java的runtime.exec创建的线程被挂起的解决办法。

java class process方法exec调用方法proccess proc.exec(command)。当command的输出内容过大时(OS的I/O buffer容纳不下输出流时)，程序会被挂起。解决此内问题的方法将command的输出流proc.getErrorStream(),proc.getInputStream()清空。以下为一示例， linux7.2,jdk1.5.0_06下编译通过。

/*************************************************************************************
*Process exec method: clearn output stream first
*by Benny Zhou
*2/27/2007
**************************************************************************************/
/*
*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. 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.
*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.
*/
import java.io.*;
import java.lang.*;
import java.util.*;

public class ProcessExec
{

static void drainInBackground(final InputStream is) {
new Thread(new Runnable(){
public void run(){
try{
while( is.read() >= 0 );
} catch(IOException e){
}
}
}).start();
}

public void UnpackupDir(String rootpath,String tarname,String backupType) throws IOException
{
String unpackdir=rootpath;
String strUnpackName = "";
Runtime r=Runtime.getRuntime();
Process prog=null;

strUnpackName="./restoreoptarfile.sh "+unpackdir +" "+tarname+" "+backupType;
try
{ System.out.println("========before process.exec()");
prog=r.exec(strUnpackName);
System.out.println("========after process.exec()");
System.out.println("========before process.waitFor()");

//==========method 2, clearn output stream first
drainInBackground(prog.getErrorStream());
drainInBackground(prog.getInputStream());

/*//==========method 1. get streams and standart out put first, still need clearn output stream
BufferedReader stderr = new BufferedReader(new InputStreamReader(prog.getErrorStream()));
String LineErr = stderr.readLine();

BufferedReader inpbuildtar = new BufferedReader(new InputStreamReader(prog.getInputStream()));
String LINE = inpbuildtar.readLine();
while (LineErr !=null)
{
System.out.println("LineError>>>"+LineErr);
LineErr = stderr.readLine();
}

while (LINE != null)
{
System.out.println("Line>>>"+LINE);
LINE = inpbuildtar.readLine();

}
*/

int progEnd = prog.waitFor();
// inpbuildtar.close();
// stderr.close();

System.out.println("========after process.waitFor()");
System.out.println("========before Runtime.gc()");
r.gc();
String unpackfiledir = unpackdir +File.separator+tarname;
File unpackfile= new File(unpackfiledir);
File dirUnpack = new File(unpackdir +File.separator+backupType+File.separator+"structure"+File.separator+"wbxsite.stc");
if(!unpackfile.exists() || !dirUnpack.exists())
{
System.out.println("ERROR>> Tar file do not unpack please check the parameter !");
System.out.println("ERROR>> Please make sure you have executed the command: <chmod +x *.sh>");
System.exit(0);
}
else
{}
}
catch(Exception e)
{
System.out.println("ERROR>> Tar file is not unpacked successfully!");
System.exit(0);
}
}

public static void main(String args[])
{
ProcessExec proexec = new ProcessExec();
String str_rootpath="/webex_doc/dfs/migrate/backup";
String str_tarname="everest@wconfig%T25L%2%2@400006466.tar";
String str_backupType="everest";

try
{
proexec.UnpackupDir(str_rootpath,str_tarname,str_backupType);
}
catch (Exception e)
{
String err = e.getMessage();
System.out.println(err);
System.exit(0);
}
}
}