[Java] Support resetting group count to current index to allow for streaming operations where the group count is difficult to determine upfront but can be limited and reset down to current index value when group is complete.

Author: mjpt777

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/java/JavaGenerator.java

@@ -342,6 +342,7 @@ private void generateGroupDecoderClassHeader(
  final String indent)
  {
  final Token groupToken = tokens.get(index);
+ final String className = formatClassName(groupName);
  final int dimensionHeaderLen = tokens.get(index + 1).encodedLength();
 
  final Token blockLengthToken = Generators.findFirst("blockLength", tokens, index);
@@ -372,14 +373,27 @@ private void generateGroupDecoderClassHeader(
  .append(indent).append(" if (buffer != this.buffer)\n")
  .append(indent).append(" {\n")
  .append(indent).append(" this.buffer = buffer;\n")
- .append(indent).append(" }\n")
- .append(indent).append(" index = -1;\n")
+ .append(indent).append(" }\n\n")
+ .append(indent).append(" index = 0;\n")
  .append(indent).append(" final int limit = parentMessage.limit();\n")
  .append(indent).append(" parentMessage.limit(limit + HEADER_SIZE);\n")
  .append(indent).append(" blockLength = (int)").append(blockLengthGet).append(";\n")
  .append(indent).append(" count = (int)").append(numInGroupGet).append(";\n")
  .append(indent).append(" }\n");
 
+ sb.append("\n")
+ .append(indent).append(" public ").append(className).append(" next()\n")
+ .append(indent).append(" {\n")
+ .append(indent).append(" if (index >= count)\n")
+ .append(indent).append(" {\n")
+ .append(indent).append(" throw new java.util.NoSuchElementException();\n")
+ .append(indent).append(" }\n\n")
+ .append(indent).append(" offset = parentMessage.limit();\n")
+ .append(indent).append(" parentMessage.limit(offset + blockLength);\n")
+ .append(indent).append(" ++index;\n\n")
+ .append(indent).append(" return this;\n")
+ .append(indent).append(" }\n");
+
  sb.append("\n")
  .append(indent).append(" public static int sbeHeaderSize()\n")
  .append(indent).append(" {\n")
@@ -392,7 +406,6 @@ private void generateGroupDecoderClassHeader(
  .append(indent).append(" return ").append(tokens.get(index).encodedLength()).append(";\n")
  .append(indent).append(" }\n");
 
- final String className = formatClassName(groupName);
  sb.append("\n")
  .append(indent).append(" public int actingBlockLength()\n")
  .append(indent).append(" {\n")
@@ -412,20 +425,7 @@ private void generateGroupDecoderClassHeader(
  .append(indent).append(" }\n\n")
  .append(indent).append(" public boolean hasNext()\n")
  .append(indent).append(" {\n")
- .append(indent).append(" return (index + 1) < count;\n")
- .append(indent).append(" }\n");
-
- sb.append("\n")
- .append(indent).append(" public ").append(className).append(" next()\n")
- .append(indent).append(" {\n")
- .append(indent).append(" if (index + 1 >= count)\n")
- .append(indent).append(" {\n")
- .append(indent).append(" throw new java.util.NoSuchElementException();\n")
- .append(indent).append(" }\n\n")
- .append(indent).append(" offset = parentMessage.limit();\n")
- .append(indent).append(" parentMessage.limit(offset + blockLength);\n")
- .append(indent).append(" ++index;\n\n")
- .append(indent).append(" return this;\n")
+ .append(indent).append(" return index < count;\n")
  .append(indent).append(" }\n");
  }
 
@@ -477,35 +477,25 @@ private void generateGroupEncoderClassHeader(
  ind + " {\n" +
  ind + " this.buffer = buffer;\n" +
  ind + " }\n\n" +
- ind + " index = -1;\n" +
+ ind + " index = 0;\n" +
  ind + " this.count = count;\n" +
  ind + " final int limit = parentMessage.limit();\n" +
+ ind + " initialLimit = limit;\n" +
  ind + " parentMessage.limit(limit + HEADER_SIZE);\n" +
  ind + " %5$s;\n" +
  ind + " %6$s;\n" +
- ind + " }\n\n",
+ ind + " }\n",
  parentMessageClassName,
  mutableBuffer,
  numInGroupToken.encoding().applicableMinValue().longValue(),
  numInGroupToken.encoding().applicableMaxValue().longValue(),
  blockLengthPut,
  numInGroupPut);
 
- sb.append(ind).append(" public static int sbeHeaderSize()\n")
- .append(ind).append(" {\n")
- .append(ind).append(" return HEADER_SIZE;\n")
- .append(ind).append(" }\n");
-
- sb.append("\n")
- .append(ind).append(" public static int sbeBlockLength()\n")
- .append(ind).append(" {\n")
- .append(ind).append(" return ").append(blockLength).append(";\n")
- .append(ind).append(" }\n");
-
  sb.append("\n")
  .append(ind).append(" public ").append(encoderName(groupName)).append(" next()\n")
  .append(ind).append(" {\n")
- .append(ind).append(" if (index + 1 >= count)\n")
+ .append(ind).append(" if (index >= count)\n")
  .append(ind).append(" {\n")
  .append(ind).append(" throw new java.util.NoSuchElementException();\n")
  .append(ind).append(" }\n\n")
@@ -514,6 +504,30 @@ private void generateGroupEncoderClassHeader(
  .append(ind).append(" ++index;\n\n")
  .append(ind).append(" return this;\n")
  .append(ind).append(" }\n");
+
+ final String countOffset = "initialLimit + " + numInGroupToken.offset();
+ final String resetCountPut = generatePut(
+ numInGroupType, countOffset, numInGroupValue, byteOrderString(numInGroupToken.encoding()));
+
+ sb.append("\n")
+ .append(ind).append(" public int resetCountToIndex()\n")
+ .append(ind).append(" {\n")
+ .append(ind).append(" count = index;\n")
+ .append(ind).append(" ").append(resetCountPut).append(";\n\n")
+ .append(ind).append(" return count;\n")
+ .append(ind).append(" }\n");
+
+ sb.append("\n")
+ .append(ind).append(" public static int sbeHeaderSize()\n")
+ .append(ind).append(" {\n")
+ .append(ind).append(" return HEADER_SIZE;\n")
+ .append(ind).append(" }\n");
+
+ sb.append("\n")
+ .append(ind).append(" public static int sbeBlockLength()\n")
+ .append(ind).append(" {\n")
+ .append(ind).append(" return ").append(blockLength).append(";\n")
+ .append(ind).append(" }\n");
  }
 
  private static String primitiveTypeName(final Token token)
@@ -595,7 +609,8 @@ private void generateGroupEncoderClassDeclaration(
  indent + " private %4$s buffer;\n" +
  indent + " private int count;\n" +
  indent + " private int index;\n" +
- indent + " private int offset;\n",
+ indent + " private int offset;\n" +
+ indent + " private int initialLimit;\n",
  className,
  dimensionHeaderSize,
  parentMessageClassName,