📅 最后修改于: 2020-11-16 06:26:24 🧑 作者: Mango
在EJB 3.0中，持久性机制用于访问数据库，容器在其中管理数据库相关的操作。开发人员可以直接在EJB业务方法中使用JDBC API调用来访问数据库。
为了演示EJB中的数据库访问，我们需要执行以下任务-
步骤1-在数据库中创建一个表。
步骤2-创建一个有业务的无状态EJB。
步骤3-更新无状态EJB。添加方法以添加记录并通过实体管理器从数据库获取记录。
步骤4-基于控制台的应用程序客户端将访问无状态EJB，以将数据持久存储在数据库中。
在默认数据库postgres中创建一个表簿。
CREATE TABLE books (
id integer PRIMARY KEY,
name varchar(50)
);
public class Book implements Serializable{
private int id;
private String name;
public Book() {
}
public int getId() {
return id;
}
...
}
@Stateless
public class LibraryPersistentBean implements LibraryPersistentBeanRemote {
public void addBook(Book book) {
//persist book using jdbc calls
}
public List getBooks() {
//get books using jdbc calls
}
...
}
构建EJB模块之后，我们需要一个客户端来访问无状态bean，这将在下一部分中创建。
让我们创建一个测试EJB应用程序以测试EJB数据库访问机制。
| Step | Description |
|---|---|
| 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 the EJB – Create Application chapter under topic Create Client to access EJB. Modify it as shown below. |
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;
}
}
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();
}
package com.tutorialspoint.stateless;
import com.tutorialspoint.entity.Book;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import javax.ejb.Stateless;
@Stateless
public class LibraryPersistentBean implements LibraryPersistentBeanRemote {
public LibraryPersistentBean() {
}
public void addBook(Book book) {
Connection con = null;
String url = "jdbc:postgresql://localhost:5432/postgres";
String driver = "org.postgresql.driver";
String userName = "sa";
String password = "sa";
List books = new ArrayList();
try {
Class.forName(driver).newInstance();
con = DriverManager.getConnection(url , userName, password);
PreparedStatement st =
con.prepareStatement("insert into book(name) values(?)");
st.setString(1,book.getName());
int result = st.executeUpdate();
} catch (SQLException ex) {
ex.printStackTrace();
} catch (InstantiationException ex) {
ex.printStackTrace();
} catch (IllegalAccessException ex) {
ex.printStackTrace();
} catch (ClassNotFoundException ex) {
ex.printStackTrace();
}
}
public List getBooks() {
Connection con = null;
String url = "jdbc:postgresql://localhost:5432/postgres";
String driver = "org.postgresql.driver";
String userName = "sa";
String password = "sa";
List books = new ArrayList();
try {
Class.forName(driver).newInstance();
con = DriverManager.getConnection(url , userName, password);
Statement st = con.createStatement();
ResultSet rs = st.executeQuery("select * from book");
Book book;
while (rs.next()) {
book = new Book();
book.setId(rs.getInt(1));
book.setName(rs.getString(2));
books.add(book);
}
} catch (SQLException ex) {
ex.printStackTrace();
} catch (InstantiationException ex) {
ex.printStackTrace();
} catch (IllegalAccessException ex) {
ex.printStackTrace();
} catch (ClassNotFoundException ex) {
ex.printStackTrace();
}
return books;
}
}
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。
我们将使用该查找字符串来获取类型为com.tutorialspoint.stateless.LibraryPersistentBeanRemote的远程业务对象。
...
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
...
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。
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 \n1. Add Book\n2. Exit \nEnter 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 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执行以下任务-
从jndi.properties加载属性并初始化InitialContext对象。
在testStatefulEjb()方法中，使用名称“ LibraryStatelessSessionBean / remote”完成jndi查找，以获得远程业务对象(有状态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。会话Bean通过EntityManager调用将书籍保留在数据库中。
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。
然后，使用名称“ LibraryStatelessSessionBean / remote”完成另一个jndi查找，以再次获取远程业务对象(有状态EJB)，并完成了书的清单。
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 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: 15 seconds)