Refactored the Async parser interface out of JsonParser into a new class JsonParserAsync. Updated the JsonParser to detect Eof and return a null instead of throwing a ParseException.

gson/src/main/java/com/google/gson/Gson.java

@@ -411,10 +411,7 @@ public final class Gson {
   @SuppressWarnings("unchecked")
   public <T> T fromJson(Reader json, Type typeOfT) throws JsonParseException {
     JsonElement root = new JsonParser().parse(json);
-    JsonDeserializationContext context = new JsonDeserializationContextDefault(
-        createDefaultObjectNavigatorFactory(), deserializers, objectConstructor);
-    T target = (T) context.deserialize(root, typeOfT);
-    return target;
+    return fromJson(root, typeOfT);
   }
 
   /**
@@ -458,6 +455,9 @@ public final class Gson {
    */
   @SuppressWarnings("unchecked")
   public <T> T fromJson(JsonElement json, Type typeOfT) throws JsonParseException {
+    if (json == null) {
+      return null;
+    }
     JsonDeserializationContext context = new JsonDeserializationContextDefault(
         createDefaultObjectNavigatorFactory(), deserializers, objectConstructor);
     T target = (T) context.deserialize(json, typeOfT);

gson/src/main/java/com/google/gson/JsonParser.java

@@ -15,6 +15,7 @@
  */
 package com.google.gson;
 
+import java.io.EOFException;
 import java.io.Reader;
 import java.io.StringReader;
 
@@ -27,21 +28,6 @@ import java.io.StringReader;
  */
 public final class JsonParser {
   
-  /**
-   * Interface to provide ability to read multiple {@link JsonElement}s from a stream 
-   * asynchronously.
-   * 
-   * @since 1.4
-   */
-  public interface AsyncReader {
-
-    /**
-     * Parse and return one {@link JsonElement} 
-     * @since 1.4
-     */
-    public JsonElement readElement();
-  }
-
   /**
    * Parses the specified JSON string into a parse tree
    * 
@@ -75,41 +61,12 @@ public final class JsonParser {
       throw new JsonParseException("Failed parsing JSON source: " + json + " to Json", e);
     } catch (OutOfMemoryError e) {
       throw new JsonParseException("Failed parsing JSON source: " + json + " to Json", e);
-    }
-  }
-  
-  /**
-   * Returns {@link AsyncReader} to allow reading of multiple {@link JsonElement}s from the 
-   * specified reader asynchronously.
-   * 
-   * @param json The data stream containing JSON elements concatenated to each other.
-   * @return {@link AsyncReader} for reading {@link JsonElement}s asynchronously.
-   * @throws JsonParseException if the incoming stream is malformed JSON.
-   * @since 1.4
-   */
-  public AsyncReader parseAsync(Reader json) throws JsonParseException {
-    return new AsyncReaderJavacc(json);
-  }
-  
-  private static class AsyncReaderJavacc implements AsyncReader {    
-    private final JsonParserJavacc parser;
-    private AsyncReaderJavacc(Reader json) {
-      parser = new JsonParserJavacc(json);      
-    }
-    
-    public JsonElement readElement() {
-      try {
-        JsonElement element = parser.parse();
-        return element;
-      } catch (TokenMgrError e) {
-        throw new JsonParseException("Failed parsing JSON source to Json", e);
-      } catch (ParseException e) {
-        throw new JsonParseException("Failed parsing JSON source to Json", e);
-      } catch (StackOverflowError e) {
-        throw new JsonParseException("Failed parsing JSON source to Json", e);
-      } catch (OutOfMemoryError e) {
-        throw new JsonParseException("Failed parsing JSON source to Json", e);
+    } catch (JsonParseException e) {
+      if (e.getCause() instanceof EOFException) {
+        return null;
+      } else {
+        throw e;
       }
-    }    
-  }
+    }
+  }  
 }

gson/src/main/java/com/google/gson/JsonParserAsync.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2009 Google Inc.
+ *
+ * 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 com.google.gson;
+
+import java.io.EOFException;
+import java.io.Reader;
+import java.io.StringReader;
+
+/**
+ * A parser that allows reading of multiple {@link JsonElement}s from the specified reader
+ * asynchronously.
+ *
+ * @author Inderjeet Singh
+ * @author Joel Leitch
+ * @since 1.4
+ */
+public final class JsonParserAsync {
+
+  private final JsonParserJavacc parser;
+
+  /**
+   * @param json The string containing JSON elements concatenated to each other.
+   * @since 1.4
+   */
+  public JsonParserAsync(String json) {
+    this(new StringReader(json));      
+  }
+  
+  /**
+   * @param reader The data stream containing JSON elements concatenated to each other.
+   * @since 1.4
+   */
+  public JsonParserAsync(Reader reader) {
+    parser = new JsonParserJavacc(reader);      
+  }
+  
+  /**
+   * Returns the next available {@link JsonElement} on the reader. Null if none available.
+   * 
+   * @return the next available {@link JsonElement} on the reader. Null if none available.
+   * @throws JsonParseException if the incoming stream is malformed JSON.
+   * @since 1.4
+   */
+  public JsonElement nextElement() throws JsonParseException {
+    try {
+      JsonElement element = parser.parse();
+      return element;
+    } catch (TokenMgrError e) {
+      throw new JsonParseException("Failed parsing JSON source to Json", e);
+    } catch (ParseException e) {
+      throw new JsonParseException("Failed parsing JSON source to Json", e);
+    } catch (StackOverflowError e) {
+      throw new JsonParseException("Failed parsing JSON source to Json", e);
+    } catch (OutOfMemoryError e) {
+      throw new JsonParseException("Failed parsing JSON source to Json", e);
+    } catch (JsonParseException e) {
+      if (e.getCause() instanceof EOFException) {
+        return null;
+      } else {
+        throw e;
+      }
+    }
+  }    
+}

gson/src/main/java/com/google/gson/JsonParserJavacc.java

@@ -1,5 +1,6 @@
 /* Generated By:JavaCC: Do not edit this line. JsonParserJavacc.java */
 package com.google.gson;
+import java.io.EOFException;
 
 @SuppressWarnings("all")
 final class JsonParserJavacc implements JsonParserJavaccConstants {
@@ -7,38 +8,60 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
   final public JsonElement parse() throws ParseException {
   JsonElement json = null;
     switch ((jj_ntk==-1)?jj_ntk():jj_ntk) {
-    case 26:
-      jj_consume_token(26);
-      break;
-    default:
-      jj_la1[0] = jj_gen;
-      ;
-    }
-    switch ((jj_ntk==-1)?jj_ntk():jj_ntk) {
-    case 27:
-      json = JsonObject();
-      break;
-    case 31:
-      json = JsonArray();
+    case 0:
+      jj_consume_token(0);
+    {if (true) throw new JsonParseException(new EOFException());}
       break;
     case DIGITS:
+    case NULL:
     case NAN:
     case INFINITY:
     case BOOLEAN:
     case SINGLE_QUOTE_LITERAL:
     case DOUBLE_QUOTE_LITERAL:
+    case 26:
+    case 27:
+    case 31:
     case 33:
-      json = JsonPrimitive();
-      break;
-    case NULL:
-      json = JsonNull();
+      switch ((jj_ntk==-1)?jj_ntk():jj_ntk) {
+      case 26:
+        jj_consume_token(26);
+        break;
+      default:
+        jj_la1[0] = jj_gen;
+        ;
+      }
+      switch ((jj_ntk==-1)?jj_ntk():jj_ntk) {
+      case 27:
+        json = JsonObject();
+        break;
+      case 31:
+        json = JsonArray();
+        break;
+      case DIGITS:
+      case NAN:
+      case INFINITY:
+      case BOOLEAN:
+      case SINGLE_QUOTE_LITERAL:
+      case DOUBLE_QUOTE_LITERAL:
+      case 33:
+        json = JsonPrimitive();
+        break;
+      case NULL:
+        json = JsonNull();
+        break;
+      default:
+        jj_la1[1] = jj_gen;
+        jj_consume_token(-1);
+        throw new ParseException();
+      }
+    {if (true) return json;}
       break;
     default:
-      jj_la1[1] = jj_gen;
+      jj_la1[2] = jj_gen;
       jj_consume_token(-1);
       throw new ParseException();
     }
-    {if (true) return json;}
     throw new Error("Missing return statement in function");
   }
 
@@ -53,7 +76,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
       Members(o);
       break;
     default:
-      jj_la1[2] = jj_gen;
+      jj_la1[3] = jj_gen;
       ;
     }
     jj_consume_token(28);
@@ -76,7 +99,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
       Members(o);
       break;
     default:
-      jj_la1[3] = jj_gen;
+      jj_la1[4] = jj_gen;
       ;
     }
   }
@@ -104,7 +127,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
                        {if (true) return value;}
       break;
     default:
-      jj_la1[4] = jj_gen;
+      jj_la1[5] = jj_gen;
       jj_consume_token(-1);
       throw new ParseException();
     }
@@ -128,7 +151,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
       Elements(array);
       break;
     default:
-      jj_la1[5] = jj_gen;
+      jj_la1[6] = jj_gen;
       ;
     }
     jj_consume_token(32);
@@ -146,7 +169,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
       Elements(array);
       break;
     default:
-      jj_la1[6] = jj_gen;
+      jj_la1[7] = jj_gen;
       ;
     }
     array.add(element);
@@ -178,7 +201,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
       o = JsonNull();
       break;
     default:
-      jj_la1[7] = jj_gen;
+      jj_la1[8] = jj_gen;
       jj_consume_token(-1);
       throw new ParseException();
     }
@@ -214,7 +237,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
                            {if (true) return value;}
       break;
     default:
-      jj_la1[8] = jj_gen;
+      jj_la1[9] = jj_gen;
       jj_consume_token(-1);
       throw new ParseException();
     }
@@ -239,7 +262,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
           fracpart = JsonFrac();
           break;
         default:
-          jj_la1[9] = jj_gen;
+          jj_la1[10] = jj_gen;
           ;
         }
         switch ((jj_ntk==-1)?jj_ntk():jj_ntk) {
@@ -247,7 +270,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
           exppart = JsonExp();
           break;
         default:
-          jj_la1[10] = jj_gen;
+          jj_la1[11] = jj_gen;
           ;
         }
     Number n;
@@ -261,7 +284,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
     {if (true) return new JsonPrimitive(n);}
         break;
       default:
-        jj_la1[11] = jj_gen;
+        jj_la1[12] = jj_gen;
         jj_consume_token(-1);
         throw new ParseException();
       }
@@ -284,14 +307,14 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
          negative = true;
         break;
       default:
-        jj_la1[12] = jj_gen;
+        jj_la1[13] = jj_gen;
         ;
       }
       jj_consume_token(INFINITY);
                                         {if (true) return new JsonPrimitive(negative ? Double.NEGATIVE_INFINITY : Double.POSITIVE_INFINITY);}
       break;
     default:
-      jj_la1[13] = jj_gen;
+      jj_la1[14] = jj_gen;
       jj_consume_token(-1);
       throw new ParseException();
     }
@@ -307,7 +330,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
          negative = true;
       break;
     default:
-      jj_la1[14] = jj_gen;
+      jj_la1[15] = jj_gen;
       ;
     }
     digits = Digits();
@@ -342,7 +365,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
       t = jj_consume_token(IDENTIFIER_SANS_EXPONENT);
       break;
     default:
-      jj_la1[15] = jj_gen;
+      jj_la1[16] = jj_gen;
       jj_consume_token(-1);
       throw new ParseException();
     }
@@ -367,7 +390,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
       t = jj_consume_token(DOUBLE_QUOTE_LITERAL);
       break;
     default:
-      jj_la1[16] = jj_gen;
+      jj_la1[17] = jj_gen;
       jj_consume_token(-1);
       throw new ParseException();
     }
@@ -427,7 +450,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
   private Token jj_scanpos, jj_lastpos;
   private int jj_la;
   private int jj_gen;
-  final private int[] jj_la1 = new int[17];
+  final private int[] jj_la1 = new int[18];
   static private int[] jj_la1_0;
   static private int[] jj_la1_1;
   static {
@@ -435,10 +458,10 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
       jj_la1_init_1();
    }
    private static void jj_la1_init_0() {
-      jj_la1_0 = new int[] {0x4000000,0x880307c0,0x31800,0x20000000,0x31800,0x880307c0,0x20000000,0x880307c0,0x30740,0x0,0x20,0x40,0x0,0x300,0x0,0x1800,0x30000,};
+      jj_la1_0 = new int[] {0x4000000,0x880307c0,0x8c0307c1,0x31800,0x20000000,0x31800,0x880307c0,0x20000000,0x880307c0,0x30740,0x0,0x20,0x40,0x0,0x300,0x0,0x1800,0x30000,};
    }
    private static void jj_la1_init_1() {
-      jj_la1_1 = new int[] {0x0,0x2,0x0,0x0,0x0,0x2,0x0,0x2,0x2,0x4,0x0,0x2,0x2,0x2,0x2,0x0,0x0,};
+      jj_la1_1 = new int[] {0x0,0x2,0x2,0x0,0x0,0x0,0x2,0x0,0x2,0x2,0x4,0x0,0x2,0x2,0x2,0x2,0x0,0x0,};
    }
   final private JJCalls[] jj_2_rtns = new JJCalls[1];
   private boolean jj_rescan = false;
@@ -455,7 +478,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
     token = new Token();
     jj_ntk = -1;
     jj_gen = 0;
-    for (int i = 0; i < 17; i++) jj_la1[i] = -1;
+    for (int i = 0; i < 18; i++) jj_la1[i] = -1;
     for (int i = 0; i < jj_2_rtns.length; i++) jj_2_rtns[i] = new JJCalls();
   }
 
@@ -470,7 +493,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
     token = new Token();
     jj_ntk = -1;
     jj_gen = 0;
-    for (int i = 0; i < 17; i++) jj_la1[i] = -1;
+    for (int i = 0; i < 18; i++) jj_la1[i] = -1;
     for (int i = 0; i < jj_2_rtns.length; i++) jj_2_rtns[i] = new JJCalls();
   }
 
@@ -481,7 +504,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
     token = new Token();
     jj_ntk = -1;
     jj_gen = 0;
-    for (int i = 0; i < 17; i++) jj_la1[i] = -1;
+    for (int i = 0; i < 18; i++) jj_la1[i] = -1;
     for (int i = 0; i < jj_2_rtns.length; i++) jj_2_rtns[i] = new JJCalls();
   }
 
@@ -492,7 +515,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
     token = new Token();
     jj_ntk = -1;
     jj_gen = 0;
-    for (int i = 0; i < 17; i++) jj_la1[i] = -1;
+    for (int i = 0; i < 18; i++) jj_la1[i] = -1;
     for (int i = 0; i < jj_2_rtns.length; i++) jj_2_rtns[i] = new JJCalls();
   }
 
@@ -502,7 +525,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
     token = new Token();
     jj_ntk = -1;
     jj_gen = 0;
-    for (int i = 0; i < 17; i++) jj_la1[i] = -1;
+    for (int i = 0; i < 18; i++) jj_la1[i] = -1;
     for (int i = 0; i < jj_2_rtns.length; i++) jj_2_rtns[i] = new JJCalls();
   }
 
@@ -512,7 +535,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
     token = new Token();
     jj_ntk = -1;
     jj_gen = 0;
-    for (int i = 0; i < 17; i++) jj_la1[i] = -1;
+    for (int i = 0; i < 18; i++) jj_la1[i] = -1;
     for (int i = 0; i < jj_2_rtns.length; i++) jj_2_rtns[i] = new JJCalls();
   }
 
@@ -629,7 +652,7 @@ final class JsonParserJavacc implements JsonParserJavaccConstants {
       la1tokens[jj_kind] = true;
       jj_kind = -1;
     }
-    for (int i = 0; i < 17; i++) {
+    for (int i = 0; i < 18; i++) {
       if (jj_la1[i] == jj_gen) {
         for (int j = 0; j < 32; j++) {
           if ((jj_la1_0[i] & (1<<j)) != 0) {

gson/src/main/java/com/google/gson/JsonParserJavaccTokenManager.java

@@ -1,5 +1,6 @@
 /* Generated By:JavaCC: Do not edit this line. JsonParserJavaccTokenManager.java */
 package com.google.gson;
+import java.io.EOFException;
 
 /** Token Manager. */
 @SuppressWarnings("all")

gson/src/main/javacc/JsonParser.jj

@@ -12,6 +12,7 @@ options {
 PARSER_BEGIN(JsonParserJavacc)
 
 package com.google.gson;
+import java.io.EOFException;
 
 @SuppressWarnings("all")
 final class JsonParserJavacc {
@@ -60,6 +61,9 @@ public JsonElement parse() :
   JsonElement json = null;
 }
 {
+  (<EOF>){
+    throw new JsonParseException(new EOFException());
+  } |
   [")]}'\n"]( json=JsonObject() |
     json=JsonArray() |
     json=JsonPrimitive() |

gson/src/test/java/com/google/gson/JsonParserAsyncTest.java

@@ -0,0 +1,19 @@
+package com.google.gson;
+
+import junit.framework.TestCase;
+
+/**
+ * Unit tests for {@link JsonParserAsync}
+ *
+ * @author Inderjeet Singh
+ */
+public class JsonParserAsyncTest extends TestCase {
+  
+  public void testParseTwoStrings() {
+    JsonParserAsync parser = new JsonParserAsync("'one' 'two'");
+    String actualOne = parser.nextElement().getAsString();
+    assertEquals("one", actualOne);
+    String actualTwo = parser.nextElement().getAsString();
+    assertEquals("two", actualTwo);
+  }
+}

gson/src/test/java/com/google/gson/functional/ObjectTest.java

@@ -178,11 +178,8 @@ public class ObjectTest extends TestCase {
   }
 
   public void testNullDeserialization() throws Exception {
-    try {
-      gson.fromJson("", Object.class);
-      fail("Null strings should not be allowed");
-    } catch (JsonParseException expected) {
-    }
+    Object object = gson.fromJson("", Object.class);
+    assertNull(object);
   }
 
   public void testNullFieldsSerialization() throws Exception {

gson/src/test/java/com/google/gson/functional/ReadersWritersTest.java

@@ -17,9 +17,8 @@ package com.google.gson.functional;
 
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
-import com.google.gson.JsonParseException;
-import com.google.gson.JsonParser;
-import com.google.gson.JsonParser.AsyncReader;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonParserAsync;
 import com.google.gson.common.TestTypes.BagOfPrimitives;
 
 import junit.framework.TestCase;
@@ -93,11 +92,10 @@ public class ReadersWritersTest extends TestCase {
     writer.write(gson.toJson("one").toCharArray());
     writer.write(gson.toJson("two").toCharArray());
     CharArrayReader reader = new CharArrayReader(writer.toCharArray());
-    JsonParser parser = new JsonParser();
-    AsyncReader asyncReader = parser.parseAsync(reader);
-    String actualOne = gson.fromJson(asyncReader.readElement(), String.class);
+    JsonParserAsync parser = new JsonParserAsync(reader);
+    String actualOne = gson.fromJson(parser.nextElement(), String.class);
     assertEquals("one", actualOne);
-    String actualTwo = gson.fromJson(asyncReader.readElement(), String.class);
+    String actualTwo = gson.fromJson(parser.nextElement(), String.class);
     assertEquals("two", actualTwo);
   }
   
@@ -109,11 +107,11 @@ public class ReadersWritersTest extends TestCase {
     BagOfPrimitives expectedTwo = new BagOfPrimitives(2, 2, false, "two");
     writer.write(gson.toJson(expectedTwo).toCharArray());
     CharArrayReader reader = new CharArrayReader(writer.toCharArray());
-    JsonParser parser = new JsonParser();
-    AsyncReader asyncReader = parser.parseAsync(reader);
-    BagOfPrimitives actualOne = gson.fromJson(asyncReader.readElement(), BagOfPrimitives.class);
+    JsonParserAsync parser = new JsonParserAsync(reader);
+    BagOfPrimitives actualOne = gson.fromJson(parser.nextElement(), BagOfPrimitives.class);
     assertEquals("one", actualOne.stringValue);
-    BagOfPrimitives actualTwo = gson.fromJson(asyncReader.readElement(), BagOfPrimitives.class);
+    BagOfPrimitives actualTwo = gson.fromJson(parser.nextElement(), BagOfPrimitives.class);
     assertEquals("two", actualTwo.stringValue);
+    JsonElement jsonElement = parser.nextElement();
   }
 }