https://tomcat.apache.org/: Tomcat Servlet Engine Core Classes and Standard implementations 
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 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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package org.apache.catalina;

import java.beans.PropertyChangeListener;
import java.io.File;

import javax.management.ObjectName;

import org.apache.catalina.connector.Request;
import org.apache.catalina.connector.Response;
import org.apache.juli.logging.Log;



A Container is an object that can execute requests received from
a client, and return responses based on those requests.  A Container may
optionally support a pipeline of Valves that process the request in an
order configured at runtime, by implementing the Pipeline interface
as well.


Containers will exist at several conceptual levels within Catalina.  The
following examples represent common cases:

    

  • Engine - Representation of the entire Catalina servlet engine,
    most likely containing one or more subcontainers that are either Host
    or Context implementations, or other custom groups.

  • Host - Representation of a virtual host containing a number
    of Contexts.

  • Context - Representation of a single ServletContext, which will
    typically contain one or more Wrappers for the supported servlets.

  • Wrapper - Representation of an individual servlet definition
    (which may support multiple servlet instances if the servlet itself
    implements SingleThreadModel).


A given deployment of Catalina need not include Containers at all of the
levels described above.  For example, an administration application
embedded within a network device (such as a router) might only contain
a single Context and a few Wrappers, or even a single Wrapper if the
application is relatively small.  Therefore, Container implementations
need to be designed so that they will operate correctly in the absence
of parent Containers in a given deployment.


A Container may also be associated with a number of support components
that provide functionality which might be shared (by attaching it to a
parent Container) or individually customized.  The following support
components are currently recognized:

    

  • Loader - Class loader to use for integrating new Java classes
    for this Container into the JVM in which Catalina is running.

  • Logger - Implementation of the log() method
    signatures of the ServletContext interface.

  • Manager - Manager for the pool of Sessions associated with
    this Container.

  • Realm - Read-only interface to a security domain, for
    authenticating user identities and their corresponding roles.

  • Resources - JNDI directory context enabling access to static
    resources, enabling custom linkages to existing server components when
    Catalina is embedded in a larger server.



Author:Craig R. McClanahan, Remy Maucherat
/**
 * A <b>Container</b> is an object that can execute requests received from
 * a client, and return responses based on those requests.  A Container may
 * optionally support a pipeline of Valves that process the request in an
 * order configured at runtime, by implementing the <b>Pipeline</b> interface
 * as well.
 * <p>
 * Containers will exist at several conceptual levels within Catalina.  The
 * following examples represent common cases:
 * <ul>
 * <li><b>Engine</b> - Representation of the entire Catalina servlet engine,
 *     most likely containing one or more subcontainers that are either Host
 *     or Context implementations, or other custom groups.
 * <li><b>Host</b> - Representation of a virtual host containing a number
 *     of Contexts.
 * <li><b>Context</b> - Representation of a single ServletContext, which will
 *     typically contain one or more Wrappers for the supported servlets.
 * <li><b>Wrapper</b> - Representation of an individual servlet definition
 *     (which may support multiple servlet instances if the servlet itself
 *     implements SingleThreadModel).
 * </ul>
 * A given deployment of Catalina need not include Containers at all of the
 * levels described above.  For example, an administration application
 * embedded within a network device (such as a router) might only contain
 * a single Context and a few Wrappers, or even a single Wrapper if the
 * application is relatively small.  Therefore, Container implementations
 * need to be designed so that they will operate correctly in the absence
 * of parent Containers in a given deployment.
 * <p>
 * A Container may also be associated with a number of support components
 * that provide functionality which might be shared (by attaching it to a
 * parent Container) or individually customized.  The following support
 * components are currently recognized:
 * <ul>
 * <li><b>Loader</b> - Class loader to use for integrating new Java classes
 *     for this Container into the JVM in which Catalina is running.
 * <li><b>Logger</b> - Implementation of the <code>log()</code> method
 *     signatures of the <code>ServletContext</code> interface.
 * <li><b>Manager</b> - Manager for the pool of Sessions associated with
 *     this Container.
 * <li><b>Realm</b> - Read-only interface to a security domain, for
 *     authenticating user identities and their corresponding roles.
 * <li><b>Resources</b> - JNDI directory context enabling access to static
 *     resources, enabling custom linkages to existing server components when
 *     Catalina is embedded in a larger server.
 * </ul>
 *
 * @author Craig R. McClanahan
 * @author Remy Maucherat
 */
public interface Container extends Lifecycle {


    // ----------------------------------------------------- Manifest Constants


    
The ContainerEvent event type sent when a child container is added
by addChild().

/**
     * The ContainerEvent event type sent when a child container is added
     * by <code>addChild()</code>.
     */
    public static final String ADD_CHILD_EVENT = "addChild";


    
The ContainerEvent event type sent when a valve is added
by addValve(), if this Container supports pipelines.

/**
     * The ContainerEvent event type sent when a valve is added
     * by <code>addValve()</code>, if this Container supports pipelines.
     */
    public static final String ADD_VALVE_EVENT = "addValve";


    
The ContainerEvent event type sent when a child container is removed
by removeChild().

/**
     * The ContainerEvent event type sent when a child container is removed
     * by <code>removeChild()</code>.
     */
    public static final String REMOVE_CHILD_EVENT = "removeChild";


    
The ContainerEvent event type sent when a valve is removed
by removeValve(), if this Container supports pipelines.

/**
     * The ContainerEvent event type sent when a valve is removed
     * by <code>removeValve()</code>, if this Container supports pipelines.
     */
    public static final String REMOVE_VALVE_EVENT = "removeValve";


    // ------------------------------------------------------------- Properties

    
Obtain the log to which events for this container should be logged.

Returns:The Logger with which this Container is associated.  If there is
        no associated Logger, return the Logger associated with the
        parent Container (if any); otherwise return null.
/**
     * Obtain the log to which events for this container should be logged.
     *
     * @return The Logger with which this Container is associated.  If there is
     *         no associated Logger, return the Logger associated with the
     *         parent Container (if any); otherwise return <code>null</code>.
     */
    public Log getLogger();


    
Return the logger name that the container will use.

Returns:the abbreviated name of this container for logging messages
/**
     * Return the logger name that the container will use.
     * @return the abbreviated name of this container for logging messages
     */
    public String getLogName();


    
Obtain the JMX name for this container.

Returns:the JMX name associated with this container.
/**
     * Obtain the JMX name for this container.
     *
     * @return the JMX name associated with this container.
     */
    public ObjectName getObjectName();


    
Obtain the JMX domain under which this container will be / has been
registered.

Returns:The JMX domain name
/**
     * Obtain the JMX domain under which this container will be / has been
     * registered.
     *
     * @return The JMX domain name
     */
    public String getDomain();


    
Calculate the key properties string to be added to an object's ObjectName to indicate that it is associated with this container. 
Returns:         A string suitable for appending to the ObjectName
/**
     * Calculate the key properties string to be added to an object's
     * {@link ObjectName} to indicate that it is associated with this container.
     *
     * @return          A string suitable for appending to the ObjectName
     *
     */
    public String getMBeanKeyProperties();


    
Return the Pipeline object that manages the Valves associated with
this Container.

Returns:The Pipeline
/**
     * Return the Pipeline object that manages the Valves associated with
     * this Container.
     *
     * @return The Pipeline
     */
    public Pipeline getPipeline();


    
Get the Cluster for this container.

Returns:The Cluster with which this Container is associated. If there is
        no associated Cluster, return the Cluster associated with our
        parent Container (if any); otherwise return null.
/**
     * Get the Cluster for this container.
     *
     * @return The Cluster with which this Container is associated. If there is
     *         no associated Cluster, return the Cluster associated with our
     *         parent Container (if any); otherwise return <code>null</code>.
     */
    public Cluster getCluster();


    
Set the Cluster with which this Container is associated.

Params:
  • cluster – the Cluster with which this Container is associated.
/**
     * Set the Cluster with which this Container is associated.
     *
     * @param cluster the Cluster with which this Container is associated.
     */
    public void setCluster(Cluster cluster);


    
Get the delay between the invocation of the backgroundProcess method on this container and its children. Child containers will not be invoked if their delay value is positive (which would mean they are using their own thread). Setting this to a positive value will cause a thread to be spawned. After waiting the specified amount of time, the thread will invoke the backgroundProcess() method on this container and all children with non-positive delay values. 
Returns:The delay between the invocation of the backgroundProcess method
        on this container and its children. A non-positive value
        indicates that background processing will be managed by the
        parent.
/**
     * Get the delay between the invocation of the backgroundProcess method on
     * this container and its children. Child containers will not be invoked if
     * their delay value is positive (which would mean they are using their own
     * thread). Setting this to a positive value will cause a thread to be
     * spawned. After waiting the specified amount of time, the thread will
     * invoke the {@link #backgroundProcess()} method on this container and all
     * children with non-positive delay values.
     *
     * @return The delay between the invocation of the backgroundProcess method
     *         on this container and its children. A non-positive value
     *         indicates that background processing will be managed by the
     *         parent.
     */
    public int getBackgroundProcessorDelay();


    
Set the delay between the invocation of the execute method on this
container and its children.

Params:
  • delay – The delay in seconds between the invocation of
             backgroundProcess methods
/**
     * Set the delay between the invocation of the execute method on this
     * container and its children.
     *
     * @param delay The delay in seconds between the invocation of
     *              backgroundProcess methods
     */
    public void setBackgroundProcessorDelay(int delay);


    
Return a name string (suitable for use by humans) that describes this
Container.  Within the set of child containers belonging to a particular
parent, Container names must be unique.

Returns:The human readable name of this container.
/**
     * Return a name string (suitable for use by humans) that describes this
     * Container.  Within the set of child containers belonging to a particular
     * parent, Container names must be unique.
     *
     * @return The human readable name of this container.
     */
    public String getName();


    
Set a name string (suitable for use by humans) that describes this
Container.  Within the set of child containers belonging to a particular
parent, Container names must be unique.

Params:
  • name – New name of this container
Throws:
  • IllegalStateException – if this Container has already been
 added to the children of a parent Container (after which the name
 may not be changed)
/**
     * Set a name string (suitable for use by humans) that describes this
     * Container.  Within the set of child containers belonging to a particular
     * parent, Container names must be unique.
     *
     * @param name New name of this container
     *
     * @exception IllegalStateException if this Container has already been
     *  added to the children of a parent Container (after which the name
     *  may not be changed)
     */
    public void setName(String name);


    
Get the parent container.

Returns:Return the Container for which this Container is a child, if
        there is one. If there is no defined parent, return
        null.
/**
     * Get the parent container.
     *
     * @return Return the Container for which this Container is a child, if
     *         there is one. If there is no defined parent, return
     *         <code>null</code>.
     */
    public Container getParent();


    
Set the parent Container to which this Container is being added as a
child.  This Container may refuse to become attached to the specified
Container by throwing an exception.

Params:
  • container – Container to which this Container is being added
 as a child
Throws:
/**
     * Set the parent Container to which this Container is being added as a
     * child.  This Container may refuse to become attached to the specified
     * Container by throwing an exception.
     *
     * @param container Container to which this Container is being added
     *  as a child
     *
     * @exception IllegalArgumentException if this Container refuses to become
     *  attached to the specified Container
     */
    public void setParent(Container container);


    
Get the parent class loader.

Returns:the parent class loader for this component. If not set, return getParent().getParentClassLoader(). If no parent has been set, return the system class loader.
/**
     * Get the parent class loader.
     *
     * @return the parent class loader for this component. If not set, return
     *         {@link #getParent()}.{@link #getParentClassLoader()}. If no
     *         parent has been set, return the system class loader.
     */
    public ClassLoader getParentClassLoader();


    
Set the parent class loader for this component. For Contexts this call is meaningful only before a Loader has
been configured, and the specified value (if non-null) should be
passed as an argument to the class loader constructor.

Params:
  • parent – The new parent class loader
/**
     * Set the parent class loader for this component. For {@link Context}s
     * this call is meaningful only <strong>before</strong> a Loader has
     * been configured, and the specified value (if non-null) should be
     * passed as an argument to the class loader constructor.
     *
     * @param parent The new parent class loader
     */
    public void setParentClassLoader(ClassLoader parent);


    
Obtain the Realm with which this Container is associated.

Returns:The associated Realm; if there is no associated Realm, the
        Realm associated with the parent Container (if any); otherwise
        return null.
/**
     * Obtain the Realm with which this Container is associated.
     *
     * @return The associated Realm; if there is no associated Realm, the
     *         Realm associated with the parent Container (if any); otherwise
     *         return <code>null</code>.
     */
    public Realm getRealm();


    
Set the Realm with which this Container is associated.

Params:
  • realm – The newly associated Realm
/**
     * Set the Realm with which this Container is associated.
     *
     * @param realm The newly associated Realm
     */
    public void setRealm(Realm realm);


    
Find the configuration path where a configuration resource
is located.

Params:
  • container – The container
  • resourceName – The resource file name
Returns:the configuration path
/**
     * Find the configuration path where a configuration resource
     * is located.
     * @param container The container
     * @param resourceName The resource file name
     * @return the configuration path
     */
    public static String getConfigPath(Container container, String resourceName) {
        StringBuilder result = new StringBuilder();
        Container host = null;
        Container engine = null;
        while (container != null) {
            if (container instanceof Host) {
                host = container;
            } else if (container instanceof Engine) {
                engine = container;
            }
            container = container.getParent();
        }
        if (host != null && ((Host) host).getXmlBase() != null) {
            result.append(((Host) host).getXmlBase()).append('/');
        } else {
            result.append("conf/");
            if (engine != null) {
                result.append(engine.getName()).append('/');
            }
            if (host != null) {
                result.append(host.getName()).append('/');
            }
        }
        result.append(resourceName);
        return result.toString();
    }


    
Return the Service to which this container belongs.

Params:
  • container – The container to start from
Returns:the Service, or null if not found
/**
     * Return the Service to which this container belongs.
     * @param container The container to start from
     * @return the Service, or null if not found
     */
    public static Service getService(Container container) {
        while (container != null && !(container instanceof Engine)) {
            container = container.getParent();
        }
        if (container == null) {
            return null;
        }
        return ((Engine) container).getService();
    }


    // --------------------------------------------------------- Public Methods


    
Execute a periodic task, such as reloading, etc. This method will be
invoked inside the classloading context of this container. Unexpected
throwables will be caught and logged.

/**
     * Execute a periodic task, such as reloading, etc. This method will be
     * invoked inside the classloading context of this container. Unexpected
     * throwables will be caught and logged.
     */
    public void backgroundProcess();


    
Add a new child Container to those associated with this Container,
if supported.  Prior to adding this Container to the set of children,
the child's setParent() method must be called, with this
Container as an argument.  This method may thrown an
IllegalArgumentException if this Container chooses not
to be attached to the specified Container, in which case it is not added

Params:
  • child – New child Container to be added
Throws:
/**
     * Add a new child Container to those associated with this Container,
     * if supported.  Prior to adding this Container to the set of children,
     * the child's <code>setParent()</code> method must be called, with this
     * Container as an argument.  This method may thrown an
     * <code>IllegalArgumentException</code> if this Container chooses not
     * to be attached to the specified Container, in which case it is not added
     *
     * @param child New child Container to be added
     *
     * @exception IllegalArgumentException if this exception is thrown by
     *  the <code>setParent()</code> method of the child Container
     * @exception IllegalArgumentException if the new child does not have
     *  a name unique from that of existing children of this Container
     * @exception IllegalStateException if this Container does not support
     *  child Containers
     */
    public void addChild(Container child);


    
Add a container event listener to this component.

Params:
  • listener – The listener to add
/**
     * Add a container event listener to this component.
     *
     * @param listener The listener to add
     */
    public void addContainerListener(ContainerListener listener);


    
Add a property change listener to this component.

Params:
  • listener – The listener to add
/**
     * Add a property change listener to this component.
     *
     * @param listener The listener to add
     */
    public void addPropertyChangeListener(PropertyChangeListener listener);


    
Obtain a child Container by name.

Params:
  • name – Name of the child Container to be retrieved
Returns:The child Container with the given name or null if
        no such child exists.
/**
     * Obtain a child Container by name.
     *
     * @param name Name of the child Container to be retrieved
     *
     * @return The child Container with the given name or <code>null</code> if
     *         no such child exists.
     */
    public Container findChild(String name);


    
Obtain the child Containers associated with this Container.

Returns:An array containing all children of this container. If this
        Container has no children, a zero-length array is returned.
/**
     * Obtain the child Containers associated with this Container.
     *
     * @return An array containing all children of this container. If this
     *         Container has no children, a zero-length array is returned.
     */
    public Container[] findChildren();


    
Obtain the container listeners associated with this Container.

Returns:An array containing the container listeners associated with this
        Container. If this Container has no registered container
        listeners, a zero-length array is returned.
/**
     * Obtain the container listeners associated with this Container.
     *
     * @return An array containing the container listeners associated with this
     *         Container. If this Container has no registered container
     *         listeners, a zero-length array is returned.
     */
    public ContainerListener[] findContainerListeners();


    
Remove an existing child Container from association with this parent
Container.

Params:
  • child – Existing child Container to be removed
/**
     * Remove an existing child Container from association with this parent
     * Container.
     *
     * @param child Existing child Container to be removed
     */
    public void removeChild(Container child);


    
Remove a container event listener from this component.

Params:
  • listener – The listener to remove
/**
     * Remove a container event listener from this component.
     *
     * @param listener The listener to remove
     */
    public void removeContainerListener(ContainerListener listener);


    
Remove a property change listener from this component.

Params:
  • listener – The listener to remove
/**
     * Remove a property change listener from this component.
     *
     * @param listener The listener to remove
     */
    public void removePropertyChangeListener(PropertyChangeListener listener);


    
Notify all container event listeners that a particular event has
occurred for this Container.  The default implementation performs
this notification synchronously using the calling thread.

Params:
  • type – Event type
  • data – Event data
/**
     * Notify all container event listeners that a particular event has
     * occurred for this Container.  The default implementation performs
     * this notification synchronously using the calling thread.
     *
     * @param type Event type
     * @param data Event data
     */
    public void fireContainerEvent(String type, Object data);


    
Log a request/response that was destined for this container but has been
handled earlier in the processing chain so that the request/response
still appears in the correct access logs.

Params:
  • request –       Request (associated with the response) to log
  • response –      Response (associated with the request) to log
  • time –          Time taken to process the request/response in
                     milliseconds (use 0 if not known)
  • useDefault –  Flag that indicates that the request/response should
                     be logged in the engine's default access log
/**
     * Log a request/response that was destined for this container but has been
     * handled earlier in the processing chain so that the request/response
     * still appears in the correct access logs.
     * @param request       Request (associated with the response) to log
     * @param response      Response (associated with the request) to log
     * @param time          Time taken to process the request/response in
     *                      milliseconds (use 0 if not known)
     * @param   useDefault  Flag that indicates that the request/response should
     *                      be logged in the engine's default access log
     */
    public void logAccess(Request request, Response response, long time,
            boolean useDefault);


    
Obtain the AccessLog to use to log a request/response that is destined
for this container. This is typically used when the request/response was
handled (and rejected) earlier in the processing chain so that the
request/response still appears in the correct access logs.

Returns:The AccessLog to use for a request/response destined for this
        container
/**
     * Obtain the AccessLog to use to log a request/response that is destined
     * for this container. This is typically used when the request/response was
     * handled (and rejected) earlier in the processing chain so that the
     * request/response still appears in the correct access logs.
     *
     * @return The AccessLog to use for a request/response destined for this
     *         container
     */
    public AccessLog getAccessLog();


    
Obtain the number of threads available for starting and stopping any
children associated with this container. This allows start/stop calls to
children to be processed in parallel.

Returns:The currently configured number of threads used to start/stop
        children associated with this container
/**
     * Obtain the number of threads available for starting and stopping any
     * children associated with this container. This allows start/stop calls to
     * children to be processed in parallel.
     *
     * @return The currently configured number of threads used to start/stop
     *         children associated with this container
     */
    public int getStartStopThreads();


    
Sets the number of threads available for starting and stopping any
children associated with this container. This allows start/stop calls to
children to be processed in parallel.

Params:
  • startStopThreads –    The new number of threads to be used
/**
     * Sets the number of threads available for starting and stopping any
     * children associated with this container. This allows start/stop calls to
     * children to be processed in parallel.
     * @param   startStopThreads    The new number of threads to be used
     */
    public void setStartStopThreads(int startStopThreads);


    
Obtain the location of CATALINA_BASE.

Returns: The location of CATALINA_BASE.
/**
     * Obtain the location of CATALINA_BASE.
     *
     * @return  The location of CATALINA_BASE.
     */
    public File getCatalinaBase();


    
Obtain the location of CATALINA_HOME.

Returns:The location of CATALINA_HOME.
/**
     * Obtain the location of CATALINA_HOME.
     *
     * @return The location of CATALINA_HOME.
     */
    public File getCatalinaHome();
}