EJB查詢語言

EJB 3.0，EJB查詢語言是相當(dāng)方便的自定義查詢編寫，不必?fù)?dān)心底層數(shù)據(jù)庫的詳細(xì)信息。這是很相似的HQL，Hibernate查詢語言，EJBQL經(jīng)常引用。

為了演示EJB中的EJBQL，我們將執(zhí)行以下任務(wù)。

• 第1步：在數(shù)據(jù)庫中創(chuàng)建表。

• 步驟2.創(chuàng)建一個(gè)有business me的無狀態(tài)EJB。

• 步驟3.更新無狀態(tài)EJB。添加方法，添加記錄以及通過實(shí)體管理器從數(shù)據(jù)庫獲取記錄。
  

• 步驟4.基于控制臺(tái)的應(yīng)用程序客戶端將訪問無狀態(tài) ejb 存在數(shù)據(jù)庫中的數(shù)據(jù)。

創(chuàng)建表

在默認(rèn)數(shù)據(jù)庫postgres中創(chuàng)建table books

CREATE TABLE books (
   id     integer PRIMARY KEY,
   name   varchar(50)
);

創(chuàng)建模型類

public class Book implements Serializable{
    
   private int id;
   private String name;

   public Book(){        
   }
   
   public int getId() {
      return id;
   }
   ...
}

創(chuàng)建無狀態(tài)EJB

@Stateless
public class LibraryPersistentBean implements LibraryPersistentBeanRemote {
	
   public void addBook(Book book) {
     //persist book using entity manager
   }    

   public List<Book> getBooks() {        
     //get books using entity manager
   }
   ...
}

構(gòu)建EJB模塊后,我們需要一個(gè)客戶端訪問無狀態(tài)bean,在下一節(jié)中我們將會(huì)創(chuàng)建。

示例應(yīng)用程序

讓我們創(chuàng)建一個(gè)測試EJB應(yīng)用程序來測試EJB的數(shù)據(jù)庫訪問機(jī)制。

EJBComponent（EJB模塊）

Book.java

package com.tutorialspoint.entity;

import java.io.Serializable;

public class Book implements Serializable{
    
   private int id;
   private String name;

   public Book(){        
   }
   
   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;
   }    
}

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;
import javax.persistence.Query;

@Stateless
public class LibraryPersistentBean implements LibraryPersistentBeanRemote {
    
   public LibraryPersistentBean(){
   }

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

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

   public List<Book> getBooks() {
      //create an ejbql expression
      String ejbQL = "From Book b where b.name like ?1";
      //create query
      Query query = entityManager.createQuery(ejbQL);
      //substitute parameter.
      query.setParameter(1, "%test%");   
      //execute the query
      return query.getResultList();
   }   
}

• 一旦你部署EjbComponent項(xiàng)目到JBoss上，注意jboss的日志。

• JBoss 已自動(dòng)創(chuàng)建我們的會(huì)話 bean-LibraryPersistentBean/remote JNDI 條目。
  

• 我們將使用這個(gè)查詢字符串獲取遠(yuǎn)程業(yè)務(wù)類型的對象
  - com.tutorialspoint.stateless.LibraryPersistentBeanRemote

JBoss應(yīng)用服務(wù)器日志輸出

...
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.stateless.LibraryPersistentBeanRemote - EJB3.x Remote Business Interface
16:30:02,723 INFO  [SessionSpecContainer] Starting jboss.j2ee:jar=EjbComponent.jar,name=LibraryPersistentBeanRemote,service=EJB3
16:30:02,723 INFO  [EJBContainer] STARTED EJB: com.tutorialspoint.stateless.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.stateless.LibraryPersistentBeanRemote - EJB3.x Remote Business Interface
...   

EJBTester（EJB客戶端）

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

• 這些屬性用于初始化Java命名服務(wù)的InitialContext對象

• InitialContext對象將被用于查找無狀態(tài)會(huì)話bean

EJBTester.java

package com.tutorialspoint.test;
   
import com.tutorialspoint.stateless.LibraryPersistentBeanRemote;
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.testEntityEjb();
   }
   
   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 testEntityEjb(){

      try {
         int choice = 1; 

         LibraryPersistentBeanRemote libraryBean =
         LibraryPersistentBeanRemote)
         ctx.lookup("LibraryPersistentBean/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執(zhí)行以下任務(wù)。

• 從 jndi.properties 加載屬性并初始化輸出對象。
  

• 在testStatefulEjb()方法中,jndi查找名稱——“LibraryStatelessSessionBean /remote”來獲取遠(yuǎn)程業(yè)務(wù)對象(有狀態(tài)的ejb)。
  

• 然后用戶顯示庫存儲(chǔ)用戶界面和他（她）被要求輸入選擇。

• 如果用戶輸入 1，系統(tǒng)將要求書名稱并保存使用無狀態(tài)會(huì)話 bean addBook() 方法的書。會(huì)話 Bean 堅(jiān)持通過實(shí)體管理器調(diào)用數(shù)據(jù)庫中的書。
  

• 如果用戶輸入2，系統(tǒng)retrives使用無狀態(tài)會(huì)話bean getBooks（）方法，并退出書籍。

• 完成另一個(gè)jndi名稱查找——“LibraryStatelessSessionBean /remote”來獲取遠(yuǎn)程業(yè)務(wù)對象(有狀態(tài)的ejb)和書的清單。

運(yùn)行客戶端訪問EJB

在項(xiàng)目資源管理器中找到EJBTester.java。右鍵單擊EJBTester類并選擇 run file 運(yùn)行文件 。

驗(yàn)證以下在 Netbeans 控制臺(tái)輸出

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
BUILD SUCCESSFUL (total time: 15 seconds)