PromisePipeTest.java

import java.util.*;

public class PromisePipeTest {
    static boolean isOver = false;
    public static void main(String[] args) {
		Promise p1 = new Promise("p1");
		Promise p2 = new Promise("p2");
		Promise p21 = new Promise("p2-1");
		Promise p211 = new Promise("p2-1-1");
		Promise p22 = new Promise("p2-2");
		Promise p3 = new Promise("p3");
		p1.pipe(p2.pipe(p21.pipe(p211)).pipe(p22)).pipe(p3).exec(new Callback() {
		    @Override
			public void onResult(String result) {
			    log("ok cb: " + result);
				isOver = true;
			}
		}, new Callback() {
		    @Override
			public void onResult(String result) {
			    log("fail cb: " + result);
				isOver = true;
			}
		});
		
		while(!isOver) {
		    try {
			    Thread.currentThread().sleep(100);
			} catch (InterruptedException e) {
			}
		}
		
		log(p1.result);
		log(p2.result);
		log(p21.result);
		log(p211.result);
		log(p22.result);
		log(p3.result);
	}
	
	static class Promise {
	    String name;
	    String result = null;
		Promise next;
		public Promise(String name) {
		    this.name = name;
		}
		
		public Promise pipe(Promise newNext) {
		    if (next == null) {
			    next = newNext;
			} else {
			    Promise theNextWithoutNext = next;
		        while (theNextWithoutNext.next != null) {
			        theNextWithoutNext = theNextWithoutNext.next;
			    }
			    theNextWithoutNext.next = newNext;
			}
			return this;
		}
	    
	    public Promise exec(final Callback allOk, final Callback fail) {
		    new Thread(name) {
			    @Override
				public void run() {
				    try {
					    sleep(100);
					} catch (InterruptedException e) {
					}
					Promise.this.result = (new Random().nextInt(2) > 0) ? getName() + " is done" : null;
					log(Promise.this.result);
					
					if (Promise.this.result == null) {
						fail.onResult(getName() + " is failed");
					} else {
					    if (Promise.this.next != null) {
					        log("NEXT");
						    Promise.this.next.exec(allOk, fail);
					    } else {
					        log("END");
							allOk.onResult("ALL DONE");
					    }
				    }
				}
			}.start();
			return this;
		}
	}
	
	public static void log(Object o) {
	    System.out.println(o == null? "null" : o.toString());
	}
	
	interface Callback {
	    void onResult(String result);
    }
}