How does PHP ZipArchive implement PDF compression function for files in compressed packages?

How does PHP ZipArchive implement PDF compression function for files in compressed packages?

Introduction:
In modern society, electronic documents have become an indispensable part of our daily life and work. Among them, PDF format documents are widely used in various scenarios because of their cross-platform, easy-to-read, and content-protected characteristics. However, as the number of documents increases, the size of PDF documents also gradually increases. In some cases, multiple PDF files need to be packaged into a compressed package and compressed to reduce the file size. This article will introduce how to use PHP's ZipArchive library to compress PDF files in compressed packages.

1. Install ZipArchive library
Before using ZipArchive, you need to ensure that PHP has installed the corresponding library. You can install it by following these steps:

1. Open a terminal or command line tool.

2. Run the following command to install the ZipArchive library:

   $ sudo apt-get install php-zip

3. After the installation is complete, restart the PHP server.

2. Create a compressed package and add PDF files
The following is a simple sample code for creating a compressed package and adding PDF files to it. Assume that we already have a folder containing multiple PDF files. We need to package these PDF files into a compressed package and compress it.

<?php
  // 创建一个压缩包
  $zip = new ZipArchive;
  $zipFilename = 'compressed.zip';
  
  if ($zip->open($zipFilename, ZipArchive::CREATE) === TRUE) {
    // 需要压缩的PDF文件所在的文件夹路径
    $pdfFolder = '/path/to/pdf/folder';
  
    // 遍历文件夹中的PDF文件，并添加到压缩包
    if ($handle = opendir($pdfFolder)) {
      while (false !== ($file = readdir($handle))) {
        if ($file != "." && $file != "..") {
          $pdfPath = $pdfFolder . '/' . $file;
  
          // 只处理PDF文件
          if(pathinfo($pdfPath, PATHINFO_EXTENSION) === 'pdf') {
            // 将PDF文件添加到压缩包中
            $zip->addFile($pdfPath, $file);
          }
        }
      }
      closedir($handle);
    }
  
    // 关闭压缩包
    $zip->close();
    echo '压缩包已创建成功，文件名为：' . $zipFilename;
  } else {
    echo '创建压缩包失败';
  }
?>

3. Use ZipArchive to compress PDF files
The following is a sample code for compressing PDF files in compressed packages through the ZipArchive library. By using the PHP ZipArchive library, we can read, compress each PDF file, and write the compressed content into a new compressed archive file.

<?php
  // 打开一个已有的压缩包
  $zip = new ZipArchive;
  $zipFilename = 'compressed.zip';
  
  if ($zip->open($zipFilename, ZipArchive::CREATE) === TRUE) {
    // 遍历压缩包中的文件
    for ($i = 0; $i < $zip->numFiles; $i++) {
      // 获取压缩包中的文件名
      $filename = $zip->getNameIndex($i);
  
      // 检查文件是否为PDF文件
      if (pathinfo($filename, PATHINFO_EXTENSION) === 'pdf') {
        // 获取文件内容
        $fileContent = $zip->getFromIndex($i);
  
        // 对文件内容进行压缩处理
        $compressedContent = compressPDF($fileContent);
  
        // 将压缩后的内容写入到压缩包中
        $zip->deleteIndex($i);
        $zip->addFromString($filename, $compressedContent);
      }
    }
  
    // 关闭压缩包
    $zip->close();
    echo '压缩完成';
  } else {
    echo '打开压缩包失败';
  }
  
  function compressPDF($content) {
    // 实现PDF文件压缩逻辑，此处省略具体实现步骤
  
    // 返回压缩后的内容
    return $compressedContent;
  }
?>

Summary:
By using the PHP ZipArchive library, we can easily implement the compression function of PDF files in the compressed package. We can create a compressed package and add PDF files to it; we can also read PDF files in existing compressed packages and compress them. In the specific compression logic implementation, we can use a third-party PDF processing library, such as Ghostscript, to compress PDF files.

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