search
HomeBackend DevelopmentPHP TutorialHow header() outputs image cache usage example

How header() outputs image cache usage example

Jun 24, 2017 pm 01:29 PM
headerpicturehowcacheoutput

When we generate the verification code, we need to directly input the image, usually using header("Content-type: image/jpeg"); to achieve this. Here is a brief introduction.

In many developments, we try to use header("Content-type: image/jpeg"); to output pictures, and try to use some php image processing technology to allow the output Pictures are more intelligent and dynamic. But we often encounter new problems. Unless you specify different URL structures and use server technology to cache images, it is very likely that these output images will consume a lot of traffic. How to cache them and call the cache the next time the user visits? (The premise is that you want this image to remain unchanged)

// put this above any php image generation code:
session_start(); 
header("Cache-Control: private, max-age=10800, pre-check=10800");
header("Pragma: private");
header("Expires: " . date(DATE_RFC822,strtotime(" 2 day")));

Add the above code above header("Content-type: image/jpeg");, which will specify the cache time of the current page (two days) and use this cache time node on the next visit.
Next, determine whether there is already a cache. If so, use the cache.

Situation 1: If the browser already caches the current page, then use it directly.

// the browser will send a $_SERVER['HTTP_IF_MODIFIED_SINCE'] if it has a cached copy 
if(isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])){
  // if the browser has a cached version of this image, send 304
  header('Last-Modified: '.$_SERVER['HTTP_IF_MODIFIED_SINCE'],true,304);
  exit;
}

Scenario 2: The browser caches the current page. Although we have updated some image information, the source image itself has not changed, and we want to use the previous cache, so we also use the cache.

$img = "some_image.png";
if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && (strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) == 
filemtime($img))) {
  // send the last mod time of the file back
  header('Last-Modified: '.gmdate('D, d M Y H:i:s', filemtime($img)).' GMT',true, 304);
  exit;
}

Of course, there are some special situations that we must consider, but the above code can basically lead our thinking. By the way, remember to put them all above header("Content-type: image/jpeg").
Let’s take a look at an example

<?php
//调整图片大小
/**
 *图片按比例调整大小的原理:
 *1、比较原图大小是否小于等于目标大小,如果是则直接采用原图宽高
 *2、如果原图大小超过目标大小,则对比原图宽高大小
 *3、如:宽>高,则宽=目标宽, 高=目标宽的比例 * 原高
 *4、如:高>宽,则高=目标高,宽=目标高的比例 * 原宽   
**/
 
$image = "test.jpg";
$max_width = 200;
$max_height = 200;
 
$size = getimagesize($image);   //得到图像的大小
$width = $size[0];             
$height = $size[1];
 
$x_ratio = $max_width / $width;
$y_ratio = $max_height / $height;
 
if (($width <= $max_width) && ($height <= $max_height))
{
    $tn_width = $width;
    $tn_height = $height;
}
elseif (($x_ratio * $height) < $max_height)
{
    $tn_height = ceil($x_ratio * $height);
    $tn_width = $max_width;
}
else
{
    $tn_width = ceil($y_ratio * $width);
    $tn_height = $max_height;
}
 
$src = imagecreatefromjpeg($image);
$dst = imagecreatetruecolor($tn_width, $tn_height); //新建一个真彩色图像
imagecopyresampled($dst, $src, 0, 0, 0, 0,$tn_width, $tn_height, $width, $height);        //重采样拷贝部分图像并调整大小
header(&#39;Content-Type: image/jpeg&#39;);
imagejpeg($dst,null,100);
imagedestroy($src);
imagedestroy($dst);
?>


The above is the detailed content of How header() outputs image cache usage example. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
How do you modify data stored in a PHP session?How do you modify data stored in a PHP session?Apr 27, 2025 am 12:23 AM

TomodifydatainaPHPsession,startthesessionwithsession_start(),thenuse$_SESSIONtoset,modify,orremovevariables.1)Startthesession.2)Setormodifysessionvariablesusing$_SESSION.3)Removevariableswithunset().4)Clearallvariableswithsession_unset().5)Destroythe

Give an example of storing an array in a PHP session.Give an example of storing an array in a PHP session.Apr 27, 2025 am 12:20 AM

Arrays can be stored in PHP sessions. 1. Start the session and use session_start(). 2. Create an array and store it in $_SESSION. 3. Retrieve the array through $_SESSION. 4. Optimize session data to improve performance.

How does garbage collection work for PHP sessions?How does garbage collection work for PHP sessions?Apr 27, 2025 am 12:19 AM

PHP session garbage collection is triggered through a probability mechanism to clean up expired session data. 1) Set the trigger probability and session life cycle in the configuration file; 2) You can use cron tasks to optimize high-load applications; 3) You need to balance the garbage collection frequency and performance to avoid data loss.

How can you trace session activity in PHP?How can you trace session activity in PHP?Apr 27, 2025 am 12:10 AM

Tracking user session activities in PHP is implemented through session management. 1) Use session_start() to start the session. 2) Store and access data through the $_SESSION array. 3) Call session_destroy() to end the session. Session tracking is used for user behavior analysis, security monitoring, and performance optimization.

How can you use a database to store PHP session data?How can you use a database to store PHP session data?Apr 27, 2025 am 12:02 AM

Using databases to store PHP session data can improve performance and scalability. 1) Configure MySQL to store session data: Set up the session processor in php.ini or PHP code. 2) Implement custom session processor: define open, close, read, write and other functions to interact with the database. 3) Optimization and best practices: Use indexing, caching, data compression and distributed storage to improve performance.

Explain the concept of a PHP session in simple terms.Explain the concept of a PHP session in simple terms.Apr 26, 2025 am 12:09 AM

PHPsessionstrackuserdataacrossmultiplepagerequestsusingauniqueIDstoredinacookie.Here'showtomanagethemeffectively:1)Startasessionwithsession_start()andstoredatain$_SESSION.2)RegeneratethesessionIDafterloginwithsession_regenerate_id(true)topreventsessi

How do you loop through all the values stored in a PHP session?How do you loop through all the values stored in a PHP session?Apr 26, 2025 am 12:06 AM

In PHP, iterating through session data can be achieved through the following steps: 1. Start the session using session_start(). 2. Iterate through foreach loop through all key-value pairs in the $_SESSION array. 3. When processing complex data structures, use is_array() or is_object() functions and use print_r() to output detailed information. 4. When optimizing traversal, paging can be used to avoid processing large amounts of data at one time. This will help you manage and use PHP session data more efficiently in your actual project.

Explain how to use sessions for user authentication.Explain how to use sessions for user authentication.Apr 26, 2025 am 12:04 AM

The session realizes user authentication through the server-side state management mechanism. 1) Session creation and generation of unique IDs, 2) IDs are passed through cookies, 3) Server stores and accesses session data through IDs, 4) User authentication and status management are realized, improving application security and user experience.

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Atom editor mac version download

Atom editor mac version download

The most popular open source editor

SAP NetWeaver Server Adapter for Eclipse

SAP NetWeaver Server Adapter for Eclipse

Integrate Eclipse with SAP NetWeaver application server.

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools

VSCode Windows 64-bit Download

VSCode Windows 64-bit Download

A free and powerful IDE editor launched by Microsoft

WebStorm Mac version

WebStorm Mac version

Useful JavaScript development tools