example.servlet.database
Class QueryServlet

java.lang.Object
  |
  +--HttpServlet
        |
        +--example.servlet.database.QueryServlet

public class QueryServlet

extends HttpServlet

Example of a database query from a servlet.

Database access has two components: looking up the data source using JNDI and using JDBC calls to retrieve the data.

The JNDI lookup finds the DataSource configured in the resin.conf or web.xml. Since the JNDI lookup only needs to happen once, it's usually put in the init() method. The database configuration looks something like the following:

 <resource-ref>
   <res-ref-name>jdbc/test
   <res-type>javax.sql.DataSource
   <init-param driver-name="com.caucho.jdbc.mysql.Driver"/>
   <init-param url="jdbc:mysql_caucho://localhost:3306/test"/>
   <init-param max-connections="20"/>
   <init-param max-idle-time="30"/>
 </resource-ref>
 

Different databasees will have different values for driver-name and url. The max-connections and max-idle-time are configuration values for Resin's database pooling. The servlet doesn't need to worry about database pooling; Resin will take care of it automatically. (The APIs used in the example are all from the J2EE standard.)

Applications should always use the following pattern for all database access. The try ... finally pattern is vital to make sure the connection is released to the pool.

 Connection conn = null;
 try {
   conn = dataSource.getConnection();
   ...
 } finally {
   if (conn != null)
     conn.close();
 }
 

See Also:

Serialized Form

Constructor Summary

QueryServlet()

Method Summary

void	doGet(HttpServletRequest request, HttpServletResponse response) Handles GET requests.
void	init() Initialize the servlet, caching the JNDI lookup of the DataSource.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

QueryServlet

public QueryServlet()

Method Detail

init

public void init()
          throws ServletException

Initialize the servlet, caching the JNDI lookup of the DataSource.

ServletException

doGet

public void doGet(HttpServletRequest request,
                  HttpServletResponse response)
           throws java.io.IOException,
                  ServletException

Handles GET requests. Resin will call the doGet method when the browser sends a GET request.

Parameters:

request - the request object contains the data from the browser's request.

response - the response object contains methods to send data back to the browser.

java.io.IOException

ServletException