最近我的项目要我在WebService里用Java调用Linux下的Shell 脚本，在网上找了一些资料，以供学习。

地址：http://brian.pontarelli.com/2005/11/11/java-runtime-exec-can-hang/     

Java Runtime exec can hang

November 11, 2005 on 4:40 pm | In Java |

The next version of Savant is going to focus heavily on the stand-alone runtime anｄ support for dialects anｄ plugins. Supporting all that is largely handled by using a simple executor framework I wrote around Java 1.4 anｄ lower’s Runtime.exec method. A few things to keep in mind when using this:

1. Always read from the streams prior to calling waitFor. Otherwise you could end up waiting forever on Windows anｄ other OS platforms whose I/O buffers can’t store enough from standard out anｄ standard error to ensure the program has finished. These platforms will pause the execution of whatever is running until something reads the buffered content from standard out anｄ standard error. I would imagine all platforms suffer from this, but some platforms have larger buffers than others. Needless to say, always read from the streams first.
2. Always read from standard error first. I ran across a bug where some OS platforms will always open standard out, but never close it. What this means is that if you read from standard out first anｄ the process only writes to standard error, you’ll hang forever waiting to read. If you read from standard error first, you’ll always be okay on these platforms because the OS seems to shutdown standard error. I think however, that the best way to handle all cases is to check both standard error anｄ standard out for readiness anｄ only read from them if they have something to offer. The downside I could see here is that error isn’t ready, but eventually will be.

可以看出：
 

• 永远要在调用waitFor()方法之前读取数据流
• 永远要先从标准错误流中读取，然后再读取标准输出流

于是将waitFor()方法放在读取数据流后调用，目前没有发现什么问题。

后面的build中在waitFor()之前读取了数据流，bat文件就可以完整执行了：

 

Process proc = Runtime.getRuntime().exec(cmd); StreamGobbler errorGobbler = new StreamGobbler(proc.getErrorStream(), "Error"); StreamGobbler outputGobbler = new StreamGobbler(proc.getInputStream(), "Output"); errorGobbler.start(); outputGobbler.start(); proc.waitFor(); class StreamGobbler extends Thread { InputStream is; String type; StreamGobbler(InputStream is, String type) { this.is = is; this.type = type; } public void run() { try { InputStreamReader isr = new InputStreamReader(is); BufferedReader br = new BufferedReader(isr); String line = null; while ((line = br.readLine()) != null) { if (type.equals("Error")) LogManager.logError(line); else LogManager.logDebug(line); } } catch (IOException ioe) { ioe.printStackTrace(); } } }

 

2. 另外一个需要注意的地方是：

     如果调用的脚本中存在像sudo这样的需要tty的命令时，使用

           String []cmdArray = new String[]{ "/bin/sh", "-c", "yourscriptname"};

 这样的调用方式，会为脚本执行创建出一个tty环境，否则，运行过程会提示"sorry, you must have a tty to run xxx"的错误。

Because some native platforms only provide limited buffer size for standard input and output streams, failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, and even deadlock.

在exec()后 立即调用waitFor()会导致进程挂起。

 

3.当调用的外部命令中包含重定向(<、>)，管道( | ) 命令时，exec(String command)的版本不能正确解析重定向、管道操作符。所以需要使用exec(String [] cmdArray)。

   如， echo "hello world" > /home/admin/newFile.txt

       ls -e | grep java

   需要使用如下的调用方式

       String []cmdArray = new String[]{ "/bin/sh", "-c", "ls -e | grep java"};

             Runtime.getRuntime().exec(cmdArray);

 

地址：http://blog.csdn.net/moreorless/archive/2009/05/14/4182883.aspx