雷林鹏分享：EJB有状态会话Bean
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有状态会话Bean是一种企业bean保存客户端的会话状态类型。有状态会话bean作为每它的名字相关的客户端状态保持在它的实例变量。 EJB容器创建一个单独的有状态会话bean来处理客户端的每个请求。只要请求范围过，有状态会话bean被销毁。
以下是创建一个有状态的EJB所需的步骤：
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.
远程接口
import javax.ejb.Remote;
@Remote
public interface LibraryStatefulSessionBeanRemote {
//add business method declarations
}
Stateful EJB
@Stateful
public class LibraryStatefulSessionBean implements LibraryStatefulSessionBeanRemote {
//implement business method
}
示例应用程序
让我们创建一个测试测试状态EJB的EJB应用程序。
Step描述
1Create 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.
2Create LibraryStatefulSessionBean.java and LibraryStatefulSessionBeanRemote as explained in the EJB - Create Application chapter. Keep rest of the files unchanged.
3Clean and Build the application to make sure business logic is working as per the requirements.
4Finally, 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.
5Now 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 bookShelf;
public LibraryStatefulSessionBean(){
bookShelf = new ArrayList();
}
public void addBook(String bookName) {
bookShelf.add(bookName);
}
public List getBooks() {
return bookShelf;
}
}
只要你部署在JBoss EjbComponent项目发现jboss的日志。
JBoss已经自动创建一个JNDI条目会话bean-LibraryStatefulSessionBean/remote。
我们将使用这个查询字符串来获得远程类型的业务对象-com.tutorialspoint.stateful.LibraryStatefulSessionBeanRemote
JBoss应用服务器的日志输出
...
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 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 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.
运行客户端访问EJB
在项目资源管理器中找到EJBTester.java。右键单击类EJBTester并选择run file.
在Netbeans控制台验证以下输出。
run:
**********************
Welcome to Book Store
**********************
Options
1. Add Book
2. Exit
Enter Choice: 1
Enter book name: Learn Java
**********************
Welcome to Book Store
**********************
Options
1. Add Book
2. Exit
Enter Choice: 2
Book(s) entered so far: 1
1. Learn Java
***Using second lookup to get library stateful object***
Book(s) entered so far: 0
BUILD SUCCESSFUL (total time: 13 seconds)
再次运行客户端访问EJB
在项目资源管理器中找到EJBTester.java。右键单击类EJBTester选择run file.
在NetBeans控制台验证以下输出.
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)
输出上面显示的状态，对于每个查询不同状态的EJB实例将被返回.
只适用于单个会话状态EJB对象值。在第二次运行时，我们没有得到任何值. (编辑：雷林鹏 来源：网络|侵删)
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