java使用renderer将pdf按页转换为图片

项目中遇到了需要把用户上传的word，execl，ppt每页截图保存。需要先用到jacob把资源转换为pdf，在通过pdf-renderer把每页截图下来。

首先下载相关jar包：下载地址

import java.awt.Image;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.lang.reflect.Method;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.security.AccessController;
import java.security.PrivilegedAction;
//如果com.sun.image找不到，就是Eclipse默认把这些受访问限制的API设成了ERROR。只要把Windows-Preferences-Java-Complicer-Errors/Warnings里面的Deprecated and restricted API中的Forbidden references(access rules)选为Warning就可以编译通过
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGEncodeParam;
import com.sun.image.codec.jpeg.JPEGImageEncoder;
import com.sun.pdfview.PDFFile;
import com.sun.pdfview.PDFPage;
public class pdfToImage {

 public static void main(String[] args) {
 String instructiopath="E:/临时文件1.pdf";
 String picturepath = "E:/临时文件1/";
 changePdfToImg(instructiopath,picturepath);
 }

  public static int changePdfToImg(String instructiopath,String picturepath) {
    int countpage =0;
    try {
      //instructiopath ="D:/instructio/2015-05-16/Android 4编程入门经典.pdf"
      //picturepath = "D:/instructio/picture/2015-05-16/"; 

      File file = new File(instructiopath);
      RandomAccessFile raf = new RandomAccessFile(file, "r");
      FileChannel channel = raf.getChannel();
      MappedByteBuffer buf = channel.map(FileChannel.MapMode.READ_ONLY,
          0, channel.size());
      PDFFile pdffile = new PDFFile(buf);
      //创建图片文件夹
      File dirfile = new File(picturepath);
        if(!dirfile.exists()){
           dirfile.mkdirs();
        }
      //获得图片页数
      countpage = pdffile.getNumPages();
      for (int i = 1; i <= pdffile.getNumPages(); i++) {
        PDFPage page = pdffile.getPage(i);
        Rectangle rect = new Rectangle(0, 0, ((int) page.getBBox()
            .getWidth()), ((int) page.getBBox().getHeight()));
        int n = 2;
        /** 图片清晰度（n>0且n<7）【pdf放大参数】 */
        Image img = page.getImage(rect.width * n, rect.height * n,
            rect, /** 放大pdf到n倍，创建图片。 */
            null, /** null for the ImageObserver */
            true, /** fill background with white */
            true /** block until drawing is done */
        );
        BufferedImage tag = new BufferedImage(rect.width * n,
            rect.height * n, BufferedImage.TYPE_INT_RGB);
        tag.getGraphics().drawImage(img, 0, 0, rect.width * n,
            rect.height * n, null);
        /**
         * File imgfile = new File("D:\\work\\mybook\\FilesNew\\img\\" +
         * i + ".jpg"); if(imgfile.exists()){
         * if(imgfile.createNewFile()) { System.out.println("创建图片："+
         * "D:\\work\\mybook\\FilesNew\\img\\" + i + ".jpg"); } else {
         * System.out.println("创建图片失败！"); } }
         */
        FileOutputStream out = new FileOutputStream(picturepath+"/" + i
            + ".png");
        /** 输出到文件流 */
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
        JPEGEncodeParam param2 = encoder.getDefaultJPEGEncodeParam(tag);
        param2.setQuality(1f, true);
        /** 1f~0.01f是提高生成的图片质量 */
        encoder.setJPEGEncodeParam(param2);
        encoder.encode(tag);
        /** JPEG编码 */
        out.close();
      }
      channel.close();
      raf.close();
      /*unmap(buf);*/  //pdf转化成图片后，释放MappedByteBuffer资源。调用unmap(buf);无效。
      /** 如果要在转图片之后删除pdf，就必须要这个关闭流和清空缓冲的方法 */
    } catch (FileNotFoundException e) {
      e.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    }
    return countpage; 

  } 

  @SuppressWarnings("unchecked")
  public static void unmap(final Object buffer) {
    AccessController.doPrivileged(new PrivilegedAction() {
      public Object run() {
        try {
          Method getCleanerMethod = buffer.getClass().getMethod(
              "cleaner", new Class[0]);
          getCleanerMethod.setAccessible(true);
          sun.misc.Cleaner cleaner = (sun.misc.Cleaner) getCleanerMethod
              .invoke(buffer, new Object[0]);
          cleaner.clean();
        } catch (Exception e) {
          e.printStackTrace();
        }
        return null;
      }
    });
  }
}

成功释放MappedByteBuffer资源

Method m = FileChannelImpl.class.getDeclaredMethod("unmap",
    MappedByteBuffer.class);
   m.setAccessible(true);
   m.invoke(FileChannelImpl.class, buf);

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