/*
 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.lang;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 * This class is used to create operating system processes.
 *
 * <p>Each {@code ProcessBuilder} instance manages a collection
 * of process attributes. The {@link #start()} method creates a new
 * {@link Process} instance with those attributes. The {@link
 * #start()} method can be invoked repeatedly from the same instance
 * to create new subprocesses with identical or related attributes.
 *
 * <p>Each process builder manages these process attributes:
 *
 * <ul>
 *
 * <li>a <i>command</i>, a list of strings which signifies the
 * external program file to be invoked and its arguments, if any.
 * Which string lists represent a valid operating system command is
 * system-dependent. For example, it is common for each conceptual
 * argument to be an element in this list, but there are operating
 * systems where programs are expected to tokenize command line
 * strings themselves - on such a system a Java implementation might
 * require commands to contain exactly two elements.
 *
 * <li>an <i>environment</i>, which is a system-dependent mapping from
 * <i>variables</i> to <i>values</i>. The initial value is a copy of
 * the environment of the current process (see {@link System#getenv()}).
 *
 * <li>a <i>working directory</i>. The default value is the current
 * working directory of the current process, usually the directory
 * named by the system property {@code user.dir}.
 *
 * <li><a name="redirect-input">a source of <i>standard input</i></a>.
 * By default, the subprocess reads input from a pipe. Java code
 * can access this pipe via the output stream returned by
 * {@link Process#getOutputStream()}. However, standard input may
 * be redirected to another source using
 * {@link #redirectInput(Redirect) redirectInput}.
 * In this case, {@link Process#getOutputStream()} will return a
 * <i>null output stream</i>, for which:
 *
 * <ul>
 * <li>the {@link OutputStream#write(int) write} methods always
 * throw {@code IOException}
 * <li>the {@link OutputStream#close() close} method does nothing
 * </ul>
 *
 * <li><a name="redirect-output">a destination for <i>standard output</i>
 * and <i>standard error</i></a>. By default, the subprocess writes standard
 * output and standard error to pipes. Java code can access these pipes
 * via the input streams returned by {@link Process#getInputStream()} and
 * {@link Process#getErrorStream()}. However, standard output and
 * standard error may be redirected to other destinations using
 * {@link #redirectOutput(Redirect) redirectOutput} and
 * {@link #redirectError(Redirect) redirectError}.
 * In this case, {@link Process#getInputStream()} and/or
 * {@link Process#getErrorStream()} will return a <i>null input
 * stream</i>, for which:
 *
 * <ul>
 * <li>the {@link InputStream#read() read} methods always return
 * {@code -1}
 * <li>the {@link InputStream#available() available} method always returns
 * {@code 0}
 * <li>the {@link InputStream#close() close} method does nothing
 * </ul>
 *
 * <li>a <i>redirectErrorStream</i> property. Initially, this property
 * is {@code false}, meaning that the standard output and error
 * output of a subprocess are sent to two separate streams, which can
 * be accessed using the {@link Process#getInputStream()} and {@link
 * Process#getErrorStream()} methods.
 *
 * <p>If the value is set to {@code true}, then:
 *
 * <ul>
 * <li>standard error is merged with the standard output and always sent
 * to the same destination (this makes it easier to correlate error
 * messages with the corresponding output)
 * <li>the common destination of standard error and standard output can be
 * redirected using
 * {@link #redirectOutput(Redirect) redirectOutput}
 * <li>any redirection set by the
 * {@link #redirectError(Redirect) redirectError}
 * method is ignored when creating a subprocess
 * <li>the stream returned from {@link Process#getErrorStream()} will
 * always be a <a href="#redirect-output">null input stream</a>
 * </ul>
 *
 * </ul>
 *
 * <p>Modifying a process builder's attributes will affect processes
 * subsequently started by that object's {@link #start()} method, but
 * will never affect previously started processes or the Java process
 * itself.
 *
 * <p>Most error checking is performed by the {@link #start()} method.
 * It is possible to modify the state of an object so that {@link
 * #start()} will fail. For example, setting the command attribute to
 * an empty list will not throw an exception unless {@link #start()}
 * is invoked.
 *
 * <p><strong>Note that this class is not synchronized.</strong>
 * If multiple threads access a {@code ProcessBuilder} instance
 * concurrently, and at least one of the threads modifies one of the
 * attributes structurally, it <i>must</i> be synchronized externally.
 *
 * <p>Starting a new process which uses the default working directory
 * and environment is easy:
 *
 * <pre> {@code
 * Process p = new ProcessBuilder("myCommand", "myArg").start();
 * }</pre>
 *
 * <p>Here is an example that starts a process with a modified working
 * directory and environment, and redirects standard output and error
 * to be appended to a log file:
 *
 * <pre> {@code
 * ProcessBuilder pb =
 * new ProcessBuilder("myCommand", "myArg1", "myArg2");
 * Map<String, String> env = pb.environment();
 * env.put("VAR1", "myValue");
 * env.remove("OTHERVAR");
 * env.put("VAR2", env.get("VAR1") + "suffix");
 * pb.directory(new File("myDir"));
 * File log = new File("log");
 * pb.redirectErrorStream(true);
 * pb.redirectOutput(Redirect.appendTo(log));
 * Process p = pb.start();
 * assert pb.redirectInput() == Redirect.PIPE;
 * assert pb.redirectOutput().file() == log;
 * assert p.getInputStream().read() == -1;
 * }</pre>
 *
 * <p>To start a process with an explicit set of environment
 * variables, first call {@link java.util.Map#clear() Map.clear()}
 * before adding environment variables.
 *
 * @author Martin Buchholz
 * @since 1.5
 */

public final class ProcessBuilder
{
 private List<String> command;
 private File directory;
 private Map<String,String> environment;
 private boolean redirectErrorStream;
 private Redirect[] redirects;

 /**
 * Constructs a process builder with the specified operating
 * system program and arguments. This constructor does <i>not</i>
 * make a copy of the {@code command} list. Subsequent
 * updates to the list will be reflected in the state of the
 * process builder. It is not checked whether
 * {@code command} corresponds to a valid operating system
 * command.
 *
 * @param command the list containing the program and its arguments
 * @throws NullPointerException if the argument is null
 */
 public ProcessBuilder(List<String> command) {
 if (command == null)
 throw new NullPointerException();
 this.command = command;
 }

 /**
 * Constructs a process builder with the specified operating
 * system program and arguments. This is a convenience
 * constructor that sets the process builder's command to a string
 * list containing the same strings as the {@code command}
 * array, in the same order. It is not checked whether
 * {@code command} corresponds to a valid operating system
 * command.
 *
 * @param command a string array containing the program and its arguments
 */
 public ProcessBuilder(String... command) {
 this.command = new ArrayList<>(command.length);
 for (String arg : command)
 this.command.add(arg);
 }

 /**
 * Sets this process builder's operating system program and
 * arguments. This method does <i>not</i> make a copy of the
 * {@code command} list. Subsequent updates to the list will
 * be reflected in the state of the process builder. It is not
 * checked whether {@code command} corresponds to a valid
 * operating system command.
 *
 * @param command the list containing the program and its arguments
 * @return this process builder
 *
 * @throws NullPointerException if the argument is null
 */
 public ProcessBuilder command(List<String> command) {
 if (command == null)
 throw new NullPointerException();
 this.command = command;
 return this;
 }

 /**
 * Sets this process builder's operating system program and
 * arguments. This is a convenience method that sets the command
 * to a string list containing the same strings as the
 * {@code command} array, in the same order. It is not
 * checked whether {@code command} corresponds to a valid
 * operating system command.
 *
 * @param command a string array containing the program and its arguments
 * @return this process builder
 */
 public ProcessBuilder command(String... command) {
 this.command = new ArrayList<>(command.length);
 for (String arg : command)
 this.command.add(arg);
 return this;
 }

 /**
 * Returns this process builder's operating system program and
 * arguments. The returned list is <i>not</i> a copy. Subsequent
 * updates to the list will be reflected in the state of this
 * process builder.
 *
 * @return this process builder's program and its arguments
 */
 public List<String> command() {
 return command;
 }

 /**
 * Returns a string map view of this process builder's environment.
 *
 * Whenever a process builder is created, the environment is
 * initialized to a copy of the current process environment (see
 * {@link System#getenv()}). Subprocesses subsequently started by
 * this object's {@link #start()} method will use this map as
 * their environment.
 *
 * <p>The returned object may be modified using ordinary {@link
 * java.util.Map Map} operations. These modifications will be
 * visible to subprocesses started via the {@link #start()}
 * method. Two {@code ProcessBuilder} instances always
 * contain independent process environments, so changes to the
 * returned map will never be reflected in any other
 * {@code ProcessBuilder} instance or the values returned by
 * {@link System#getenv System.getenv}.
 *
 * <p>If the system does not support environment variables, an
 * empty map is returned.
 *
 * <p>The returned map does not permit null keys or values.
 * Attempting to insert or query the presence of a null key or
 * value will throw a {@link NullPointerException}.
 * Attempting to query the presence of a key or value which is not
 * of type {@link String} will throw a {@link ClassCastException}.
 *
 * <p>The behavior of the returned map is system-dependent. A
 * system may not allow modifications to environment variables or
 * may forbid certain variable names or values. For this reason,
 * attempts to modify the map may fail with
 * {@link UnsupportedOperationException} or
 * {@link IllegalArgumentException}
 * if the modification is not permitted by the operating system.
 *
 * <p>Since the external format of environment variable names and
 * values is system-dependent, there may not be a one-to-one
 * mapping between them and Java's Unicode strings. Nevertheless,
 * the map is implemented in such a way that environment variables
 * which are not modified by Java code will have an unmodified
 * native representation in the subprocess.
 *
 * <p>The returned map and its collection views may not obey the
 * general contract of the {@link Object#equals} and
 * {@link Object#hashCode} methods.
 *
 * <p>The returned map is typically case-sensitive on all platforms.
 *
 * <p>If a security manager exists, its
 * {@link SecurityManager#checkPermission checkPermission} method
 * is called with a
 * {@link RuntimePermission}{@code ("getenv.*")} permission.
 * This may result in a {@link SecurityException} being thrown.
 *
 * <p>When passing information to a Java subprocess,
 * <a href=System.html#EnvironmentVSSystemProperties>system properties</a>
 * are generally preferred over environment variables.
 *
 * @return this process builder's environment
 *
 * @throws SecurityException
 * if a security manager exists and its
 * {@link SecurityManager#checkPermission checkPermission}
 * method doesn't allow access to the process environment
 *
 * @see Runtime#exec(String[],String[],java.io.File)
 * @see System#getenv()
 */
 public Map<String,String> environment() {
 SecurityManager security = System.getSecurityManager();
 if (security != null)
 security.checkPermission(new RuntimePermission("getenv.*"));

 if (environment == null)
 environment = ProcessEnvironment.environment();

 assert environment != null;

 return environment;
 }

 // Only for use by Runtime.exec(...envp...)
 ProcessBuilder environment(String[] envp) {
 assert environment == null;
 if (envp != null) {
 environment = ProcessEnvironment.emptyEnvironment(envp.length);
 assert environment != null;

 for (String envstring : envp) {
 // Before 1.5, we blindly passed invalid envstrings
 // to the child process.
 // We would like to throw an exception, but do not,
 // for compatibility with old broken code.

 // Silently discard any trailing junk.
 if (envstring.indexOf((int) '\u0000') != -1)
 envstring = envstring.replaceFirst("\u0000.*", "");

 int eqlsign =
 envstring.indexOf('=', ProcessEnvironment.MIN_NAME_LENGTH);
 // Silently ignore envstrings lacking the required `='.
 if (eqlsign != -1)
 environment.put(envstring.substring(0,eqlsign),
 envstring.substring(eqlsign+1));
 }
 }
 return this;
 }

 /**
 * Returns this process builder's working directory.
 *
 * Subprocesses subsequently started by this object's {@link
 * #start()} method will use this as their working directory.
 * The returned value may be {@code null} -- this means to use
 * the working directory of the current Java process, usually the
 * directory named by the system property {@code user.dir},
 * as the working directory of the child process.
 *
 * @return this process builder's working directory
 */
 public File directory() {
 return directory;
 }

 /**
 * Sets this process builder's working directory.
 *
 * Subprocesses subsequently started by this object's {@link
 * #start()} method will use this as their working directory.
 * The argument may be {@code null} -- this means to use the
 * working directory of the current Java process, usually the
 * directory named by the system property {@code user.dir},
 * as the working directory of the child process.
 *
 * @param directory the new working directory
 * @return this process builder
 */
 public ProcessBuilder directory(File directory) {
 this.directory = directory;
 return this;
 }

 // ---------------- I/O Redirection ----------------

 /**
 * Implements a <a href="#redirect-output">null input stream</a>.
 */
 static class NullInputStream extends InputStream {
 static final NullInputStream INSTANCE = new NullInputStream();
 private NullInputStream() {}
 public int read() { return -1; }
 public int available() { return 0; }
 }

 /**
 * Implements a <a href="#redirect-input">null output stream</a>.
 */
 static class NullOutputStream extends OutputStream {
 static final NullOutputStream INSTANCE = new NullOutputStream();
 private NullOutputStream() {}
 public void write(int b) throws IOException {
 throw new IOException("Stream closed");
 }
 }

 /**
 * Represents a source of subprocess input or a destination of
 * subprocess output.
 *
 * Each {@code Redirect} instance is one of the following:
 *
 * <ul>
 * <li>the special value {@link #PIPE Redirect.PIPE}
 * <li>the special value {@link #INHERIT Redirect.INHERIT}
 * <li>a redirection to read from a file, created by an invocation of
 * {@link Redirect#from Redirect.from(File)}
 * <li>a redirection to write to a file, created by an invocation of
 * {@link Redirect#to Redirect.to(File)}
 * <li>a redirection to append to a file, created by an invocation of
 * {@link Redirect#appendTo Redirect.appendTo(File)}
 * </ul>
 *
 * <p>Each of the above categories has an associated unique
 * {@link Type Type}.
 *
 * @since 1.7
 */
 public static abstract class Redirect {
 /**
 * The type of a {@link Redirect}.
 */
 public enum Type {
 /**
 * The type of {@link Redirect#PIPE Redirect.PIPE}.
 */
 PIPE,

 /**
 * The type of {@link Redirect#INHERIT Redirect.INHERIT}.
 */
 INHERIT,

 /**
 * The type of redirects returned from
 * {@link Redirect#from Redirect.from(File)}.
 */
 READ,

 /**
 * The type of redirects returned from
 * {@link Redirect#to Redirect.to(File)}.
 */
 WRITE,

 /**
 * The type of redirects returned from
 * {@link Redirect#appendTo Redirect.appendTo(File)}.
 */
 APPEND
 };

 /**
 * Returns the type of this {@code Redirect}.
 * @return the type of this {@code Redirect}
 */
 public abstract Type type();

 /**
 * Indicates that subprocess I/O will be connected to the
 * current Java process over a pipe.
 *
 * This is the default handling of subprocess standard I/O.
 *
 * <p>It will always be true that
 * <pre> {@code
 * Redirect.PIPE.file() == null &&
 * Redirect.PIPE.type() == Redirect.Type.PIPE
 * }</pre>
 */
 public static final Redirect PIPE = new Redirect() {
 public Type type() { return Type.PIPE; }
 public String toString() { return type().toString(); }};

 /**
 * Indicates that subprocess I/O source or destination will be the
 * same as those of the current process. This is the normal
 * behavior of most operating system command interpreters (shells).
 *
 * <p>It will always be true that
 * <pre> {@code
 * Redirect.INHERIT.file() == null &&
 * Redirect.INHERIT.type() == Redirect.Type.INHERIT
 * }</pre>
 */
 public static final Redirect INHERIT = new Redirect() {
 public Type type() { return Type.INHERIT; }
 public String toString() { return type().toString(); }};

 /**
 * Returns the {@link File} source or destination associated
 * with this redirect, or {@code null} if there is no such file.
 *
 * @return the file associated with this redirect,
 * or {@code null} if there is no such file
 */
 public File file() { return null; }

 /**
 * When redirected to a destination file, indicates if the output
 * is to be written to the end of the file.
 */
 boolean append() {
 throw new UnsupportedOperationException();
 }

 /**
 * Returns a redirect to read from the specified file.
 *
 * <p>It will always be true that
 * <pre> {@code
 * Redirect.from(file).file() == file &&
 * Redirect.from(file).type() == Redirect.Type.READ
 * }</pre>
 *
 * @param file The {@code File} for the {@code Redirect}.
 * @throws NullPointerException if the specified file is null
 * @return a redirect to read from the specified file
 */
 public static Redirect from(final File file) {
 if (file == null)
 throw new NullPointerException();
 return new Redirect() {
 public Type type() { return Type.READ; }
 public File file() { return file; }
 public String toString() {
 return "redirect to read from file \"" + file + "\"";
 }
 };
 }

 /**
 * Returns a redirect to write to the specified file.
 * If the specified file exists when the subprocess is started,
 * its previous contents will be discarded.
 *
 * <p>It will always be true that
 * <pre> {@code
 * Redirect.to(file).file() == file &&
 * Redirect.to(file).type() == Redirect.Type.WRITE
 * }</pre>
 *
 * @param file The {@code File} for the {@code Redirect}.
 * @throws NullPointerException if the specified file is null
 * @return a redirect to write to the specified file
 */
 public static Redirect to(final File file) {
 if (file == null)
 throw new NullPointerException();
 return new Redirect() {
 public Type type() { return Type.WRITE; }
 public File file() { return file; }
 public String toString() {
 return "redirect to write to file \"" + file + "\"";
 }
 boolean append() { return false; }
 };
 }

 /**
 * Returns a redirect to append to the specified file.
 * Each write operation first advances the position to the
 * end of the file and then writes the requested data.
 * Whether the advancement of the position and the writing
 * of the data are done in a single atomic operation is
 * system-dependent and therefore unspecified.
 *
 * <p>It will always be true that
 * <pre> {@code
 * Redirect.appendTo(file).file() == file &&
 * Redirect.appendTo(file).type() == Redirect.Type.APPEND
 * }</pre>
 *
 * @param file The {@code File} for the {@code Redirect}.
 * @throws NullPointerException if the specified file is null
 * @return a redirect to append to the specified file
 */
 public static Redirect appendTo(final File file) {
 if (file == null)
 throw new NullPointerException();
 return new Redirect() {
 public Type type() { return Type.APPEND; }
 public File file() { return file; }
 public String toString() {
 return "redirect to append to file \"" + file + "\"";
 }
 boolean append() { return true; }
 };
 }

 /**
 * Compares the specified object with this {@code Redirect} for
 * equality. Returns {@code true} if and only if the two
 * objects are identical or both objects are {@code Redirect}
 * instances of the same type associated with non-null equal
 * {@code File} instances.
 */
 public boolean equals(Object obj) {
 if (obj == this)
 return true;
 if (! (obj instanceof Redirect))
 return false;
 Redirect r = (Redirect) obj;
 if (r.type() != this.type())
 return false;
 assert this.file() != null;
 return this.file().equals(r.file());
 }

 /**
 * Returns a hash code value for this {@code Redirect}.
 * @return a hash code value for this {@code Redirect}
 */
 public int hashCode() {
 File file = file();
 if (file == null)
 return super.hashCode();
 else
 return file.hashCode();
 }

 /**
 * No public constructors. Clients must use predefined
 * static {@code Redirect} instances or factory methods.
 */
 private Redirect() {}
 }

 private Redirect[] redirects() {
 if (redirects == null)
 redirects = new Redirect[] {
 Redirect.PIPE, Redirect.PIPE, Redirect.PIPE
 };
 return redirects;
 }

 /**
 * Sets this process builder's standard input source.
 *
 * Subprocesses subsequently started by this object's {@link #start()}
 * method obtain their standard input from this source.
 *
 * <p>If the source is {@link Redirect#PIPE Redirect.PIPE}
 * (the initial value), then the standard input of a
 * subprocess can be written to using the output stream
 * returned by {@link Process#getOutputStream()}.
 * If the source is set to any other value, then
 * {@link Process#getOutputStream()} will return a
 * <a href="#redirect-input">null output stream</a>.
 *
 * @param source the new standard input source
 * @return this process builder
 * @throws IllegalArgumentException
 * if the redirect does not correspond to a valid source
 * of data, that is, has type
 * {@link Redirect.Type#WRITE WRITE} or
 * {@link Redirect.Type#APPEND APPEND}
 * @since 1.7
 */
 public ProcessBuilder redirectInput(Redirect source) {
 if (source.type() == Redirect.Type.WRITE ||
 source.type() == Redirect.Type.APPEND)
 throw new IllegalArgumentException(
 "Redirect invalid for reading: " + source);
 redirects()[0] = source;
 return this;
 }

 /**
 * Sets this process builder's standard output destination.
 *
 * Subprocesses subsequently started by this object's {@link #start()}
 * method send their standard output to this destination.
 *
 * <p>If the destination is {@link Redirect#PIPE Redirect.PIPE}
 * (the initial value), then the standard output of a subprocess
 * can be read using the input stream returned by {@link
 * Process#getInputStream()}.
 * If the destination is set to any other value, then
 * {@link Process#getInputStream()} will return a
 * <a href="#redirect-output">null input stream</a>.
 *
 * @param destination the new standard output destination
 * @return this process builder
 * @throws IllegalArgumentException
 * if the redirect does not correspond to a valid
 * destination of data, that is, has type
 * {@link Redirect.Type#READ READ}
 * @since 1.7
 */
 public ProcessBuilder redirectOutput(Redirect destination) {
 if (destination.type() == Redirect.Type.READ)
 throw new IllegalArgumentException(
 "Redirect invalid for writing: " + destination);
 redirects()[1] = destination;
 return this;
 }

 /**
 * Sets this process builder's standard error destination.
 *
 * Subprocesses subsequently started by this object's {@link #start()}
 * method send their standard error to this destination.
 *
 * <p>If the destination is {@link Redirect#PIPE Redirect.PIPE}
 * (the initial value), then the error output of a subprocess
 * can be read using the input stream returned by {@link
 * Process#getErrorStream()}.
 * If the destination is set to any other value, then
 * {@link Process#getErrorStream()} will return a
 * <a href="#redirect-output">null input stream</a>.
 *
 * <p>If the {@link #redirectErrorStream redirectErrorStream}
 * attribute has been set {@code true}, then the redirection set
 * by this method has no effect.
 *
 * @param destination the new standard error destination
 * @return this process builder
 * @throws IllegalArgumentException
 * if the redirect does not correspond to a valid
 * destination of data, that is, has type
 * {@link Redirect.Type#READ READ}
 * @since 1.7
 */
 public ProcessBuilder redirectError(Redirect destination) {
 if (destination.type() == Redirect.Type.READ)
 throw new IllegalArgumentException(
 "Redirect invalid for writing: " + destination);
 redirects()[2] = destination;
 return this;
 }

 /**
 * Sets this process builder's standard input source to a file.
 *
 * <p>This is a convenience method. An invocation of the form
 * {@code redirectInput(file)}
 * behaves in exactly the same way as the invocation
 * {@link #redirectInput(Redirect) redirectInput}
 * {@code (Redirect.from(file))}.
 *
 * @param file the new standard input source
 * @return this process builder
 * @since 1.7
 */
 public ProcessBuilder redirectInput(File file) {
 return redirectInput(Redirect.from(file));
 }

 /**
 * Sets this process builder's standard output destination to a file.
 *
 * <p>This is a convenience method. An invocation of the form
 * {@code redirectOutput(file)}
 * behaves in exactly the same way as the invocation
 * {@link #redirectOutput(Redirect) redirectOutput}
 * {@code (Redirect.to(file))}.
 *
 * @param file the new standard output destination
 * @return this process builder
 * @since 1.7
 */
 public ProcessBuilder redirectOutput(File file) {
 return redirectOutput(Redirect.to(file));
 }

 /**
 * Sets this process builder's standard error destination to a file.
 *
 * <p>This is a convenience method. An invocation of the form
 * {@code redirectError(file)}
 * behaves in exactly the same way as the invocation
 * {@link #redirectError(Redirect) redirectError}
 * {@code (Redirect.to(file))}.
 *
 * @param file the new standard error destination
 * @return this process builder
 * @since 1.7
 */
 public ProcessBuilder redirectError(File file) {
 return redirectError(Redirect.to(file));
 }

 /**
 * Returns this process builder's standard input source.
 *
 * Subprocesses subsequently started by this object's {@link #start()}
 * method obtain their standard input from this source.
 * The initial value is {@link Redirect#PIPE Redirect.PIPE}.
 *
 * @return this process builder's standard input source
 * @since 1.7
 */
 public Redirect redirectInput() {
 return (redirects == null) ? Redirect.PIPE : redirects[0];
 }

 /**
 * Returns this process builder's standard output destination.
 *
 * Subprocesses subsequently started by this object's {@link #start()}
 * method redirect their standard output to this destination.
 * The initial value is {@link Redirect#PIPE Redirect.PIPE}.
 *
 * @return this process builder's standard output destination
 * @since 1.7
 */
 public Redirect redirectOutput() {
 return (redirects == null) ? Redirect.PIPE : redirects[1];
 }

 /**
 * Returns this process builder's standard error destination.
 *
 * Subprocesses subsequently started by this object's {@link #start()}
 * method redirect their standard error to this destination.
 * The initial value is {@link Redirect#PIPE Redirect.PIPE}.
 *
 * @return this process builder's standard error destination
 * @since 1.7
 */
 public Redirect redirectError() {
 return (redirects == null) ? Redirect.PIPE : redirects[2];
 }

 /**
 * Sets the source and destination for subprocess standard I/O
 * to be the same as those of the current Java process.
 *
 * <p>This is a convenience method. An invocation of the form
 * <pre> {@code
 * pb.inheritIO()
 * }</pre>
 * behaves in exactly the same way as the invocation
 * <pre> {@code
 * pb.redirectInput(Redirect.INHERIT)
 * .redirectOutput(Redirect.INHERIT)
 * .redirectError(Redirect.INHERIT)
 * }</pre>
 *
 * This gives behavior equivalent to most operating system
 * command interpreters, or the standard C library function
 * {@code system()}.
 *
 * @return this process builder
 * @since 1.7
 */
 public ProcessBuilder inheritIO() {
 Arrays.fill(redirects(), Redirect.INHERIT);
 return this;
 }

 /**
 * Tells whether this process builder merges standard error and
 * standard output.
 *
 * <p>If this property is {@code true}, then any error output
 * generated by subprocesses subsequently started by this object's
 * {@link #start()} method will be merged with the standard
 * output, so that both can be read using the
 * {@link Process#getInputStream()} method. This makes it easier
 * to correlate error messages with the corresponding output.
 * The initial value is {@code false}.
 *
 * @return this process builder's {@code redirectErrorStream} property
 */
 public boolean redirectErrorStream() {
 return redirectErrorStream;
 }

 /**
 * Sets this process builder's {@code redirectErrorStream} property.
 *
 * <p>If this property is {@code true}, then any error output
 * generated by subprocesses subsequently started by this object's
 * {@link #start()} method will be merged with the standard
 * output, so that both can be read using the
 * {@link Process#getInputStream()} method. This makes it easier
 * to correlate error messages with the corresponding output.
 * The initial value is {@code false}.
 *
 * @param redirectErrorStream the new property value
 * @return this process builder
 */
 public ProcessBuilder redirectErrorStream(boolean redirectErrorStream) {
 this.redirectErrorStream = redirectErrorStream;
 return this;
 }

 /**
 * Starts a new process using the attributes of this process builder.
 *
 * <p>The new process will
 * invoke the command and arguments given by {@link #command()},
 * in a working directory as given by {@link #directory()},
 * with a process environment as given by {@link #environment()}.
 *
 * <p>This method checks that the command is a valid operating
 * system command. Which commands are valid is system-dependent,
 * but at the very least the command must be a non-empty list of
 * non-null strings.
 *
 * <p>A minimal set of system dependent environment variables may
 * be required to start a process on some operating systems.
 * As a result, the subprocess may inherit additional environment variable
 * settings beyond those in the process builder's {@link #environment()}.
 *
 * <p>If there is a security manager, its
 * {@link SecurityManager#checkExec checkExec}
 * method is called with the first component of this object's
 * {@code command} array as its argument. This may result in
 * a {@link SecurityException} being thrown.
 *
 * <p>Starting an operating system process is highly system-dependent.
 * Among the many things that can go wrong are:
 * <ul>
 * <li>The operating system program file was not found.
 * <li>Access to the program file was denied.
 * <li>The working directory does not exist.
 * </ul>
 *
 * <p>In such cases an exception will be thrown. The exact nature
 * of the exception is system-dependent, but it will always be a
 * subclass of {@link IOException}.
 *
 * <p>Subsequent modifications to this process builder will not
 * affect the returned {@link Process}.
 *
 * @return a new {@link Process} object for managing the subprocess
 *
 * @throws NullPointerException
 * if an element of the command list is null
 *
 * @throws IndexOutOfBoundsException
 * if the command is an empty list (has size {@code 0})
 *
 * @throws SecurityException
 * if a security manager exists and
 * <ul>
 *
 * <li>its
 * {@link SecurityManager#checkExec checkExec}
 * method doesn't allow creation of the subprocess, or
 *
 * <li>the standard input to the subprocess was
 * {@linkplain #redirectInput redirected from a file}
 * and the security manager's
 * {@link SecurityManager#checkRead checkRead} method
 * denies read access to the file, or
 *
 * <li>the standard output or standard error of the
 * subprocess was
 * {@linkplain #redirectOutput redirected to a file}
 * and the security manager's
 * {@link SecurityManager#checkWrite checkWrite} method
 * denies write access to the file
 *
 * </ul>
 *
 * @throws IOException if an I/O error occurs
 *
 * @see Runtime#exec(String[], String[], java.io.File)
 */
 public Process start() throws IOException {
 // Must convert to array first -- a malicious user-supplied
 // list might try to circumvent the security check.
 String[] cmdarray = command.toArray(new String[command.size()]);
 cmdarray = cmdarray.clone();

 for (String arg : cmdarray)
 if (arg == null)
 throw new NullPointerException();
 // Throws IndexOutOfBoundsException if command is empty
 String prog = cmdarray[0];

 SecurityManager security = System.getSecurityManager();
 if (security != null)
 security.checkExec(prog);

 String dir = directory == null ? null : directory.toString();

 for (int i = 1; i < cmdarray.length; i++) {
 if (cmdarray[i].indexOf('\u0000') >= 0) {
 throw new IOException("invalid null character in command");
 }
 }

 try {
 return ProcessImpl.start(cmdarray,
 environment,
 dir,
 redirects,
 redirectErrorStream);
 } catch (IOException | IllegalArgumentException e) {
 String exceptionInfo = ": " + e.getMessage();
 Throwable cause = e;
 if ((e instanceof IOException) && security != null) {
 // Can not disclose the fail reason for read-protected files.
 try {
 security.checkRead(prog);
 } catch (SecurityException se) {
 exceptionInfo = "";
 cause = se;
 }
 }
 // It's much easier for us to create a high-quality error
 // message than the low-level C code which found the problem.
 throw new IOException(
 "Cannot run program \"" + prog + "\""
 + (dir == null ? "" : " (in directory \"" + dir + "\")")
 + exceptionInfo,
 cause);
 }
 }
}