EJB3.0提供了攔截業務方法的規範使用@ AroundInvoke註釋註釋的方法調用。一個攔截器方法被稱爲包含EJBContainer的業務方法調用前攔截。下面的例子是一個攔截器方法簽名
@AroundInvoke
public Object methodInterceptor(InvocationContext ctx) throws Exception
{
System.out.println("*** Intercepting call to LibraryBean method: "
+ ctx.getMethod().getName());
return ctx.proceed();
}
攔截器方法可以應用在三個層面上的約束
Default - 默認的攔截器被調用內deployment.Default攔截每個bean只能應用於通過XML(ejb-jar.xml)。
Class - 類級別攔截所有的bean的方法被調用。類級別攔截器可以應用通過XML註釋(ejb-jar.xml)。
Method - 方法級別的攔截器是一個特定的bean的方法調用。方法級的攔截器可以應用通過XML註釋(ejb-jar.xml)。
我們在這裏討論類級別攔截。
Interceptor class
package com.tutorialspoint.interceptor;
import javax.interceptor.AroundInvoke;
import javax.interceptor.InvocationContext;
public class BusinessInterceptor {
@AroundInvoke
public Object methodInterceptor(InvocationContext ctx) throws Exception
{
System.out.println("*** Intercepting call to LibraryBean method: "
+ ctx.getMethod().getName());
return ctx.proceed();
}
}
Remote Interface
import javax.ejb.Remote;
@Remote
public interface LibraryBeanRemote {
//add business method declarations
}
Intercepted Stateless EJB
@Interceptors ({BusinessInterceptor.class})
@Stateless
public class LibraryBean implements LibraryBeanRemote {
//implement business method
}
示例應用程序
讓我們創建一個測試測試截獲的無狀態EJB的EJB應用程序。
Step描述
1Create a project with a name EjbComponent under a package com.tutorialspoint.interceptoras explained in the EJB - Create Application chapter. You can also use the project created inEJB - Create Application chapter as such for this chapter to understand intercepted ejb concepts.
2Create LibraryBean.java and LibraryBeanRemote under packagecom.tutorialspoint.interceptor 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)
LibraryBeanRemote.java
package com.tutorialspoint.interceptor;
import java.util.List;
import javax.ejb.Remote;
@Remote
public interface LibraryBeanRemote {
void addBook(String bookName);
List getBooks();
}
LibraryBean.java
package com.tutorialspoint.interceptor;
import java.util.ArrayList;
import java.util.List;
import javax.ejb.Stateless;
import javax.interceptor.Interceptors;
@Interceptors ({BusinessInterceptor.class})
@Stateless
public class LibraryBean implements LibraryBeanRemote {
List bookShelf;
public LibraryBean(){
bookShelf = new ArrayList();
}
public void addBook(String bookName) {
bookShelf.add(bookName);
}
public List getBooks() {
return bookShelf;
}
}
只要你部署在JBoss EjbComponent項目，會注意到jboss的日誌。
JBoss已經自動爲我們的會話bean創建一個JNDI條目 - LibraryBean/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.LibraryBeanRemote
JBoss應用服務器的日誌輸出
...
16:30:01,401 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:
LibraryBean/remote - EJB3.x Default Remote Business Interface
LibraryBean/remote-com.tutorialspoint.interceptor.LibraryBeanRemote - EJB3.x Remote Business Interface
16:30:02,723 INFO [SessionSpecContainer] Starting jboss.j2ee:jar=EjbComponent.jar,name=LibraryBean,service=EJB3
16:30:02,723 INFO [EJBContainer] STARTED EJB: com.tutorialspoint.interceptor.LibraryBeanRemote ejbName: LibraryBean
16:30:02,731 INFO [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:
LibraryBean/remote - EJB3.x Default Remote Business Interface
LibraryBean/remote-com.tutorialspoint.interceptor.LibraryBeanRemote - 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.testInterceptedEjb();
}
private void showGUI(){
System.out.println("**********************");
System.out.println("Welcome to Book Store");
System.out.println("**********************");
System.out.print("Options \n1. Add Book\n2. Exit \nEnter Choice: ");
}
private void testInterceptedEjb(){
try {
int choice = 1;
LibraryBeanRemote libraryBean =
LibraryBeanRemote)ctx.lookup("LibraryBean/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++;
}
} 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。
JNDI查找testInterceptedEjb()方法，完成了名稱 - “LibraryBean/remote”獲得遠程業務對象(無狀態EJB)。
如果用戶輸入1，系統要求輸入書籍名稱和節約使用無狀態的會話bean addBook()方法的書。會話Bean存儲在它的實例變量的書。
如果用戶輸入2，系統檢索書使用狀態會話Bean getBooks()方法和退出。
Run Client to access 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 Java
**********************
Welcome to Book Store
**********************
Options
1. Add Book
2. Exit
Enter Choice: 2
Book(s) entered so far: 1
1. Learn Java
BUILD SUCCESSFUL (total time: 13 seconds)
JBoss應用服務器的日誌輸出
驗證下面的輸出在JBoss應用服務器的日誌輸出。
....
09:55:40,741 INFO [STDOUT] *** Intercepting call to LibraryBean method: addBook
09:55:43,661 INFO [STDOUT] *** Intercepting call to LibraryBean method: getBooks
(編輯：雷林鵬 來源：網絡|侵刪)