EJB查询语言
EJB3.0,EJB查询语言编写自定义的查询非常方便,不用担心底层数据库的详细信息。这是很相似的HQL(Hibernate查询语言),通常被称为按名称EJBQL。
要理解熟悉ejb的EJBQL,要做好以下几项工作。
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步骤 1. 在数据库中创建表.
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步骤 2. 创建一个无状态EJB.
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步骤 3. 更新无状态的EJB。添加添加记录并获得通过实体管理器从数据库中记录的方法。
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步骤 4. 一个基于控制台应用程序客户端将访问无状态EJB的持久化数据库中的数据。
创建数据库表
创建表 books 在默认数据库 postgres.
CREATE TABLE books ( id integer PRIMARY KEY, name varchar(50) );
创建模型类
public class Book implements Serializable{ private int id; private String name; public Book(){ } public int getId() { return id; } ... }
创建无状态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 } ... }
构建EJB模块后,我们需要一个无状态的bean,我们将在下一节要创建客户端来访问。
示例应用程序
让我们创建一个测试EJB应用程序来测试EJB的数据库访问机制。
Step | Description |
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1 | Create a project with a name EjbComponent under a package com.tutorialspoint.entity 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 ejb data access concepts. |
2 | Create Book.java under package com.tutorialspoint.entity and modify it as shown below. |
3 | Create LibraryPersistentBean.java and LibraryPersistentBeanRemote as explained in the EJB - Create Application chapter and modify them as shown below. |
4 | Clean and Build the application to make sure business logic is working as per the requirements. |
5 | 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. |
6 | Now 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. Modify it as shown below. |
EJBComponent (EJB Module)
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(); } }
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只要在JBoss部署 EjbComponent项目,会注意到jboss的日志。
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JBoss已经自动为我们的会话bean创建一个JNDI条目 -LibraryPersistentBean/remote.
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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.stateless.LibraryPersistentBeanRemote
JBoss应用服务器的日志输出
... 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.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 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
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这些属性是用来初始化InitialContext对象的Java命名服务
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InitialContext的对象将被用于查找无状态会话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做以下任务。
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jndi.properties中加载和初始化的InitialContext对象。
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在testStatefulEjb()方法,JNDI名称进行查找 - "LibraryStatelessSessionBean/remote" 以获得远程业务对象(状态EJB)。
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然后用户显示一个库存储的用户界面和他/她被要求输入选择。
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如果用户输入1,系统要求输入书籍名称和节省了使用无状态的会话bean addBook()方法。会话Bean坚持这本书中通过EntityManager的调用数据库。
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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。
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然后另一个JNDI名称进行查找 - "LibraryStatelessSessionBean/remote"获得远程业务对象(状态EJB)再次列出书籍。
运行客户端访问EJB
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 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)