstr = input.readline(); Customer cust = custaddr.getcustomer(integer.parseint(idstr)); if (cust!= null) { Address addr = cust.getaddress(); System.out.println("-> Customer: Name = " + cust.getname() + ", Address = " + addr.getaddress()); else { System.out.println("No Customer information for " + idstr); else if (choice.equals("2")) { System.out.print("Name: "); String name = input.readline(); System.out.print("Address: "); String address = input.readline(); System.out.print("Zip: "); String zip = input.readline(); custaddr.addcustomeraddress(name, address, zip); System.out.println("Persisted Customer information for " + name); else if (choice.equals("3")) { exit = true; catch (Throwable ex) { ex.printstacktrace(system.err);

6 Next, we will compile and deploy the EJB jar my_ejb_beans.jar into the JBoss Application Server. Now, open a Terminal window and execute the script CustAddrClient.sh as illustrated below: $./CustAddrClient.sh 1. Get Customer Information 2. New Customer Information 3. Quit 2 Name: Swaminathan Bhaskar Address: 100 North Pole Zip: Persisted Customer information for Swaminathan Bhaskar 1. Get Customer Information 2. New Customer Information 3. Quit 1 Id: 1 -> Customer: Name = Swaminathan Bhaskar, Address = 100 North Pole 1. Get Customer Information 2. New Customer Information 3. Quit 2 Name: Bill Gates Address: 200 South Pole Zip: Persisted Customer information for Bill Gates 1. Get Customer Information 2. New Customer Information 3. Quit 1 Id: 2 -> Customer: Name = Bill Gates, Address = 200 South Pole 1. Get Customer Information 2. New Customer Information 3. Quit 3 As you see, when we query for a Customer, its related Address entity is also automatically fetched for us. We have successfully deployed and executed the example depicting the unidirectional one-to-one relationship between any Customer and their Address. Let us explore the case of bidirectional one-to-one entity relationship. The relationship between any Driver and their License is one-to-one bidirectional relationship because one can look up the Driver

7 given a License and also vice versa. The following diagram illustrates the relationship: Before we proceed with the example, we need to setup the two tables in the MySQL database testdb as follows: CREATE TABLE LICENSE_TBL ( LIC_ID INTEGER AUTO_INCREMENT, NUMBER VARCHAR(25) NOT NULL, STATE CHAR(2) NOT NULL, PRIMARY KEY PK_LIC_ID(LIC_ID) ); CREATE TABLE DRIVER_TBL ( NAME VARCHAR(50) NOT NULL, AGE INTEGER, DRV_LIC_ID INTEGER, PRIMARY KEY PK_NAME(NAME), CONSTRAINT DRV_LIC_FK FOREIGN KEY (DRV_LIC_ID) REFERENCES LICENSE_TBL(LIC_ID) ); The following code shows the Driver Entity Bean: Name: Bhaskar S package drvlic.common; public class Driver implements java.io.serializable { private static final long serialversionuid = private String name; private private License license; public String getname() { return name;

8 public void setname(string n) { name = n; public License getlicense() { return license; public void setlicense(license arg) { license = arg; public int getage() { return age; public void setage(int age) { this.age = age; annotation indicates that the Driver entity is related to the License entity via the join column DRV_LIC_ID. The following code shows the License Entity Bean: Name: Bhaskar S package drvlic.common; public class License implements java.io.serializable { private static final long serialversionuid = private int id; private String number; private String private Driver driver; public int getid() { return id; public void setid(int id) { this.id = id; public String getnumber() { return number; public void setnumber(string arg) { number = arg;

9 public String getstate() { return state; public void setstate(string arg) { state = arg; public Driver getdriver() { return driver; public void setdriver(driver arg) { driver = arg; The License entity uses auto generated primary key column (ADDR_ID). annotation with the mappedby attribute is what sets the bidirectional relationship with the Driver entity. The mappedby attribute indicates that the one-to-one mapping between Driver and License entities is specified in the Driver entity in the data member named license. The following code shows the Remote interface for DriverLicense: Name: Bhaskar S package drvlic.remote; import javax.ejb.remote; import public interface DriverLicense { public Driver getdriver(string name); public License getlicense(int id); public void adddriverlicense(string name, int age, String number, String state); The DriverLicense interface allows us to add a new Driver and its related License, lookup an existing Driver and its related License, or lookup an existing License and its related Driver (bidirectional relationship). The following shows the code for DriverLicenseBean stateless session bean: Name: Bhaskar S package drvlic.ejb; import drvlic.remote.driverlicense;

10 import drvlic.common.; import javax.ejb.stateless; import javax.persistence.entitymanager; import public class DriverLicenseBean implements DriverLicense private EntityManager public Driver getdriver(string name) { Driver drv = _emgr.find(driver.class, name); if (drv!= null) { System.out.println("-> Driver<Query>: Age = " + drv.getage() + ", License No = " + drv.getlicense().getnumber()); return public License getlicense(int id) { License lic = _emgr.find(license.class, id); if (lic!= null) { System.out.println("-> License<Query>: Age = " + lic.getdriver().getage() + ", License No = " + lic.getnumber()); return public void adddriverlicense(string name, int age, String number, String state) { License lic = new License(); lic.setnumber(number); lic.setstate(state); Driver drv = new Driver(); drv.setname(name); drv.setage(age); drv.setlicense(lic); lic.setdriver(drv); _emgr.persist(drv); System.out.println("-> DriverLicense<Persist>: Age = " + lic.getdriver().getage() + ", License No = " + lic.getnumber()); If we skip the step highlighted in the code, we will encounter a NullPointerException. This step is what completes the bidirectional relationship. The following shows the code for a standalone client that is accessing the DriverLicenseBean stateless session bean through the remote interface DriverLicense: Name: Bhaskar S package drvlic.client; import drvlic.remote.driverlicense; import drvlic.common.; import java.io.bufferedreader; import java.io.inputstreamreader; import javax.naming.context;

11 import javax.naming.initialcontext; public class DriverLicenseClient { public static void main(string[] args) { try { BufferedReader input = new BufferedReader(new InputStreamReader(System.in)); Context ctx = new InitialContext(); DriverLicense drvlic = (DriverLicense) ctx.lookup("driverlicense/remote"); boolean exit = false; while (! exit) { System.out.println("1. Get Driver Information"); System.out.println("2. Get License Information"); System.out.println("3. New Driver-License Information"); System.out.println("4. Quit"); String choice = input.readline(); if (choice.equals("1")) { System.out.print("Name: "); String name = input.readline(); Driver drv = drvlic.getdriver(name); if (drv!= null) { License lic = drv.getlicense(); System.out.println("-> Driver: Age = " + drv.getage() + ", License No = " + lic.getnumber()); else { System.out.println("No Driver information for " + name); else if (choice.equals("2")) { System.out.print("Id: "); String idstr = input.readline(); License lic = drvlic.getlicense(integer.parseint(idstr)); if (lic!= null) { Driver drv = lic.getdriver(); System.out.println("-> License: Age = " + drv.getage() + ", License No = " + lic.getnumber()); else { System.out.println("No License information for " + idstr); else if (choice.equals("3")) { System.out.print("Name: "); String name = input.readline(); System.out.print("Age: "); String agestr = input.readline(); System.out.print("Number: "); String number = input.readline(); System.out.print("State: "); String state = input.readline(); drvlic.adddriverlicense(name, Integer.parseInt(agestr), number, state); System.out.println("Persisted Driver-License information for " + name); else if (choice.equals("4")) { exit = true; catch (Throwable ex) { ex.printstacktrace(system.err); Next, we will compile and deploy the EJB jar my_ejb_beans.jar into the JBoss Application Server.

12 Now, open a Terminal window and execute the script DriverLicense.sh as illustrated below: $./DriverLicense.sh 1. Get Driver Information 2. Get License Information 3. New Driver-License Information 4. Quit 3 Name: Swaminathan Bhaskar Age: 40 Number: State: NJ Persisted Driver-License information for Swaminathan Bhaskar 1. Get Driver Information 2. Get License Information 3. New Driver-License Information 4. Quit 1 Name: Swaminathan Bhaskar -> Driver: Age = 40, License No = Get Driver Information 2. Get License Information 3. New Driver-License Information 4. Quit 2 Id: 1 -> License: Age = 40, License No = Get Driver Information 2. Get License Information 3. New Driver-License Information 4. Quit 4 As you see, when we query for a Driver, its related License entity is also automatically fetched for us. Similarly, when we query for a License, its related Driver entity is also automatically fetched for us. We have successfully deployed and executed the example depicting the bidirectional one-to-one relationship between any Driver and their License. Let us explore the many-to-one entity relationship. There is only Unidirectional many-to-one. The Bidirectional many-to-one is the same as Bidirectional one-to-many. Hence, in the following example we will look at unidirectional many-to-one. The relationship between the Items in an Order is many-to-one unidirectional relationship. Each Item entity knows which Order entity it is associated with, but the Order entity is oblivious of that relationship. The following diagram illustrates the relationship:

13 Before we proceed with the example, we need to setup the two tables in the MySQL database testdb as follows: CREATE TABLE ORDER_TBL ( ORDER_NO INTEGER AUTO_INCREMENT, ORDER_DATE DATE NOT NULL, CUST_NAME VARCHAR(50) NOT NULL, PRIMARY KEY PK_ORDER_NO(ORDER_NO) ); CREATE TABLE ITEM_TBL ( ITEM_NAME VARCHAR(25) NOT NULL, QUANTITY INTEGER, ITEM_ORD_NO INTEGER, PRIMARY KEY PK_NAME(ITEM_NAME), CONSTRAINT ITEM_ORD_FK FOREIGN KEY (ITEM_ORD_NO) REFERENCES ORDER_TBL(ORDER_NO) ); The following code shows the Order Entity Bean: Name: Bhaskar S package itmord.common; import java.util.date; public class Order implements java.io.serializable { private static final long serialversionuid = private int private Date private String name; public int getno() { return no;

14 public void setno(int n) { no = n; public Date getdate() { return date; public void setdate(date d) { date = d; public String getname() { return name; public void setname(string n) { name = n; public String tostring() { StringBuffer sb = new StringBuffer(); sb.append("-> Order no: "); sb.append(no); sb.append(", Order date: "); sb.append(date.tostring()); sb.append(", Customer name: "); sb.append(name); return sb.tostring(); The Order entity uses auto generated primary key column (ORDER_NO). The following code shows the Item Entity Bean: Name: Bhaskar S package itmord.common; public class Item implements java.io.serializable { private static final long serialversionuid private String private private Order order; public String getname() { return name; public void setname(string n) { name = n;

15 public int getqty() { return qty; public void setqty(int q) { qty = q; public Order getorder() { return order; public void setorder(order ord) { order = ord; annotation indicates the many-to-one relationship between the Item and the Order entity. The following code shows the Remote interface for ItemOrder: Name: Bhaskar S package itmord.remote; import java.util.date; import javax.ejb.remote; import public interface ItemOrder { public void addorderwithitems(date dt, String name, String[] item, Integer[] qty); public Order getorderforitem(string name); The ItemOrder interface allows us to add a new Order and its related Items or lookup an existing Order corresponding to an Item. The following shows the code for ItemOrderBean stateless session bean: Name: Bhaskar S package itmord.ejb; import java.util.date; import itmord.common.; import itmord.remote.itemorder; import javax.ejb.stateless; import javax.persistence.entitymanager;

16 import public class ItemOrderBean implements ItemOrder private EntityManager public void addorderwithitems(date dt, String name, String[] item, Integer[] qty) { Order ord = new Order(); ord.setdate(dt); ord.setname(name); _emgr.persist(ord); for (int i = 0; i < item.length; i++) { Item itm = new Item(); itm.setname(item[i]); itm.setqty(qty[i]); itm.setorder(ord); public Order getorderforitem(string name) { Item itm = _emgr.find(item.class, name); if (itm!= null) { return itm.getorder(); return null; The following shows the code for a standalone client that is accessing the ItemOrderBean stateless session bean through the remote interface ItemOrder: Name: Bhaskar S package itmord.client; import java.util.; import itmord.common.; import itmord.remote.itemorder; import java.io.bufferedreader; import java.io.inputstreamreader; import javax.naming.context; import javax.naming.initialcontext; public class ItemOrderClient { public static void main(string[] args) { try { BufferedReader input = new BufferedReader(new InputStreamReader(System.in)); Context ctx = new InitialContext(); ItemOrder stub = (ItemOrder) ctx.lookup("itemorder/remote"); boolean exit = false; while (! exit) { System.out.println("1. Add New Order With Items"); System.out.println("2. Get Order For Item"); System.out.println("3. Quit");

17 String choice = input.readline(); if (choice.equals("1")) { System.out.print("Customer Name: "); String name = input.readline(); List<String> items = new ArrayList<String>(); List<Integer> qtys = new ArrayList<Integer>(); for (;;) { System.out.print("Item Name <Enter to quit>: "); String itm = input.readline(); if (itm!= null && itm.trim().length() > 0) { System.out.print("Quantity: "); String qstr = input.readline(); int qt = Integer.parseInt(qstr); if (qt > 0) { items.add(itm); qtys.add(qt); else { break; if (items.size() > 0) { stub.addorderwithitems(new Date(), name, items.toarray(new String[0]), qtys.toarray(new Integer[0])); System.out.println("-> Persisted new order with items"); items.clear(); qtys.clear(); else if (choice.equals("2")) { System.out.print("Item Name: "); String itm = input.readline(); Order ord = stub.getorderforitem(itm); if (ord!= null) { System.out.println(ord.toString()); else { System.out.println("-> No order found for item " + itm); else if (choice.equals("3")) { exit = true; catch (Throwable ex) { ex.printstacktrace(system.err); Next, we will compile and deploy the EJB jar my_ejb_beans.jar into the JBoss Application Server. Now, open a Terminal window and execute the script ItemOrder.sh as illustrated below: $./ItemOrder.sh 1. Add New Order With Items 2. Get Order For Item 3. Quit 1 Customer Name: Swaminathan Bhaskar Item Name <Enter to quit>: Item-1

18 Quantity: 2 Item Name <Enter to quit>: Item-2 Quantity: 1 Item Name <Enter to quit>: Item-3 Quantity: 2 Item Name <Enter to quit>: -> Persisted new order with items 1. Add New Order With Items 2. Get Order For Item 3. Quit 2 Item Name: Item-2 -> Order no: 1, Order date: :00:00.0, Customer name: Swaminathan Bhaskar 1. Add New Order With Items 2. Get Order For Item 3. Quit 3 We have successfully deployed and executed the example depicting the unidirectional many-to-one relationship between an Order and its Items. We will continue to explore EJB Entity Beans Using Java Persistence in Part-6.3 of this series.

Exploring EJB3 With JBoss Application Server Part 6.3

By Swaminathan Bhaskar 02/07/2009 Exploring EJB3 With JBoss Application Server Part 6.3 In this part, we will continue to explore Entity Beans Using Java Persistence API (JPA). In the previous part, we