ProcessBuilder

ProcessBuilder

ProcessBuilder provides another way to start and manage processes (that is, programs). As explained earlier, all processes are represented by the Process class, and a process can be started by Runtime.exec( ). ProcessBuilder offers more control over the processes. For example, you can set the current working directory.

ProcessBuilder defines these constructors:

ProcessBuilder(List<String> args) ProccessBuilder(String ... args)

Here, args is a list of arguments that specify the name of the program to be executed along with any required command-line arguments. In the first constructor, the arguments are passed in a List. In the second, they are specified through a varargs parameter. Table 17-12 describes the methods defined by ProcessBuilder.

In Table 17-12, notice the methods that use the ProcessBuilder.Redirect class. This abstract class encapsulates an I/O source or target linked to a subprocess. Among other things, these methods enable you to redirect the source or target of I/O operations. For example, you can redirect to a file by calling to( ), redirect from a file by calling from( ), and append to a file by calling appendTo( ). A File object linked to the file can be obtained by calling file( ). These methods are shown here:

static ProcessBuilder.Redirect to(File f ) static ProcessBuilder.Redirect from(File f )

static ProcessBuilder.Redirect appendTo(File f ) File file( )

Another method supported by ProcessBuilder.Redirect is type( ), which returns a value of the enumeration type ProcessBuilder.Redirect.Type. This enumeration describes the type of the redirection. It defines these values: APPEND, INHERIT, PIPE, READ, or WRITE.

ProcessBuilder.Redirect also defines the constants INHERIT and PIPE.

To create a process using ProcessBuilder, simply create an instance of ProcessBuilder, specifying the name of the program and any needed arguments. To begin execution of the program, call start( ) on that instance. Here is an example that executes the Windows text editor notepad. Notice that it specifies the name of the file to edit as an argument.

class PBDemo {

public static void main(String args[]) {

try {

ProcessBuilder proc =

new ProcessBuilder("notepad.exe", "testfile"); proc.start();

} catch (Exception e) { System.out.println("Error executing notepad.");

}

}

}