HADOOP-120. In ArrayWritable, prevent creation with null value class and improve documentation. Contributed by Cameron Pope.

git-svn-id: https://svn.apache.org/repos/asf/lucene/hadoop/trunk@577010 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -249,6 +249,9 @@ Trunk (unreleased changes)
     HADOOP-1878.  Add space between priority links on job details
     page. (Thomas Friol via cutting)
 
+    HADOOP-120.  In ArrayWritable, prevent creation with null value
+    class, and improve documentation.  (Cameron Pope via cutting)
+
 
 Release 0.14.1 - 2007-09-04
 

src/java/org/apache/hadoop/io/ArrayWritable.java

@@ -21,16 +21,29 @@ package org.apache.hadoop.io;
 import java.io.*;
 import java.lang.reflect.Array;
 
-/** A Writable for arrays containing instances of a class. */
+/** 
+ * A Writable for arrays containing instances of a class. The elements of this
+ * writable must all be instances of the same class. If this writable will be
+ * the input for a Reducer, you will need to create a subclass that sets the
+ * value to be of the proper type.
+ *
+ * For example:
+ * <code>
+ * public class IntArrayWritable extends ArrayWritable {
+ *   public IntArrayWritable() { 
+ *     super(IntWritable.class); 
+ *   }	
+ * }
+ * </code>
+ */
 public class ArrayWritable implements Writable {
   private Class valueClass;
   private Writable[] values;
 
-  public ArrayWritable() {
-    this.valueClass = null;
-  }
-
   public ArrayWritable(Class valueClass) {
+    if (valueClass == null) { 
+      throw new IllegalArgumentException("null valueClass"); 
+    }    
     this.valueClass = valueClass;
   }
 
@@ -46,13 +59,6 @@ public class ArrayWritable implements Writable {
     }
   }
 
-  public void setValueClass(Class valueClass) {
-    if (valueClass != this.valueClass) {
-      this.valueClass = valueClass;
-      this.values = null;
-    }
-  }
-  
   public Class getValueClass() {
     return valueClass;
   }

src/test/org/apache/hadoop/io/TestArrayWritable.java

@@ -0,0 +1,64 @@
+/**
+ * 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
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.io;
+
+import java.io.*;
+
+import junit.framework.TestCase;
+
+/** Unit tests for ArrayWritable */
+public class TestArrayWritable extends TestCase {
+	
+  static class TextArrayWritable extends ArrayWritable {
+    public TextArrayWritable() {
+      super(Text.class);
+    }
+  }
+	
+  public TestArrayWritable(String name) { 
+    super(name); 
+  }
+	
+  /**
+   * If valueClass is undefined, readFields should throw an exception indicating
+   * that the field is null. Otherwise, readFields should succeed.	
+   */
+  public void testThrowUndefinedValueException() throws IOException {
+    // Get a buffer containing a simple text array
+    Text[] elements = {new Text("zero"), new Text("one"), new Text("two")};
+    TextArrayWritable sourceArray = new TextArrayWritable();
+    sourceArray.set(elements);
+
+    // Write it to a normal output buffer
+    DataOutputBuffer out = new DataOutputBuffer();
+    DataInputBuffer in = new DataInputBuffer();
+    sourceArray.write(out);
+
+    // Read the output buffer with TextReadable. Since the valueClass is defined,
+    // this should succeed
+    TextArrayWritable destArray = new TextArrayWritable();
+    in.reset(out.getData(), out.getLength());
+    destArray.readFields(in);
+    Writable[] destElements = destArray.get();
+    assertTrue(destElements.length == elements.length);
+    for (int i = 0; i < elements.length; i++) {
+      assertEquals(destElements[i],elements[i]);
+    }
+  }
+}