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<!DOCTYPE document [
<!ENTITY project SYSTEM "project.xml">
]>
<document url="jndi-resources-howto.html">
<section name="Table of Contents">
<toc/>
</section>
<section name="Introduction">
<p>Tomcat provides a JNDI <strong>InitialContext</strong> implementation
instance for each web application running under it, in a manner that is
compatible with those provided by a
<a href="https://jakarta.ee/">Jakarta EE</a> application server. The Jakarta EE
standard provides a standard set of elements in the
<code>/WEB-INF/web.xml</code> file to reference/define resources.</p>
<p>See the following Specifications for more information about programming APIs
for JNDI, and for the features supported by Jakarta EE servers, which Tomcat
emulates for the services that it provides:</p>
<ul>
<li><a href="http://docs.oracle.com/javase/7/docs/technotes/guides/jndi/index.html">
Java Naming and Directory Interface</a> (included in JDK 1.4 onwards)</li>
<li><a href="https://jakarta.ee/specifications/platform/9/"> Jakarta EE Platform
Specification</a> (in particular, see Chapter 5 on <em>Naming</em>)</li>
</ul>
</section>
<section name="web.xml configuration" >
<p>The following elements may be used in the web application deployment
descriptor (<code>/WEB-INF/web.xml</code>) of your web application to define
resources:</p>
<ul>
<li><code><strong><env-entry></strong></code> - Environment entry, a
single-value parameter that can be used to configure how the application
will operate.</li>
<li><code><strong><resource-ref></strong></code> - Resource reference,
which is typically to an object factory for resources such as a JDBC
<code>DataSource</code>, a Jakarta Mail <code>Session</code>, or custom
object factories configured into Tomcat.</li>
<li><code><strong><resource-env-ref></strong></code> - Resource
environment reference, a new variation of <code>resource-ref</code>
added in Servlet 2.4 that is simpler to configure for resources
that do not require authentication information.</li>
</ul>
<p>Providing that Tomcat is able to identify an appropriate resource factory to
use to create the resource and that no further configuration information is
required, Tomcat will use the information in <code>/WEB-INF/web.xml</code> to
create the resource.</p>
<p>Tomcat provides a number of Tomcat specific options for JNDI resources that
cannot be specified in web.xml. These include <code>closeMethod</code> that
enables faster cleaning-up of JNDI resources when a web application stops and
<code>singleton</code> that controls whether or not a new instance of the
resource is created for every JNDI lookup. To use these configuration options
the resource must be specified in a web application's
<a href="config/context.html"><code><Context></code></a> element or in the
<a href="config/globalresources.html">
<code><strong><GlobalNamingResources></strong></code></a> element of
<code>$CATALINA_BASE/conf/server.xml</code>.</p>
</section>
<section name="context.xml configuration">
<p>If Tomcat is unable to identify the appropriate resource factory and/or
additional configuration information is required, additional Tomcat specific
configuration must be specified before Tomcat can create the resource.
Tomcat specific resource configuration is entered in
the <a href="config/context.html"><code><Context></code></a> elements that
can be specified in either <code>$CATALINA_BASE/conf/server.xml</code> or,
preferably, the per-web-application context XML file
(<code>META-INF/context.xml</code>).</p>
<p>Tomcat specific resource configuration is performed using the following
elements in the <a href="config/context.html"><code><Context></code></a> element:</p>
<ul>
<li><a href="config/context.html#Environment_Entries"><Environment></a> -
Configure names and values for scalar environment entries that will be
exposed to the web application through the JNDI
<code>InitialContext</code> (equivalent to the inclusion of an
<code><env-entry></code> element in the web application
deployment descriptor).</li>
<li><a href="config/context.html#Resource_Definitions"><Resource></a> -
Configure the name and data type of a resource made available to the
application (equivalent to the inclusion of a
<code><resource-ref></code> element in the web application
deployment descriptor).</li>
<li><a href="config/context.html#Resource_Links"><ResourceLink></a> -
Add a link to a resource defined in the global JNDI context. Use resource
links to give a web application access to a resource defined in
the <a href="config/globalresources.html"><GlobalNamingResources></a>
child element of the <a href="config/server.html"><Server></a> element.</li>
<li><a href="config/context.html#Transaction"><Transaction></a> -
Add a resource factory for instantiating the UserTransaction object
instance that is available at <code>java:comp/UserTransaction</code>.</li>
</ul>
<p>Any number of these elements may be nested inside a
<a href="config/context.html"><code><Context></code></a> element and will
be associated only with that particular web application.</p>
<p>If a resource has been defined in a
<a href="config/context.html"><code><Context></code></a> element it is not
necessary for that resource to be defined in <code>/WEB-INF/web.xml</code>.
However, it is recommended to keep the entry in <code>/WEB-INF/web.xml</code>
to document the resource requirements for the web application.</p>
<p>Where the same resource name has been defined for a
<code><env-entry></code> element included in the web application
deployment descriptor (<code>/WEB-INF/web.xml</code>) and in an
<code><Environment></code> element as part of the
<a href="config/context.html"><code><Context></code></a> element for the
web application, the values in the deployment descriptor will take precedence
<strong>only</strong> if allowed by the corresponding
<code><Environment></code> element (by setting the <code>override</code>
attribute to "true").</p>
</section>
<section name="Global configuration">
<p>Tomcat maintains a separate namespace of global resources for the
entire server. These are configured in the
<a href="config/globalresources.html">
<code><strong><GlobalNamingResources></strong></code></a> element of
<code>$CATALINA_BASE/conf/server.xml</code>. You may expose these resources to
web applications by using a
<a href="config/context.html#Resource_Links"><ResourceLink></a> to include it in the per-web-application context.</p>
<p>If a resource has been defined using a
<a href="config/context.html#Resource_Links"><ResourceLink></a>, it is not
necessary for that resource to be defined in <code>/WEB-INF/web.xml</code>.
However, it is recommended to keep the entry in <code>/WEB-INF/web.xml</code>
to document the resource requirements for the web application.</p>
</section>
<section name="Using resources">
<p>The <code>InitialContext</code> is configured as a web application is
initially deployed, and is made available to web application components (for
read-only access). All configured entries and resources are placed in
the <code>java:comp/env</code> portion of the JNDI namespace, so a typical
access to a resource - in this case, to a JDBC <code>DataSource</code> -
would look something like this:</p>
// Look up our data source
DataSource ds = (DataSource)
envCtx.lookup("jdbc/EmployeeDB");
// Allocate and use a connection from the pool
Connection conn = ds.getConnection();
... use this connection to access the database ...
conn.close();]]></source>
</section>
<section name="Tomcat Standard Resource Factories">
<p>Tomcat includes a series of standard resource factories that can
provide services to your web applications, but give you configuration
flexibility (via the
<a href="config/context.html"><code><Context></code></a> element)
without modifying the web application or the deployment descriptor. Each
subsection below details the configuration and usage of the standard resource
factories.</p>
<p>See <a href="#Adding_Custom_Resource_Factories">Adding Custom
Resource Factories</a> for information about how to create, install,
configure, and use your own custom resource factory classes with
Tomcat.</p>
<p><em>NOTE</em> - Of the standard resource factories, only the "JDBC Data Source" and "User Transaction" factories are mandated to
be available on other platforms, and then they are required only if
the platform implements the Jakarta EE specs.
All other standard resource factories, plus custom resource factories
that you write yourself, are specific to Tomcat and cannot be assumed
to be available on other containers.</p>
<subsection name="Generic JavaBean Resources">
<h5>0. Introduction</h5>
<p>This resource factory can be used to create objects of <em>any</em>
Java class that conforms to standard JavaBeans naming conventions (i.e.
it has a zero-arguments constructor, and has property setters that
conform to the setFoo() naming pattern. The resource factory will
only create a new instance of the appropriate bean class every time a
<code>lookup()</code> for this entry is made if the <code>singleton</code>
attribute of the factory is set to <code>false</code>.</p>
<p>The steps required to use this facility are described below.</p>
<h5>1. Create Your JavaBean Class</h5>
<p>Create the JavaBean class which will be instantiated each time
that the resource factory is looked up. For this example, assume
you create a class <code>com.mycompany.MyBean</code>, which looks
like this:</p>
<source><![CDATA[package com.mycompany;
public class MyBean {
private String foo = "Default Foo";
public String getFoo() {
return (this.foo);
}
public void setFoo(String foo) {
this.foo = foo;
}
private int bar = 0;
public int getBar() {
return (this.bar);
}
public void setBar(int bar) {
this.bar = bar;
}
}]]></source>
<h5>2. Declare Your Resource Requirements</h5>
<p>Next, modify your web application deployment descriptor
(<code>/WEB-INF/web.xml</code>) to declare the JNDI name under which
you will request new instances of this bean. The simplest approach is
to use a <code><resource-env-ref></code> element, like this:</p>
<p><strong>WARNING</strong> - Be sure you respect the element ordering
that is required by the DTD for web application deployment descriptors!
See the
<a href="https://cwiki.apache.org/confluence/display/TOMCAT/Specifications">Servlet
Specification</a> for details.</p>
<h5>3. Code Your Application's Use Of This Resource
<p>A typical use of this resource environment reference might look
like this:</p>
<p>To configure Tomcat's resource factory, add an element like this to the
<a href="config/context.html"><code><Context></code></a> element for
this web application.</p>
<p>Note that the resource name (here, <code>bean/MyBeanFactory</code>
must match the value specified in the web application deployment
descriptor. We are also initializing the value of the <code>bar</code>
property, which will cause <code>setBar(23)</code> to be called before
the new bean is returned. Because we are not initializing the
<code>foo</code> property (although we could have), the bean will
contain whatever default value is set up by its constructor.</p>
<p>If the bean property is of type <code>String</code>, the BeanFactory
will call the property setter using the provided property value. If the
bean property type is a primitive or a primitive wrapper, the the
BeanFactory will convert the value to the appropriate primitive or
primitive wrapper and then use that value when calling the setter. Some
beans have properties with types that cannot automatically be converted
from <code>String</code>. If the bean provides an alternative setter with
the same name that does take a <code>String</code>, the BeanFactory will
attempt to use that setter. If the BeanFactory cannot use the value or
perform an appropriate conversion, setting the property will fail with a
NamingException.</p>
<p>The <code>forceString</code> property available in earlier Tomcat
releases has been removed as a security hardening measure.</p>
</subsection>
<subsection name="Memory UserDatabase Resources">
<h5>0. Introduction</h5>
<p>UserDatabase resources are typically configured as global resources for
use by a UserDatabase realm. Tomcat includes a UserDatabaseFactory that
creates UserDatabase resources backed by an XML file - usually
<code>tomcat-users.xml</code>.</p>
<p>The steps required to set up a global UserDatabase resource are described
below.</p>
<h5>1. Create/edit the XML file</h5>
<p>The XML file is typically located at
<code>$CATALINA_BASE/conf/tomcat-users.xml</code> however, you are free to
locate the file anywhere on the file system. It is recommended that the XML
files are placed in <code>$CATALINA_BASE/conf</code>. A typical XML would
look like:</p>
<p>Next, modify <code>$CATALINA_BASE/conf/server.xml</code> to create the
UserDatabase resource based on your XML file. It should look something like
this:</p>
<source><![CDATA[<Resource name="UserDatabase"
auth="Container" type="org.apache.catalina.UserDatabase"
description="User database that can be updated and saved"
factory="org.apache.catalina.users.MemoryUserDatabaseFactory"
pathname="conf/tomcat-users.xml"
readonly="false" />]]></source>
<p>The <code>pathname</code> attribute can be a URL, an absolute path or a
relative path. If relative, it is relative to <code>$CATALINA_BASE</code>.
</p>
<p>The <code>readonly</code> attribute is optional and defaults to
<code>true</code> if not supplied. If the XML is writable then it will be
written to when Tomcat starts. <strong>WARNING:</strong> When the file is
written it will inherit the default file permissions for the user Tomcat
is running as. Ensure that these are appropriate to maintain the security
of your installation.</p>
<p>If referenced in a Realm, the UserDatabase will, by default, monitor
<code>pathname</code> for changes and reload the file if a change in the
last modified time is observed. This can be disabled by setting the
<code>watchSource</code> attribute to <code>false</code>.
</p>
<h5>3. Configure the Realm</h5>
<p>Configure a UserDatabase Realm to use this resource as described in the
<a href="config/realm.html">Realm configuration documentation</a>.</p>
<p>Tomcat also include a <code>UserDatabase</code> that uses a
<code>DataSource</code> resource as the backend. The backend resource
must be declared in the same JNDI context as the user database that will use
it.</p>
<p>The steps required to set up a global UserDatabase resource are described
below.</p>
<h5>1. Database schema</h5>
<p>The database shema for the user database is flexible. It can be the same
as the schema used for the <code>DataSourceRealm</code>, with only a table
for users (user name, password), and another one listing the roles
associated with each user. To support the full <code>UserDatabase</code>
features, it must include additional tables for groups, and is
compatible with referential integrity between users, groups and roles.</p>
<p>The full featured schema with groups and referential integrity
could be:</p>
<source><![CDATA[create table users (
user_name varchar(32) not null primary key,
user_pass varchar(64) not null,
user_fullname varchar(128)
-- Add more attributes as needed
);
<p>Next, modify <code>$CATALINA_BASE/conf/server.xml</code> to create the
UserDatabase resource based on your <code>DataSource</code> and its schema.
It should look something like this:</p>
<source><![CDATA[<Resource name="UserDatabase" auth="Container" type="org.apache.catalina.UserDatabase"
description="User database that can be updated and saved"
factory="org.apache.catalina.users.DataSourceUserDatabaseFactory"
dataSourceName="jdbc/authority" readonly="false"
userTable="users" userNameCol="user_name" userCredCol="user_pass"
userRoleTable="user_roles" roleNameCol="role_name"
roleTable="roles" groupTable="groups" userGroupTable="user_groups"
groupRoleTable="group_roles" groupNameCol="group_name" />]]></source>
<p>The <code>dataSourceName</code> attribute is the JNDI name of the
<code>DataSource</code> that will be the backend for the
<code>UserDatabase</code>. It must be declared in the same JNDI
<code>Context</code> as the <code>UserDatabase</code>. Please refer to the
<a href="#JDBC_Data_Sources"><code>DataSource</code> resources</a>
documentation for further instructions.</p>
<p>The <code>readonly</code> attribute is optional and defaults to
<code>true</code> if not supplied. If the database is writable then changes
made through the Tomcat management to the <code>UserDatabase</code> can
be persisted to the database using the <code>save</code> operation.</p>
<p>Alternately, changes can also be made directly to the backend database.
</p>
<h5>3. Resource configuration</h5>
<attributes>
<attribute name="dataSourceName" required="true">
<p>The name of the JNDI JDBC DataSource for this UserDatabase.</p>
</attribute>
<attribute name="groupNameCol" required="false">
<p>Name of the column, in the "groups", "group roles" and "user groups"
tables, that contains the group's name.
</attribute>
<attribute name="groupRoleTable" required="false">
<p>Name of the "group roles" table, which must contain columns
named by the <code>groupNameCol</code> and <code>roleNameCol</code>
attributes.</p>
</attribute>
<attribute name="groupTable" required="false">
<p>Name of the "groups" table, which must contain columns named
by the <code>groupNameCol</code> attribute.</p>
</attribute>
<attribute name="readonly" required="false">
<p>If this is set to <code>true</code>, then changes to the
<code>UserDatabase</code> can be persisted to the
<code>DataSource</code> by using the <code>save</code> method.
The default value is <code>true</code>.</p>
</attribute>
<attribute name="roleAndGroupDescriptionCol" required="false">
<p>Name of the column, in the "roles" and "groups" tables, that contains
the description for the roles and groups.</p>
</attribute>
<attribute name="roleNameCol" required="false">
<p>Name of the column, in the "roles", "user roles" and "group roles"
tables, which contains a role name assigned to the corresponding
user.</p>
<p>This attribute is <strong>required</strong> in majority of
configurations. See <strong>allRolesMode</strong> attribute of the
associated realm for a rare case when it can be omitted.</p>
</attribute>
<attribute name="roleTable" required="false">
<p>Name of the "roles" table, which must contain columns named
by the <code>roleNameCol</code> attribute.</p>
</attribute>
<attribute name="userCredCol" required="true">
<p>Name of the column, in the "users" table, which contains
the user's credentials (i.e. password). If a
<code>CredentialHandler</code> is specified, this component
will assume that the passwords have been encoded with the
specified algorithm. Otherwise, they will be assumed to be
in clear text.</p>
</attribute>
<attribute name="userGroupTable" required="false">
<p>Name of the "user groups" table, which must contain columns
named by the <code>userNameCol</code> and <code>groupNameCol</code>
attributes.</p>
</attribute>
<attribute name="userNameCol" required="true">
<p>Name of the column, in the "users", "user groups" and "user roles"
tables, that contains the user's username.
</attribute>
<attribute name="userFullNameCol" required="false">
<p>Name of the column, in the "users" table, that contains the user's
full name.</p>
</attribute>
<attribute name="userRoleTable" required="false">
<p>Name of the "user roles" table, which must contain columns
named by the <code>userNameCol</code> and <code>roleNameCol</code>
attributes.</p>
<p>This attribute is <strong>required</strong> in majority of
configurations. See <strong>allRolesMode</strong> attribute of the
associated realm for a rare case when it can be omitted.</p>
</attribute>
<attribute name="userTable" required="true">
<p>Name of the "users" table, which must contain columns named
by the <code>userNameCol</code> and <code>userCredCol</code>
attributes.</p>
</attribute>
</attributes>
<h5>4. Configure the Realm</h5>
<p>Configure a UserDatabase Realm to use this resource as described in the
<a href="config/realm.html">Realm configuration documentation</a>.</p>
</subsection>
<subsection name="Jakarta Mail Sessions">
<h5>0. Introduction</h5>
<p>In many web applications, sending electronic mail messages is a
required part of the system's functionality. The
<a href="https://jakartaee.github.io/mail-api/">Jakarta Mail</a> API
makes this process relatively straightforward, but requires many
configuration details that the client application must be aware of
(including the name of the SMTP host to be used for message sending).</p>
<p>Tomcat includes a standard resource factory that will create
<code>jakarta.mail.Session</code> session instances for you, already
configured to connect to an SMTP server.
In this way, the application is totally insulated from changes in the
email server configuration environment - it simply asks for, and receives,
a preconfigured session whenever needed.</p>
<p>The steps required for this are outlined below.</p>
<h5>1. Declare Your Resource Requirements</h5>
<p>The first thing you should do is modify the web application deployment
descriptor (<code>/WEB-INF/web.xml</code>) to declare the JNDI name under
which you will look up preconfigured sessions. By convention, all such
names should resolve to the <code>mail</code> subcontext (relative to the
standard <code>java:comp/env</code> naming context that is the root of
all provided resource factories. A typical <code>web.xml</code> entry
might look like this:</p>
<source><![CDATA[<resource-ref>
<description>
Resource reference to a factory for jakarta.mail.Session
instances that may be used for sending electronic mail
messages, preconfigured to connect to the appropriate
SMTP server.
</description>
<res-ref-name>
mail/Session
</res-ref-name>
<res-type>
jakarta.mail.Session
</res-type>
<res-auth>
Container
</res-auth>
</resource-ref>]]></source>
<p><strong>WARNING</strong> - Be sure you respect the element ordering
that is required by the DTD for web application deployment descriptors!
See the
<a href="https://cwiki.apache.org/confluence/display/TOMCAT/Specifications">Servlet
Specification</a> for details.</p>
<h5>2. Code Your Application's Use Of This Resource
<p>A typical use of this resource reference might look like this:</p>
<source><![CDATA[Context initCtx = new InitialContext();
Context envCtx = (Context) initCtx.lookup("java:comp/env");
Session session = (Session) envCtx.lookup("mail/Session");
Message message = new MimeMessage(session);
message.setFrom(new InternetAddress(request.getParameter("from")));
InternetAddress to[] = new InternetAddress[1];
to[0] = new InternetAddress(request.getParameter("to"));
message.setRecipients(Message.RecipientType.TO, to);
message.setSubject(request.getParameter("subject"));
message.setContent(request.getParameter("content"), "text/plain");
Transport.send(message);]]></source>
<p>Note that the application uses the same resource reference name
that was declared in the web application deployment descriptor. This
is matched up against the resource factory that is configured in the
<a href="config/context.html"><code><Context></code></a> element
for the web application as described below.</p>
<h5>3. Configure Tomcat's Resource Factory
<p>To configure Tomcat's resource factory, add an elements like this to the
<a href="config/context.html"><code><Context></code></a> element for
this web application.</p>
<p>Note that the resource name (here, <code>mail/Session</code>) must
match the value specified in the web application deployment descriptor.
Customize the value of the <code>mail.smtp.host</code> parameter to
point at the server that provides SMTP service for your network.</p>
<p>Additional resource attributes and values will be converted to properties
and values and passed to
<code>jakarta.mail.Session.getInstance(java.util.Properties)</code> as part of
the <code>java.util.Properties</code> collection. In addition to the
properties defined in Appendix A of the Jakarta Mail specification, individual
providers may also support additional properties.
</p>
<p>If the resource is configured with a <code>password</code> attribute and
either a <code>mail.smtp.user</code> or <code>mail.user</code> attribute
then Tomcat's resource factory will configure and add a
<code>jakarta.mail.Authenticator</code> to the mail session.</p>
<p>Unpackage the distribution and place jakarta.mail-api-2.1.0.jar into
$CATALINA_HOME/lib so that it is available to Tomcat during the
initialization of the mail Session Resource.
<strong>Note:</strong> placing this jar in both $CATALINA_HOME/lib and a web
application's lib folder will cause an error, so ensure you have it in the
$CATALINA_HOME/lib location only.
</p>
<p>Unpackage the implementation and place the jar file(s) into
$CATALINA_HOME/lib.</p>
<p>Note: Other implementations may be available</p>
<h5>6. Restart Tomcat</h5>
<p>For the additional JAR to be visible to Tomcat, it is necessary for the
Tomcat instance to be restarted.</p>
<h5>Example Application</h5>
<p>The <code>/examples</code> application included with Tomcat contains
an example of utilizing this resource factory. It is accessed via the "JSP Examples" link. The source code for the servlet that actually
sends the mail message is in
<code>/WEB-INF/classes/SendMailServlet.java</code>.</p>
<p><strong>WARNING</strong> - The default configuration assumes that there
is an SMTP server listing on port 25 on <code>localhost</code>. If this is
not the case, edit the
<a href="config/context.html"><code><Context></code></a> element for
this web application and modify the parameter value for the
<code>mail.smtp.host</code> parameter to be the host name of an SMTP server
on your network.</p>
</subsection>
<subsection name="JDBC Data Sources">
<h5>0. Introduction</h5>
<p>Many web applications need to access a database via a JDBC driver,
to support the functionality required by that application. The Jakarta EE
Platform Specification requires Jakarta EE Application Servers to make
available a <em>DataSource</em> implementation (that is, a connection
pool for JDBC connections) for this purpose. Tomcat offers exactly
the same support, so that database-based applications you develop on
Tomcat using this service will run unchanged on any Jakarta EE server.</p>
<p><strong>NOTE</strong> - The default data source support in Tomcat
is based on the <strong>DBCP 2</strong> connection pool from the
<a href="https://commons.apache.org/">Commons</a>
project. However, it is possible to use any other connection pool
that implements <code>javax.sql.DataSource</code>, by writing your
own custom resource factory, as described
<a href="#Adding_Custom_Resource_Factories">below</a>.</p>
<h5>1. Install Your JDBC Driver</h5>
<p>Use of the <em>JDBC Data Sources</em> JNDI Resource Factory requires
that you make an appropriate JDBC driver available to both Tomcat internal
classes and to your web application. This is most easily accomplished by
installing the driver's JAR file(s) into the
<code>$CATALINA_HOME/lib</code> directory, which makes the driver
available both to the resource factory and to your application.</p>
<h5>2. Declare Your Resource Requirements</h5>
<p>Next, modify the web application deployment descriptor
(<code>/WEB-INF/web.xml</code>) to declare the JNDI name under
which you will look up preconfigured data source. By convention, all such
names should resolve to the <code>jdbc</code> subcontext (relative to the
standard <code>java:comp/env</code> naming context that is the root of
all provided resource factories. A typical <code>web.xml</code> entry
might look like this:</p>
<source><![CDATA[<resource-ref>
<description>
Resource reference to a factory for java.sql.Connection
instances that may be used for talking to a particular
database that is configured in the <Context>
configuration for the web application.
</description>
<res-ref-name>
jdbc/EmployeeDB
</res-ref-name>
<res-type>
javax.sql.DataSource
</res-type>
<res-auth>
Container
</res-auth>
</resource-ref>]]></source>
<p><strong>WARNING</strong> - Be sure you respect the element ordering
that is required by the DTD for web application deployment descriptors!
See the
<a href="https://cwiki.apache.org/confluence/display/TOMCAT/Specifications">Servlet
Specification</a> for details.</p>
<h5>3. Code Your Application's Use Of This Resource
<p>A typical use of this resource reference might look like this:</p>
<source><![CDATA[Context initCtx = new InitialContext();
Context envCtx = (Context) initCtx.lookup("java:comp/env");
DataSource ds = (DataSource)
envCtx.lookup("jdbc/EmployeeDB");
Connection conn = ds.getConnection();
... use this connection to access the database ...
conn.close();]]></source>
<p>Note that the application uses the same resource reference name that was
declared in the web application deployment descriptor. This is matched up
against the resource factory that is configured in the
<a href="config/context.html"><code><Context></code></a> element for
the web application as described below.</p>
<h5>4. Configure Tomcat's Resource Factory
<p>To configure Tomcat's resource factory, add an element like this to the
<a href="config/context.html"><code><Context></code></a> element for
the web application.</p>
<p>Note that the resource name (here, <code>jdbc/EmployeeDB</code>) must
match the value specified in the web application deployment descriptor.</p>
<p>This example assumes that you are using the HypersonicSQL database
JDBC driver. Customize the <code>driverClassName</code> and
<code>driverName</code> parameters to match your actual database's
JDBC driver and connection URL.</p>
<p>The configuration properties for Tomcat's standard data source
resource factory
(<code>org.apache.tomcat.dbcp.dbcp2.BasicDataSourceFactory</code>) are
as follows:</p>
<ul>
<li><strong>driverClassName</strong> - Fully qualified Java class name
of the JDBC driver to be used.</li>
<li><strong>username</strong> - Database username to be passed to our
JDBC driver.</li>
<li><strong>password</strong> - Database password to be passed to our
JDBC driver.</li>
<li><strong>url</strong> - Connection URL to be passed to our JDBC driver.
(For backwards compatibility, the property <code>driverName</code>
is also recognized.)</li>
<li><strong>initialSize</strong> - The initial number of connections
that will be created in the pool during pool initialization. Default: 0</li>
<li><strong>maxTotal</strong> - The maximum number of connections
that can be allocated from this pool at the same time. Default: 8</li>
<li><strong>minIdle</strong> - The minimum number of connections that
will sit idle in this pool at the same time. Default: 0</li>
<li><strong>maxIdle</strong> - The maximum number of connections that
can sit idle in this pool at the same time. Default: 8</li>
<li><strong>maxWaitMillis</strong> - The maximum number of milliseconds that the
pool will wait (when there are no available connections) for a
connection to be returned before throwing an exception. Default: -1 (infinite)</li>
</ul>
<p>Some additional properties handle connection validation:</p>
<ul>
<li><strong>validationQuery</strong> - SQL query that can be used by the
pool to validate connections before they are returned to the
application. If specified, this query MUST be an SQL SELECT
statement that returns at least one row.</li>
<li><strong>validationQueryTimeout</strong> - Timeout in seconds
for the validation query to return. Default: -1 (infinite)</li>
<li><strong>testOnBorrow</strong> - true or false: whether a connection
should be validated using the validation query each time it is
borrowed from the pool. Default: true</li>
<li><strong>testOnReturn</strong> - true or false: whether a connection
should be validated using the validation query each time it is
returned to the pool. Default: false</li>
</ul>
<p>The optional evictor thread is responsible for shrinking the pool
by removing any connections which are idle for a long time. The evictor
does not respect <code>minIdle</code>. Note that you do not need to
activate the evictor thread if you only want the pool to shrink according
to the configured <code>maxIdle</code> property.</p>
<p>The evictor is disabled by default and can be configured using
the following properties:</p>
<ul>
<li><strong>timeBetweenEvictionRunsMillis</strong> - The number of
milliseconds between consecutive runs of the evictor.
Default: -1 (disabled)</li>
<li><strong>numTestsPerEvictionRun</strong> - The number of connections
that will be checked for idleness by the evictor during each
run of the evictor. Default: 3</li>
<li><strong>minEvictableIdleTimeMillis</strong> - The idle time in
milliseconds after which a connection can be removed from the pool
by the evictor. Default: 30*60*1000 (30 minutes)</li>
<li><strong>testWhileIdle</strong> - true or false: whether a connection
should be validated by the evictor thread using the validation query
while sitting idle in the pool. Default: false</li>
</ul>
<p>Another optional feature is the removal of abandoned connections.
A connection is called abandoned if the application does not return it
to the pool for a long time. The pool can close such connections
automatically and remove them from the pool. This is a workaround
for applications leaking connections.</p>
<p>The abandoning feature is disabled by default and can be configured
using the following properties:</p>
<ul>
<li><strong>removeAbandonedOnBorrow</strong> - true or false: whether to
remove abandoned connections from the pool when a connection is
borrowed. Default: false</li>
<li><strong>removeAbandonedOnMaintenance</strong> - true or false: whether
to remove abandoned connections from the pool during pool maintenance.
Default: false</li>
<li><strong>removeAbandonedTimeout</strong> - The number of
seconds after which a borrowed connection is assumed to be abandoned.
Default: 300</li>
<li><strong>logAbandoned</strong> - true or false: whether to log
stack traces for application code which abandoned a statement
or connection. This adds serious overhead. Default: false</li>
</ul>
<p>Finally there are various properties that allow further fine tuning
of the pool behaviour:</p>
<ul>
<li><strong>defaultAutoCommit</strong> - true or false: default
auto-commit state of the connections created by this pool.
Default: true</li>
<li><strong>defaultReadOnly</strong> - true or false: default
read-only state of the connections created by this pool.
Default: false</li>
<li><strong>defaultTransactionIsolation</strong> - This sets the
default transaction isolation level. Can be one of
<code>NONE</code>, <code>READ_COMMITTED</code>,
<code>READ_UNCOMMITTED</code>, <code>REPEATABLE_READ</code>,
<code>SERIALIZABLE</code>. Default: no default set</li>
<li><strong>poolPreparedStatements</strong> - true or false: whether to
pool PreparedStatements and CallableStatements. Default: false</li>
<li><strong>maxOpenPreparedStatements</strong> - The maximum number of open
statements that can be allocated from the statement pool at the same time.
Default: -1 (unlimited)</li>
<li><strong>defaultCatalog</strong> - The name of the default catalog.
Default: not set</li>
<li><strong>connectionInitSqls</strong> - A list of SQL statements
run once after a Connection is created. Separate multiple statements
by semicolons (<code>;</code>). Default: no statement</li>
<li><strong>connectionProperties</strong> - A list of driver specific
properties passed to the driver for creating connections. Each
property is given as <code>name=value</code>, multiple properties
are separated by semicolons (<code>;</code>). Default: no properties</li>
<li><strong>accessToUnderlyingConnectionAllowed</strong> - true or false: whether
accessing the underlying connections is allowed. Default: false</li>
</ul>
<p>For more details, please refer to the Commons DBCP 2 documentation.</p>
</subsection>
</section>
<section name="Adding Custom Resource Factories">
<p>If none of the standard resource factories meet your needs, you can write
your own factory and integrate it into Tomcat, and then configure the use
of this factory in the
<a href="config/context.html"><code><Context></code></a> element for
the web application. In the example below, we will create a factory that only
knows how to create <code>com.mycompany.MyBean</code> beans from the
<a href="#Generic_JavaBean_Resources">Generic JavaBean Resources</a> example
above.</p>
<h4>1. Write A Resource Factory Class</h4>
<p>You must write a class that implements the JNDI service provider
<code>javax.naming.spi.ObjectFactory</code> interface. Every time your
web application calls <code>lookup()</code> on a context entry that is
bound to this factory (assuming that the factory is configured with
<code>singleton="false"</code>), the
<code>getObjectInstance()</code> method is called, with the following
arguments:</p>
<ul>
<li><strong>Object obj</strong> - The (possibly null) object containing
location or reference information that can be used in creating an object.
For Tomcat, this will always be an object of type
<code>javax.naming.Reference</code>, which contains the class name of
this factory class, as well as the configuration properties (from the
<a href="config/context.html"><code><Context></code></a> for the
web application) to use in creating objects to be returned.</li>
<li><strong>Name name</strong> - The name to which this factory is bound
relative to <code>nameCtx</code>, or <code>null</code> if no name
is specified.</li>
<li><strong>Context nameCtx</strong> - The context relative to which the
<code>name</code> parameter is specified, or <code>null</code> if
<code>name</code> is relative to the default initial context.</li>
<li><strong>Hashtable environment</strong> - The (possibly null)
environment that is used in creating this object. This is generally
ignored in Tomcat object factories.</li>
</ul>
<p>To create a resource factory that knows how to produce <code>MyBean</code>
instances, you might create a class like this:</p>
public class MyBeanFactory implements ObjectFactory {
public Object getObjectInstance(Object obj,
Name name2, Context nameCtx, Hashtable environment)
throws NamingException {
// Acquire an instance of our specified bean class
MyBean bean = new MyBean();
// Customize the bean properties from our attributes
Reference ref = (Reference) obj; Enumeration addrs = ref.getAll();
while (addrs.hasMoreElements()) {
RefAddr addr = (RefAddr) addrs.nextElement();
String name = addr.getType();
String value = (String) addr.getContent();
if (name.equals("foo")) {
bean.setFoo(value);
} else if (name.equals("bar")) {
try {
bean.setBar(Integer.parseInt(value));
} catch (NumberFormatException e) {
throw new NamingException("Invalid 'bar' value " + value);
}
}
}
// Return the customized instance
return (bean);
}
}]]></source>
<p>In this example, we are unconditionally creating a new instance of
the <code>com.mycompany.MyBean</code> class, and populating its properties
based on the parameters included in the <code><ResourceParams></code> element that configures this factory (see below). You should note that any
parameter named <code>factory</code> should be skipped - that parameter is
used to specify the name of the factory class itself (in this case,
<code>com.mycompany.MyBeanFactory</code>) rather than a property of the
bean being configured.</p>
<p>You will need to compile this class against a class path that includes
all of the JAR files in the <code>$CATALINA_HOME/lib</code> directory. When you are through,
place the factory class (and the corresponding bean class) unpacked under
<code>$CATALINA_HOME/lib</code>, or in a JAR file inside
<code>$CATALINA_HOME/lib</code>. In this way, the required class
files are visible to both Catalina internal resources and your web
application.</p>
<h4>2. Declare Your Resource Requirements</h4>
<p>Next, modify your web application deployment descriptor
(<code>/WEB-INF/web.xml</code>) to declare the JNDI name under which
you will request new instances of this bean. The simplest approach is
to use a <code><resource-env-ref></code> element, like this:</p>
<p><strong>WARNING</strong> - Be sure you respect the element ordering
that is required by the DTD for web application deployment descriptors!
See the
<a href="https://cwiki.apache.org/confluence/display/TOMCAT/Specifications">Servlet
Specification</a> for details.</p>
<h4>3. Code Your Application's Use Of This Resource
<p>A typical use of this resource environment reference might look
like this:</p>
<p>To configure Tomcat's resource factory, add an elements like this to the
<a href="config/context.html"><code><Context></code></a> element for
this web application.</p>
<p>Note that the resource name (here, <code>bean/MyBeanFactory</code>
must match the value specified in the web application deployment
descriptor. We are also initializing the value of the <code>bar</code>
property, which will cause <code>setBar(23)</code> to be called before
the new bean is returned. Because we are not initializing the
<code>foo</code> property (although we could have), the bean will
contain whatever default value is set up by its constructor.</p>
<p>You will also note that, from the application developer's perspective,
the declaration of the resource environment reference, and the programming
used to request new instances, is identical to the approach used for the
<em>Generic JavaBean Resources</em> example. This illustrates one of the
advantages of using JNDI resources to encapsulate functionality - you can
change the underlying implementation without necessarily having to
modify applications using the resources, as long as you maintain
compatible APIs.</p>
</section>
</body>
</document>
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