[Java] Cope with optional composites not being present when pretty printing decoders for debugging. Issue aeron-io#708.

Author: mjpt777

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

@@ -3207,9 +3207,7 @@ private void appendDecoderDisplay(
  if (fieldToken.signal() == Signal.BEGIN_FIELD)
  {
  final Token encodingToken = fields.get(i + 1);
-
  final String fieldName = formatPropertyName(fieldToken.name());
- append(sb, indent, "//" + fieldToken);
  lengthBeforeLastGeneratedSeparator = writeTokenDisplay(fieldName, encodingToken, sb, indent);
 
  i += fieldToken.componentTokenCount();
@@ -3228,8 +3226,6 @@ private void appendDecoderDisplay(
  throw new IllegalStateException("tokens must begin with BEGIN_GROUP: token=" + groupToken);
  }
 
- append(sb, indent, "//" + groupToken);
-
  final String groupName = formatPropertyName(groupToken.name());
  final String groupDecoderName = decoderName(formatClassName(groupToken.name()));
 
@@ -3261,8 +3257,6 @@ private void appendDecoderDisplay(
  throw new IllegalStateException("tokens must begin with BEGIN_VAR_DATA: token=" + varDataToken);
  }
 
- append(sb, indent, "//" + varDataToken);
-
  final String characterEncoding = varData.get(i + 3).encoding().characterEncoding();
  final String varDataName = formatPropertyName(varDataToken.name());
  append(sb, indent, "builder.append(\"" + varDataName + Separators.KEY_VALUE + "\");");
@@ -3293,8 +3287,6 @@ private void appendDecoderDisplay(
  private int writeTokenDisplay(
  final String fieldName, final Token typeToken, final StringBuilder sb, final String indent)
  {
- append(sb, indent, "//" + typeToken);
-
  if (typeToken.encodedLength() <= 0 || typeToken.isConstantEncoding())
  {
  return -1;
@@ -3343,8 +3335,19 @@ private int writeTokenDisplay(
  break;
 
  case BEGIN_COMPOSITE:
- append(sb, indent, fieldName + "().appendTo(builder);");
+ {
+ final String typeName = formatClassName(decoderName(typeToken.applicableTypeName()));
+ append(sb, indent, "final " + typeName + " " + fieldName + " = " + fieldName + "();");
+ append(sb, indent, "if (" + fieldName + " != null)");
+ append(sb, indent, "{");
+ append(sb, indent, " " + fieldName + ".appendTo(builder);");
+ append(sb, indent, "}");
+ append(sb, indent, "else");
+ append(sb, indent, "{");
+ append(sb, indent, " builder.append(\"null\");");
+ append(sb, indent, "}");
  break;
+ }
  }
 
  final int lengthBeforeFieldSeparator = sb.length();