Java : ProcessBuilder.Redirect with Examples

ProcessBuilder.Redirect (Java SE 19 & JDK 19) API Examples.
You will find code examples on most ProcessBuilder.Redirect methods.

Summary

Represents a source of subprocess input or a destination of subprocess output.

Class diagram

Please see also : ProcessBuilder

public class Child {
    public static void main(String[] args) {
        System.out.println("  OUT 1");
        System.out.println("  OUT 2");
        System.out.println("  OUT 3");
    }
}

public class Main {
    public static void main(String[] args) throws IOException, InterruptedException {
        System.out.println("main : start");

        final var builder = new ProcessBuilder("java", "Child");
        final var process = builder.redirectOutput(ProcessBuilder.Redirect.INHERIT).start();
        System.out.println("waitFor : " + process.waitFor());

        System.out.println("main : end");
    }
}

// Result
// ↓
//> java Main
//main : start
//  OUT 1
//  OUT 2
//  OUT 3
//waitFor : 0
//main : end

Fields

static final ProcessBuilder.Redirect DISCARD

Indicates that subprocess output will be discarded.

public class Child {
    public static void main(String[] args) {
        System.out.println("  OUT 1");
        System.out.println("  OUT 2");
        System.out.println("  OUT 3");
    }
}

public class Main {
    public static void main(String[] args) throws IOException, InterruptedException {
        System.out.println("main : start");

        final var builder = new ProcessBuilder("java", "Child");
        if (args.length == 1 && "discard".equals(args[0])) {
            System.out.println("Discard!");
            builder.redirectOutput(ProcessBuilder.Redirect.DISCARD);
        }
        System.out.println("redirect : " + builder.redirectOutput());

        final var process = builder.start();
        try (final var reader = process.inputReader()) {
            reader.lines().forEach(System.out::println);
        }

        System.out.println("waitFor : " + process.waitFor());

        System.out.println("main : end");
    }
}

// Result
// ↓
//> java Main
//main : start
//redirect : PIPE
//  OUT 1
//  OUT 2
//  OUT 3
//waitFor : 0
//main : end
//
//> java Main discard
//main : start
//Discard!
//redirect : WRITE
//waitFor : 0
//main : end

static final ProcessBuilder.Redirect INHERIT

Indicates that subprocess I/O source or destination will be the same as those of the current process.

public class Child {
    public static void main(String[] args) {
        System.out.println("  OUT 1");
        System.out.println("  OUT 2");
        System.out.println("  OUT 3");
    }
}

public class Main {
    public static void main(String[] args) throws IOException, InterruptedException {
        System.out.println("main : start");

        final var builder = new ProcessBuilder("java", "Child");
        if (args.length == 1 && "inherit".equals(args[0])) {
            System.out.println("Inherit!");
            builder.redirectOutput(ProcessBuilder.Redirect.INHERIT);
        }
        System.out.println("redirect : " + builder.redirectOutput());

        final var process = builder.start();
        System.out.println("waitFor : " + process.waitFor());

        System.out.println("main : end");
    }
}

// Result
// ↓
//> java Main
//main : start
//redirect : PIPE
//waitFor : 0
//main : end
//
//> java Main inherit
//main : start
//Inherit!
//redirect : INHERIT
//  OUT 1
//  OUT 2
//  OUT 3
//waitFor : 0
//main : end

static final ProcessBuilder.Redirect PIPE

Indicates that subprocess I/O will be connected to the current Java process over a pipe.

public class Child {
    public static void main(String[] args) {
        System.out.println("  OUT 1");
        System.out.println("  OUT 2");
        System.out.println("  OUT 3");
    }
}

public class Main {
    public static void main(String[] args) throws IOException, InterruptedException {
        System.out.println("main : start");

        final var builder = new ProcessBuilder("java", "Child");
        final var redirect = builder.redirectOutput();
        System.out.println("pipe : " + redirect.equals(ProcessBuilder.Redirect.PIPE));

        final var process = builder.start();
        try (final var reader = process.inputReader()) {
            reader.lines().forEach(System.out::println);
        }

        System.out.println("waitFor : " + process.waitFor());

        System.out.println("main : end");
    }
}

// Result
// ↓
//> java Main
//main : start
//pipe : true
//  OUT 1
//  OUT 2
//  OUT 3
//waitFor : 0
//main : end

Methods

static ProcessBuilder.Redirect appendTo (File file)

Returns a redirect to append to the specified file.

public class Child {
    public static void main(String[] args) {
        System.out.println("OUT 1");
        System.out.println("OUT 2");
        System.out.println("OUT 3");
    }
}

public class Main {
    public static void main(String[] args) throws IOException, InterruptedException {
        System.out.println("main : start");

        final var file = Path.of("aaa.txt");
        Files.writeString(file, """
                abcd
                1234
                """);

        final var redirect = ProcessBuilder.Redirect.appendTo(file.toFile());
        final var builder = new ProcessBuilder("java", "Child");

        final var process = builder.redirectOutput(redirect).start();
        System.out.println("waitFor : " + process.waitFor());

        System.out.println("main : end");
    }
}

// Result
// ↓
//> java Main
//main : start
//waitFor : 0
//main : end
//
//> cat aaa.txt
//abcd
//1234
//OUT 1
//OUT 2
//OUT 3

boolean equals (Object obj)

Compares the specified object with this Redirect for equality.

final var redirect1 = ProcessBuilder.Redirect.DISCARD;
final var redirect2 = ProcessBuilder.Redirect.INHERIT;

System.out.println(redirect1.equals(redirect2)); // false

final var redirect3 = ProcessBuilder.Redirect.to(Path.of("aaa.txt").toFile());
final var redirect4 = ProcessBuilder.Redirect.to(Path.of("aaa.txt").toFile());
final var redirect5 = ProcessBuilder.Redirect.to(Path.of("bbb.txt").toFile());

System.out.println(redirect3.equals(redirect4)); // true
System.out.println(redirect3.equals(redirect5)); // false

File file ()

Returns the File source or destination associated with this redirect, or null if there is no such file.

System.out.println(ProcessBuilder.Redirect.DISCARD.file()); // NUL
System.out.println(ProcessBuilder.Redirect.INHERIT.file()); // null
System.out.println(ProcessBuilder.Redirect.PIPE.file()); // null

final var path = Path.of("R:", "java-work", "aaa.txt");
System.out.println(ProcessBuilder.Redirect.to(path.toFile()).file()); // R:\java-work\aaa.txt

static ProcessBuilder.Redirect from (File file)

Returns a redirect to read from the specified file.

public class Child {
    public static void main(String[] args) {
        System.out.println("child : start");

        final var sc = new Scanner(System.in);
        while (sc.hasNext()) {
            final var next = sc.next();

            if ("quit".equals(next)) {
                System.out.println("  Quit!");
                break;
            }

            System.out.println("  next : " + next);
        }

        System.out.println("child : end");
    }
}

public class Main {
    public static void main(String[] args) throws IOException, InterruptedException {
        System.out.println("main : start");

        final var file = Path.of("aaa.txt");
        Files.writeString(file, """
                abcd
                1234
                quit
                """);

        final var redirect = ProcessBuilder.Redirect.from(file.toFile());
        final var builder = new ProcessBuilder("java", "Child");

        final var process = builder.redirectInput(redirect).start();
        try (final var reader = process.inputReader()) {
            reader.lines().forEach(System.out::println);
        }

        System.out.println("waitFor : " + process.waitFor());

        System.out.println("main : end");
    }
}

// Result
// ↓
//> java Main
//main : start
//child : start
//  next : abcd
//  next : 1234
//  Quit!
//child : end
//waitFor : 0
//main : end

int hashCode ()

Returns a hash code value for this Redirect.

final var ret1 = ProcessBuilder.Redirect.DISCARD.hashCode();
System.out.println(ret1); // 1277460

final var ret2 = ProcessBuilder.Redirect.INHERIT.hashCode();
System.out.println(ret2); // 573958827

final var ret3 = ProcessBuilder.Redirect.to(Path.of("aaa.txt").toFile()).hashCode();
System.out.println(ret3); // -1239232814

static ProcessBuilder.Redirect to (File file)

Returns a redirect to write to the specified file.

public class Child {
    public static void main(String[] args) {
        System.out.println("OUT 1");
        System.out.println("OUT 2");
        System.out.println("OUT 3");
    }
}

public class Main {
    public static void main(String[] args) throws IOException, InterruptedException {
        System.out.println("main : start");

        final var file = Path.of("aaa.txt");
        Files.writeString(file, """
                abcd
                1234
                """);

        final var redirect = ProcessBuilder.Redirect.to(file.toFile());
        final var builder = new ProcessBuilder("java", "Child");

        final var process = builder.redirectOutput(redirect).start();
        System.out.println("waitFor : " + process.waitFor());

        System.out.println("main : end");
    }
}

// Result
// ↓
//> java Main
//main : start
//waitFor : 0
//main : end
//
//> cat aaa.txt
//OUT 1
//OUT 2
//OUT 3

abstract ProcessBuilder.Redirect.Type type ()

Returns the type of this Redirect.

System.out.println(ProcessBuilder.Redirect.DISCARD.type()); // WRITE
System.out.println(ProcessBuilder.Redirect.INHERIT.type()); // INHERIT
System.out.println(ProcessBuilder.Redirect.PIPE.type()); // PIPE

final var path = Path.of("R:", "java-work", "aaa.txt");
System.out.println(ProcessBuilder.Redirect.to(path.toFile()).type()); // WRITE
System.out.println(ProcessBuilder.Redirect.from(path.toFile()).type()); // READ

API Examples

Java : ProcessBuilder.Redirect with Examples

Summary

Fields

static final ProcessBuilder.Redirect DISCARD

static final ProcessBuilder.Redirect INHERIT

static final ProcessBuilder.Redirect PIPE

Methods

static ProcessBuilder.Redirect appendTo (File file)

boolean equals (Object obj)

File file ()

static ProcessBuilder.Redirect from (File file)

int hashCode ()

static ProcessBuilder.Redirect to (File file)

abstract ProcessBuilder.Redirect.Type type ()

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