ProcessBufferProcessor 的核心是进行消息处理，会调用消息处理器，同时会将消息放到OutputBuffer 中
ProcessBufferProcessor 实际上是ProcessBuffer 中Disruptor 的一个handler
核心处理
handleMessage 方法
private void handleMessage(@Nonnull Message msg) {
msg.addStream(defaultStreamProvider.get());
Messages messages = msg;
// 消息处理器，进行消息加工
for (MessageProcessor messageProcessor : orderedMessageProcessors) {
messages = messageProcessor.process(messages);
}
for (Message message : messages) {
message.ensureValidTimestamp();
if (!message.hasField(Message.FIELD_GL2_MESSAGE_ID) || isNullOrEmpty(message.getFieldAs(String.class, Message.FIELD_GL2_MESSAGE_ID))) {
// Set the message ID once all message processors have finished
// See documentation of Message.FIELD_GL2_MESSAGE_ID for details
message.addField(Message.FIELD_GL2_MESSAGE_ID, ulid.nextULID());
}
// The processing time should only be set once all message processors have finished
message.setProcessingTime(Tools.nowUTC());
// 消息处理标记
processingStatusRecorder.updatePostProcessingReceiveTime(message.getReceiveTime());
if(failureSubmissionService.submitProcessingErrors(message)) {
// 消息放到 outputBuffer 中
outputBuffer.insertBlocking(message);
}
}
}
MessageProcessor
MessageProcessor 会调用Filter 进行消息的加工
参考实现 
包含的filter 实现 
参考资料
https://github.com/Graylog2/graylog2-server/blob/626be1f0d80506705b5ba41fbea33c2ec0164bc0/graylog2-server/src/main/java/org/graylog2/shared/buffers/processors/ProcessBufferProcessor.java
https://github.com/Graylog2/graylog2-server/blob/626be1f0d80506705b5ba41fbea33c2ec0164bc0/graylog2-server/src/main/java/org/graylog2/plugin/messageprocessors/MessageProcessor.java
https://github.com/Graylog2/graylog2-server/blob/626be1f0d80506705b5ba41fbea33c2ec0164bc0/graylog2-server/src/main/java/org/graylog2/plugin/filters/MessageFilter.java