UnboundID Server SDK

UnboundID Server SDK Documentation

ExampleHTTPServletExtension.java

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 * The contents of this file are subject to the terms of the
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 *
 * You can obtain a copy of the license at
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package com.unboundid.directory.sdk.examples;



import java.util.Arrays;
import java.util.Enumeration;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.Filter;

import com.unboundid.directory.sdk.http.api.HTTPServletExtension;
import com.unboundid.directory.sdk.http.config.HTTPServletExtensionConfig;
import com.unboundid.directory.sdk.http.types.HTTPServerContext;
import com.unboundid.ldap.sdk.LDAPException;
import com.unboundid.ldap.sdk.ResultCode;
import com.unboundid.util.args.ArgumentException;
import com.unboundid.util.args.ArgumentParser;
import com.unboundid.util.args.StringArgument;



/**
 * This class provides a simple example of an HTTP servlet extension which will
 * create a simple "Hello, World!" servlet.  It has two configuration arguments:
 * <UL>
 *   <LI>name -- The name to display in the servlet's hello message.  If this is
 *       not provided, then a default value of "World" will be used.</LI>
 *   <LI>path -- The path that should be used to invoke the servlet.  If this is
 *       not provided, then a default value of "/hello" will be used.</LI>
 * </UL>
 */
public final class ExampleHTTPServletExtension
       extends HTTPServletExtension
{
  /**
   * The name of the argument that will be used to specify the name that should
   * be used in the greeting.
   */
  private static final String ARG_NAME_NAME = "name";



  /**
   * The name of the argument that will be used to specify the path that will be
   * used to access the servlet.
   */
  private static final String ARG_NAME_PATH = "path";



  /**
   * The servlet filter that will be used with the servlet.
   */
  private static final ExampleServletFilter FILTER = new ExampleServletFilter();



  // Indicates whether one or more init parameters were provided.
  private static volatile boolean initParametersProvided = false;

  // Indicates whether the post-registration method has been called.
  private static volatile boolean postRegistrationMethodCalled = false;

  // Indicates whether the post-shutdown method has been called.
  private static volatile boolean postShutdownMethodCalled = false;

  // Indicates whether the servlet context was available in the
  // post-registration method.
  private static volatile boolean servletContextAvailable = false;

  // The servlet that has been created.
  private volatile ExampleHelloServlet servlet;

  // The path that will be used for the servlet.
  private volatile String path;



  /**
   * Creates a new instance of this HTTP servlet extension.  All HTTP servlet
   * extension implementations must include a default constructor, but any
   * initialization should generally be done in the {@code createServlet}
   * method.
   */
  public ExampleHTTPServletExtension()
  {
    servlet = null;
    path    = null;
  }



  /**
   * Retrieves a human-readable name for this extension.
   *
   * @return  A human-readable name for this extension.
   */
  @Override()
  public String getExtensionName()
  {
    return "Example HTTP Servlet Extension";
  }



  /**
   * Retrieves a human-readable description for this extension.  Each element
   * of the array that is returned will be considered a separate paragraph in
   * generated documentation.
   *
   * @return  A human-readable description for this extension, or {@code null}
   *          or an empty array if no description should be available.
   */
  @Override()
  public String[] getExtensionDescription()
  {
    return new String[]
    {
      "This HTTP servlet extension serves an example that may be used to " +
           "demonstrate the process for creating a third-party HTTP servlet " +
           "extension.  It will create a simple servlet which displays a " +
           "hello message."
    };
  }



  /**
   * Updates the provided argument parser to define any configuration arguments
   * which may be used by this HTTP servlet extension.  The argument parser may
   * also be updated to define relationships between arguments (e.g., to specify
   * required, exclusive, or dependent argument sets).
   *
   * @param  parser  The argument parser to be updated with the configuration
   *                 arguments which may be used by this HTTP servlet extension.
   *
   * @throws  ArgumentException  If a problem is encountered while updating the
   *                             provided argument parser.
   */
  @Override()
  public void defineConfigArguments(final ArgumentParser parser)
         throws ArgumentException
  {
    // Add an argument that allows you to specify the name to use in the
    // greeting.
    Character shortIdentifier = null;
    String    longIdentifier  = ARG_NAME_NAME;
    boolean   required        = false;
    int       maxOccurrences  = 1;
    String    placeholder     = "{name}";
    String    description     = "The name to use in the greeting.";
    String    defaultValue    = "World";
    parser.addArgument(new StringArgument(shortIdentifier, longIdentifier,
         required, maxOccurrences, placeholder, description, defaultValue));


    // Add an argument that allows you to specify the request path.
    shortIdentifier = null;
    longIdentifier  = ARG_NAME_PATH;
    required        = false;
    maxOccurrences  = 1;
    placeholder     = "{path}";
    description     = "The path to use to access the servlet.  Note that " +
         "changes to this argument will only take effect if the associated " +
         "HTTP connection handler (or the entire server) is stopped and " +
         "re-started.";
    defaultValue    = "/hello";
    parser.addArgument(new StringArgument(shortIdentifier, longIdentifier,
         required, maxOccurrences, placeholder, description, defaultValue));
  }



  /**
   * Creates an HTTP servlet extension using the provided information.
   *
   * @param  serverContext  A handle to the server context for the server in
   *                        which this extension is running.
   * @param  config         The general configuration for this HTTP servlet
   *                        extension.
   * @param  parser         The argument parser which has been initialized from
   *                        the configuration for this HTTP servlet extension.
   *
   * @return  The HTTP servlet that has been created.
   *
   * @throws  LDAPException  If a problem is encountered while attempting to
   *                         create the HTTP servlet.
   */
  @Override()
  public ExampleHelloServlet createServlet(
              final HTTPServerContext serverContext,
              final HTTPServletExtensionConfig config,
              final ArgumentParser parser)
         throws LDAPException
  {
    // Get the new greeting name.
    final StringArgument nameArg =
         (StringArgument) parser.getNamedArgument(ARG_NAME_NAME);

    // Get the servlet path.
    final StringArgument pathArg =
         (StringArgument) parser.getNamedArgument(ARG_NAME_PATH);
    path = pathArg.getValue();

    servlet = new ExampleHelloServlet(nameArg.getValue());
    return servlet;
  }



  /**
   * Retrieves a list of the request paths for which the associated servlet
   * should be invoked.  This method will be called after the
   * {@link #createServlet} method has been used to create the servlet instance.
   *
   * @return  A list of the request paths for which the associated servlet
   *          should be invoked.
   */
  @Override()
  public List<String> getServletPaths()
  {
    return Arrays.asList(path);
  }



  /**
   * Retrieves a map of initialization parameters that should be provided to the
   * servlet when it is initialized.
   *
   * @return  A map of initialization parameters that should be provided to the
   *          servlet when it is initialized, or an empty map if no
   *          initialization parameters are needed.
   */
  @Override()
  public Map<String,String> getServletInitParameters()
  {
    final LinkedHashMap<String,String> initParameters =
         new LinkedHashMap<String,String>(1);
    initParameters.put("foo", "bar");
    return initParameters;
  }



  /**
   * Retrieves the order in which the servlet should be started.  A value
   * greater than or equal to zero guarantees that the servlet will be started
   * as soon as the servlet engine has been started, in order of ascending
   * servlet init order values, before the {@code doPostRegistrationProcessing}
   * method has been called.  If the value is less than zero, the servlet may
   * not be started until a request is received for one of its registered paths.
   *
   * @return  The order in which the servlet should be started, or a negative
   *          value if startup order does not matter.
   */
  @Override()
  public int getServletInitOrder()
  {
    return 0;
  }



  /**
   * Retrieves a list of servlet filter instances that should be installed with
   * the created servlet instance, in the order they should be invoked.  If the
   * servlet is to be registered with multiple paths, then these filters will be
   * installed for all of those paths.
   *
   * @return  A list of servlet filter instances that should be installed with
   *          the created servlet instance, in the order that they should be
   *          invoked.  It may be {@code null} or empty if no servlet filters
   *          should be installed.
   */
  @Override()
  public List<Filter> getServletFilters()
  {
    return Arrays.<Filter>asList(FILTER);
  }



  /**
   * Performs any processing that may be needed after the servlet has been
   * registered with the servlet engine.  If the value returned from
   * {@link #getServletInitOrder()} is greater than or equal to zero, then the
   * servlet will have been started before this method is called.  If the value
   * returned from {@code getServletInitOrder()} is negative, then the servlet
   * may or may not have been started by the time this method is called.
   * <BR><BR>
   * Note that the associated servlet can also perform any necessary
   * initialization processing in the {@code init} method provided by the
   * servlet API.
   */
  @Override()
  public void doPostRegistrationProcessing()
  {
    final Enumeration<String> nameEnum = servlet.getInitParameterNames();
    initParametersProvided =
         ((nameEnum != null) && nameEnum.hasMoreElements());

    servletContextAvailable = (servlet.getServletContext() != null);

    postRegistrationMethodCalled = true;
  }



  /**
   * Performs any processing that may be needed after the servlet has been
   * taken out of service and the associated servlet engine has been shut down.
   * <BR><BR>
   * Note that the associated servlet can also perform any necessary
   * finalization processing in the {@code destroy} method provided by the
   * servlet API.  That method will be called after the servlet has been taken
   * out of service, but before the servlet engine has been shut down.
   */
  @Override()
  public void doPostShutdownProcessing()
  {
    postShutdownMethodCalled = true;
  }



  /**
   * Indicates whether the configuration contained in the provided argument
   * parser represents a valid configuration for this extension.
   *
   * @param  config               The general configuration for this HTTP
   *                              servlet extension.
   * @param  parser               The argument parser which has been initialized
   *                              with the proposed configuration.
   * @param  unacceptableReasons  A list that can be updated with reasons that
   *                              the proposed configuration is not acceptable.
   *
   * @return  {@code true} if the proposed configuration is acceptable, or
   *          {@code false} if not.
   */
  @Override()
  public boolean isConfigurationAcceptable(
                      final HTTPServletExtensionConfig config,
                      final ArgumentParser parser,
                      final List<String> unacceptableReasons)
  {
    // No special validation is required.
    return true;
  }



  /**
   * Attempts to apply the configuration contained in the provided argument
   * parser.
   *
   * @param  config                The general configuration for this HTTP
   *                               servlet extension.
   * @param  parser                The argument parser which has been
   *                               initialized with the new configuration.
   * @param  adminActionsRequired  A list that can be updated with information
   *                               about any administrative actions that may be
   *                               required before one or more of the
   *                               configuration changes will be applied.
   * @param  messages              A list that can be updated with information
   *                               about the result of applying the new
   *                               configuration.
   *
   * @return  A result code that provides information about the result of
   *          attempting to apply the configuration change.
   */
  @Override()
  public ResultCode applyConfiguration(final HTTPServletExtensionConfig config,
                                       final ArgumentParser parser,
                                       final List<String> adminActionsRequired,
                                       final List<String> messages)
  {
    // Get the new greeting name.
    final StringArgument nameArg =
         (StringArgument) parser.getNamedArgument(ARG_NAME_NAME);
    servlet.setName(nameArg.getValue());

    // The path will not change dynamically.  If a different path was given,
    // then report that as a required administrative action.
    final StringArgument pathArg =
         (StringArgument) parser.getNamedArgument(ARG_NAME_PATH);
    if (! path.equals(pathArg.getValue()))
    {
      adminActionsRequired.add("Changes to the servlet path will not take " +
           "effect until the HTTP connection handler (or entire server) is " +
           "restarted.");
    }

    return ResultCode.SUCCESS;
  }



  /**
   * Retrieves a map containing examples of configurations that may be used for
   * this extension.  The map key should be a list of sample arguments, and the
   * corresponding value should be a description of the behavior that will be
   * exhibited by the extension when used with that configuration.
   *
   * @return  A map containing examples of configurations that may be used for
   *          this extension.  It may be {@code null} or empty if there should
   *          not be any example argument sets.
   */
  @Override()
  public Map<List<String>,String> getExamplesArgumentSets()
  {
    final LinkedHashMap<List<String>,String> exampleMap =
         new LinkedHashMap<List<String>,String>(1);

    exampleMap.put(
         Arrays.asList(
              ARG_NAME_NAME + "=John",
              ARG_NAME_PATH + "=/hello"),
         "Create a simple servlet that will display 'Hello, John!' whenever " +
              "an HTTP request is received with a path of '/hello'.");

    return exampleMap;
  }



  /**
   * Indicates whether initialization parameters were provided to the servlet.
   *
   * @return  {@code true} if initialization parameters were provided to the
   *          servlet, or {@code false} if not.
   */
  public static boolean initParametersProvided()
  {
    return initParametersProvided;
  }



  /**
   * Indicates whether the {@code doPostRegistrationProcessing} method was
   * called for this servlet.
   *
   * @return  {@code true} if the {@code doPostRegistrationProcessing} method
   *          was called for this servlet, or {@code false} if not.
   */
  public static boolean postRegistrationMethodCalled()
  {
    return postRegistrationMethodCalled;
  }



  /**
   * Indicates whether the {@code doPostShutdownProcessing} method was called
   * for this servlet.
   *
   * @return  {@code true} if the {@code doPostShutdownProcessing} method was
   *          called for this servlet, or {@code false} if not.
   */
  public static boolean postShutdownMethodCalled()
  {
    return postShutdownMethodCalled;
  }



  /**
   * Indicates whether the a servlet context instance was available to the
   * servlet when the {@code doPostRegistrationProcessing} method was called.
   *
   * @return  {@code true} if a servlet context instance was available, or
   *          {@code false} if not.
   */
  public static boolean servletContextAvailable()
  {
    return servletContextAvailable;
  }



  /**
   * Indicates whether all filter processing has been invoked.
   *
   * @return  {@code true} if all filter processing has been invoked, or
   *          {@code false} if at least some element of filter processing has
   *          not yet been invoked.
   */
  public static boolean filterProcessingInvoked()
  {
    return FILTER.initInvoked() &&
         FILTER.preChainInvoked() &&
         FILTER.postChainInvoked() &&
         FILTER.destroyInvoked();
  }
}