首页 \ 问答 \ 链接一系列异步调用(Chain a series of asynchronous calls)

链接一系列异步调用(Chain a series of asynchronous calls)

 我有一系列的异步操作 
 

private void doSomething(){
  get("/something", new Callback(){
    void onComplete(String data){
      updateUi(something, data);           
      doSomethingElse();
    }
  });
}

private void doSomethingElse(){
  get("/something/else", new Callback(){
    void onComplete(String data){
      updateUi(somethingElse, data);
      doYetAnotherThing();
    }
  });
}

private void doYetAnotherThing(){
  get("/yet/another/thing", new Callback(){
    void onComplete(String data){
      updateUi(yetAnotherThing, data);
      allDone();
    }
  });
}

 

 这有几个问题： 
 

     
 
  1.  由于每个回调都与“下一步”有内在联系，因此无法在其他地方重复使用任何回调 
    2.  
 
  2.  重新排序操作或插入其他操作是非直观的，并涉及到所有地方跳跃。 
    3.  

 

 我已经看过以下选项来减轻这一点： 
 

     
 
  1.  ExecuterService#invokeAll - 我没有看到这个解决方案如何在没有阻塞的情况下使用。 
    2.  
 
  2.  RxJava--如果可以的话，我宁愿避免在我的应用程序中出现这种范式转变！ 
    3.  
 
  3.  番石榴的ListenableFutures及其transform方法。 我看到这在互联网螺母周围的少数地方提到，我真的不知道这将如何解决我的问题。 
    4.  

 

 所以，问题是：在Java中链接一系列异步调用的好模式是什么？ 因为我需要一个适用于Android应用程序的解决方案，所以需要使用Java 7。 

I have a series of asynchronous operations 
 

private void doSomething(){
  get("/something", new Callback(){
    void onComplete(String data){
      updateUi(something, data);           
      doSomethingElse();
    }
  });
}

private void doSomethingElse(){
  get("/something/else", new Callback(){
    void onComplete(String data){
      updateUi(somethingElse, data);
      doYetAnotherThing();
    }
  });
}

private void doYetAnotherThing(){
  get("/yet/another/thing", new Callback(){
    void onComplete(String data){
      updateUi(yetAnotherThing, data);
      allDone();
    }
  });
}

 

This suffers from few problems:
 

     
 
  1. Cannot reuse any of the callbacks elsewhere since each is intrinsically tied to the "next step"
    2.  
 
  2. Re-ordering operations or inserting another operation is non-intuitive and involves jumping all over the place.
    3.  

 

I have looked at the following options to mitigate this:
 

     
 
  1. ExecuterService#invokeAll - I don't see how this solution can be used without blocking.
    2.  
 
  2. RxJava - I would prefer to avoid such a paradigm shift in my application if I can!
    3.  
 
  3. Guava's ListenableFutures and its transform method. I saw this referred to in few places around the interwebs nut I honestly don't see how this would solve my problem.
    4.  

 

So, the question is: What would be a good pattern to chain a series of asynchronous calls in Java? Looking for a solution that works with Java 7 since I need this for an Android app.

原文：https://stackoverflow.com/questions/26059300
更新时间：2022-01-26 13:01

最满意答案

 这应该让你开始http://jsfiddle.net/0ao9oa7a/ 
 

     
 
  •  获取所有记录的点 
    •  
 
  •  过滤出相近的点（我使用5个像素） 
    •  
 
  •  找出每对连续点的角度（atan2） 
    •  
 
  •  找出每对连续角度之间的绝对差异 
    •  
 
  •  
  
       
   
    •  在最大差异之前丢弃所有角度 
      •  
  
    •  
 
  •  平均剩余的角度（平均所有点矢量然后atan2回到一个角度） 
    •  

 

 码 
 

function process(points) {
    if(points.length === 0) { 
        txt = "Not enough points\n" + txt;
        return null; 
    }
    // compress points, removing those that are too close together
    var newPoints = [];
    newPoints.push(points[0]);
    for(var i = 1; i < points.length; i++) {
        if(Math.sqrt(Math.pow(points[i].x - newPoints[newPoints.length - 1].x, 2) + Math.pow(points[i].y - newPoints[newPoints.length - 1].y, 2)) > 5) {
            newPoints.push(points[i]);
        }
    }
    points = newPoints;
    if(points.length < 2) { 
        txt = "Not enough points\n" + txt;
        return null; 
    }
    // get all of the angles
    var angles = [];
    for(var i=0; i < points.length - 1; i++) {
        var rad = Math.atan2(points[i + 1].y - points[i].y, points[i + 1].x - points[i].x);
        angles[i] = rad;
        txt += "x: " + (points[i].x|0) + " y: " + (points[i].y|0) + " x: " + (points[i+1].x|0) + " y: " + (points[i+1].y|0) + " [" + ((rad * 180 / Math.PI)|0) + "]" + "\n";
    }
    txt += "\n";
    // get all of the diffs between angles
    // save the index of the max diff
    var absDiffs = [];
    var maxDiff = -1;
    var maxDiffAngleIndex = -1;
    for(var i=0; i < points.length - 1; i++) {
        var delta = Math.abs(angles[i] - angles[i + 1]);
        if(delta >= maxDiff) {
            maxDiff = delta;
            maxDiffAngleIndex = i + 1;
        }
    }
    if(maxDiffAngleIndex == -1) {
        txt = "Angle: " + angles[0] + " : " + (angles[0] * 180 / Math.PI) + "\n" + txt;
        return angles[0];
    } else if(maxDiffAngleIndex == angles.length - 1) {
        txt = "Angle: " + angles[angle.length - 1] + " : " + (angles[angles.length - 1] * 180 / Math.PI) + "\n" + txt;
        return angles[angles.length - 1];
    } else {
        // find the average angle from the index to the end
        var sumX = 0;
        var sumY = 0;
        for(var i = maxDiffAngleIndex; i < angles.length; i++) {
            sumX += Math.cos(angles[i]);
            sumY += Math.sin(angles[i]);
        }
        var avgX = sumX / (angles.length - maxDiffAngleIndex);
        var avgY = sumY / (angles.length - maxDiffAngleIndex);
        //
        var avgAngle = Math.atan2(avgY, avgX);
        txt = "Angle: " + avgAngle + " : " + (avgAngle * 180 / Math.PI) + "\n" + txt;
        return avgAngle;
    }
}


This should get you started http://jsfiddle.net/0ao9oa7a/
 

     
 
  • Get all of the recorded points
    •  
 
  • Filter out points that are close together (I use 5 pixels)
    •  
 
  • Find the angles of each consecutive pair of points (atan2)
    •  
 
  • Find the absolute differences between each consecutive pair of angles
    •  
 
  •  
  
       
   
    • Throw away all of the angles before the max difference
      •  
  
    •  
 
  • Average the remaining angles (average all point vectors then atan2 back into an angle)
    •  

 

Code
 

function process(points) {
    if(points.length === 0) { 
        txt = "Not enough points\n" + txt;
        return null; 
    }
    // compress points, removing those that are too close together
    var newPoints = [];
    newPoints.push(points[0]);
    for(var i = 1; i < points.length; i++) {
        if(Math.sqrt(Math.pow(points[i].x - newPoints[newPoints.length - 1].x, 2) + Math.pow(points[i].y - newPoints[newPoints.length - 1].y, 2)) > 5) {
            newPoints.push(points[i]);
        }
    }
    points = newPoints;
    if(points.length < 2) { 
        txt = "Not enough points\n" + txt;
        return null; 
    }
    // get all of the angles
    var angles = [];
    for(var i=0; i < points.length - 1; i++) {
        var rad = Math.atan2(points[i + 1].y - points[i].y, points[i + 1].x - points[i].x);
        angles[i] = rad;
        txt += "x: " + (points[i].x|0) + " y: " + (points[i].y|0) + " x: " + (points[i+1].x|0) + " y: " + (points[i+1].y|0) + " [" + ((rad * 180 / Math.PI)|0) + "]" + "\n";
    }
    txt += "\n";
    // get all of the diffs between angles
    // save the index of the max diff
    var absDiffs = [];
    var maxDiff = -1;
    var maxDiffAngleIndex = -1;
    for(var i=0; i < points.length - 1; i++) {
        var delta = Math.abs(angles[i] - angles[i + 1]);
        if(delta >= maxDiff) {
            maxDiff = delta;
            maxDiffAngleIndex = i + 1;
        }
    }
    if(maxDiffAngleIndex == -1) {
        txt = "Angle: " + angles[0] + " : " + (angles[0] * 180 / Math.PI) + "\n" + txt;
        return angles[0];
    } else if(maxDiffAngleIndex == angles.length - 1) {
        txt = "Angle: " + angles[angle.length - 1] + " : " + (angles[angles.length - 1] * 180 / Math.PI) + "\n" + txt;
        return angles[angles.length - 1];
    } else {
        // find the average angle from the index to the end
        var sumX = 0;
        var sumY = 0;
        for(var i = maxDiffAngleIndex; i < angles.length; i++) {
            sumX += Math.cos(angles[i]);
            sumY += Math.sin(angles[i]);
        }
        var avgX = sumX / (angles.length - maxDiffAngleIndex);
        var avgY = sumY / (angles.length - maxDiffAngleIndex);
        //
        var avgAngle = Math.atan2(avgY, avgX);
        txt = "Angle: " + avgAngle + " : " + (avgAngle * 180 / Math.PI) + "\n" + txt;
        return avgAngle;
    }
}

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