Exec component

Available in Camel 2.3

The exec component can be used to execute system commands.

Dependencies

Maven users need to add the following dependency to their pom.xml

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-exec</artifactId>
  <version>${camel-version}</version>
</dependency>

where ${camel-version} must be replaced by the actual version of Camel (2.3.0 or higher).

URI format

exec://executable[?options]

where executable is the name, or file path, of the system command that will be executed. If executable name is used (e.g. exec:java), the executable must in the system path.

URI options

Name

Default value

Description

args

null

The arguments of the executable. The arguments may be one or many
whitespace-separated tokens, that can be quoted with " - e.g. args="arg 1" arg2 will use two arguments arg 1 and arg2. To include the quotes use "" - e.g. args=""arg 1"" arg2 will use the arguments "arg 1" and arg2.

workingDir

null

The directory in which the command should be executed. If null, the working directory of the current process will be used.

timeout

Long.MAX_VALUE

The timeout, in milliseconds, after which the executable should be terminated. If execution has not completed within the timeout, the component will send a termination request.

outFile

null

The name of a file, created by the executable, that should be considered as its output. If no outFile is set, the standard output (stdout) of the executable will be used instead.

binding

a DefaultExecBinding instance

A reference to a org.apache.commons.exec.ExecBinding in the Registry.

commandExecutor

a DefaultCommandExecutor instance

A reference to a org.apache.commons.exec.ExecCommandExecutor in the Registry that customizes the command execution. The default command executor utilizes the commons-exec library, which adds a shutdown hook for every executed command.

useStderrOnEmptyStdout

false

A boolean indicating that when stdout is empty, this component will populate the Camel Message Body with stderr. This behavior is disabled (false) by default.

Message headers

The supported headers are defined in org.apache.camel.component.exec.ExecBinding.

Name

Type

Message

Description

ExecBinding.EXEC_COMMAND_EXECUTABLE

String

in

The name of the system command that will be executed. Overrides executable in the URI.

ExecBinding.EXEC_COMMAND_ARGS

java.util.List<String>

in

Command-line arguments to pass to the executed process. The arguments are used literally - no quoting is applied. Overrides any existing args in the URI.

ExecBinding.EXEC_COMMAND_ARGS

String

in

Camel 2.5: The arguments of the executable as a Single string where each argument is whitespace separated (see args in URI option). The arguments are used literally, no quoting is applied. Overrides any existing args in the URI.

ExecBinding.EXEC_COMMAND_OUT_FILE

String

in

The name of a file, created by the executable, that should be considered as its output. Overrides any existing outFile in the URI.

ExecBinding.EXEC_COMMAND_TIMEOUT

long

in

The timeout, in milliseconds, after which the executable should be terminated. Overrides any existing timeout in the URI.

ExecBinding.EXEC_COMMAND_WORKING_DIR

String

in

The directory in which the command should be executed. Overrides any existing workingDir in the URI.

ExecBinding.EXEC_EXIT_VALUE

int

out

The value of this header is the exit value of the executable. Non-zero exit values typically indicate abnormal termination. Note that the exit value is OS-dependent.

ExecBinding.EXEC_STDERR

java.io.InputStream

out

The value of this header points to the standard error stream (stderr) of the executable. If no stderr is written, the value is null.

ExecBinding.EXEC_USE_STDERR_ON_EMPTY_STDOUT

boolean

in

Indicates that when stdout is empty, this component will populate the Camel Message Body with stderr. This behavior is disabled (false) by default.

Message body

If the Exec component receives an in message body that is convertible to java.io.InputStream, it is used to feed input to the executable via its stdin. After execution, the message body is the result of the execution,- that is, an org.apache.camel.components.exec.ExecResult instance containing the stdout, stderr, exit value, and out file. This component supports the following ExecResult type converters for convenience:

From

To

ExecResult

java.io.InputStream

ExecResult

String

ExecResult

byte []

ExecResult

org.w3c.dom.Document

If an out file is specified (in the endpoint via outFile or the message headers via ExecBinding.EXEC_COMMAND_OUT_FILE), converters will return the content of the out file. If no out file is used, then this component will convert the stdout of the process to the target type. For more details, please refer to the usage examples below.

Usage examples

Executing word count (Linux)

The example below executes wc (word count, Linux) to count the words in file /usr/share/dict/words. The word count (output) is written to the standard output stream of wc.

from("direct:exec")
.to("exec:wc?args=--words /usr/share/dict/words")
.process(new Processor() {
     public void process(Exchange exchange) throws Exception {
       // By default, the body is ExecResult instance
       assertIsInstanceOf(ExecResult.class, exchange.getIn().getBody());
       // Use the Camel Exec String type converter to convert the ExecResult to String
       // In this case, the stdout is considered as output
       String wordCountOutput = exchange.getIn().getBody(String.class);
       // do something with the word count
     }
});

Executing java

The example below executes java with 2 arguments: -server and -version, provided that java is in the system path. 

from("direct:exec")
.to("exec:java?args=-server -version")

The example below executes java in c:\temp with 3 arguments: -server, -version and the sytem property user.name.

from("direct:exec")
.to("exec:c:/program files/jdk/bin/java?args=-server -version -Duser.name=Camel&workingDir=c:/temp")

Executing Ant scripts

The following example executes Apache Ant (Windows only) with the build file CamelExecBuildFile.xml, provided that ant.bat is in the system path, and that CamelExecBuildFile.xml is in the current directory.

from("direct:exec")
.to("exec:ant.bat?args=-f CamelExecBuildFile.xml")

In the next example, the ant.bat command redirects its output to CamelExecOutFile.txt with -l. The file CamelExecOutFile.txt is used as the out file with outFile=CamelExecOutFile.txt. The example assumes that ant.bat is in the system path, and that CamelExecBuildFile.xml is in the current directory.

from("direct:exec")
.to("exec:ant.bat?args=-f CamelExecBuildFile.xml -l CamelExecOutFile.txt&outFile=CamelExecOutFile.txt")
.process(new Processor() {
     public void process(Exchange exchange) throws Exception {
        InputStream outFile = exchange.getIn().getBody(InputStream.class);
        assertIsInstanceOf(InputStream.class, outFile);
        // do something with the out file here
     }
  });

Executing echo (Windows)

Commands such as echo and dir can be executed only with the command interpreter of the operating system. This example shows how to execute such a command - echo - in Windows.

from("direct:exec").to("exec:cmd?args=/C echo echoString")

See Also

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2 Comments

  1. Mitko Kolev

    Hi, I found some minor issues in the documentation:

    • The first sentence should be:

      The exec component can be used to execute system commands.

    • Section URI options: In the description of useStderrOnEmptyStdout, stdout should be used instead of stdin.
    • Section Message headers
      • In the description of ExecBinding.EXEC_USE_STDERR_ON_EMPTY_STDOUT stdout should be used instead of stdin
      • In the table it should be placed before the out message headers to avoid confusion.
      • Additionally

        Overrides existing useStderrOnEmptyStdout in the URI.

        should be added in the description.

    What about such text for both useStderrOnEmptyStdout and ExecBinding.EXEC_USE_STDERR_ON_EMPTY_STDOUT:

    • useStderrOnEmptyStdout:

      Uses stderr in the message body, when the stdout is empty. The default value is false.

    • ExecBinding.EXEC_USE_STDERR_ON_EMPTY_STDOUT:

      Uses stderr in the message body, when the stdout is empty. Overrides existing useStderrOnEmptyStdout in the URI.

    Regards,
    Mitko

    1. Reuben Garrett

      thanks for the feedback! i'm scrubbing the documentation for minor issues and i believe i've addressed most of those you identified.