Index: lucene/core/src/java/org/apache/lucene/codecs/Codec.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/codecs/Codec.java	(revision 1365957)
+++ lucene/core/src/java/org/apache/lucene/codecs/Codec.java	(working copy)
@@ -86,6 +86,21 @@
     return loader.availableServices();
   }
   
+  /** 
+   * Reloads the codec list from the given {@link ClassLoader}.
+   * Changes to the codecs are visible after the method ends, all
+   * iterators ({@link #availableCodecs()},...) stay consistent. 
+   * 
+   * <p><b>NOTE:</b> Only new codecs are added, existing ones are
+   * never removed or replaced.
+   * 
+   * <p><em>This method is expensive and should only be called for discovery
+   * of new codecs on the given classpath/classloader!</em>
+   */
+  public static void reloadCodecs(ClassLoader classloader) {
+    loader.reload(classloader);
+  }
+  
   private static Codec defaultCodec = Codec.forName("Lucene40");
   
   /** expert: returns the default codec used for newly created
Index: lucene/core/src/java/org/apache/lucene/codecs/PostingsFormat.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/codecs/PostingsFormat.java	(revision 1365957)
+++ lucene/core/src/java/org/apache/lucene/codecs/PostingsFormat.java	(working copy)
@@ -70,4 +70,19 @@
   public static Set<String> availablePostingsFormats() {
     return loader.availableServices();
   }
+  
+  /** 
+   * Reloads the postings format list from the given {@link ClassLoader}.
+   * Changes to the postings formats are visible after the method ends, all
+   * iterators ({@link #availablePostingsFormats()},...) stay consistent. 
+   * 
+   * <p><b>NOTE:</b> Only new postings formats are added, existing ones are
+   * never removed or replaced.
+   * 
+   * <p><em>This method is expensive and should only be called for discovery
+   * of new postings formats on the given classpath/classloader!</em>
+   */
+  public static void reloadPostingsFormats(ClassLoader classloader) {
+    loader.reload(classloader);
+  }
 }
Index: lucene/core/src/java/org/apache/lucene/util/NamedSPILoader.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/util/NamedSPILoader.java	(revision 1365957)
+++ lucene/core/src/java/org/apache/lucene/util/NamedSPILoader.java	(working copy)
@@ -28,16 +28,34 @@
  * Helper class for loading named SPIs from classpath (e.g. Codec, PostingsFormat).
  * @lucene.internal
  */
-// TODO: would be nice to have case insensitive lookups.
 public final class NamedSPILoader<S extends NamedSPILoader.NamedSPI> implements Iterable<S> {
 
-  private final Map<String,S> services;
+  private volatile Map<String,S> services = Collections.emptyMap();
   private final Class<S> clazz;
 
   public NamedSPILoader(Class<S> clazz) {
+    this(clazz, Thread.currentThread().getContextClassLoader());
+  }
+  
+  public NamedSPILoader(Class<S> clazz, ClassLoader classloader) {
     this.clazz = clazz;
-    final SPIClassIterator<S> loader = SPIClassIterator.get(clazz);
-    final LinkedHashMap<String,S> services = new LinkedHashMap<String,S>();
+    reload(classloader);
+  }
+  
+  /** 
+   * Reloads the internal SPI list from the given {@link ClassLoader}.
+   * Changes to the service list are visible after the method ends, all
+   * iterators ({@link #iterator()},...) stay consistent. 
+   * 
+   * <p><b>NOTE:</b> Only new service providers are added, existing ones are
+   * never removed or replaced.
+   * 
+   * <p><em>This method is expensive and should only be called for discovery
+   * of new service providers on the given classpath/classloader!</em>
+   */
+  public void reload(ClassLoader classloader) {
+    final LinkedHashMap<String,S> services = new LinkedHashMap<String,S>(this.services);
+    final SPIClassIterator<S> loader = SPIClassIterator.get(clazz, classloader);
     while (loader.hasNext()) {
       final Class<? extends S> c = loader.next();
       try {
Index: solr/core/src/java/org/apache/solr/core/SolrResourceLoader.java
===================================================================
--- solr/core/src/java/org/apache/solr/core/SolrResourceLoader.java	(revision 1365958)
+++ solr/core/src/java/org/apache/solr/core/SolrResourceLoader.java	(working copy)
@@ -37,6 +37,8 @@
 import org.apache.lucene.analysis.util.TokenFilterFactory;
 import org.apache.lucene.analysis.util.TokenizerFactory;
 import org.apache.lucene.analysis.util.AnalysisSPILoader;
+import org.apache.lucene.codecs.Codec;
+import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.util.WeakIdentityMap;
 import org.apache.solr.common.ResourceLoader;
 import org.apache.solr.handler.admin.CoreAdminHandler;
@@ -112,7 +114,7 @@
     
     this.classLoader = createClassLoader(null, parent);
     addToClassLoader("./lib/", null);
-    
+    // reloadCodecSPI(); -> already done by the line above
     this.coreProperties = coreProperties;
   }
 
@@ -143,6 +145,7 @@
   void addToClassLoader(final String baseDir, final FileFilter filter) {
     File base = FileUtils.resolvePath(new File(getInstanceDir()), baseDir);
     this.classLoader = replaceClassLoader(classLoader, base, filter);
+    reloadCodecSPI();
   }
   
   /**
@@ -163,11 +166,17 @@
                                                 return pathname.equals(file);
                                               }
                                             });
+      reloadCodecSPI();
     } else {
       log.error("Can't find (or read) file to add to classloader: " + file);
     }
   }
   
+  private void reloadCodecSPI() {
+    Codec.reloadCodecs(this.classLoader);
+    PostingsFormat.reloadPostingsFormats(this.classLoader);
+  }
+  
   private static URLClassLoader replaceClassLoader(final URLClassLoader oldLoader,
                                                    final File base,
                                                    final FileFilter filter) {