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ProcessBuilder.javaAPI DocJava SE 6 API18186Tue Jun 10 00:25:36 BST 2008java.lang

ProcessBuilder

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 {@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.

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 {@link 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 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 {@link Process#getInputStream()} and {@link Process#getErrorStream()} methods. If the value is set to true, the standard error is merged with the standard output. This makes it easier to correlate error messages with the corresponding output. In this case, the merged data can be read from the stream returned by {@link Process#getInputStream()}, while reading from the stream returned by {@link Process#getErrorStream()} will get an immediate end of file.

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.

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.

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:

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"));
Process p = pb.start();

To start a process with an explicit set of environment variables, first call {@link java.util.Map#clear() Map.clear()} before adding environment variables.

since
1.5

Fields Summary
private List
command
private File
directory
private Map
environment
private boolean
redirectErrorStream
Constructors Summary
public ProcessBuilder(List 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.

param
command The list containing the program and its arguments
throws
NullPointerException If the argument is null

	if (command == null)
	    throw new NullPointerException();
	this.command = command;
    
public ProcessBuilder(String 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.

param
command A string array containing the program and its arguments

	this.command = new ArrayList<String>(command.length);
	for (String arg : command)
	    this.command.add(arg);
    
Methods Summary
public java.lang.ProcessBuildercommand(java.util.List 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.

param
command The list containing the program and its arguments
return
This process builder
throws
NullPointerException If the argument is null

	if (command == null)
	    throw new NullPointerException();
	this.command = command;
	return this;
    
public java.lang.ProcessBuildercommand(java.lang.String 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.

param
command A string array containing the program and its arguments
return
This process builder

	this.command = new ArrayList<String>(command.length);
	for (String arg : command)
	    this.command.add(arg);
	return this;
    
public java.util.Listcommand()
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.

return
This process builder's program and its arguments

	return command;
    
public java.io.Filedirectory()
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 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.

return
This process builder's working directory

	return directory;
    
public java.lang.ProcessBuilderdirectory(java.io.File 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 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.

param
directory The new working directory
return
This process builder

	this.directory = directory;
	return this;
    
public java.util.Mapenvironment()
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.

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 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 {@link System#getenv System.getenv}.

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 {@link NullPointerException}. Attempting to query the presence of a key or value which is not of type {@link String} will throw a {@link ClassCastException}.

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.

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 {@link Object#equals} and {@link Object#hashCode} methods.

The returned map is typically case-sensitive on all platforms.

If a security manager exists, its {@link SecurityManager#checkPermission checkPermission} method is called with a {@link RuntimePermission}("getenv.*") permission. This may result in a {@link SecurityException} being thrown.

When passing information to a Java subprocess, system properties 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()

	SecurityManager security = System.getSecurityManager();
	if (security != null)
	    security.checkPermission(new RuntimePermission("getenv.*"));

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

	assert environment != null;

	return environment;
    
java.lang.ProcessBuilderenvironment(java.lang.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;
    
public booleanredirectErrorStream()
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 {@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 false.

return
This process builder's redirectErrorStream property

	return redirectErrorStream;
    
public java.lang.ProcessBuilderredirectErrorStream(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 {@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 false.

param
redirectErrorStream The new property value
return
This process builder

	this.redirectErrorStream = redirectErrorStream;
	return this;
    
public java.lang.Processstart()
Starts a new process using the attributes of this process builder.

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()}.

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.

If there is a security manager, its {@link SecurityManager#checkExec checkExec} method is called with the first component of this object's command array as its argument. This may result in a {@link SecurityException} 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.

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}.

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 0)
throws
SecurityException If a security manager exists and its {@link SecurityManager#checkExec checkExec} method doesn't allow creation of the subprocess
throws
IOException If an I/O error occurs
see
Runtime#exec(String[], String[], java.io.File)
see
SecurityManager#checkExec(String)

	// 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()]);
	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();

	try {
	    return ProcessImpl.start(cmdarray,
				     environment,
				     dir,
				     redirectErrorStream);
	} catch (IOException e) {
	    // 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 + "\")")
		+ ": " + e.getMessage(),
		e);
	}