Executing another application from Java

Question

I need to execute a batch file which executes another Java application  I don t care whether it executes successfully or not and I don t have to capture any errors   Is it possible to do this with ProcessBuilder  What are the consequences if I do not capture errors   However  my requirement is just to execute another Java application

User · Answer

If you don t care about the return value you could just use Runtime getRuntime   exec  path to your batch file

User · Answer

Yes it is possible using ProcessBuilder   ProcessBuilder example   import java io    import java util     public class CmdProcessBuilder     public static void main String args          throws InterruptedException IOException          List lt String gt  command   new ArrayList lt String gt         command add args 0          ProcessBuilder builder   new ProcessBuilder command       Map lt String  String gt  environ   builder environment         final Process process   builder start        InputStream is   process getInputStream        InputStreamReader isr   new InputStreamReader is       BufferedReader br   new BufferedReader isr       String line      while   line   br readLine       null          System out println line             System out println  Program terminated             Check these examples   http   www rgagnon com javadetails java-0014 html  http   www java-tips org java-se-tips java util from-runtime exec-to-processbuilder html

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Here is an example of how to use ProcessBuilder to execute your remote application   Since you do not care about input output and or errors  you can do as follows   List lt String gt  args   new ArrayList lt String gt     args add   script bat       command name args add   -option       optional args added as separate list items ProcessBuilder pb   new ProcessBuilder  args   Process p   pb start    p waitFor      the waitFor   method will wait until the process had ended before continuing   This method returns the error code of the process but  since you don t care about it  I didn t put it in the example

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I could see that there is a better library than the apache commons exec library  You can execute your job using Java Secure Shell  JSch    I had the same problem  I used JSch to solve this problem  Apache commons had some issues running commands on a different server  Plus JSch gave me result and errors InputStreams  I found it more elegant  Sample solution can be found here   http   wiki jsch org index php Manual 2FExamples 2FJschExecExample      import java io InputStream      import java io BufferedReader      import java io InputStreamReader       import org apache commons exec         import com jcraft        import com jcraft jsch JSch      import com jcraft jsch Session      import com jcraft jsch ChannelExec       import java util Arrays      import java util List      import java util ArrayList      import java util HashMap        public class  exec linux cmd           public HashMap lt String List lt String gt  gt  exec cmd                   String USERNAME                  String PASSWORD                  String host                  int port                  String cmd                        List lt String gt  result   new ArrayList lt String gt                 List lt String gt  errors   new ArrayList lt String gt                 HashMap lt String List lt String gt  gt  result map   new HashMap lt String List lt String gt  gt               String line    echo  eval hostname                try              JSch jsch   new JSch                                 Open a new session  with your username  host and port               Set the password and call connect                session connect   opens a new connection to remote SSH server                Once the connection is established  you can initiate a new channel                this channel is needed to connect and remotely execute the program                             Session session   jsch getSession USERNAME  host  port               session setConfig  StrictHostKeyChecking    no                session setPassword PASSWORD               session connect                   create the excution channel over the session             ChannelExec channelExec    ChannelExec session openChannel  exec                    Gets an InputStream for this channel  All data arriving in as messages from the remote side can be read from this stream              InputStream in   channelExec getInputStream                InputStream err   channelExec getErrStream                    Set the command that you want to execute                In our case its the remote shell script              channelExec setCommand cmd                  Execute the command             channelExec connect                    read the results stream             BufferedReader reader   new BufferedReader new InputStreamReader in                   read the errors stream  This will be null if no error occured             BufferedReader err reader   new BufferedReader new InputStreamReader err                String line                 Read each line from the buffered reader and add it to result list                You can also simple print the result here              while   line   reader readLine       null                                result add line                              while   line   err reader readLine       null                                errors add line                                retrieve the exit status of the remote command corresponding to this channel             int exitStatus   channelExec getExitStatus                System out println exitStatus                  Safely disconnect channel and disconnect session  If not done then it may cause resource leak             channelExec disconnect                session disconnect                System out println exitStatus               result map put  result   result               result map put  error   errors                if exitStatus  lt  0                   System out println  Done-- gt      exitStatus                   System out println Arrays asList result map                      return errors                            else if exitStatus  gt  0                   System out println  Done -- gt     exitStatus                   System out println Arrays asList result map                      return errors                            else                 System out println  Done                    System out println Arrays asList result map                     return result                                           catch  Exception e                                System out print e                              return result map                         CommandLine commandLine   CommandLine parse cmd             DefaultExecutor executor   new DefaultExecutor              executor setExitValue 1             int exitValue   executor execute commandLine               public static void main String   args                                String line   args 0                  final String USERNAME   abc      username for remote host                final String PASSWORD   abc      password of the remote host                final String host    3 98 22 10      remote host address                final int port 22     remote host port                HashMap lt String List lt String gt  gt  result   new HashMap lt String List lt String gt  gt                       String cmd    echo  eval hostname       command to execute on remote host                exec linux cmd ex   new exec linux cmd                    result   ex exec cmd USERNAME  PASSWORD   host  port  cmd                  System out println  Result --- gt      result get  result                    System out println  Error Msg --- gt     result get  error                      System out println Arrays asList result                                      for  int i  0  i  lt  result get  result   size   i                                             System out println result get  result   get i                                                             EDIT 1  In order to find your process  if its a long-running one  being executed on Unix  use the ps -aux   grep java  The process ID should be listed alongwith the unix command you are executing

User · Answer

The Runtime getRuntime   exec   approach is quite troublesome  as you ll find out shortly   Take a look at the Apache Commons Exec project  It abstracts you way of a lot of the common problems associated with using the Runtime getRuntime   exec   and ProcessBuilder API   It s as simple as   String line    myCommand exe   CommandLine commandLine   CommandLine parse line   DefaultExecutor executor   new DefaultExecutor    executor setExitValue 1   int exitValue   executor execute commandLine

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I assume that you know how to execute the command using the ProcessBuilder   Executing a command from Java always should read the stdout and stderr streams from the process  Otherwise it can happen that the buffer is full and the process cannot continue because writing its stdout or stderr blocks

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You can execute a batch instruction  or any other application using  Runtime getRuntime   exec cmd      cmd is the  command or te application path    Also yo can wait for executing and getting the return code  to check if its executed correctly  with this code     Process p   Runtime getRuntime   exec cmd     p waitFor      int exitVal   p exitValue      You have a full explanation of different types of calls here http   www rgagnon com javadetails java-0014 html

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I know this is an older thread  but I figure it might be worthwhile for me to put in my implementation since I found this thread trying to do the same thing as OP  except with Root level access  but didn t really find a solution I was looking for   The below method creates a static Root level shell that is used for just executing commands without regard to error checking or even if the command executed successfully    I use it an Android flashlight app I ve created that allows setting the LED to different level of brightness   By removing all the error checking and other fluff I can get the LED to switch to a specified brightness level in as little as 3ms  which opens the door to LightTones  RingTones with light    More details on the app itself can be found here  http   forum xda-developers com showthread php t 2659842  Below is the class in its entirety     public class Shell       private static Shell rootShell   null      private final Process proc      private final OutputStreamWriter writer       private Shell String cmd  throws IOException           this proc   new ProcessBuilder cmd  redirectErrorStream true  start            this writer   new OutputStreamWriter this proc getOutputStream     UTF-8               public void cmd String command             try               writer write command   n                writer flush              catch  IOException e                   public void close             try               if  writer    null     writer close                    if proc    null     proc destroy                                 catch  IOException ignore                public static void exec String command      Shell get   cmd command            public static Shell get             if  Shell rootShell    null                while  Shell rootShell    null                    try     Shell rootShell   new Shell  su      Open with Root Privileges                    catch  IOException e                                         return Shell rootShell            Then anywhere in my app to run a command  for instance changing the LED brightness  I just call   Shell exec  echo     bt getLevel        gt     flashfile

User · Answer

You could simply use Runtime exec

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Below snippet code is written to compile and run external JAVA program using ProcessBuilder  same way we can run any external program  Make sure JAVA HOME must be set in OS environment  see more  package com itexpert exam   import java io BufferedReader  import java io IOException  import java io InputStream  import java io InputStreamReader    public class JavaProcessBuilder           Provide absolute JAVA file path      private static final String JAVA FILE LOCATION    D   Test java    public static void main String args    throws IOException      String command       javac  JAVA FILE LOCATION       ProcessBuilder processBuilder   new ProcessBuilder command        Process process   processBuilder start                   Check if any errors or compilation errors encounter then print on Console               if  process getErrorStream   read      -1            print  Compilation Errors  process getErrorStream                          Check if javac process execute successfully or Not        0 - successful             if  process exitValue      0            process   new ProcessBuilder new String    java   -cp   d      Test    start                Check if RuntimeException or Errors encounter during execution then print errors on console             Otherwise print Output                    if  process getErrorStream   read      -1                print  Errors   process getErrorStream                       else              print  Output   process getInputStream                         private static void print String status InputStream input  throws IOException      BufferedReader in   new BufferedReader new InputStreamReader input        System out println                  status                                 String line   null      while  line   in readLine       null            System out println line             in close

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