husted 2002/12/28 17:19:32
Modified: doc/faqs project.xml index.xml
Added: doc/faqs database.xml
Log:
Combine pieces from Model and Configuration to create Accessing a Database HowTo.
Revision Changes Path
1.8 +3 -0 jakarta-struts/doc/faqs/project.xml
Index: project.xml
===================================================================
RCS file: /home/cvs/jakarta-struts/doc/faqs/project.xml,v
retrieving revision 1.7
retrieving revision 1.8
diff -u -r1.7 -r1.8
--- project.xml 28 Dec 2002 22:27:48 -0000 1.7
+++ project.xml 29 Dec 2002 01:19:32 -0000 1.8
@@ -24,6 +24,9 @@
href="actionForm.html"
name="Action Forms"/>
<item
+ href="database.html"
+ name="Database"/>
+ <item
href="indexedprops.html"
name="Indexed Properties"/>
<item
1.7 +4 -0 jakarta-struts/doc/faqs/index.xml
Index: index.xml
===================================================================
RCS file: /home/cvs/jakarta-struts/doc/faqs/index.xml,v
retrieving revision 1.6
retrieving revision 1.7
diff -u -r1.6 -r1.7
--- index.xml 28 Dec 2002 22:27:48 -0000 1.6
+++ index.xml 29 Dec 2002 01:19:32 -0000 1.7
@@ -38,6 +38,10 @@
</li>
<li>
+ <a href="database.html">Accessing a Database</a>
+ </li>
+
+ <li>
<a href="indexedprops.html">Indexed Properties, Mapped Properties, and Indexed
Tags</a>
</li>
1.1 jakarta-struts/doc/faqs/database.xml
Index: database.xml
===================================================================
<?xml version="1.0"?>
<document url="./database.xml">
<properties>
<author>Craig R. McClanahan</author>
<author>Mike Schachter</author>
<author>Ted Husted</author>
<author>Martin Cooper</author> <author>Ed Burns</author>
<title>Accessing a Database</title>
</properties>
<body>
<chapter href="actionForm" name="How to Access a Database">
<section name="Accessing a Database" href="database">
<p>
Ideally, the business logic layer should encapsulate the data access
details, including acquiring a database connection.
However, some application designs expect that the caller able to provide a
with a database connection or DataSource instance.
When this is the case, the Struts DataSource manager can make it easy for
your Action to produce these resources on demand.
</p>
<p>
The Struts DataSource manager is configured as an element in the
<a href="../userGuide/configuration.html#data-source_config">
Struts configuration file</a> (struts-config.xml).
The manager can used to deploy any connection pool that implements the
<code>javax.sql.DataSource</code> interface and is configurable totally
from JavaBean properties.
If your DBMS or container provides a connection pool that meets these
requirements, then that component might your first choice.
</p>
<p>
The Jakarta Commons dbcp's BasicDataSource
[<code>org.apache.commons.dbcp.BasicDataSource</code>] also works well
with the DataSource manager, if a native component is not available.
The Struts distribution includes a Generic DataSource class in its util
package, but this is now only a wrapper around the BasicDataSource.
The GenericDataSource class is deprecated as of Struts 1.1 and replaced
by direct use of the BasicDataSource.
</p>
<p>
This is how you would specify a default data source for your application
from the struts-config.xml:
</p>
<pre><code><![CDATA[
<data-sources>
<!-- configuration for GenericDataSource wrapper -->
<data-source>
<set-property
property="autoCommit"
value="false"/>
<set-property
property="description"
value="Example Data Source Configuration"/>
<set-property
property="driverClass"
value="org.postgresql.Driver"/>
<set-property
property="maxCount"
value="4"/>
<set-property
property="minCount"
value="2"/>
<set-property
property="password"
value="mypassword"/>
<set-property
property="url"
value="jdbc:postgresql://localhost/mydatabase"/>
<set-property
property="user"
value="myusername"/>
</data-source>
</data-sources>
]]></code></pre>
<p>
This is how you would specify a DBCP BasicDataSource for your application:
</p>
<pre><code><![CDATA[
<data-sources>
<!-- configuration for commons BasicDataSource -->
<data-source type="org.apache.commons.dbcp.BasicDataSource">
<set-property
property="driverClassName"
value="org.postgresql.Driver" />
<set-property
property="url"
value="jdbc:postgresql://localhost/mydatabase" />
<set-property
property="maxActive"
value="10" />
<set-property
property="maxWait"
value="5000" />
<set-property
property="defaultAutoCommit"
value="false" />
<set-property
property="defaultReadOnly"
value="false" />
</data-source>
</data-sources>
]]></code></pre>
<p>
Note that you can define as many datasource objects as your application
requires and refer to each using a logical name.
This can be useful in providing better security or scalability, or even
to test datasource implementations against each other.
</p>
<p>
After a DataSource is defined, here is an example of using the
manager to establish a connection from within an Action's
<code>execute</code> method.
</p>
<pre><code>
public ActionForward
execute(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception
{
javax.sql.DataSource dataSource;
java.sql.Connection myConnection;
try {
dataSource = getDataSource(request);
myConnection = dataSource.getConnection();
//do what you wish with myConnection
} catch (SQLException sqle) {
getServlet().log("Connection.process", sqle);
} finally {
//enclose this in a finally block to make
//sure the connection is closed
try {
myConnection.close();
} catch (SQLException e) {
getServlet().log("Connection.close", e);
}
}
}
</code></pre>
<p>
<i>Note: Since Struts is now using commons-dbcp for all it's data-source
needs, the query you provide for the pingQuery attribute must return at
least one row.</i>
</p>
<p>
<b>Example:</b> <code>SELECT COUNT(*) FROM VALIDTABLE</code>
</p>
<p>
Just be sure you to replace "VALIDTABLE" with the name of a valid table
in your database.
</p>
</section>
</chapter>
</body>
</document>
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