EJB-Blob / Clobs - 芒果文档

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📜 EJB-Blob / Clobs

📅 最后修改于: 2020-11-16 06:23:16 🧑 作者: Mango

EJB 3.0使用@Lob注释提供对Blob和Clob类型的支持。可以使用@Lob注释映射以下Java类型。

java.sql.Blob
java.sql.Clob
字节[]
串
可序列化的对象

@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;
   }
   ...
}

应用范例

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

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.

创建/更改书表

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

EJBComponent(EJB模块)

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 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 getBooks() {
      return entityManager.createQuery("From Book").getResultList();
   }
}

在JBOSS上部署EjbComponent项目后，请注意jboss日志。
JBoss已经为我们的会话bean- LibraryPersistentBean / remote自动创建了一个JNDI条目。
我们将使用此查找字符串获取类型为com.tutorialspoint.interceptor.LibraryPersistentBeanRemote的远程业务对象。

JBoss应用服务器日志输出

...
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客户端)

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

这些属性用于初始化Java命名服务的InitialContext对象。
InitialContext对象将用于查找无状态会话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 = ""+bookName+"";
               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 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。

从jndi.properties加载属性并初始化InitialContext对象。
在testInterceptedEjb()方法中，使用名称“ LibraryPersistenceBean /远程”完成jndi查找，以获取远程业务对象(无状态EJB)。
然后，向用户显示一个库存储用户界面，并要求他/她输入选择。
如果用户输入1，则系统会询问书名并使用无状态会话bean addBook()方法保存书。 Session Bean将书存储在数据库中。
如果用户输入2，则系统使用无状态会话bean getBooks()方法检索书籍并退出。

运行客户端以访问EJB

在项目资源管理器中找到EJBTester.java。右键单击EJBTester类，然后选择运行文件。

在Netbeans控制台中验证以下输出。

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 ]
learn testing
BUILD SUCCESSFUL (total time: 20 seconds)