EJB有狀態Bean

有狀態會話Bean是一種企業bean保存客戶端的會話狀態類型。有狀態會話bean作爲每它的名字相關的客戶端狀態保持在它的實例變量。 EJB容器創建一個單獨的有狀態會話bean來處理客戶端的每個請求。只要請求範圍過，有狀態會話bean被銷燬。

以下是創建一個有狀態的EJB所需的步驟：

Create a remote/local interface exposing the business methods.
This interface will be used by the ejb client application.
Use @Local annotation if ejb client is in same environment where ejb session bean is to be deployed.
Use @Remote annotation if ejb client is in different environment where ejb session bean is to be deployed.
Create a stateful session bean implementing the above interface.
Use @Stateful annotation to signify it a stateful bean. EJB Container automatically creates the relevant configurations or interfaces required by reading this annotation during deployment.

遠程接口

import javax.ejb.Remote; @Remote public interface LibraryStatefulSessionBeanRemote { //add business method declarations }

Stateful EJB

@Stateful public class LibraryStatefulSessionBean implements LibraryStatefulSessionBeanRemote { //implement business method }

示例應用程序

讓我們創建一個測試測試狀態EJB的EJB應用程序。

Step

描述

Create a project with a name EjbComponent under a package com.tutorialspoint.stateful as explained in the EJB - Create Application chapter. You can also use the project created in EJB - Create Application chapter as such for this chapter to understand stateful ejb concepts.

Create LibraryStatefulSessionBean.java and LibraryStatefulSessionBeanRemote as explained in the EJB - Create Application chapter. Keep rest of the files unchanged.

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

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.

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.

EJBComponent (EJB Module)

LibraryStatefulSessionBeanRemote.java

package com.tutorialspoint.stateful; import java.util.List; import javax.ejb.Remote; @Remote public interface LibraryStatefulSessionBeanRemote { void addBook(String bookName); List getBooks(); }

LibraryStatefulSessionBean.java

package com.tutorialspoint.stateful; import java.util.ArrayList; import java.util.List; import javax.ejb.Stateful; @Stateful public class LibraryStatefulSessionBean implements LibraryStatefulSessionBeanRemote { List<String> bookShelf; public LibraryStatefulSessionBean(){ bookShelf = new ArrayList<String>(); } public void addBook(String bookName) { bookShelf.add(bookName); } public List<String> getBooks() { return bookShelf; } }

只要你部署在JBoss EjbComponent項目發現jboss的日誌。
JBoss已經自動創建一個JNDI條目會話bean-LibraryStatefulSessionBean/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.stateful.LibraryStatefulSessionBeanRemote

JBoss應用服務器的日誌輸出

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

LibraryStatefulSessionBean/remote - EJB3.x Default Remote Business Interface
LibraryStatefulSessionBean/remote-com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote - 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

These properties are used to initialize the InitialContext object of java naming service
InitialContext object will be used to lookup stateful session bean

EJBTester.java

package com.tutorialspoint.test; import com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote; 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.testStatelessEjb(); } private void showGUI(){ System.out.println("**********************"); System.out.println("Welcome to Book Store"); System.out.println("**********************"); System.out.print("Options

Add Book
Exit
Enter Choice: "); } private void testStatelessEjb(){ try { int choice = 1; LibraryStatefulSessionBeanRemote libraryBean = LibraryStatefulSessionBeanRemote)ctx.lookup("LibraryStatefulSessionBean/remote"); while (choice != 2) { String bookName; showGUI(); String strChoice = brConsoleReader.readLine(); choice = Integer.parseInt(strChoice); if (choice == 1) { System.out.print("Enter book name: "); bookName = brConsoleReader.readLine(); Book book = new Book(); book.setName(bookName); 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()); i++; } LibraryStatefulSessionBeanRemote libraryBean1 = (LibraryStatefulSessionBeanRemote)ctx.lookup("LibraryStatefulSessionBean/remote"); List<String> booksList1 = libraryBean1.getBooks(); System.out.println( "***Using second lookup to get library stateful object***"); System.out.println( "Book(s) entered so far: " + booksList1.size()); for (int i = 0; i < booksList1.size(); ++i) { System.out.println((i+1)+". " + booksList1.get(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 is doing the following tasks.

Load properties from jndi.properties and initialize the InitialContext object.
In testStatefulEjb() method, jndi lookup is done with name - "LibraryStatefulSessionBean/remote" to obtain the remote business object (stateful 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 stateful session bean addBook() method. Session Bean is storing the book in its instance variable.
If user enters 2, system retrieves books using stateful session bean getBooks() method and exits.
Then another jndi lookup is done with name - "LibraryStatefulSessionBean/remote" to obtain the remote business object (stateful ejb) again and listing of books is done.

運行客戶端訪問EJB

在項目資源管理器中找到EJBTester.java。右鍵單擊類EJBTester並選擇run file.

在Netbeans控制檯驗證以下輸出。

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

Add Book
Exit
Enter Choice: 1
Enter book name: Learn Java
**********************
Welcome to Book Store
**********************
Options
Add Book
Exit
Enter Choice: 2
Book(s) entered so far: 1
Learn Java
***Using second lookup to get library stateful object***
Book(s) entered so far: 0
BUILD SUCCESSFUL (total time: 13 seconds)

再次運行客戶端訪問EJB

在項目資源管理器中找到EJBTester.java。右鍵單擊類EJBTester選擇run file.

在NetBeans控制檯驗證以下輸出.

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

Add Book
Exit
Enter Choice: 2
Book(s) entered so far: 0
***Using second lookup to get library stateful object***
Book(s) entered so far: 0
BUILD SUCCESSFUL (total time: 12 seconds)

輸出上面顯示的狀態，對於每個查詢不同狀態的EJB實例將被返回.
只適用於單個會話狀態EJB對象值。在第二次運行時，我們沒有得到任何值.