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

1

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.

2

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

3

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

4

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.

5

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

  1. Add Book
  2. 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

  1. Add Book
  2. Exit
    Enter Choice: 1
    Enter book name: Learn Java
    **********************
    Welcome to Book Store
    **********************
    Options
  3. Add Book
  4. Exit
    Enter Choice: 2
    Book(s) entered so far: 1
  5. 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

  1. Add Book
  2. 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.