java pdf转图片

public static List<byte[]> pdf2image(String pdfFilePath) throws Exception{
        File tempDir = null;
        try{
            tempDir = Files.createTempDir();
            Process proc = new ProcessBuilder("gs", "-sDEVICE=pngalpha", "-o", tempDir + File.separator + "%03d.png", "-sDEVICE=pngalpha", "-r144", pdfFilePath)
                               .redirectErrorStream(true)
                               .start(); 
            
            ArrayList<String> output = new ArrayList<String>();
            BufferedReader br = new BufferedReader(new InputStreamReader(proc.getInputStream()));
            String line = null;
            while ((line = br.readLine()) != null)
                output.add(line);
            
            logger.info("执行gs命令的输出：" + StringUtils.join(output, System.lineSeparator()));
            
            if (0 != proc.waitFor())
                throw new Exception("转换失败");
            
            File[] files = tempDir.listFiles();

            Arrays.sort(files, new Comparator<File>() {
                public int compare(File f1, File f2) {
                    return f1.getName().compareTo(f2.getName());
                }
            });
            
            List<byte[]> images = new ArrayList<>();
            for(File file : files)
                images.add(IOUtils.toByteArray(new FileInputStream(file)));
            
            return images;
            
            
        }finally{
            if(tempDir != null)
                FileUtils.deleteDirectory(tempDir);
        }
    }