java/src/main/com/google/appengine/tools/development/ContainerUtils.java

   1 // Copyright 2011 Google Inc. All Rights Reserved.
   2
   3 package com.google.appengine.tools.development;
   4
   5 import com.google.appengine.tools.info.SdkInfo;
   6
   7 import java.util.Iterator;
   8
   9 /**
  10  * helper to load a {@link ContainerService} instance
  11  *
  12  */
  13 public class ContainerUtils {
  14   /**
  15    * Load a {@link ContainerService} instance based on the implementation
  16    * located by the {@code ServiceLoader}.
  17    *
  18    * When more than one implementations are found, an
  19    * <code>IllegalArgumentException</code> will be thrown. In other words,
  20    * only one {@link ContainerService} implementation should be packaged and
  21    * deployed.
  22    *
  23    * To ease debugging/testing (e.g. from IDE), an internal system property is
  24    * defined to explicitly specify a required container service provider, such
  25    * as -Ddevappserver.container=OpenGSEContainerService.
  26    *
  27    * Classpath resource(s) that match
  28    * META-INF/services/com.google.appengine.tools.development.ContainerService
  29    * are used to resolve the ContainerService implementations.
  30    *
  31    * If using an IDE, create a package/directory called META-INF/services/ and
  32    * add a text file with the name
  33    * "com.google.appengine.tools.development.ContainerService" containing one
  34    * line - the implementation class (some IDEs have a resource pattern that
  35    * is used to determine which files are added to the runtime classpath. If
  36    * your implementation class isn't being recognized, adjusting this pattern
  37    * to include the text file may help.
  38    *
  39    *
  40    * @return the deployed {@link ContainerService} instance.
  41    * @throws IllegalArgumentException if {@code ServiceLoader} fails to find
  42    *         any {@link ContainerService} implementation or more than one
  43    *         {@link ContainerService} implementations are available.
  44    */
  45   public static ContainerService loadContainer() {
  46     @SuppressWarnings({"unchecked", "sunapi"})
  47     Iterator<ContainerService> containerLoader =
  48         sun.misc.Service.providers(ContainerService.class,
  49             DevAppServerImpl.class.getClassLoader());
  50     String containerClazz = System.getProperty("devappserver.container");
  51     ContainerService result = null;
  52     while (containerLoader.hasNext()) {
  53       ContainerService container = containerLoader.next();
  54       if (containerClazz == null || containerClazz.length() == 0) {
  55         if (result == null) {
  56           result = container;
  57         } else {
  58           System.err.println("Warning: Found more than one servlet container provider: "
  59               + result.getClass() + ", " + container.getClass()
  60               + ". And the first one will be used!");
  61           break;
  62         }
  63       } else {
  64         if (container.getClass().getName().endsWith(containerClazz)) {
  65           result = container;
  66           break;
  67         }
  68       }
  69     }
  70     if (result == null) {
  71       throw new IllegalArgumentException("Cannot load any servlet container.");
  72     }
  73     return result;
  74   }
  75
  76   /**
  77    * @return the server info string with the dev-appserver version
  78    */
  79   public static String getServerInfo() {
  80     return "Google App Engine Development/" + SdkInfo.getLocalVersion().getRelease();
  81   }
  82 }