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C # tutorial
A common use of JSON is to read data from a web server, and display the data in a web page.This chapter will teach you how to exchange JSON data between the client and a PHP server
PHP has some built-in functions to handle JSON.
Objects in PHP can be converted into JSON by using the PHP function json_encode():
<?php
$myObj->name = "John";
$myObj->age = 30;
$myObj->city = "New
York";
$myJSON = json_encode($myObj);
echo $myJSON;
?>
Here is a JavaScript on the client, using an AJAX call to request the PHP file from the example above:
Use JSON.parse() to convert the result into a JavaScript object:
const xmlhttp = new XMLHttpRequest();
xmlhttp.onload = function() {
const myObj = JSON.parse(this.responseText);
document.getElementById("demo").innerHTML = myObj.name;
}
xmlhttp.open("GET", "demo_file");
xmlhttp.send();
Arrays in PHP will also be converted into JSON when using the PHP function json_encode():
<?php
$myArr = array("John", "Mary", "Peter", "Sally");
$myJSON = json_encode($myArr);
echo $myJSON;
?>
Here is a JavaScript on the client, using an AJAX call to request the PHP file from the array example above:
Use JSON.parse() to convert the result into a JavaScript array:
var xmlhttp = new XMLHttpRequest();
xmlhttp.onload = function() {
const myObj = JSON.parse(this.responseText);
document.getElementById("demo").innerHTML = myObj[2];
}
xmlhttp.open("GET", "demo_file_array", true);
xmlhttp.send();
PHP is a server side programming language, and can be used to access a database.
Imagine you have a database on your server, and you want to send a request to it from the client where you ask for the 10 first rows in a table called "customers".
On the client, make a JSON object that describes the numbers of rows you want to return.
Before you send the request to the server, convert the JSON object into a string and send it as a parameter to the url of the PHP page:
Use JSON.stringify() to convert the JavaScript object into JSON:
const limit = {"limit":10};
const dbParam = JSON.stringify(limit);
xmlhttp = new XMLHttpRequest();
xmlhttp.onload = function() {
document.getElementById("demo").innerHTML = this.responseText;
}
xmlhttp.open("GET","json_demo_db?x=" + dbParam);
xmlhttp.send();
Example explained:
Take a look at the PHP file:
<?php
header("Content-Type: application/json; charset=UTF-8");
$obj =
json_decode($_GET["x"], false);
$conn = new mysqli("myServer", "myUser", "myPassword", "Northwind");
$stmt = $conn->prepare("SELECT name FROM customers LIMIT ?");
$stmt->bind_param("s", $obj->limit);
$stmt->execute();
$result = $stmt->get_result();
$outp = $result->fetch_all(MYSQLI_ASSOC);
echo json_encode($outp);
?>
PHP File explained:
xmlhttp.onload = function() {
const myObj = JSON.parse(this.responseText);
let text = "";
for (let x in myObj) {
text += myObj[x].name + "<br>";
}
document.getElementById("demo").innerHTML = text;
}
When sending data to the server, it is often best to use the HTTP POST
method.
To send AJAX requests using the POST
method, specify the method, and the correct header.
The data sent to the server must now be an argument to the send()
method:
const dbParam = JSON.stringify({"limit":10});
const xmlhttp = new XMLHttpRequest();
xmlhttp.onload = function() {
const myObj = JSON.parse(this.responseText);
let text ="";
for (let x in myObj) {
text += myObj[x].name + "<br>";
}
document.getElementById("demo").innerHTML = text;
}
xmlhttp.open("POST", "json_demo_db_post");
xmlhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
xmlhttp.send("x=" + dbParam);
The only difference in the PHP file is the method for getting the transferred data.
Use $_POST instead of $_GET:
<?php
header("Content-Type: application/json; charset=UTF-8");
$obj =
json_decode($_POST["x"], false);
$conn = new mysqli("myServer", "myUser", "myPassword", "Northwind");
$stmt = $conn->prepare("SELECT name FROM customers LIMIT ?");
$stmt->bind_param("s",
$obj->limit);
$stmt->execute();
$result = $stmt->get_result();
$outp = $result->fetch_all(MYSQLI_ASSOC);
echo json_encode($outp);
?>