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package org.daisy.common.messaging;
import org.slf4j.Logger;
/**
* An object that can modify an underlying message by appending child messages to it or by closing it.
*/
public interface MessageAppender {
/**
* Append a child to the underlying message.
*
* @return the appended message
*/
public MessageAppender append(MessageBuilder message);
/**
* Close the underlying message.
*
* If a message is closed, the progress becomes 1 and no child message can be appended.
*/
public void close();
/**
* {@link Logger} that appends messages to the underlying message.
*/
public default Logger asLogger() {
return new AbstractLogger() {
protected void logMessage(MessageBuilder msg) {
MessageAppender.this.append(msg).close();
}
};
}
/**
* Returns the "active" block in the current "message thread".
*
* A message thread is a collection of messages that belong to the same {@link
* Message#getOwnerId() owner} ("job") and {@link Thread thread}.
*
* The active block is the portion of the process currently in progress. Whenever a new {@link
* MessageImpl} is created it becomes the new active block of that thread, until it is closed,
* and if its parent belongs to the same thread it then becomes the active block.
*
* This method assumes that different jobs are run in different threads.
*/
public static MessageAppender getActiveBlock() {
return MessageImpl.activeBlock.get();
}
/**
* Returns the active block in the specified message thread.
*
* This method is intended to be used by the JobProgressAppender class which receives
* log messages with "message-thread" info attached to them through the {@link org.slf4j.MDC}
* mechanism.
*/
public static MessageAppender getActiveBlock(String threadId) {
if (threadId == null)
throw new IllegalArgumentException();
return MessageImpl.activeBlockInThread.get(new MessageImpl.MessageThread(threadId));
}
/**
* {@link Logger} that appends messages to the active block at the time of the log calls.
*/
public static Logger getActiveBlockLogger() {
return new AbstractLogger() {
protected void logMessage(MessageBuilder msg) {
MessageAppender activeBlock = MessageAppender.getActiveBlock();
// we need an active block otherwise we have no place to send the message to
if (activeBlock != null)
activeBlock.append(msg).close();
}
};
}
}