(接上例)JPA中实现增删改查及事务控制
上例：使用EJB3的EntityBean连接数据库(http://blog.csdn.net/kunshan_shenbin/archive/2008/06/08/2525454.aspx)中介绍了如何在EJB3中使用实体Bean的方法。这次准备记录一下使用实体Bean实现增删改查及事务控制的方法。
需要修改下面几个文件：
BookDao.java
package com.cecltd.ejb3;
import java.util.List;
import com.cecltd.domain.Book;
public interface BookDao {
public List getBookList();
public Book getBook(int id);
public void updateBook(Book book);
public void insertBook(int id);
public void deleteBook(int id);
}
BookDaoBean.java
package com.cecltd.ejb3.impl;
import java.util.List;
import javax.ejb.Remote;
import javax.ejb.Stateless;
import javax.ejb.TransactionAttribute;
import javax.ejb.TransactionAttributeType;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;
import com.cecltd.domain.Book;
import com.cecltd.ejb3.BookDao;
@Stateless
@Remote(BookDao.class)
public class BookDaoBean implements BookDao {
@PersistenceContext
protected EntityManager em;
public List getBookList() {
Query query = em.createQuery("from Book order by ISBN asc");
List list = query.getResultList();
return list;
}
public Book getBook(int id){
return em.find(Book.class, Integer.valueOf(id));
}
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public void updateBook(Book book) {
em.merge(book);
}
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public void insertBook(int id) {
Book book = new Book();
book.setNM("复制书");
book.setCNT("复制书内容概要");
book.setISBN(getBook(id).getISBN());
book.setPBLDT(getBook(id).getPBLDT());
em.persist(book);
}
@TransactionAttribute(TransactionAttributeType.REQUIRED)
public void deleteBook(int id) {
em.remove(getBook(id));
}
}
EntityBeanClient.java
package test;
import java.io.UnsupportedEncodingException;
import java.sql.SQLException;
import java.util.List;
import java.util.Properties;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import com.cecltd.domain.Book;
import com.cecltd.ejb3.BookDao;
public class EntityBeanClient {
public static void main(String[] args) throws NamingException, SQLException, UnsupportedEncodingException {
Properties props = new Properties();
props.setProperty("java.naming.factory.initial", "org.jnp.interfaces.NamingContextFactory");
props.setProperty("java.naming.provider.url", "127.0.0.1:1099");
props.setProperty("java.naming.factory.url.pkgs", "org.jboss.naming:org.jnp.interfaces");
InitialContext ctx = new InitialContext(props);
BookDao bookDao = (BookDao)ctx.lookup("BookDaoBean/remote");
List list = bookDao.getBookList();
for (int i = 0; i < list.size(); i++) {
Book book = (Book)list.get(i);
System.out.println(book.getID() + " " + book.getNM() + " " + book.getISBN());
}
Book book = bookDao.getBook(1);
book.setNM("深入浅出 Hibernate");
bookDao.updateBook(book);
System.out.println(bookDao.getBook(1).getNM());;
System.out.println(bookDao.getBookList().size());
bookDao.insertBook(1);
System.out.println(bookDao.getBookList().size());
bookDao.deleteBook(14);
System.out.println(bookDao.getBookList().size());
}
}
==============================================================
关于事物：JPA允许使用@TransactionAttribute 注释来定义一个事物。其参数的含义是：
详细请参阅：http://blog.csdn.net/zxl315/archive/2008/04/03/2246201.aspx
==============================================================
关于实体bean中主键@GeneratedValue注释的参数：
一般需要根据数据库而定。MSSQL,MYSQL使用strategy = GenerationType.IDENTITY；而Oracle则使用GenerationType.SEQUENCE；当不能确定时，使用strategy = GenerationType.AUTO比较保险。
==============================================================关于MYSQL中文乱码问题
因为当前使用的是中文环境，请确保mysql-ds.xml文件中connection-url属性是否有追加了characterEncoding=gbk
下面给出一个范例：
<?xml version="1.0" encoding="UTF-8"?>
<!-- $Id: mysql-ds.xml 63175 2007-05-21 16:26:06Z rrajesh $ -->
<!-- Datasource config for MySQL using 3.0.9 available from:
http://www.mysql.com/downloads/api-jdbc-stable.html
-->
<datasources>
<local-tx-datasource>
<jndi-name>MySqlDS</jndi-name>
<connection-url>jdbc:mysql://127.0.0.1:3306/compass?characterEncoding=gbk</connection-url>
<driver-class>com.mysql.jdbc.Driver</driver-class>
<user-name>root</user-name>
<password>root</password>
<exception-sorter-class-name>org.jboss.resource.adapter.jdbc.vendor.MySQLExceptionSorter</exception-sorter-class-name>
<!-- should only be used on drivers after 3.22.1 with "ping" support
<valid-connection-checker-class-name>org.jboss.resource.adapter.jdbc.vendor.MySQLValidConnectionChecker</valid-connection-checker-class-name>
-->
<!-- sql to call when connection is created
<new-connection-sql>some arbitrary sql</new-connection-sql>
-->
<!-- sql to call on an existing pooled connection when it is obtained from pool - MySQLValidConnectionChecker is preferred for newer drivers
<check-valid-connection-sql>some arbitrary sql</check-valid-connection-sql>
-->
<!-- corresponding type-mapping in the standardjbosscmp-jdbc.xml -->
<metadata>
<type-mapping>mySQL</type-mapping>
</metadata>
</local-tx-datasource>
</datasources>
其他参考资源：http://www.matrix.org.cn/thread.shtml?topicId=34877&forumId=38