juneau-core/juneau-marshall/src/main/java/org/apache/juneau/utils/StackTraceDatabase.java

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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.utils;

import java.util.concurrent.*;

/**
 * An in-memory cache of stack traces.
 *
 * <p>
 * Used for preventing duplication of stack traces in log files and replacing them with small hashes.
 */
public class StackTraceDatabase {

	private final ConcurrentHashMap<Integer,StackTraceInfo> db = new ConcurrentHashMap<>();
	private final String stopClass;

	/**
	 * Constructor.
	 */
	public StackTraceDatabase() {
		this.stopClass = null;
	}

	/**
	 * Constructor.
	 *
	 * @param stopClass When this class is encountered in a stack trace, stop calculating the hash.
	 */
	public StackTraceDatabase(Class<?> stopClass) {
		this.stopClass = stopClass == null ? "" : stopClass.getName();
	}

	/**
	 * Retrieves the stack trace information for the specified exception.
	 *
	 * @param e The exception.
	 * @param timeout The timeout in milliseconds to cache the hash for this stack trace.
	 * @return The stack trace info, never <jk>null</jk>.
	 */
	public StackTraceInfo getStackTraceInfo(Throwable e, int timeout) {
		int hash = hash(e);
		StackTraceInfo stc = db.get(hash);
		if (stc != null && stc.timeout > System.currentTimeMillis()) {
			stc.incrementAndClone();
			return stc.clone();
		}
		synchronized (db) {
			stc = new StackTraceInfo(timeout, hash);
			db.put(hash, stc);
			return stc.clone();
		}
	}

	private int hash(Throwable t) {
		int i = 0;
		while (t != null) {
			for (StackTraceElement e : t.getStackTrace()) {
				if (e.getClassName().equals(stopClass))
					break;
				if (e.getClassName().indexOf('$') == -1)
					i ^= e.hashCode();
			}
			t = t.getCause();
		}
		return i;
	}

	/**
	 * Clears out the stack trace cache.
	 */
	public void reset() {
		db.clear();
	}
}