Simple Stopwatch that keeps a cache of running tasks.

Stopwatch.java

import java.util.Collections;
import java.util.Map;
import java.util.TreeMap;

/**
 * Usage:
 * 
 * Stopwatch.start("watchName");
 * ...
 * Stopwatch.end("watchName");
 * 
 * Stopwatch.start("loadingResource");
 * ...
 * Stopwatch.end("loadingResource");
 * ...
 * 
 * Stopwatch.getRunning().entrySet().stream().forEach(e -> {
 *            System.out.println(e.getKey() + " => nanos: " + e.getValue().getElapsedTime());
 *      });
 * 
 * Output would be:
 * 
 * InitComparator => nanos: 1800910
 * loadingAgainstPattern => nanos: 187572841
 * loadingResources => nanos: 1013792631
 * sorting => nanos: 3599532
 * 
 * @author juan.fernandez
 */
public class Stopwatch {
    private static final Map<String, Stopwatch> RUNNING = new TreeMap<>();
    private long startedAt;
    private long endedAt;
    
    public static Map<String, Stopwatch> getRunning() {
        return Collections.unmodifiableMap(RUNNING);
    }
    
    public static void start(String name) {
        RUNNING.put(name, new Stopwatch().start());
    }
    
    public static void end(String name) {
        Stopwatch task = RUNNING.get(name);
        if (task == null) {
            throw new IllegalArgumentException("no task aftre name: " + name);
        }
        task.end();
    }
    
    public static long getElapsedTime(String name) {
        Stopwatch task = RUNNING.get(name);
        if (task == null) {
            throw new IllegalArgumentException("no task after name: " + name);
        }
        return task.getElapsedTime();
    }
    
    private Stopwatch start() {
        startedAt = System.nanoTime();
        return this;
    }
    
    private Stopwatch end() {
        endedAt = System.nanoTime();
        return this;
    }
    
    public long getElapsedTime() {
        if (endedAt == 0 || startedAt == 0) {
            throw new IllegalStateException("either startedAt or endedAt are not set.");
        }
        return endedAt - startedAt;
    }
}