EJB嵌入對象

EJB 3.0中提供了選項嵌入到實體bean的Java POJO（普通Java對象）和嵌入式POJO類的方法允許列名映射。嵌入一個java的POJO必須定義了@ Embeddable註解。

@Embeddable public class Publisher implements Serializable{ private String name; private String address; ... }

上面的類可以使用@ Embedded批註嵌入

@Entity public class Book implements Serializable{ private int id; private String name; private Publisher publisher; ... @Embedded @AttributeOverrides({ @AttributeOverride(name = "name", column = @Column(name = "PUBLISHER")), @AttributeOverride(name = "address", column = @Column(name = "PUBLISHER_ADDRESS")) }) public Publisher getPublisher() { return publisher; } ... }

示例應用程序

讓我們創建一個測試EJB應用程序來測試EJB 3.0中的嵌入對象。

Step

描述

1

Create a project with a name EjbComponent under a package com.tutorialspoint.entity as explained in the EJB - Create Application chapter. Please use the project created in EJB - Persistence chapter as such for this chapter to understand embedded objects in ejb concepts.

2

Create Publisher.java under package com.tutorialspoint.entity as explained in the EJB - Create Application chapter. Keep rest of the files unchanged.

3

Create Book.java under package com.tutorialspoint.entity. Use EJB - Persistence chapter as reference. Keep rest of the files unchanged.

4

Clean and Build the application to make sure business logic is working as per the requirements.

5

Finally, deploy the application in the form of jar file on JBoss Application Server. JBoss Application server will get started automatically if it is not started yet.

6

Now create the ejb client, a console based application in the same way as explained in theEJB - Create Application chapter under topic Create Client to access EJB.

Create/Alter book table

CREATE TABLE book ( id integer PRIMARY KEY, name varchar(50) ); Alter table book add publisher varchar(100); Alter table book add publisher_address varchar(200);

EJBComponent (EJB Module)

Publisher.java

package com.tutorialspoint.entity; import java.io.Serializable; import javax.persistence.Embeddable; @Embeddable public class Publisher implements Serializable{ private String name; private String address; public Publisher(){} public Publisher(String name, String address){ this.name = name; this.address = address; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public String toString(){ return name + "," + address; } }

Book.java

package com.tutorialspoint.entity; import com.tutorialspoint.callback.BookCallbackListener; import java.io.Serializable; import javax.persistence.AttributeOverride; import javax.persistence.AttributeOverrides; import javax.persistence.Column; import javax.persistence.Embedded; import javax.persistence.Entity; import javax.persistence.EntityListeners; import javax.persistence.GeneratedValue; import javax.persistence.GenerationType; import javax.persistence.Id; import javax.persistence.Table; @Entity @Table(name="book") public class Book implements Serializable{ private int id; private String name; private Publisher publisher; public Book(){ } @Id @GeneratedValue(strategy= GenerationType.IDENTITY) @Column(name="id") public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Embedded @AttributeOverrides({ @AttributeOverride(name = "name", column = @Column(name = "PUBLISHER")), @AttributeOverride(name = "address", column = @Column(name = "PUBLISHER_ADDRESS")) }) public Publisher getPublisher() { return publisher; } public void setPublisher(Publisher publisher) { this.publisher = publisher; } }

LibraryPersistentBeanRemote.java

package com.tutorialspoint.stateless; import com.tutorialspoint.entity.Book; import java.util.List; import javax.ejb.Remote; @Remote public interface LibraryPersistentBeanRemote { void addBook(Book bookName); List<Book> getBooks(); }

LibraryPersistentBean.java

package com.tutorialspoint.stateless; import com.tutorialspoint.entity.Book; import java.util.List; import javax.ejb.Stateless; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; @Stateless public class LibraryPersistentBean implements LibraryPersistentBeanRemote { public LibraryPersistentBean(){ } @PersistenceContext(unitName="EjbComponentPU") private EntityManager entityManager; public void addBook(Book book) { entityManager.persist(book); } public List<Book> getBooks() { return entityManager.createQuery("From Book").getResultList(); } }

• 一旦你部署EjbComponent項目在Jboss應用服務器 ，發現jboss的日誌。

• JBoss已經自動爲我們的會話bean創建一個JNDI入口 - LibraryPersistentBean/remote.

• 我們將使用這個查詢字符串來獲得遠程類型的業務對象 -com.tutorialspoint.interceptor.LibraryPersistentBeanRemote

JBoss應用服務器的日誌輸出

...
16:30:01,401 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:
LibraryPersistentBean/remote - EJB3.x Default Remote Business Interface
LibraryPersistentBean/remote-com.tutorialspoint.interceptor.LibraryPersistentBeanRemote - EJB3.x Remote Business Interface
16:30:02,723 INFO [SessionSpecContainer] Starting jboss.j2ee:jar=EjbComponent.jar,name=LibraryPersistentBean,service=EJB3
16:30:02,723 INFO [EJBContainer] STARTED EJB: com.tutorialspoint.interceptor.LibraryPersistentBeanRemote ejbName: LibraryPersistentBean
16:30:02,731 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:

LibraryPersistentBean/remote - EJB3.x Default Remote Business Interface
LibraryPersistentBean/remote-com.tutorialspoint.interceptor.LibraryPersistentBeanRemote - EJB3.x Remote Business Interface
...

EJBTester (EJB Client)

jndi.properties

java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces
java.naming.provider.url=localhost

• 這些屬性是用來初始化InitialContext對象的Java命名服務

• InitialContext的對象將被用於查找無狀態會話bean

EJBTester.java

package com.tutorialspoint.test; import com.tutorialspoint.stateful.LibraryBeanRemote; import java.io.BufferedReader; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStreamReader; import java.util.List; import java.util.Properties; import javax.naming.InitialContext; import javax.naming.NamingException; public class EJBTester { BufferedReader brConsoleReader = null; Properties props; InitialContext ctx; { props = new Properties(); try { props.load(new FileInputStream("jndi.properties")); } catch (IOException ex) { ex.printStackTrace(); } try { ctx = new InitialContext(props); } catch (NamingException ex) { ex.printStackTrace(); } brConsoleReader = new BufferedReader(new InputStreamReader(System.in)); } public static void main(String[] args) { EJBTester ejbTester = new EJBTester(); ejbTester.testEmbeddedObjects(); } private void showGUI(){ System.out.println("**********************"); System.out.println("Welcome to Book Store"); System.out.println("**********************"); System.out.print("Options

1. Add Book
2. Exit
   Enter Choice: "); } private void testEmbeddedObjects(){ try { int choice = 1; LibraryPersistentBeanRemote libraryBean = (LibraryPersistentBeanRemote) ctx.lookup("LibraryPersistentBean/remote"); while (choice != 2) { String bookName; String publisherName; String publisherAddress; showGUI(); String strChoice = brConsoleReader.readLine(); choice = Integer.parseInt(strChoice); if (choice == 1) { System.out.print("Enter book name: "); bookName = brConsoleReader.readLine(); System.out.print("Enter publisher name: "); publisherName = brConsoleReader.readLine(); System.out.print("Enter publisher address: "); publisherAddress = brConsoleReader.readLine(); Book book = new Book(); book.setName(bookName); book.setPublisher (new Publisher(publisherName,publisherAddress)); libraryBean.addBook(book); } else if (choice == 2) { break; } } List<Book> booksList = libraryBean.getBooks(); System.out.println("Book(s) entered so far: " + booksList.size()); int i = 0; for (Book book:booksList) { System.out.println((i+1)+". " + book.getName()); System.out.println("Publication: "+book.getPublisher()); i++; } } catch (Exception e) { System.out.println(e.getMessage()); e.printStackTrace(); }finally { try { if(brConsoleReader !=null){ brConsoleReader.close(); } } catch (IOException ex) { System.out.println(ex.getMessage()); } } } }

EJBTester做以下任務。

• jndi.properties中加載和初始化的InitialContext對象。

• In testInterceptedEjb() method, jndi lookup is done with name - "LibraryPersistenceBean/remote" to obtain the remote business object (stateless ejb).

• Then user is shown a library store User Interface and he/she is asked to enter choice.

• If user enters 1, system asks for book name and saves the book using stateless session bean addBook() method. Session Bean is storing the book in database.

• If user enters 2, system retrives books using stateless session bean getBooks() method and exits.

運行客戶端訪問EJB

在項目資源管理器中找到EJBTester.java。右鍵點擊上EJBTester類，並選擇 run file.

在Netbeans控制檯驗證以下輸出。

run:
**********************
Welcome to Book Store
**********************
Options

1. Add Book
2. Exit
   Enter Choice: 1
   Enter book name: learn html5
   Enter publisher name: SAMS
   Enter publisher address: DELHI
   **********************
   Welcome to Book Store
   **********************
   Options
3. Add Book
4. Exit
   Enter Choice: 2
   Book(s) entered so far: 1
5. learn html5
   Publication: SAMS,DELHI
   BUILD SUCCESSFUL (total time: 21 seconds)