Summary of cross-domain access issues between AJax and Jsonp-JS Tutorial-php.cn

#JavaScript's AJax

AJAX is "Asynchronous Javascript And XML" (Asynchronous JavaScript and XML)
An important technology used in designing AJax is the XMLHttpRequest object.

How to create an XMLHttpRequest object:

xmlhttp = new ActiveObject("Microsoft.XMLHTTP"); // Creation method supported by IE browser
xmlhttp = new XMLHTTPRequest( ); // Creation method supported by FireFox, Opera and other browsers
XMLHttp is a set of APIs that can transmit or receive XML and other data through http protocol in scripting languages such as Javascript, VbScript, Jscript and so on. Can be used to simulate http GET and POST requests.
You can determine whether the window.XMLHttpRequest object is available and then create an XMLHttpRequest object.

The following are the properties and usage methods of the XMLHttpRequest object. They are pasted and commented in detail.

<html> 
<head> 
<title>XMLHTTPRequest对象的说明DEMO</title> 
<script language="javascript" type="text/javascript"> 
<!-- 
var xmlhttp; 
// 创建一个XMLHTTPRequest对象 
function createXMLHTTPRequext(){ 
  if(window.ActiveXObject) { 
    xmlhttp = new ActiveXObject(&#39;Microsoft.XMLHTTP&#39;); 
  } 
  else if(window.XMLHTTPRequest){ 
    xmlhttp = new XMLHTTPRequest(); 
  } 
} 
function PostOrder(xmldoc) 
{ 
  createXMLHTTPRequext(); 
 
  // 方法：open 
  // 创建一个新的http请求，并指定此请求的方法、URL以及验证信息 
  // 语法：oXMLHttpRequest.open(bstrMethod, bstrUrl, varAsync, bstrUser, bstrPassword); 
  // 参数 
  // bstrMethod 
  // http方法，例如：POST、GET、PUT及PROPFIND。大小写不敏感。 
  // bstrUrl 
  // 请求的URL地址，可以为绝对地址也可以为相对地址。 
  // varAsync[可选] 
  // 布尔型，指定此请求是否为异步方式，默认为true。如果为真，当状态改变时会调用onreadystatechange属性指定的回调函数。 
  // bstrUser[可选] 
  // 如果服务器需要验证，此处指定用户名，如果未指定，当服务器需要验证时，会弹出验证窗口。 
  // bstrPassword[可选] 
  // 验证信息中的密码部分，如果用户名为空，则此值将被忽略。 
  // 备注：调用此方法后，可以调用send方法向服务器发送数据。 
  xmlhttp.Open("get", "http://localhost/example.htm", false); 
  // var book = xmlhttp.responseXML.selectSingleNode("//book[@id=&#39;bk101&#39;]"); 
  // alert(book.xml); 
 
  // 属性：onreadystatechange 
  // onreadystatechange：指定当readyState属性改变时的事件处理句柄 
  // 语法：oXMLHttpRequest.onreadystatechange = funcMyHandler; 
  // 如下的例子演示当XMLHTTPRequest对象的readyState属性改变时调用HandleStateChange函数， 
  // 当数据接收完毕后（readystate == 4）此页面上的一个按钮将被激活 
  // 备注：此属性只写，为W3C文档对象模型的扩展. 
  xmlhttp.onreadystatechange= HandleStateChange; 
 
  // 方法：send 
  // 发送请求到http服务器并接收回应 
  // 语法：oXMLHttpRequest.send(varBody); 
  // 参数：varBody （欲通过此请求发送的数据。） 
  // 备注：此方法的同步或异步方式取决于open方法中的bAsync参数，如果bAsync == False，此方法将会等待请求完成或者超时时才会返回，如果bAsync == True，此方法将立即返回。 
  // This method takes one optional parameter, which is the requestBody to use. The acceptable VARIANT input types are BSTR, SAFEARRAY of UI1 (unsigned bytes), IDispatch to an XML Document Object Model (DOM) object, and IStream *. You can use only chunked encoding (for sending) when sending IStream * input types. The component automatically sets the Content-Length header for all but IStream * input types. 
  // 如果发送的数据为BSTR，则回应被编码为utf-8, 必须在适当位置设置一个包含charset的文档类型头。 
  // If the input type is a SAFEARRAY of UI1, the response is sent as is without additional encoding. The caller must set a Content-Type header with the appropriate content type. 
  // 如果发送的数据为XML DOM object，则回应将被编码为在xml文档中声明的编码，如果在xml文档中没有声明编码，则使用默认的UTF-8。 
  // If the input type is an IStream *, the response is sent as is without additional encoding. The caller must set a Content-Type header with the appropriate content type. 
 
  xmlhttp.Send(xmldoc); 
 
  // 方法：getAllResponseHeaders 
  // 获取响应的所有http头 
  // 语法：strValue = oXMLHttpRequest.getAllResponseHeaders(); 
  // 备注：每个http头名称和值用冒号分割，并以\r\n结束。当send方法完成后才可调用该方法。 
  alert(xmlhttp.getAllResponseHeaders()); 
  // 方法：getResponseHeader 
  // 从响应信息中获取指定的http头 
  // 语法：strValue = oXMLHttpRequest.getResponseHeader(bstrHeader); 
  // 备注：当send方法成功后才可调用该方法。如果服务器返回的文档类型为"text/xml", 则这句话 
  // xmlhttp.getResponseHeader("Content-Type");将返回字符串"text/xml"。可以使用getAllResponseHeaders方法获取完整的http头信息。 
  alert(xmlhttp.getResponseHeader("Content-Type")); // 输出http头中的Content-Type列：当前web服务器的版本及名称。 
 
  document.frmTest.myButton.disabled = true; 
 
  // 方法：abort 
  // 取消当前请求 
  // 语法：oXMLHttpRequest.abort(); 
  // 备注：调用此方法后，当前请求返回UNINITIALIZED 状态。 
  // xmlhttp.abort(); 
 
  // 方法：setRequestHeader 
  // 单独指定请求的某个http头 
  // 语法：oXMLHttpRequest.setRequestHeader(bstrHeader, bstrValue); 
  // 参数：bstrHeader（字符串，头名称。） 
  // bstrValue（字符串，值。） 
  // 备注：如果已经存在已此名称命名的http头，则覆盖之。此方法必须在open方法后调用。 
  // xmlhttp.setRequestHeader(bstrHeader, bstrValue); 
  } 
  function HandleStateChange() 
  { 
  // 属性：readyState 
  // 返回XMLHTTP请求的当前状态 
  // 语法：lValue = oXMLHttpRequest.readyState; 
  // 备注：变量，此属性只读，状态用长度为4的整型表示.定义如下： 
  // 0 (未初始化) 对象已建立，但是尚未初始化（尚未调用open方法） 
  // 1 (初始化) 对象已建立，尚未调用send方法 
  // 2 (发送数据) send方法已调用，但是当前的状态及http头未知 
  // 3 (数据传送中) 已接收部分数据，因为响应及http头不全，这时通过responseBody和responseText获取部分数据会出现错误， 
  // 4 (完成) 数据接收完毕,此时可以通过通过responseBody和responseText获取完整的回应数据 
  if (xmlhttp.readyState == 4){ 
    document.frmTest.myButton.disabled = false; 
 
    // 属性：responseBody 
    // 返回某一格式的服务器响应数据 
    // 语法：strValue = oXMLHttpRequest.responseBody; 
    // 备注：变量，此属性只读，以unsigned array格式表示直接从服务器返回的未经解码的二进制数据。 
    alert(xmlhttp.responseBody); 
 
    // 属性：responseStream 
    // 以Ado Stream对象的形式返回响应信息 
    // 语法：strValue = oXMLHttpRequest.responseStream; 
    // 备注：变量，此属性只读，以Ado Stream对象的形式返回响应信息。 
    alert(xmlhttp.responseStream); 
 
    // 属性：responseText 
    // 将响应信息作为字符串返回 
    // 语法：strValue = oXMLHttpRequest.responseText; 
    // 备注：变量，此属性只读，将响应信息作为字符串返回。XMLHTTP尝试将响应信息解码为Unicode字符串， 
    // XMLHTTP默认将响应数据的编码定为UTF-8，如果服务器返回的数据带BOM(byte-order mark)，XMLHTTP可 
    // 以解码任何UCS-2 (big or little endian)或者UCS-4 数据。注意，如果服务器返回的是xml文档，此属 
    // 性并不处理xml文档中的编码声明。你需要使用responseXML来处理。 
    alert(xmlhttp.responseText); 
 
    // 属性：responseXML 
    // 将响应信息格式化为Xml Document对象并返回 
    // 语法：var objDispatch = oXMLHttpRequest.responseXML; 
    // 备注：变量，此属性只读，将响应信息格式化为Xml Document对象并返回。如果响应数据不是有效的XML文档， 
    // 此属性本身不返回XMLDOMParseError，可以通过处理过的DOMDocument对象获取错误信息。 
    alert("Result = " + xmlhttp.responseXML.xml); 
 
    // 属性：status 
    // 返回当前请求的http状态码 
    // 语法：lValue = oXMLHttpRequest.status; 
    // 返回值：长整形标准http状态码，定义如下： 
    // Number:Description 
    // 100:Continue
    // 101:Switching protocols 
    // 200:OK 
    // 201:Created 
    // 202:Accepted 
    // 203:Non-Authoritative Information 
    // 204:No Content 
    // 205:Reset Content 
    // 206:Partial Content 
    // 300:Multiple Choices 
    // 301:Moved Permanently 
    // 302:Found 
    // 303:See Other 
    // 304:Not Modified 
    // 305:Use Proxy 
    // 307:Temporary Redirect 
    // 400:Bad Request 
    // 401:Unauthorized 
    // 402:Payment Required 
    // 403:Forbidden 
    // 404:Not Found 
    // 405:Method Not Allowed 
    // 406:Not Acceptable 
    // 407:Proxy Authentication Required 
    // 408:Request Timeout 
    // 409:Conflict 
    // 410:Gone 
    // 411:Length Required 
    // 412:Precondition Failed 
    // 413:Request Entity Too Large 
    // 414:Request-URI Too Long 
    // 415:Unsupported Media Type 
    // 416:Requested Range Not Suitable 
    // 417:Expectation Failed 
    // 500:Internal Server Error 
    // 501:Not Implemented 
    // 502:Bad Gateway 
    // 503:Service Unavailable 
    // 504:Gateway Timeout 
    // 505:HTTP Version Not Supported 
    // 备注：长整形，此属性只读，返回当前请求的http状态码,此属性仅当数据发送并接收完毕后才可获取。 
    alert(xmlhttp.status);
 
    // 属性：statusText 
    // 返回当前请求的响应行状态 
    // 语法：strValue = oXMLHttpRequest.statusText; 
    // 备注：字符串，此属性只读，以BSTR返回当前请求的响应行状态,此属性仅当数据发送并接收完毕后才可获取。 
    alert(xmlhttp.statusText); 
  } 
} 
 
//--> 
</script> 
</head> 
<body> 
  <form name="frmTest"> 
    <input name="myButton" type="button" value="Click Me" onclick="PostOrder(&#39;http://localhost/example.htm&#39;);"> 
  </form> 
</body> 
</html>

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To put it simply, it is a process of using the XMLHttpRequest object to make a request to the server, and then getting the information returned by the server.

The above is the Ajax technical principle of JavaScript. It is completely different from the principle of Jsonp implementing cross-domain access that will be discussed later.

JQuery's AJax

JQuery encapsulates the ajax technology, making it more convenient to use.

$.General form of ajax

$.ajax({
  type: &#39;POST&#39;,
  url: url ,
  data: data ,
  dataType: dataType
  success: success ,  
});

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When the scene is different, we need to use Ajax instead. 1. Assemble json data. 2. Serialize table content. var formParam = $("#form1").serialize(); 3. Splice URLs. . . For example, when there are special strings (such as &) in our data, string splicing is not easy to use, which may make the submitted content incomplete. At this time, it will be easier to use Json.

Using jsonp to achieve cross-domain access

What is Jsonp? What does

have to do with json?

How does jsonp achieve cross-domain access?

First explain why Ajax cannot be accessed across domains and why browsers restrict cross-domain access.

Assuming that the browser supports cross-domain access, we can access site B through XmlHttpRequest at site A. At this time, we have passed the verification of site B and obtained the cookie of site B. Then we can freely When you visit site B, site A can impersonate site B to perform all operations on site B that do not require further verification. This is quite dangerous.

How do we obtain cross-domain data?

We found that when calling js files on a Web page, it is not affected by whether it is cross-domain (not only that, we also found that all tags with the "src" attribute have cross-domain capabilities, such as script, img, iframe, etc. We can use this property of js to obtain the data we want.

In order to facilitate the client to use data, an informal transmission protocol has gradually formed. People call it JSONP. One of the key points of this protocol is to allow users to pass a callback parameter to the server. Then when the server returns data, it will use this callback parameter as a function name to wrap the JSON data, so that the client can customize it at will. Use your own function to automatically process the returned data.

Let’s take a look at what jsonp does.

1. We know that even cross-domain js files. The code in (of course it complies with the web script security policy), the web page can also be executed unconditionally. There is a remote.js file in the root directory of the remote server remoteserver.com with the following code:

alert('I am Remote file');

The local server localserver.com has a jsonp.html page code as follows:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title></title>
  <script type="text/javascript" src="http://remoteserver.com/remote.js"></script>
</head>
<body>
</body>
</html>

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There is no doubt that a prompt form will pop up on the page, indicating that the cross-domain call is successful. This is the most basic idea of jsonp.

2. Now we define a function in the jsonp.html page, and then call it by passing in data in the remote remote.js. The jsonp.html page code is as follows:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title></title>
  <script type="text/javascript">
  var localHandler = function(data){
    alert(&#39;我是本地函数，可以被跨域的remote.js文件调用，远程js带来的数据是：&#39; + data.result);
  };
  </script>
  <script type="text/javascript" src="http://remoteserver.com/remote.js"></script>
</head>
<body>
</body>
</html>

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remote.js file code is as follows:

localHandler({"result":"I am the data brought by remote js"});

Check the result after running, the page will pop up a prompt window successfully , showing that the local function was successfully called by the cross-domain remote js, and the data brought by the remote js was received. The purpose of cross-domain access to data has been achieved, but how do I let the remote js know the name of the local function it should call? What?

3. You can pass a parameter to tell the server "I want a js code that calls the XXX function, please return it to me", so the server can generate the js script according to the client's needs. Responded.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title></title>
  <script type="text/javascript">
  // 得到航班信息查询结果后的回调函数
  var flightHandler = function(data){
    alert(&#39;你查询的航班结果是：票价 &#39; + data.price + &#39; 元，&#39; + &#39;余票 &#39; + data.tickets + &#39; 张。&#39;);
  };
  // 提供jsonp服务的url地址（不管是什么类型的地址，最终生成的返回值都是一段javascript代码）
  var url = "http://flightQuery.com/jsonp/flightResult.aspx?code=CA1998&callback=flightHandler";
  // 创建script标签，设置其属性
  var script = document.createElement(&#39;script&#39;);
  script.setAttribute(&#39;src&#39;, url);
  // 把script标签加入head，此时调用开始
  document.getElementsByTagName(&#39;head&#39;)[0].appendChild(script);
  </script>
</head>
<body>
</body>
</html>

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On the server side, we get the callback and assemble the required js.

String callback = request.getParemeter("callback");

response.getWriter. print(callback + "(" + json +")");

The content returned to the page is:

flightHandler({
  "code": "CA1998",
  "price": 1780,
  "tickets": 5
});

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4.Jquery also encapsulates jsonp. (The form is more like ajax)

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml" >
 <head>
   <title>Untitled Page</title>
   <script type="text/javascript" src=jquery.min.js"></script>
   <script type="text/javascript">
   jQuery(document).ready(function(){
    $.ajax({
       type: "get",
       async: false,
       url: "http://flightQuery.com/jsonp/flightResult.aspx?code=CA1998",
       dataType: "jsonp",
       jsonp: "callback",//传递给请求处理程序或页面的，用以获得jsonp回调函数名的参数名(一般默认为:callback)
       jsonpCallback:"flightHandler",//自定义的jsonp回调函数名称，默认为jQuery自动生成的随机函数名，也可以写"?"，jQuery会自动为你处理数据
       success: function(json){
         alert(&#39;您查询到航班信息：票价： &#39; + json.price + &#39; 元，余票： &#39; + json.tickets + &#39; 张。&#39;);
       },
       error: function(){
         alert(&#39;fail&#39;);
       }
     });
   });
   </script>
   </head>
 <body>
 </body>
 </html>

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Finally, Ajax and jsonp are two completely different things. The core of ajax is to obtain non-this page content through XmlHttpRequest, while the core of jsonp is to dynamically add script tags to call the js script provided by the server.

How to obtain cross-domain data through JSONP in jQuery

######The first method is to set the dataType to 'jsonp' in the ajax function: ###

$.ajax({
    dataType: &#39;jsonp&#39;,
    jsonp:&#39;callback&#39;,
    url: &#39;http://www.a.com/user?id=123&#39;,   
    success: function(data){   
        //处理data数据   
    }   
});

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第二种方法是利用getJSON来实现，只要在地址中加上callback=?参数即可：

$.getJSON(&#39;http://www.a.com/user?id=123&callback=?&#39;, function(data){  
    //处理data数据  
});

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也可以简单地使用getScript方法：

//此时也可以在函数外定义foo方法  
function foo(data){  
    //处理data数据  
}  
$.getJSON(&#39;http://www.a.com/user?id=123&callback=foo&#39;);

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JSONP的应用

JSONP在开放API中可以起到非常重要的作用，开放API是运用在开发者自己的应用上，而许多应用往往是在开发者的服务器上而不是在新浪微博的服务器上，因此跨域请求数据成为开发者们所需要解决的一大问题，广大开放平台应该实现对JSONP的支持，这一点新浪微博开放平台便做的非常好（虽然某些API里没有说明，但实际上是可以使用JSONP方式调用的）。

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