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
java" id="highlighter_17301">
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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;
}
});
}
}
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成功释放mappedbytebuffer资源
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method m = filechannelimpl.class.getdeclaredmethod("unmap",
mappedbytebuffer.class);
m.setaccessible(true);
m.invoke(filechannelimpl.class, buf);
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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服务器之家。
原文链接：https://blog.csdn.net/papima/article/details/79078840