Package com.bioanalyticalcomputing.util

Class ProcessWrapper

java.lang.Object

com.bioanalyticalcomputing.util.ProcessWrapper

public final class ProcessWrapper
extends java.lang.Object

ProcessWrapper encapsulates the steps needed to run a program using the ProcessBuilder class. To prevent side effects, ProcessWrapper decouples input commands from its internal ProcessBuilder and uses wrapper methods to isolate the state of the ProcessBuilder. ProcessWrapper removes direct access to all ProcessBuilder methods and allows only indirect access to ProcessBuilder.command() and ProcessBuilder.inheritIO().

ProcessWrapper.getCommand() returns a copy of the internal ProcessBuilder command, and ProcessWrapper.setCommand() creates a copy of a new command for the internal ProcessBuilder. ProcessWrapper sets the redirectErrorStream property for the internal ProcessBuilder to true.

Note that ProcessWrapper methods are not synchronized, and ProcessWrapper has not been tested with external synchronization.

Following are some simple ProcessWrapper examples (using Python 2.7.16 on macOS Catalina):

      // Run a program and print the output:
      ProcessWrapper processWrapper = new ProcessWrapper("python", "-c", "print('Hello, world!')");
      processWrapper.run();
      processWrapper.printOutput();
      // Expected output:
      // Hello, world!

      // Modify the input:
      List<String> exampleCommand = processWrapper.getCommand();
      exampleCommand.remove(exampleCommand.size() - 1);
      exampleCommand.add("print('Hello')");
      processWrapper.setCommand(exampleCommand);
      processWrapper.run();

      // Work with the output:
      List<String> exampleOutput = processWrapper.getOutput();
      if (exampleOutput.size() > 0)
          System.out.println(exampleOutput.get(0) + " again!");
      // Expected output:
      // Hello again!
 

Constructor Summary

Constructors

Constructor	Description
ProcessWrapper(String... command)	Passes the command to the second constructor.
ProcessWrapper(List<String> command)	Creates a ProcessWrapper and an internal ProcessBuilder using a copy of the command.

Method Summary

Modifier and Type	Method	Description
List<String>	getCommand()	Returns a copy of the current ProcessBuilder command.
List<String>	getOutput()	Returns a copy of the output from the command that the ProcessBuilder has executed.
void	inheritIO()	Calls the inheritIO() method of the internal ProcessBuilder.
void	printOutput()	Prints the output from the command that the ProcessBuilder has executed.
void	run()	Executes the command specified by either a ProcessWrapper constructor or ProcessWrapper.setCommand() and collects the output from the internal ProcessBuilder.
void	setCommand(List<String> command)	Replaces the current command for the internal ProcessBuilder with a copy of the passed command.

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ProcessWrapper

public ProcessWrapper(String... command)

Passes the command to the second constructor.

Parameters:

command - the command to be passed to the internal ProcessBuilder for execution

ProcessWrapper

public ProcessWrapper(List<String> command)

Creates a ProcessWrapper and an internal ProcessBuilder using a copy of the command. The internal command cannot be modified outside of the constructed task builder (since the internal command List is a copy and Strings are immutable).

Parameters:

command - the command to be passed to the internal ProcessBuilder for execution

Method Detail

inheritIO

public void inheritIO()

Calls the inheritIO() method of the internal ProcessBuilder.

getCommand

public List<String> getCommand()

Returns a copy of the current ProcessBuilder command. Changes made to the returned command will not be reflected in the state of the internal ProcessBuilder (since the returned command List is a copy and Strings are immutable).

Returns:

a copy of the current ProcessBuilder command

setCommand

public void setCommand(List<String> command)

Replaces the current command for the internal ProcessBuilder with a copy of the passed command. Changes made to the original command will not be reflected in the state of the internal ProcessBuilder (since the internal command List is a copy and Strings are immutable).

Parameters:

command - the new command to be copied into the internal ProcessBuilder

run

public void run()

Executes the command specified by either a ProcessWrapper constructor or ProcessWrapper.setCommand() and collects the output from the internal ProcessBuilder.

getOutput

public List<String> getOutput()

Returns a copy of the output from the command that the ProcessBuilder has executed.

Returns:

the output from the executed command

printOutput

public void printOutput()

Prints the output from the command that the ProcessBuilder has executed.