Java 利用Linux Openssl 库计算文件校验码
在传统Java编程中, 我们可以另用ProcessBuilder类来创建系统进程或者Runtime类来取得JVM的接口对象运行我们指定的系统命令, 并且可以通过读入器来获取系统的out以及err输出.这里有一个简单的例子, 没有用过的同学可以参考一下.http://wuhongyu.iteye.com/blog/461477
由于前段时间有这样的一个需求, 尽可能快的算出Hadoop系统里的MD码, 我曾经想过另用Java的Digest类来读取文件, 然后工作交给Digest类来完成, 可没想到的是Java的这个类算MD校验码，效率及其的低下，我在XP上算50M的文件, 居然花费8秒钟的时间.直接放弃. 这个Demo我也顺便推荐一下:
http://www.javablogging.com/?s=Java+Digest+SHA1+MD5
后来google该问题的解决方案, 有一个比较有意思的贴子Fast MD5 Implementation in Java, 呵呵, 由于时间关系, 没来的急看,分享一下：
http://www.twmacinta.com/myjava/fast_md5.php
Fast MD5.. 总给我一个不太舒服的感觉, 最后还是决定放弃使用. 由于Hadoop运行于Linux 环境, 回过神来我想到了Linux上的openssl库. 大伙都知道openssl 里其中就有计算数据的安全通信命令. $cat XXX | openssl sha1.
这里有一个问题, 由于hadoop的文件是存在于集群的, 而openssl 是接受本地文件作为参数的, 我可以把文件从HDFS里读出, 然后再构造文件供openssl 计算. 不过这种方式太囧.
我的解决方法是另用Runtime获取运行对象, 直接执行openssl sha1命令, 其实当系统执行该命令的时候会等待输入的. 此时我可以通过我的文件输入流把数据打印到等待输入的输出流上。
// TODO this is a job. not a filedescriptorprotected void handle(FileDescriptor job) throws IOException {if (job == null || job.path == null) {log.warn("Invalid job: " + job);}// wait for GC. Configuration conf = new Configuration();Path path = new Path(job.path);FileSystem fs = path.getFileSystem(conf);if (!fs.exists(path) || !fs.isFile(path)) {log.warn("*HADLEJOB file does not exist for path: " + path);return;}InputStream is = fs.open(path);// Run a commandString cmd = "openssl sha1";boolean completed = false;Process process = null; // Sub process used to execute the commandint exitCode;process = Runtime.getRuntime().exec(cmd);BufferedOutputStream os = new BufferedOutputStream(process.getOutputStream(), 4096);byte buf[] = new byte;while (true) {int bytesRead = is.read(buf);if (bytesRead == -1) {break;}os.write(buf, 0, bytesRead);}os.flush();os.close();final BufferedReader errReader = new BufferedReader(new InputStreamReader(process.getErrorStream()));BufferedReader inReader = new BufferedReader(new InputStreamReader(process.getInputStream()));final StringBuffer errMsg = new StringBuffer();// read error and input streams as this would free up the buffers// free the error stream bufferThread errThread = new Thread(){public void run() {try {String line = errReader.readLine();while ((line != null) && !isInterrupted()) {errMsg.append(line);errMsg.append(System.getProperty("line.separator"));line = errReader.readLine();}} catch (IOException ioe) {log.warn("Error reading the error stream", ioe);}}};try {errThread.start();} catch (IllegalStateException ise) {}try {String line = inReader.readLine();if (line == null) {throw new IOException("Exception a line not the end of stream");}job.set_sha1(line.trim());// clear the input stream bufferline = inReader.readLine();while (line != null) {line = inReader.readLine();}// wait for the process to finish and check the exit codeexitCode = process.waitFor();try {errThread.join();} catch (InterruptedException ie) {log.warn("Interrupted while reading the error stream", ie);}completed = true;if (exitCode != 0) {throw new IOException(exitCode + errMsg.toString());}} catch (InterruptedException ie) {throw new IOException(ie.toString());} finally {// close the input streamtry {inReader.close();} catch (IOException e) {log.warn("Error whilke closing the input stream", e);}if (!completed) {errThread.interrupt();}try {errReader.close();}catch(IOException ioe){log.warn("Error while closing the error stream", ioe);}process.destroy();}}
该执行方法运行于线程池中, 下一个贴子我将记录真正应用中线程池的实现, 提供线程池的大小设置, shrink等实现.
页:
[1]