EJB有状态会话Bean
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:
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Create a remote/local interface exposing the business methods.
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This interface will be used by the ejb client application.
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Use @Local annotation if ejb client is in same environment where ejb session bean is to be deployed.
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Use @Remote annotation if ejb client is in different environment where ejb session bean is to be deployed.
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Create a stateful session bean implementing the above interface.
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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 |
---|---|
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项目发现jboss的日志。
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JBoss已经自动创建一个JNDI条目会话bean-LibraryStatefulSessionBean/remote。
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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
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These properties are used to initialize the InitialContext object of java naming service
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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.
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Load properties from jndi.properties and initialize the InitialContext object.
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In testStatefulEjb() method, jndi lookup is done with name - "LibraryStatefulSessionBean/remote" to obtain the remote business object (stateful ejb).
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Then user is shown a library store User Interface and he/she is asked to enter choice.
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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.
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If user enters 2, system retrieves books using stateful session bean getBooks() method and exits.
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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)
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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.
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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.