EJB3.0提供了拦截业务方法的规范使用@ AroundInvoke注释注释的方法调用。一个拦截器方法被称为包含EJBContainer的业务方法调用前拦截。下面的例子是一个拦截器方法签名
@AroundInvoke
public Object methodInterceptor(InvocationContext ctx) throws Exception
{
System.out.println("*** Intercepting call to LibraryBean method: "
+ ctx.getMethod().getName());
return ctx.proceed();
}
拦截器方法可以应用在三个层面上的约束
-
Default - 默认的拦截器被调用内deployment.Default拦截每个bean只能应用于通过XML（ejb-jar.xml）。
-
Class - 类级别拦截所有的bean的方法被调用。类级别拦截器可以应用通过XML注释（ejb-jar.xml）。
-
Method - 方法级别的拦截器是一个特定的bean的方法调用。方法级的拦截器可以应用通过XML注释（ejb-jar.xml）。
我们在这里讨论类级别拦截。
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
}
让我们创建一个测试测试截获的无状态EJB的EJB应用程序。
| Step | 描述 |
|---|---|
| 1 | Create a project with a name EjbComponent under a package com.tutorialspoint.interceptor_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 intercepted ejb concepts. |
| 2 | Create LibraryBean.java and LibraryBeanRemote under package_com.tutorialspoint.interceptor_ 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 the_EJB - Create Application_ chapter under topic Create Client to access EJB. |
package com.tutorialspoint.interceptor;
import java.util.List;
import javax.ejb.Remote;
@Remote
public interface LibraryBeanRemote {
void addBook(String bookName);
List getBooks();
}
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<String> bookShelf;
public LibraryBean(){
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，会注意到jboss的日志。
-
JBoss已经自动为我们的会话bean创建一个JNDI条目 - LibraryBean/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.interceptor.LibraryBeanRemote
...
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
...
java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory
java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces
java.naming.provider.url=localhost
-
这些属性是用来初始化InitialContext对象的Java命名服务
-
InitialContext的对象将被用于查找无状态会话bean
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
1\. Add Book
2\. Exit
Enter 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<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++;
}
} 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做以下任务。
-
jndi.properties中加载和初始化的InitialContext对象。
-
JNDI查找testInterceptedEjb（）方法，完成了名称 - “LibraryBean/remote”获得远程业务对象（无状态EJB）。
-
如果用户输入1，系统要求输入书籍名称和节约使用无状态的会话bean addBook（）方法的书。会话Bean存储在它的实例变量的书。
-
如果用户输入2，系统检索书使用状态会话Bean getBooks（）方法和退出。
在项目资源管理器中找到EJBTester.java。右键点击上EJBTester类，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
BUILD SUCCESSFUL (total time: 13 seconds)
验证下面的输出在JBoss应用服务器的日志输出。
....
09:55:40,741 INFO [STDOUT] *** Intercepting call to LibraryBean method: addBook
09:55:43,661 INFO [STDOUT] *** Intercepting call to LibraryBean method: getBooks