Ejb 简明教程

EJB - Blobs/Clobs

EJB 3.0 使用 @Lob 注解提供对 Blob 和 Clob 类型的支持。可以使用 @Lob 注解映射以下 java 类型。

EJB 3.0 provides support for Blob and Clob types using @Lob annotation. Following java types can be mapped using @Lob annotation.

java.sql.Blob
java.sql.Clob
byte[]
String
Serializable Object

@Entity
@Table(name="books")
@EntityListeners(BookCallbackListener.class)
public class Book implements Serializable{
   ...
   private byte[] image;

   @Lob @Basic(fetch= FetchType.EAGER)
   public byte[] getImage() {
      return image;
   }
   ...
}

Example Application

让我们创建一个测试 EJB 应用程序来测试 EJB 3.0 中的 blob/clob 支持。

Let us create a test EJB application to test blob/clob support in EJB 3.0.

Step	Description
1	Create a project with a name EjbComponent under a package com.tutorialspoint.entity as explained in the EJB - Create Application chapter. Please use the project created in EJB - Persistence chapter as such for this chapter to understand clob/blob objects in ejb concepts.
2	Create Book.java under package com.tutorialspoint.entity. Use EJB - Persistence chapter as reference. 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 a 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.

Create/Alter Book Table

CREATE TABLE book (
   id     integer PRIMARY KEY,
   name   varchar(50)
);
Alter table book add image bytea;
Alter table book add xml text;

EJBComponent (EJB Module)

Book.java

package com.tutorialspoint.entity;

import com.tutorialspoint.callback.BookCallbackListener;
import java.io.Serializable;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.EntityListeners;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.Table;

@Entity
@Table(name="book")
public class Book implements Serializable{

   private int id;
   private String name;
   private byte[] image;
   private String xml;

   public Book() {
   }

   @Id
   @GeneratedValue(strategy= GenerationType.IDENTITY)
   @Column(name="id")
   public int getId() {
      return id;
   }

   public void setId(int id) {
      this.id = id;
   }

   public String getName() {
      return name;
   }

   public void setName(String name) {
      this.name = name;
   }

   @Lob @Basic(fetch= FetchType.EAGER)
   public byte[] getImage() {
      return image;
   }

   public void setImage(byte[] image) {
      this.image = image;
   }

   @Lob @Basic(fetch= FetchType.EAGER)
   public String getXml() {
      return xml;
   }

   public void setXml(String xml) {
      this.xml = xml;
   }
}

LibraryPersistentBeanRemote.java

package com.tutorialspoint.stateless;

import com.tutorialspoint.entity.Book;
import java.util.List;
import javax.ejb.Remote;

@Remote
public interface LibraryPersistentBeanRemote {

   void addBook(Book bookName);

   List<Book> getBooks();

}

LibraryPersistentBean.java

package com.tutorialspoint.stateless;

import com.tutorialspoint.entity.Book;
import java.util.List;
import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

@Stateless
public class LibraryPersistentBean implements LibraryPersistentBeanRemote {

   public LibraryPersistentBean() {
   }

   @PersistenceContext(unitName="EjbComponentPU")
   private EntityManager entityManager;

   public void addBook(Book book) {
      entityManager.persist(book);
   }

   public List<Book> getBooks() {
      return entityManager.createQuery("From Book").getResultList();
   }
}

As soon as you deploy the EjbComponent project on JBOSS, notice the jboss log.
JBoss has automatically created a JNDI entry for our session bean - LibraryPersistentBean/remote.
We will using this lookup string to get remote business object of type - com.tutorialspoint.interceptor.LibraryPersistentBeanRemote

JBoss Application Server Log Output

...
16:30:01,401 INFO  [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:
   LibraryPersistentBean/remote - EJB3.x Default Remote Business Interface
   LibraryPersistentBean/remote-com.tutorialspoint.interceptor.LibraryPersistentBeanRemote - EJB3.x Remote Business Interface
16:30:02,723 INFO  [SessionSpecContainer] Starting jboss.j2ee:jar=EjbComponent.jar,name=LibraryPersistentBean,service=EJB3
16:30:02,723 INFO  [EJBContainer] STARTED EJB: com.tutorialspoint.interceptor.LibraryPersistentBeanRemote ejbName: LibraryPersistentBean
16:30:02,731 INFO  [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:

   LibraryPersistentBean/remote - EJB3.x Default Remote Business Interface
   LibraryPersistentBean/remote-com.tutorialspoint.interceptor.LibraryPersistentBeanRemote - 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 stateless session 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.testBlobClob();
   }

   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 testBlobClob() {

      try {
         int choice = 1;

         LibraryPersistentBeanRemote libraryBean =
        (LibraryPersistentBeanRemote)
         ctx.lookup("LibraryPersistentBean/remote");

         while (choice != 2) {
            String bookName;
            String publisherName;
            String publisherAddress;
            showGUI();
            String strChoice = brConsoleReader.readLine();
            choice = Integer.parseInt(strChoice);
            if (choice == 1) {
               System.out.print("Enter book name: ");
               bookName = brConsoleReader.readLine();
               String xml = "<book><name>"+bookName+"</name></book>";
               Book book = new Book();
               book.setName(bookName);
               byte[] imageBytes = {0x32, 0x32,0x32, 0x32,0x32,
               0x32,0x32, 0x32,
               0x32, 0x32,0x32, 0x32,0x32, 0x32,0x32, 0x32,
               0x32, 0x32,0x32, 0x32,0x32, 0x32,0x32, 0x32
               };
               book.setImage(imageBytes);
               book.setXml(xml);

               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());
            byte[] imageByts = book.getImage();
            if(imageByts != null) {
               System.out.print("image bytes: [");
               for(int j = 0; j < imageByts.length ; j++) {
                  System.out.print("0x"
                  + String.format("%x", imageByts[j]) +" ");
               }
               System.out.println("]");
            }
            System.out.println(book.getXml());
            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 执行以下任务。

EJBTester performs the following tasks.

Load properties from jndi.properties and initialize the InitialContext object.
In testInterceptedEjb() method, jndi lookup is done with name - "LibraryPersistenceBean/remote" to obtain the remote business object (stateless EJB).
Then the user is shown a library store User Interface and he/she is asked to enter a choice.
If the user enters 1, the system asks for book name and saves the book using stateless session bean addBook() method. Session Bean is storing the book in database.
If the user enters 2, the system retrieves books using stateless session bean getBooks() method and exits.

Run Client to Access EJB

在项目浏览器中找到EJBTester.java。右键单击EJBTester类并选择 run file 。

Locate EJBTester.java in project explorer. Right click on EJBTester class and select run file.

在Netbeans控制台中验证以下输出。

Verify the following output in Netbeans console.

run:
**********************
Welcome to Book Store
**********************
Options
1. Add Book
2. Exit
Enter Choice: 1
Enter book name: learn testing
**********************
Welcome to Book Store
**********************
Options
1. Add Book
2. Exit
Enter Choice: 2
Book(s) entered so far: 1
1. learn testing
image bytes: [
   0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 0x32 ]
<book><name>learn testing</name></book>
BUILD SUCCESSFUL (total time: 20 seconds)