跨域请求在网页上非常常见。很多网页从不同服务器上载入 CSS, 图片，Js脚本等。

在现代浏览器中，为了数据的安全，所有请求被严格限制在同一域名下，如果需要调用不同站点的数据，需要通过跨域来解决。

1. PHP 和 MySql 代码实例
   <?php
   header("Access-Control-Allow-Origin: *");
   header("Content-Type: application/json; charset=UTF-8");

$conn = new mysqli("myServer", "myUser", "myPassword", "Northwind");

$result = $conn->query("SELECT CompanyName, City, Country FROM Customers");

$outp = "";
while($rs = $result->fetch_array(MYSQLI_ASSOC)) {
if ($outp != "") {$outp .= ",";}
$outp .= ‘{"Name":"‘ . $rs["CompanyName"] . ‘",‘;
$outp .= ‘"City":"‘ . $rs["City"] . ‘",‘;
$outp .= ‘"Country":"‘. $rs["Country"] . ‘"}‘;
}
$outp =‘{"records":[‘.$outp.‘]}‘;
$conn->close();

echo($outp);

www.djznrobot.com

?>

2. PHP 和 MS Access 代码实例
   <?php
   header("Access-Control-Allow-Origin: *");
   header("Content-Type: application/json; charset=ISO-8859-1");

$conn = new COM("ADODB.Connection");
$conn->open("PROVIDER=Microsoft.Jet.OLEDB.4.0;Data Source=Northwind.mdb");

$rs = $conn->execute("SELECT CompanyName, City, Country FROM Customers");

$outp = "";
while (!$rs->EOF) {
if ($outp != "") {$outp .= ",";}
$outp .= ‘{"Name":"‘ . $rs["CompanyName"] . ‘",‘;
$outp .= ‘"City":"‘ . $rs["City"] . ‘",‘;
$outp .= ‘"Country":"‘. $rs["Country"] . ‘"}‘;
$rs->MoveNext();
}
$outp =‘{"records":[‘.$outp.‘]}‘;

$conn->close();

echo ($outp);
?>

3. ASP.NET, VB 和 MS Access 代码实例
   <%@ Import Namespace="System.IO"%>
   <%@ Import Namespace="System.Data"%>
   <%@ Import Namespace="System.Data.OleDb"%>
   <%
   Response.AppendHeader("Access-Control-Allow-Origin", "*")
   Response.AppendHeader("Content-type", "application/json")
   Dim conn As OleDbConnection
   Dim objAdapter As OleDbDataAdapter
   Dim objTable As DataTable
   Dim objRow As DataRow
   Dim objDataSet As New DataSet()
   Dim outp
   Dim c
   conn = New OledbConnection("Provider=Microsoft.Jet.OLEDB.4.0;data source=Northwind.mdb")
   objAdapter = New OledbDataAdapter("SELECT CompanyName, City, Country FROM Customers", conn)
   objAdapter.Fill(objDataSet, "myTable")
   objTable=objDataSet.Tables("myTable")

outp = ""
c = chr(34)
for each x in objTable.Rows
if outp <> "" then outp = outp & ","
outp = outp & "{" & c & "Name" & c & ":" & c & x("CompanyName") & c & ","
outp = outp & c & "City" & c & ":" & c & x("City") & c & ","
outp = outp & c & "Country" & c & ":" & c & x("Country") & c & "}"
next

outp ="{" & c & "records" & c & ":[" & outp & "]}"
response.write(outp)
conn.close
%>

4. ASP.NET, VB Razor 和 SQL Lite 代码实例br/>@{
   Response.AppendHeader("Access-Control-Allow-Origin", "*")
   Response.AppendHeader("Content-type", "application/json")
   var db = Database.Open("Northwind");
   var query = db.Query("SELECT CompanyName, City, Country FROM Customers");
   var outp =""
   var c = chr(34)
   }
   @foreach(var row in query)
   {
   if outp <> "" then outp = outp + ","
   outp = outp + "{" + c + "Name" + c + ":" + c + @row.CompanyName + c + ","
   outp = outp + c + "City" + c + ":" + c + @row.City + c + ","
   outp = outp + c + "Country" + c + ":" + c + @row.Country + c + "}"
   }
   outp ="{" + c + "records" + c + ":[" + outp + "]}"
   @outp

关于跨域 HTTP 请求