[SHRINKDESC-20] Allow empty contents for Descriptors on import.

Originally contributed by Andy Gibson in: https://github.com/andygibson/descriptors/commit/2a4bbd403dff44d91c5fa288549bdf0f1779ab2a

Refactored by ALR to match current backing design

api/src/main/java/org/jboss/shrinkwrap/descriptor/api/ApiExposition.java

@@ -0,0 +1,61 @@
+/*
+ * JBoss, Home of Professional Open Source
+ * Copyright 2011, Red Hat Middleware LLC, and individual contributors
+ * by the @authors tag. See the copyright.txt in the distribution for a
+ * full listing of individual contributors.
+ *
+ * Licensed 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
+ * limitations under the License.
+ */
+package org.jboss.shrinkwrap.descriptor.api;
+
+/**
+ * Indirection exposing some package-private methods
+ * in the Descriptors API to the implementation classes.
+ * 
+ * TO BE MOVED TO THE impl-base PACKAGE ONCE IT EXISTS; the user API
+ * should NOT see this on the compilation ClassPath: SHRINKDESC-42
+ * 
+ * @author <a href="mailto:alr@jboss.org">Andrew Lee Rubinger</a>
+ */
+// Mark as @Deprecated just to show that this will move
+@Deprecated
+public final class ApiExposition
+{
+   //-------------------------------------------------------------------------------------||
+   // Constructor ------------------------------------------------------------------------||
+   //-------------------------------------------------------------------------------------||
+
+   /**
+    * No instances permitted
+    */
+   private ApiExposition()
+   {
+      throw new UnsupportedOperationException("No instances permitted");
+   }
+
+   //-------------------------------------------------------------------------------------||
+   // Functional Methods -----------------------------------------------------------------||
+   //-------------------------------------------------------------------------------------||
+
+   /**
+    * Creates a {@link Descriptor} instance from the specified implementation
+    * class name, also using the specified name
+    * @param implClass
+    * @param descriptorName
+    * @return
+    * @throws IllegalArgumentException If either argument is not specified
+    */
+   public static Descriptor createFromImplModelType(final Class<? extends Descriptor> implClass, String descriptorName)
+         throws IllegalArgumentException
+   {
+      return DescriptorInstantiator.createFromImplModelType(implClass, descriptorName);
+   }
+}

api/src/main/java/org/jboss/shrinkwrap/descriptor/api/DescriptorInstantiator.java

@@ -86,33 +86,63 @@ private DescriptorInstantiator()
     * @return
     * @throws IllegalArgumentException If the user view class was not specified
     */
-   static <T extends Descriptor> T createFromUserView(final Class<T> userViewClass, String descriptorName) throws IllegalArgumentException
+   static <T extends Descriptor> T createFromUserView(final Class<T> userViewClass, String descriptorName)
+         throws IllegalArgumentException
    {
       // Get the construction information
       final DescriptorConstructionInfo info = getDescriptorConstructionInfoForUserView(userViewClass);
-
+
+      final Class<? extends Descriptor> implClass = info.implClass;
+      String name = info.defaultName;
+      if (descriptorName != null)
+      {
+         name = descriptorName;
+      }
+
+      // Make model class 
+      final Descriptor descriptor = createFromImplModelType(implClass, name);
+
+      // Return
+      return userViewClass.cast(descriptor);
+   }
+
+   /**
+    * Creates a {@link Descriptor} instance from the specified implementation
+    * class name, also using the specified name
+    * @param implClass
+    * @param descriptorName
+    * @return
+    * @throws IllegalArgumentException If either argument is not specified
+    */
+   static Descriptor createFromImplModelType(final Class<? extends Descriptor> implClass, String descriptorName)
+         throws IllegalArgumentException
+   {
+      // Precondition checks
+      if (implClass == null)
+      {
+         throw new IllegalArgumentException("implClass must be specified");
+      }
+      if (descriptorName == null || descriptorName.length() == 0)
+      {
+         throw new IllegalArgumentException("descriptorName must be specified");
+      }
+
       // Get the constructor to use in making the new instance
       final Constructor<? extends Descriptor> ctor;
       try
       {
-         ctor = info.implClass.getConstructor(String.class);
+         ctor = implClass.getConstructor(String.class);
       }
       catch (final NoSuchMethodException nsme)
       {
-         throw new RuntimeException(info.implClass + " must contain a constructor with a single String argument");
-      }
-
-      String name = info.defaultName;
-      if(descriptorName != null)
-      {
-         name = descriptorName;
+         throw new RuntimeException(implClass + " must contain a constructor with a single String argument");
       }
 
       // Create a new descriptor instance using the backing model
       final Descriptor descriptor;
       try
       {
-         descriptor = ctor.newInstance(name);
+         descriptor = ctor.newInstance(descriptorName);
       }
       // Handle all construction errors equally
       catch (final Exception e)
@@ -121,8 +151,7 @@ static <T extends Descriptor> T createFromUserView(final Class<T> userViewClass,
       }
 
       // Return
-      return userViewClass.cast(descriptor);
-
+      return descriptor;
    }
 
    /**

api/src/main/java/org/jboss/shrinkwrap/descriptor/impl/base/DescriptorImporterBase.java

@@ -23,6 +23,7 @@
 import java.io.InputStream;
 import java.lang.reflect.Constructor;
 
+import org.jboss.shrinkwrap.descriptor.api.ApiExposition;
 import org.jboss.shrinkwrap.descriptor.api.Descriptor;
 import org.jboss.shrinkwrap.descriptor.api.DescriptorImportException;
 import org.jboss.shrinkwrap.descriptor.api.DescriptorImporter;
@@ -46,7 +47,7 @@ public abstract class DescriptorImporterBase<T extends Descriptor> implements De
     */
    private final Class<T> endUserViewImplType;
 
-   private final String descriptorName; 
+   private final String descriptorName;
 
    //-------------------------------------------------------------------------------------||
    // Constructor ------------------------------------------------------------------------||
@@ -60,7 +61,7 @@ public abstract class DescriptorImporterBase<T extends Descriptor> implements De
     * @throws IllegalArgumentException If the model type is not specified
     * @throws IllegalArgumentException If the descriptorName not specified
     */
-   public DescriptorImporterBase(final Class<T> endUserViewImplType, String descriptorName)
+   public DescriptorImporterBase(final Class<T> endUserViewImplType, final String descriptorName)
          throws IllegalArgumentException
    {
       // Precondition checks
@@ -74,7 +75,6 @@ public DescriptorImporterBase(final Class<T> endUserViewImplType, String descrip
       }
 
       // Set
-
       this.endUserViewImplType = endUserViewImplType;
       this.descriptorName = descriptorName;
    }
@@ -108,11 +108,17 @@ public T from(final File file) throws IllegalArgumentException, DescriptorImport
    public T from(final String string) throws IllegalArgumentException, DescriptorImportException
    {
       // Precondition check
-      if (string == null || string.length() == 0)
+      if (string == null)
       {
          throw new IllegalArgumentException("Input must be specified");
       }
 
+      // Check if empty String  
+      if (string.trim().length() == 0)
+      {
+         return endUserViewImplType.cast(ApiExposition.createFromImplModelType(endUserViewImplType, descriptorName));
+      }
+
       // Return
       return this.from(new ByteArrayInputStream(string.getBytes()));
    }
@@ -165,4 +171,5 @@ public T from(final InputStream in) throws IllegalArgumentException, DescriptorI
     * @return The Root node extracted.
     */
    public abstract Node importRootNode(InputStream stream) throws DescriptorImportException;
+
 }

api/src/main/java/org/jboss/shrinkwrap/descriptor/impl/base/XMLImporter.java

@@ -46,11 +46,17 @@ public Node importRootNode(InputStream stream) throws DescriptorImportException
    {
       try
       {
+         // Empty contents?  If so, no root Node
+         if (stream.available() == 0)
+         {
+            return null;
+         }
+
          DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
          factory.setNamespaceAware(true);
          DocumentBuilder builder = factory.newDocumentBuilder();
-         Document doc = builder.parse(stream); 
-
+         Document doc=builder.parse(stream); 
+         
          Node root = new Node(doc.getDocumentElement().getNodeName());
          readRecursive(root, doc.getDocumentElement());
          return root;

api/src/test/java/org/jboss/shrinkwrap/descriptor/api/DescriptorImporterTestCase.java

@@ -19,6 +19,7 @@
 import java.io.ByteArrayInputStream;
 import java.io.InputStream;
 
+import org.jboss.shrinkwrap.descriptor.api.spec.cdi.beans.BeansDescriptor;
 import org.jboss.shrinkwrap.descriptor.api.spec.servlet.web.WebAppDescriptor;
 import org.junit.Assert;
 import org.junit.Test;
@@ -78,4 +79,43 @@ public void shouldThrowExceptionOnMissingInputStream() throws Exception
    {
       Descriptors.importAs(WebAppDescriptor.class).from((InputStream) null);
    }
+
+   /**
+    * SHRINKDESC-20
+    */
+   @Test(expected = IllegalArgumentException.class)
+   public void shouldThrowExceptionOnMissingString() throws Exception
+   {
+      Descriptors.importAs(WebAppDescriptor.class).from((String) null);
+   }
+
+   /**
+    * SHRINKDESC-20
+    */
+   @Test
+   public void shouldBeAbleToImportWhiteSpaceString()
+   {
+      BeansDescriptor descriptor = Descriptors.importAs(BeansDescriptor.class).from("  \n  \n  ");
+      Assert.assertNotNull("Verify the descriptor was created from an empty string",descriptor);
+   }
+
+   /**
+    * SHRINKDESC-20
+    */
+   @Test
+   public void shouldBeAbleToImportEmptyString()
+   {
+      BeansDescriptor descriptor = Descriptors.importAs(BeansDescriptor.class).from("");
+      Assert.assertNotNull("Verify the descriptor was created from an empty string",descriptor);
+   }
+
+   /**
+    * SHRINKDESC-20
+    */
+   @Test
+   public void shouldBeAbleToImportEmptyFile()
+   {
+      BeansDescriptor descriptor = Descriptors.importAs(BeansDescriptor.class).from(getClass().getResourceAsStream("/empty.xml"));
+      Assert.assertNotNull("Verify the descriptor was created from and empty file",descriptor);
+   }
 }