Chapter 40. Exec

Exec component

Available in Apache 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 Apache 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 has not finished 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 considered as output.
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. It 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 the executable in the URI.
ExecBinding.EXEC_COMMAND_ARGS java.util.List<String> in The arguments of the executable. The arguments are used literally, no quoting is applied. Overrides 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 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 output of the executable. Overrides 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

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 in the standart 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")