Eclipse + JBoss 5 + EJB3 Development Guide (6): Writing the first entity Bean program

The EJB3 container manages entity beans through the Entitymanager object, the primary function of which is to map each other between records and JavaBean. For example, we find a record from a database that has field1 and field2 two fields, assuming a JavaBean, and also contains Field1 and Field2 properties. Then Entitymanager can map the values in this record to the Field1 and Field2 properties of JavaBean. In other words, a record in the database corresponds to an JavaBean object instance. Here's a simple example to show how to implement a program that applies entity beans. In this example, a stateless session bean is used to look up a record from a datasheet through a Entitymanager object, map the record to an object instance of an entity bean, and then return a field value for that record through the session Bean's method.

Table Name: T_users

Fields and records in a table

　　　 id　　　 name　　　 password_md5
　　 　 1　　　　 bill　　　 TaokQpoNJQb02eafO/JgYw==

First, configure the JBoss database connection pool

Create a Mysql-ds.xml file in the <jboss installation directory >\server\default\deploy directory, which reads as follows:

<?xml　version="1.0"　encoding="UTF-8"?>
<datasources>
　　<local-tx-datasource>
　　　　<jndi-name>MyPIM</jndi-name>
　　　　<connection-url>jdbc:mysql://localhost:3306/pim</connection-url>
　　　　<driver-class>com.mysql.jdbc.Driver</driver-class>
　　　　<user-name>root</user-name>
　　　　<password>1234</password>
　　　　<exception-sorter-class- name>org.jboss.resource.adapter.jdbc.vendor.MySQLExceptionSorter</exception-sorter- class-name>
　　　　<metadata>
　　　　　　　<type-mapping>mySQL</type-mapping>
　　　　</metadata>
　　</local-tx-datasource>
</datasources>

The Mysql-ds.xml file is used to configure the MySQL data source. In fact, the file can be found in the <jboss installation directory >\docs\examples\jca directory, and the reader needs to change the database name, username and password, and Jndi name to their own. Finally, copy the modified Mysql-ds.xml file into the Deploy directory (this file name must be called).

A JDBC driver (jar file) is required to connect to the MySQL database and copy the file to the <jboss installation directory >\server\default\lib directory.