ProcessBuilder (Java SE 9 & JDK 9 ) (original) (raw)

public final class ProcessBuilder
extends Object
This class is used to create operating system processes.
Each ProcessBuilder instance manages a collection of process attributes. The start() method creates a newProcess instance with those attributes. The start() method can be invoked repeatedly from the same instance to create new subprocesses with identical or related attributes.
The startPipeline method can be invoked to create a pipeline of new processes that send the output of each process directly to the next process. Each process has the attributes of its respective ProcessBuilder.
Each process builder manages these process attributes:

• a command, 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.
• an environment, which is a system-dependent mapping from_variables_ to values. The initial value is a copy of the environment of the current process (see System.getenv()).
• a working directory. The default value is the current working directory of the current process, usually the directory named by the system property user.dir.
• a source of standard input. By default, the subprocess reads input from a pipe. Java code can access this pipe via the output stream returned byProcess.getOutputStream(). However, standard input may be redirected to another source usingredirectInput. In this case, Process.getOutputStream() will return a_null output stream_, for which:
  * the write methods always throw IOException
  * the close method does nothing
• a destination for standard output and standard error. By default, the subprocess writes standard output and standard error to pipes. Java code can access these pipes via the input streams returned by Process.getOutputStream() andProcess.getErrorStream(). However, standard output and standard error may be redirected to other destinations usingredirectOutput andredirectError. In this case, Process.getInputStream() and/orProcess.getErrorStream() will return a null input stream, for which:
  * the read methods always return-1
  * the available method always returns0
  * the close method does nothing
• a redirectErrorStream property. Initially, this property is false, meaning that the standard output and error output of a subprocess are sent to two separate streams, which can be accessed using the Process.getInputStream() and Process.getErrorStream() methods.
  If the value is set to true, then:
  * 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)
  * the common destination of standard error and standard output can be redirected usingredirectOutput
  * any redirection set by theredirectError method is ignored when creating a subprocess
  * the stream returned from Process.getErrorStream() will always be a null input stream

Modifying a process builder's attributes will affect processes subsequently started by that object's start() method, but will never affect previously started processes or the Java process itself.
Most error checking is performed by the start() method. It is possible to modify the state of an object so that start() will fail. For example, setting the command attribute to an empty list will not throw an exception unless start() is invoked.
Note that this class is not synchronized. If multiple threads access a ProcessBuilder instance concurrently, and at least one of the threads modifies one of the attributes structurally, it must be synchronized externally.
Starting a new process which uses the default working directory and environment is easy:
Process p = new ProcessBuilder("myCommand", "myArg").start();
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:
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;
To start a process with an explicit set of environment variables, first call Map.clear() before adding environment variables.
Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.
Since:
1.5

• • Constructor Detail

     * #### ProcessBuilder  
     public ProcessBuilder​([List](../../java/util/List.html "interface in java.util")<[String](../../java/lang/String.html "class in java.lang")> command)  
     Constructs a process builder with the specified operating system program and arguments. This constructor does _not_ make a copy of the `command` list. Subsequent updates to the list will be reflected in the state of the process builder. It is not checked whether`command` corresponds to a valid operating system command.  
     Parameters:  
     `command` \- the list containing the program and its arguments  
     * #### ProcessBuilder  
     public ProcessBuilder​([String](../../java/lang/String.html "class in java.lang")... 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 `command` array, in the same order. It is not checked whether`command` corresponds to a valid operating system command.  
     Parameters:  
     `command` \- a string array containing the program and its arguments  

  • Method Detail

    * #### command  
    public [ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang") command​([List](../../java/util/List.html "interface in java.util")<[String](../../java/lang/String.html "class in java.lang")> command)  
    Sets this process builder's operating system program and arguments. This method does _not_ make a copy of the`command` list. Subsequent updates to the list will be reflected in the state of the process builder. It is not checked whether `command` corresponds to a valid operating system command.  
    Parameters:  
    `command` \- the list containing the program and its arguments  
    Returns:  
    this process builder  
    * #### command  
    public [ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang") command​([String](../../java/lang/String.html "class in java.lang")... command)  
    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`command` array, in the same order. It is not checked whether `command` corresponds to a valid operating system command.  
    Parameters:  
    `command` \- a string array containing the program and its arguments  
    Returns:  
    this process builder  
    * #### command  
    public [List](../../java/util/List.html "interface in java.util")<[String](../../java/lang/String.html "class in java.lang")> command​()  
    Returns this process builder's operating system program and arguments. The returned list is _not_ a copy. Subsequent updates to the list will be reflected in the state of this process builder.  
    Returns:  
    this process builder's program and its arguments  
    * #### environment  
    public [Map](../../java/util/Map.html "interface in java.util")<[String](../../java/lang/String.html "class in java.lang"),[String](../../java/lang/String.html "class in java.lang")> environment​()  
    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[System.getenv()](../../java/lang/System.html#getenv--)). Subprocesses subsequently started by this object's [start()](../../java/lang/ProcessBuilder.html#start--) method will use this map as their environment.  
    The returned object may be modified using ordinary [Map](../../java/util/Map.html "interface in java.util") operations. These modifications will be visible to subprocesses started via the [start()](../../java/lang/ProcessBuilder.html#start--) method. Two `ProcessBuilder` instances always contain independent process environments, so changes to the returned map will never be reflected in any other`ProcessBuilder` instance or the values returned by[System.getenv](../../java/lang/System.html#getenv-java.lang.String-).  
    If the system does not support environment variables, an empty map is returned.  
    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 [NullPointerException](../../java/lang/NullPointerException.html "class in java.lang"). Attempting to query the presence of a key or value which is not of type [String](../../java/lang/String.html "class in java.lang") will throw a [ClassCastException](../../java/lang/ClassCastException.html "class in java.lang").  
    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[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang") or[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang") if the modification is not permitted by the operating system.  
    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.  
    The returned map and its collection views may not obey the general contract of the [Object.equals(java.lang.Object)](../../java/lang/Object.html#equals-java.lang.Object-) and[Object.hashCode()](../../java/lang/Object.html#hashCode--) methods.  
    The returned map is typically case-sensitive on all platforms.  
    If a security manager exists, its[checkPermission](../../java/lang/SecurityManager.html#checkPermission-java.security.Permission-) method is called with a[RuntimePermission](../../java/lang/RuntimePermission.html "class in java.lang")`("getenv.*")` permission. This may result in a [SecurityException](../../java/lang/SecurityException.html "class in java.lang") being thrown.  
    When passing information to a Java subprocess,[system properties](System.html#EnvironmentVSSystemProperties) are generally preferred over environment variables.  
    Returns:  
    this process builder's environment  
    Throws:  
    `[SecurityException](../../java/lang/SecurityException.html "class in java.lang")` \- if a security manager exists and its[checkPermission](../../java/lang/SecurityManager.html#checkPermission-java.security.Permission-) method doesn't allow access to the process environment  
    See Also:  
    [Runtime.exec(String\[\],String\[\],java.io.File)](../../java/lang/Runtime.html#exec-java.lang.String:A-java.lang.String:A-java.io.File-), [System.getenv()](../../java/lang/System.html#getenv--)  
    * #### directory  
    public [File](../../java/io/File.html "class in java.io") directory​()  
    Returns this process builder's working directory. Subprocesses subsequently started by this object's [start()](../../java/lang/ProcessBuilder.html#start--) method will use this as their working directory. The returned value may be `null` \-- this means to use the working directory of the current Java process, usually the directory named by the system property `user.dir`, as the working directory of the child process.  
    Returns:  
    this process builder's working directory  
    * #### directory  
    public [ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang") directory​([File](../../java/io/File.html "class in java.io") directory)  
    Sets this process builder's working directory. Subprocesses subsequently started by this object's [start()](../../java/lang/ProcessBuilder.html#start--) method will use this as their working directory. The argument may be `null` \-- this means to use the working directory of the current Java process, usually the directory named by the system property `user.dir`, as the working directory of the child process.  
    Parameters:  
    `directory` \- the new working directory  
    Returns:  
    this process builder  
    * #### redirectInput  
    public [ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang") redirectInput​([ProcessBuilder.Redirect](../../java/lang/ProcessBuilder.Redirect.html "class in java.lang") source)  
    Sets this process builder's standard input source. Subprocesses subsequently started by this object's [start()](../../java/lang/ProcessBuilder.html#start--) method obtain their standard input from this source.  
    If the source is [Redirect.PIPE](../../java/lang/ProcessBuilder.Redirect.html#PIPE) (the initial value), then the standard input of a subprocess can be written to using the output stream returned by [Process.getOutputStream()](../../java/lang/Process.html#getOutputStream--). If the source is set to any other value, then[Process.getOutputStream()](../../java/lang/Process.html#getOutputStream--) will return a[null output stream](#redirect-input).  
    Parameters:  
    `source` \- the new standard input source  
    Returns:  
    this process builder  
    Throws:  
    `[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if the redirect does not correspond to a valid source of data, that is, has type[WRITE](../../java/lang/ProcessBuilder.Redirect.Type.html#WRITE) or[APPEND](../../java/lang/ProcessBuilder.Redirect.Type.html#APPEND)  
    Since:  
    1.7  
    * #### redirectOutput  
    public [ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang") redirectOutput​([ProcessBuilder.Redirect](../../java/lang/ProcessBuilder.Redirect.html "class in java.lang") destination)  
    Sets this process builder's standard output destination. Subprocesses subsequently started by this object's [start()](../../java/lang/ProcessBuilder.html#start--) method send their standard output to this destination.  
    If the destination is [Redirect.PIPE](../../java/lang/ProcessBuilder.Redirect.html#PIPE) (the initial value), then the standard output of a subprocess can be read using the input stream returned by [Process.getInputStream()](../../java/lang/Process.html#getInputStream--). If the destination is set to any other value, then[Process.getInputStream()](../../java/lang/Process.html#getInputStream--) will return a[null input stream](#redirect-output).  
    Parameters:  
    `destination` \- the new standard output destination  
    Returns:  
    this process builder  
    Throws:  
    `[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if the redirect does not correspond to a valid destination of data, that is, has type[READ](../../java/lang/ProcessBuilder.Redirect.Type.html#READ)  
    Since:  
    1.7  
    * #### redirectError  
    public [ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang") redirectError​([ProcessBuilder.Redirect](../../java/lang/ProcessBuilder.Redirect.html "class in java.lang") destination)  
    Sets this process builder's standard error destination. Subprocesses subsequently started by this object's [start()](../../java/lang/ProcessBuilder.html#start--) method send their standard error to this destination.  
    If the destination is [Redirect.PIPE](../../java/lang/ProcessBuilder.Redirect.html#PIPE) (the initial value), then the error output of a subprocess can be read using the input stream returned by [Process.getErrorStream()](../../java/lang/Process.html#getErrorStream--). If the destination is set to any other value, then[Process.getErrorStream()](../../java/lang/Process.html#getErrorStream--) will return a[null input stream](#redirect-output).  
    If the [redirectErrorStream](../../java/lang/ProcessBuilder.html#redirectErrorStream--) attribute has been set `true`, then the redirection set by this method has no effect.  
    Parameters:  
    `destination` \- the new standard error destination  
    Returns:  
    this process builder  
    Throws:  
    `[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- if the redirect does not correspond to a valid destination of data, that is, has type[READ](../../java/lang/ProcessBuilder.Redirect.Type.html#READ)  
    Since:  
    1.7  
    * #### redirectInput  
    public [ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang") redirectInput​([File](../../java/io/File.html "class in java.io") file)  
    Sets this process builder's standard input source to a file.  
    This is a convenience method. An invocation of the form`redirectInput(file)` behaves in exactly the same way as the invocation[redirectInput](../../java/lang/ProcessBuilder.html#redirectInput-java.lang.ProcessBuilder.Redirect-) `(Redirect.from(file))`.  
    Parameters:  
    `file` \- the new standard input source  
    Returns:  
    this process builder  
    Since:  
    1.7  
    * #### redirectOutput  
    public [ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang") redirectOutput​([File](../../java/io/File.html "class in java.io") file)  
    Sets this process builder's standard output destination to a file.  
    This is a convenience method. An invocation of the form`redirectOutput(file)` behaves in exactly the same way as the invocation[redirectOutput](../../java/lang/ProcessBuilder.html#redirectOutput-java.lang.ProcessBuilder.Redirect-) `(Redirect.to(file))`.  
    Parameters:  
    `file` \- the new standard output destination  
    Returns:  
    this process builder  
    Since:  
    1.7  
    * #### redirectError  
    public [ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang") redirectError​([File](../../java/io/File.html "class in java.io") file)  
    Sets this process builder's standard error destination to a file.  
    This is a convenience method. An invocation of the form`redirectError(file)` behaves in exactly the same way as the invocation[redirectError](../../java/lang/ProcessBuilder.html#redirectError-java.lang.ProcessBuilder.Redirect-) `(Redirect.to(file))`.  
    Parameters:  
    `file` \- the new standard error destination  
    Returns:  
    this process builder  
    Since:  
    1.7  
    * #### redirectInput  
    public [ProcessBuilder.Redirect](../../java/lang/ProcessBuilder.Redirect.html "class in java.lang") redirectInput​()  
    Returns this process builder's standard input source. Subprocesses subsequently started by this object's [start()](../../java/lang/ProcessBuilder.html#start--) method obtain their standard input from this source. The initial value is [Redirect.PIPE](../../java/lang/ProcessBuilder.Redirect.html#PIPE).  
    Returns:  
    this process builder's standard input source  
    Since:  
    1.7  
    * #### redirectOutput  
    public [ProcessBuilder.Redirect](../../java/lang/ProcessBuilder.Redirect.html "class in java.lang") redirectOutput​()  
    Returns this process builder's standard output destination. Subprocesses subsequently started by this object's [start()](../../java/lang/ProcessBuilder.html#start--) method redirect their standard output to this destination. The initial value is [Redirect.PIPE](../../java/lang/ProcessBuilder.Redirect.html#PIPE).  
    Returns:  
    this process builder's standard output destination  
    Since:  
    1.7  
    * #### redirectError  
    public [ProcessBuilder.Redirect](../../java/lang/ProcessBuilder.Redirect.html "class in java.lang") redirectError​()  
    Returns this process builder's standard error destination. Subprocesses subsequently started by this object's [start()](../../java/lang/ProcessBuilder.html#start--) method redirect their standard error to this destination. The initial value is [Redirect.PIPE](../../java/lang/ProcessBuilder.Redirect.html#PIPE).  
    Returns:  
    this process builder's standard error destination  
    Since:  
    1.7  
    * #### inheritIO  
    public [ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang") inheritIO​()  
    Sets the source and destination for subprocess standard I/O to be the same as those of the current Java process.  
    This is a convenience method. An invocation of the form  
     `  
     pb.inheritIO()  
     `  
     behaves in exactly the same way as the invocation  
     `  
     pb.redirectInput(Redirect.INHERIT)  
       .redirectOutput(Redirect.INHERIT)  
       .redirectError(Redirect.INHERIT)  
     `  
     This gives behavior equivalent to most operating system command interpreters, or the standard C library function`system()`.  
    Returns:  
    this process builder  
    Since:  
    1.7  
    * #### redirectErrorStream  
    public boolean redirectErrorStream​()  
    Tells whether this process builder merges standard error and standard output.  
    If this property is `true`, then any error output generated by subprocesses subsequently started by this object's[start()](../../java/lang/ProcessBuilder.html#start--) method will be merged with the standard output, so that both can be read using the[Process.getInputStream()](../../java/lang/Process.html#getInputStream--) method. This makes it easier to correlate error messages with the corresponding output. The initial value is `false`.  
    Returns:  
    this process builder's `redirectErrorStream` property  
    * #### redirectErrorStream  
    public [ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang") redirectErrorStream​(boolean redirectErrorStream)  
    Sets this process builder's `redirectErrorStream` property.  
    If this property is `true`, then any error output generated by subprocesses subsequently started by this object's[start()](../../java/lang/ProcessBuilder.html#start--) method will be merged with the standard output, so that both can be read using the[Process.getInputStream()](../../java/lang/Process.html#getInputStream--) method. This makes it easier to correlate error messages with the corresponding output. The initial value is `false`.  
    Parameters:  
    `redirectErrorStream` \- the new property value  
    Returns:  
    this process builder  
    * #### start  
    public [Process](../../java/lang/Process.html "class in java.lang") start​()  
                  throws [IOException](../../java/io/IOException.html "class in java.io")  
    Starts a new process using the attributes of this process builder.  
    The new process will invoke the command and arguments given by [command()](../../java/lang/ProcessBuilder.html#command--), in a working directory as given by [directory()](../../java/lang/ProcessBuilder.html#directory--), with a process environment as given by [environment()](../../java/lang/ProcessBuilder.html#environment--).  
    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.  
    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 [environment()](../../java/lang/ProcessBuilder.html#environment--).  
    If there is a security manager, its[checkExec](../../java/lang/SecurityManager.html#checkExec-java.lang.String-) method is called with the first component of this object's`command` array as its argument. This may result in a [SecurityException](../../java/lang/SecurityException.html "class in java.lang") being thrown.  
    Starting an operating system process is highly system-dependent. Among the many things that can go wrong are:  
             * The operating system program file was not found.  
             * Access to the program file was denied.  
             * The working directory does not exist.  
             * Invalid character in command argument, such as NUL.  
    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 [IOException](../../java/io/IOException.html "class in java.io").  
    If the operating system does not support the creation of processes, an [UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang") will be thrown.  
    Subsequent modifications to this process builder will not affect the returned [Process](../../java/lang/Process.html "class in java.lang").  
    Returns:  
    a new [Process](../../java/lang/Process.html "class in java.lang") object for managing the subprocess  
    Throws:  
    `[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if an element of the command list is null  
    `[IndexOutOfBoundsException](../../java/lang/IndexOutOfBoundsException.html "class in java.lang")` \- if the command is an empty list (has size `0`)  
    `[SecurityException](../../java/lang/SecurityException.html "class in java.lang")` \- if a security manager exists and  
             * its[checkExec](../../java/lang/SecurityManager.html#checkExec-java.lang.String-) method doesn't allow creation of the subprocess, or  
             * the standard input to the subprocess was[redirected from a file](../../java/lang/ProcessBuilder.html#redirectInput-java.lang.ProcessBuilder.Redirect-) and the security manager's[checkRead](../../java/lang/SecurityManager.html#checkRead-java.lang.String-) method denies read access to the file, or  
             * the standard output or standard error of the subprocess was[redirected to a file](../../java/lang/ProcessBuilder.html#redirectOutput-java.lang.ProcessBuilder.Redirect-) and the security manager's[checkWrite](../../java/lang/SecurityManager.html#checkWrite-java.lang.String-) method denies write access to the file  
    `[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- If the operating system does not support the creation of processes.  
    `[IOException](../../java/io/IOException.html "class in java.io")` \- if an I/O error occurs  
    See Also:  
    [Runtime.exec(String\[\], String\[\], java.io.File)](../../java/lang/Runtime.html#exec-java.lang.String:A-java.lang.String:A-java.io.File-)  
    * #### startPipeline  
    public static [List](../../java/util/List.html "interface in java.util")<[Process](../../java/lang/Process.html "class in java.lang")> startPipeline​([List](../../java/util/List.html "interface in java.util")<[ProcessBuilder](../../java/lang/ProcessBuilder.html "class in java.lang")> builders)  
                                       throws [IOException](../../java/io/IOException.html "class in java.io")  
    Starts a Process for each ProcessBuilder, creating a pipeline of processes linked by their standard output and standard input streams. The attributes of each ProcessBuilder are used to start the respective process except that as each process is started, its standard output is directed to the standard input of the next. The redirects for standard input of the first process and standard output of the last process are initialized using the redirect settings of the respective ProcessBuilder. All other `ProcessBuilder` redirects should be[Redirect.PIPE](../../java/lang/ProcessBuilder.Redirect.html#PIPE).  
     All input and output streams between the intermediate processes are not accessible. The [standard input](../../java/lang/Process.html#getOutputStream--) of all processes except the first process are _null output streams_ The [standard output](../../java/lang/Process.html#getInputStream--) of all processes except the last process are _null input streams_.  
     The [redirectErrorStream](../../java/lang/ProcessBuilder.html#redirectErrorStream) of each ProcessBuilder applies to the respective process. If set to `true`, the error stream is written to the same stream as standard output.  
     If starting any of the processes throws an Exception, all processes are forcibly destroyed.  
     The `startPipeline` method performs the same checks on each ProcessBuilder as does the [start()](../../java/lang/ProcessBuilder.html#start--) method. The new process will invoke the command and arguments given by [command()](../../java/lang/ProcessBuilder.html#command--), in a working directory as given by [directory()](../../java/lang/ProcessBuilder.html#directory--), with a process environment as given by [environment()](../../java/lang/ProcessBuilder.html#environment--).  
     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.  
     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 [environment()](../../java/lang/ProcessBuilder.html#environment--).  
     If there is a security manager, its[checkExec](../../java/lang/SecurityManager.html#checkExec-java.lang.String-) method is called with the first component of this object's`command` array as its argument. This may result in a [SecurityException](../../java/lang/SecurityException.html "class in java.lang") being thrown.  
     Starting an operating system process is highly system-dependent. Among the many things that can go wrong are:  
             * The operating system program file was not found.  
             * Access to the program file was denied.  
             * The working directory does not exist.  
             * Invalid character in command argument, such as NUL.  
     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 [IOException](../../java/io/IOException.html "class in java.io").  
     If the operating system does not support the creation of processes, an [UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang") will be thrown.  
     Subsequent modifications to this process builder will not affect the returned [Process](../../java/lang/Process.html "class in java.lang").  
    API Note:  
    For example to count the unique imports for all the files in a file hierarchy on a Unix compatible platform:  
    ```  
     String directory = "/home/duke/src";  
     ProcessBuilder[] builders = {  
                  new ProcessBuilder("find", directory, "-type", "f"),  
                        new ProcessBuilder("xargs", "grep", "-h", "^import "),  
                        new ProcessBuilder("awk", "{print $2;}"),  
                        new ProcessBuilder("sort", "-u")};  
     List<Process> processes = ProcessBuilder.startPipeline(  
             Arrays.asList(builders));  
     Process last = processes.get(processes.size()-1);  
     try (InputStream is = last.getInputStream();  
             Reader isr = new InputStreamReader(is);  
             BufferedReader r = new BufferedReader(isr)) {  
         long count = r.lines().count();  
     }  
           
    ```  
    Parameters:  
    `builders` \- a List of ProcessBuilders  
    Returns:  
    a `List<Process>`es started from the corresponding ProcessBuilder  
    Throws:  
    `[IllegalArgumentException](../../java/lang/IllegalArgumentException.html "class in java.lang")` \- any of the redirects except the standard input of the first builder and the standard output of the last builder are not [ProcessBuilder.Redirect.PIPE](../../java/lang/ProcessBuilder.Redirect.html#PIPE).  
    `[NullPointerException](../../java/lang/NullPointerException.html "class in java.lang")` \- if an element of the command list is null or if an element of the ProcessBuilder list is null or the builders argument is null  
    `[IndexOutOfBoundsException](../../java/lang/IndexOutOfBoundsException.html "class in java.lang")` \- if the command is an empty list (has size `0`)  
    `[SecurityException](../../java/lang/SecurityException.html "class in java.lang")` \- if a security manager exists and  
             * its[checkExec](../../java/lang/SecurityManager.html#checkExec-java.lang.String-) method doesn't allow creation of the subprocess, or  
             * the standard input to the subprocess was[redirected from a file](../../java/lang/ProcessBuilder.html#redirectInput-java.lang.ProcessBuilder.Redirect-) and the security manager's[checkRead](../../java/lang/SecurityManager.html#checkRead-java.lang.String-) method denies read access to the file, or  
             * the standard output or standard error of the subprocess was[redirected to a file](../../java/lang/ProcessBuilder.html#redirectOutput-java.lang.ProcessBuilder.Redirect-) and the security manager's[checkWrite](../../java/lang/SecurityManager.html#checkWrite-java.lang.String-) method denies write access to the file  
    `[UnsupportedOperationException](../../java/lang/UnsupportedOperationException.html "class in java.lang")` \- If the operating system does not support the creation of processes  
    `[IOException](../../java/io/IOException.html "class in java.io")` \- if an I/O error occurs  
    Since:  
    9