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(); //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);

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。