[学习交流] Java实现PDF文件转换为图片

引入依赖
----

```xml
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.4.RELEASE</version>
<relativePath/>
</parent>

<dependencies>

<dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
      <groupId>org.icepdf.os</groupId>
      <artifactId>icepdf-core</artifactId>
      <version>6.2.2</version>
</dependency>
</dependencies>
```

前端页面
----

```html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>PDf转换图片</title>
<style>
      .submitButton {
         margin-top: 20px;
         margin-left: 150px;
         background-color: #e37e10;
         border-radius: 10px;
         border: 1px solid #ff8300;
      }
</style>
</head>
<body>
<div style="text-align: center">
<h1>PDF转换图片工具</h1>
<form action="/pdf/to/image" enctype="multipart/form-data" method="post" onsubmit="return allowFileType()">
      <input type="file" id="file" name="file" placeholder="请选择PDF文件" onchange="allowFileType()" style="border: 1px solid black;"><br>
      <input type="submit" value="一键转换图片" class="submitButton">
</form>
</div>
</body>
<script>
function allowFileType() {
      let file = document.getElementById("file").files[0];
      let fileName = file.name;
      let suffix = fileName.substring(fileName.lastIndexOf("."),fileName.length).toLowerCase();
      if('.pdf' != suffix) {
         alert("只允许传入PDF格式的文件！");
         return false;
      }
      return true;
}
</script>
</html>
```

控制层接口
-----

```java
package com.hrp.controller;

import com.hrp.util.ImageUtils;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.multipart.MultipartFile;

import javax.servlet.http.HttpServletResponse;

/**
* @description: 用于处理Pdf相关的请求
*/
@Controller
@RequestMapping("pdf")
public class PdfController {

@PostMapping("to/image")
public void pdfToImage(@RequestParam("file") MultipartFile file,HttpServletResponse response) throws Exception{
      ImageUtils.pdfToImage(file,response);
}

}

```

Image工具类
--------
外汇常见问题https://www.kaifx.cn/lists/question/

```java
package com.hrp.util;

import org.icepdf.core.pobjects.Document;
import org.icepdf.core.pobjects.Page;
import org.icepdf.core.util.GraphicsRenderingHints;
import org.springframework.stereotype.Component;
import org.springframework.web.multipart.MultipartFile;

import javax.imageio.ImageIO;
import javax.servlet.http.HttpServletResponse;
import java.awt.image.BufferedImage;
import java.io.*;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;

/**
* @description: PDF转换为图片的工具类
*/
@Component
public class ImageUtils {

/**
   * 图片文件格式
   */
public static final String FORMAT_NAME = "png";
/**
   * 图片文件后缀名
   */
public static final String PNG_SUFFIX = ".png";
/**
   * 压缩文件后缀名
   */
public static final String ZIP_SUFFIX = ".zip";

/**
   * 对外的开放接口，用于将PDF文件转换为图片文件压缩包进行下载
   *
   * @param file SpringMVC获取的图片文件
   * @param response
   * @throws Exception
   */
public static void pdfToImage(MultipartFile file, HttpServletResponse response) throws Exception {
      File zipFile = generateImageFile(file);
      downloadZipFile(zipFile, response);
}

/**
   * 将PDF文件转换为多张图片并放入一个压缩包中
   *
   * @param file SpringMVC获取的图片文件
   * @return 图片文件压缩包
   * @throws Exception 抛出异常
   */
private static File generateImageFile(MultipartFile file) throws Exception {
      String fileName = file.getOriginalFilename();
      Document document = new Document();
      document.setByteArray(file.getBytes(), 0, file.getBytes().length, fileName);

      List<File> fileList = new ArrayList<>();
      for (int i = 0; i < document.getNumberOfPages(); i++) {
         BufferedImage image = (BufferedImage) document.getPageImage(i, GraphicsRenderingHints.SCREEN,
                  Page.BOUNDARY_CROPBOX, 0F, 2.5F);
         File imageFile = new File((i + 1) + PNG_SUFFIX);
         ImageIO.write(image, FORMAT_NAME, imageFile);
         image.flush();
         fileList.add(imageFile);
      }
      document.dispose();

      String directoryName = fileName.substring(0, fileName.lastIndexOf("."));
      File zipFile = new File(directoryName + ZIP_SUFFIX);
      ZipOutputStream zos = new ZipOutputStream(new FileOutputStream(zipFile));
      zipFile(fileList, zos);
      zos.close();
      return zipFile;
}

/**
   * 下载zip文件
   *
   * @param zipFile  zip压缩文件
   * @param response HttpServletResponse
   * @throws IOException IO异常
   */
private static void downloadZipFile(File zipFile, HttpServletResponse response) throws IOException {
      FileInputStream fis = new FileInputStream(zipFile);
      byte[] bytes = new byte[fis.available()];
      fis.read(bytes);
      fis.close();

      response.reset();
      response.setCharacterEncoding("UTF-8");
      response.setHeader("Content-Type", "application/x-msdownload");
      response.setHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(zipFile.getName(), "UTF-8"));
      OutputStream out = response.getOutputStream();
      out.write(bytes);
      out.flush();
      out.close();
      zipFile.delete();
}

/**
   * 压缩文件
   *
   * @param inputFiles 具体需要压缩的文件集合
   * @param zos       ZipOutputStream对象
   * @throws IOException IO异常
   */
private static void zipFile(List<File> inputFiles, ZipOutputStream zos) throws IOException {
      byte[] buffer = new byte[1024];
      for (File file : inputFiles) {
         if (file.exists()) {
            if (file.isFile()) {
                  BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));
                  zos.putNextEntry(new ZipEntry(file.getName()));
                  int size = 0;
                  while ((size = bis.read(buffer)) > 0) {
                     zos.write(buffer, 0, size);
                  }
                  zos.closeEntry();
                  bis.close();
                  file.delete();
            } else {
                  File[] files = file.listFiles();
                  List<File> childrenFileList = Arrays.asList(files);
                  zipFile(childrenFileList, zos);
            }
         }
      }
}

}
```

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[学习交流] Java实现PDF文件转换为图片

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