Difference between ProcessBuilder and Runtime exec

Question

I m trying to execute an external command from java code  but there s a difference I ve noticed between Runtime getRuntime   exec      and new ProcessBuilder      start     When using Runtime   Process p   Runtime getRuntime   exec installation path                                           uninstall path                                           uninstall command                                           uninstall arguments   p waitFor      the exitValue is 0 and the command is terminated ok   However  with ProcessBuilder   Process p    new ProcessBuilder installation path                                        uninstall path                                    uninstall command                                   uninstall arguments   start    p waitFor      the exit value is 1001 and the command terminates in the middle  although waitFor returns   What should I do to fix the problem with ProcessBuilder

User · Accepted Answer

The various overloads of Runtime getRuntime   exec      take either an array of strings or a single string   The single-string overloads of exec   will tokenise the string into an array of arguments  before passing the string array onto one of the exec   overloads that takes a string array   The ProcessBuilder constructors  on the other hand  only take a varargs array of strings or a List of strings  where each string in the array or list is assumed to be an individual argument   Either way  the arguments obtained are then joined up into a string that is passed to the OS to execute   So  for example  on Windows   Runtime getRuntime   exec  C  DoStuff exe -arg1 -arg2      will run a DoStuff exe program with the two given arguments   In this case  the command-line gets tokenised and put back together   However   ProcessBuilder b   new ProcessBuilder  C  DoStuff exe -arg1 -arg2      will fail  unless there happens to be a program whose name is DoStuff exe -arg1 -arg2 in C     This is because there s no tokenisation  the command to run is assumed to have already been tokenised   Instead  you should use  ProcessBuilder b   new ProcessBuilder  C  DoStuff exe    -arg1    -arg2      or alternatively  List lt String gt  params   java util Arrays asList  C  DoStuff exe    -arg1    -arg2    ProcessBuilder b   new ProcessBuilder params

User · Answer

Yes there is a difference      The Runtime exec String  method takes a single command string that it splits into a command and a sequence of arguments   The ProcessBuilder constructor takes a  varargs  array of strings   The first string is the command name and the rest of them are the arguments    There is an alternative constructor that takes a list of strings  but none that takes a single string consisting of the command and arguments     So what you are telling ProcessBuilder to do is to execute a  command  whose name has spaces and other junk in it   Of course  the operating system can t find a command with that name  and the command execution fails

User · Answer

There are no difference between ProcessBuilder start   and Runtime exec   because implementation of Runtime exec   is   public Process exec String command  throws IOException       return exec command  null  null      public Process exec String command  String   envp  File dir      throws IOException       if  command length      0          throw new IllegalArgumentException  Empty command         StringTokenizer st   new StringTokenizer command       String   cmdarray   new String st countTokens         for  int i   0  st hasMoreTokens    i            cmdarray i    st nextToken        return exec cmdarray  envp  dir      public Process exec String   cmdarray  String   envp  File dir      throws IOException       return new ProcessBuilder cmdarray           environment envp           directory dir           start        So code   List lt String gt  list   new ArrayList lt  gt     new StringTokenizer command   asIterator    forEachRemaining str - gt  list add  String  str    new ProcessBuilder String   list toArray                 environment envp               directory dir               start      should be the same as   Runtime exec command    Thanks dave thompson 085 for comment

User · Answer

Look at how Runtime getRuntime   exec   passes the String command to the ProcessBuilder  It uses a tokenizer and explodes the command into individual tokens  then invokes exec String   cmdarray          which constructs a ProcessBuilder   If you construct the ProcessBuilder with an array of strings instead of a single one  you ll get to the same result   The ProcessBuilder constructor takes a String    vararg  so passing the whole command as a single String has the same effect as invoking that command in quotes in a terminal   shell   command with args

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