android token 超时,异步回调怎么实现会比较优雅

PhoneGap的js回调有几种实现方式。其中一种是ajax。
我们先来看一下js端相关代码：

// file: lib/android/plugin/android/callback.js
define("cordova/plugin/android/callback", function(require, exports, mole) {

var port = null,
token = null,
xmlhttp;

function startXhr() {
// cordova/exec depends on this mole, so we can't require cordova/exec on the mole level.
var exec = require('cordova/exec'),
xmlhttp = new XMLHttpRequest();

// Callback function when XMLHttpRequest is ready
xmlhttp.onreadystatechange=function(){
if (!xmlhttp) {
return;
}
if (xmlhttp.readyState === 4){
// If callback has JavaScript statement to execute
if (xmlhttp.status === 200) {

// Need to url decode the response
var msg = decodeURIComponent(xmlhttp.responseText);
setTimeout(startXhr, 1);
exec.processMessages(msg);
}

// If callback ping (used to keep XHR request from timing out)
else if (xmlhttp.status === 404) {
setTimeout(startXhr, 10);
}

// 0 == Page is unloading.
// 400 == Bad request.
// 403 == invalid token.
// 503 == server stopped.
else {
console.log("JSCallback Error: Request failed with status " + xmlhttp.status);
exec.setNativeToJsBridgeMode(exec.nativeToJsModes.POLLING);
}
}
};

if (port === null) {
port = prompt("getPort", "gap_callbackServer:");
}
if (token === null) {
token = prompt("getToken", "gap_callbackServer:");
}
xmlhttp.open("GET", "http://127.0.0.1:"+port+"/"+token , true);
xmlhttp.send();
}

mole.exports = {
start: function() {
startXhr();
},

stop: function() {
if (xmlhttp) {
var tmp = xmlhttp;
xmlhttp = null;
tmp.abort();
}
},

isAvailable: function() {
return ("true" != prompt("usePolling", "gap_callbackServer:"));
}
};

});

主要的处理是startXhr函数。它向java的server端发起了ajax请求，在onreadystatechange这个回调函数中等待server端返回结果。如果server端返回的结果正确，则再通过setTimeout(startXhr, 1)函数，1豪秒后再重新向server端发起ajax请求。如果从server返回的结果状态是404，则每隔10豪秒，重新向server端发起ajax请求。
接下来看看server端是如何处理的。server端的处理代码是CallbackServer.java中的run()方法中。
先看server端的源码：
它通过serverSocket来模拟http的server端。其中，jsMessageQueue中是从java端发送的js消息，serverSocket在接收到客户端（js端）的请求后，会将jsMessageQueue中的js代码发送到客户端（js端）。

/**
* Start running the server.
* This is called automatically when the server thread is started.
*/
public void run() {

// Start server
try {
this.active = true;
String request;
waitSocket = new ServerSocket(0);
this.port = waitSocket.getLocalPort();
//Log.d(LOG_TAG, "CallbackServer -- using port " +this.port);
this.token = java.util.UUID.randomUUID().toString();
//Log.d(LOG_TAG, "CallbackServer -- using token "+this.token);

while (this.active) {
//Log.d(LOG_TAG, "CallbackServer: Waiting for data on socket");
Socket connection = waitSocket.accept();
BufferedReader xhrReader = new BufferedReader(new InputStreamReader(connection.getInputStream()), 40);
DataOutputStream output = new DataOutputStream(connection.getOutputStream());
request = xhrReader.readLine();
String response = "";
//Log.d(LOG_TAG, "CallbackServerRequest="+request);
if (this.active && (request != null)) {
if (request.contains("GET")) {

// Get requested file
String[] requestParts = request.split(" ");

// Must have security token
if ((requestParts.length == 3) && (requestParts[1].substring(1).equals(this.token))) {
//Log.d(LOG_TAG, "CallbackServer -- Processing GET request");
String payload = null;

// Wait until there is some data to send, or send empty data every 10 sec
// to prevent XHR timeout on the client
while (this.active) {
if (jsMessageQueue != null) {
payload = jsMessageQueue.popAndEncode();
if (payload != null) {
break;
}
}
synchronized (this) {
try {
this.wait(10000); // prevent timeout from happening
//Log.d(LOG_TAG, "CallbackServer>>> break <<<");
break;
} catch (Exception e) {
}
}
}

// If server is still running
if (this.active) {

// If no data, then send 404 back to client before it times out
if (payload == null) {
//Log.d(LOG_TAG, "CallbackServer -- sending data 0");
response = "HTTP/1.1 404 NO DATA\r\n\r\n "; // need to send content otherwise some Android devices fail, so send space
}
else {
//Log.d(LOG_TAG, "CallbackServer -- sending item");
response = "HTTP/1.1 200 OK\r\n\r\n";
response += encode(payload, "UTF-8");
}
}
else {
response = "HTTP/1.1 503 Service Unavailable\r\n\r\n ";
}
}
else {
response = "HTTP/1.1 403 Forbidden\r\n\r\n ";
}
}
else {
response = "HTTP/1.1 400 Bad Request\r\n\r\n ";
}
//Log.d(LOG_TAG, "CallbackServer: response="+response);
//Log.d(LOG_TAG, "CallbackServer: closing output");
output.writeBytes(response);
output.flush();
}
output.close();
xhrReader.close();
}
} catch (IOException e) {
e.printStackTrace();
}
this.active = false;
//Log.d(LOG_TAG, "CallbackServer.startServer() - EXIT");
}

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