4 批量消息样例

批量发送消息能显著提高传递小消息的性能。限制是这些批量消息应该有相同的topic，相同的waitStoreMsgOK，而且不能是延时消息。此外，这一批消息的总大小不应超过4MB。

4.1 发送批量消息

如果您每次只发送不超过4MB的消息，则很容易使用批处理，样例如下：

String topic = "BatchTest";
List<Message> messages = new ArrayList<>();
messages.add(new Message(topic, "TagA", "OrderID001", "Hello world 0".getBytes()));
messages.add(new Message(topic, "TagA", "OrderID002", "Hello world 1".getBytes()));
messages.add(new Message(topic, "TagA", "OrderID003", "Hello world 2".getBytes()));
try {
   producer.send(messages);
} catch (Exception e) {
   e.printStackTrace();
   //处理error
}

4.2 消息列表分割

复杂度只有当你发送大批量时才会增长，你可能不确定它是否超过了大小限制（4MB）。这时候你最好把你的消息列表分割一下：

public class ListSplitter implements Iterator<List<Message>> { 
    private final int SIZE_LIMIT = 1024 * 1024 * 4;
    private final List<Message> messages;
    private int currIndex;
    public ListSplitter(List<Message> messages) { 
        this.messages = messages;
    }
    @Override public boolean hasNext() {
        return currIndex < messages.size(); 
    }
    @Override public List<Message> next() { 
        int startIndex = getStartIndex();
        int nextIndex = startIndex;
        int totalSize = 0;
        for (; nextIndex < messages.size(); nextIndex++) {
            Message message = messages.get(nextIndex); 
            int tmpSize = calcMessageSize(message);
            if (tmpSize + totalSize > SIZE_LIMIT) {
                break; 
            } else {
                totalSize += tmpSize; 
            }
        }
        List<Message> subList = messages.subList(startIndex, nextIndex); 
        currIndex = nextIndex;
        return subList;
    }
    private int getStartIndex() {
        Message currMessage = messages.get(currIndex); 
        int tmpSize = calcMessageSize(currMessage); 
        while(tmpSize > SIZE_LIMIT) {
            currIndex += 1;
            Message message = messages.get(curIndex); 
            tmpSize = calcMessageSize(message);
        }
        return currIndex; 
    }
    private int calcMessageSize(Message message) {
        int tmpSize = message.getTopic().length() + message.getBody().length(); 
        Map<String, String> properties = message.getProperties();
        for (Map.Entry<String, String> entry : properties.entrySet()) {
            tmpSize += entry.getKey().length() + entry.getValue().length(); 
        }
        tmpSize = tmpSize + 20; // 增加⽇日志的开销20字节
        return tmpSize; 
    }
}
//把大的消息分裂成若干个小的消息
ListSplitter splitter = new ListSplitter(messages);
while (splitter.hasNext()) {
  try {
      List<Message>  listItem = splitter.next();
      producer.send(listItem);
  } catch (Exception e) {
      e.printStackTrace();
      //处理error
  }
}