Java Doc for ProcessBuilder.java in  » 6.0-JDK-Core » lang » java » lang » Java Source Code / Java DocumentationJava Source Code and Java Documentation

Each ProcessBuilder instance manages a collection of process attributes. The ProcessBuilder.start() method creates a new Process instance with those attributes. The ProcessBuilder.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 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 Process.getInputStream and 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 Process.getInputStream , while reading from the stream returned by Process.getErrorStream will get an immediate end of file.

Modifying a process builder's attributes will affect processes subsequently started by that object's ProcessBuilder.start() method, but will never affect previously started processes or the Java process itself.

Most error checking is performed by the ProcessBuilder.start() method. It is possible to modify the state of an object so that ProcessBuilder.start() will fail. For example, setting the command attribute to an empty list will not throw an exception unless ProcessBuilder.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 java.util.Map.clear Map.clear() before adding environment variables.
since:
   1.5

If this property is true, then any error output generated by subprocesses subsequently started by this object's ProcessBuilder.start() method will be merged with the standard output, so that both can be read using the Process.getInputStream method.

If this property is true, then any error output generated by subprocesses subsequently started by this object's ProcessBuilder.start() method will be merged with the standard output, so that both can be read using the Process.getInputStream method.

The new process will invoke the command and arguments given by ProcessBuilder.command() , in a working directory as given by ProcessBuilder.directory() , with a process environment as given by ProcessBuilder.environment() .

This method checks that the command is a valid operating system command.

The returned object may be modified using ordinary java.util.Map Map operations. These modifications will be visible to subprocesses started via the ProcessBuilder.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 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 NullPointerException . Attempting to query the presence of a key or value which is not of type String will throw a 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 UnsupportedOperationException or 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 Object.equals and Object.hashCode methods.

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

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

When passing information to a Java subprocess, system properties are generally preferred over environment variables.

If this property is true, then any error output generated by subprocesses subsequently started by this object's ProcessBuilder.start() method will be merged with the standard output, so that both can be read using the Process.getInputStream method. This makes it easier to correlate error messages with the corresponding output. The initial value is false.

If this property is true, then any error output generated by subprocesses subsequently started by this object's ProcessBuilder.start() method will be merged with the standard output, so that both can be read using the Process.getInputStream method. This makes it easier to correlate error messages with the corresponding output. The initial value is false.

The new process will invoke the command and arguments given by ProcessBuilder.command() , in a working directory as given by ProcessBuilder.directory() , with a process environment as given by ProcessBuilder.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 SecurityManager.checkExec checkExec method is called with the first component of this object's command array as its argument. This may result in a 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 IOException .

Subsequent modifications to this process builder will not affect the returned Process .