Apache Camel: Stream

Stream Component

The stream: component provides access to the System.in, System.out and System.err streams as well as allowing streaming of file and URL.

URI format

stream:in[?options]
stream:out[?options]
stream:err[?options]
stream:header[?options]

In addition, the file and url endpoint URIs are supported in Camel 2.0:

stream:file?fileName=/foo/bar.txt
stream:url[?options]

If the stream:header URI is specified, the stream header is used to find the stream to write to. This option is available only for stream producers (that is, it cannot appear in from()).

You can append query options to the URI in the following format, ?option=value&option=value&...

Options

Name	Default Value	Description
`delay`	`0`	Initial delay in milliseconds before consuming or producing the stream.
`encoding`	JVM Default	As of 1.4, you can configure the encoding (is a charset name) to use text-based streams (for example, message body is a `String` object). If not provided, Camel uses the JVM default Charset.
`promptMessage`	`null`	Camel 2.0: Message prompt to use when reading from `stream:in`; for example, you could set this to `Enter a command:`
`promptMessageDelay`	`0`	Camel 2.0: Optional delay in milliseconds before showing the message prompt. Can be used during system startup to avoid message prompts being written while other logging is done to the system out.
`promptDelay`	`0`	Camel 2.0: Optional delay in milliseconds before showing the message prompt.
`promptInitialDelay`	`2000`	Camel 2.0: Initial delay in milliseconds before showing the message prompt. This delay occurs only once. Can be used during system startup to avoid message prompts being written while other logging is done to the system out.
`fileName`	`null`	Camel 2.0: When using the `stream:file` URI format, this option specifies the filename to stream to/from.
`scanStream`	`false`	Camel 2.0: To be used for continuously reading a stream such as the unit `tail` command.
`scanStreamDelay`	`0`	Camel 2.0: Delay in milliseconds between read attempts when using `scanStream`.

Message content

The stream: component supports either String or byte[] for writing to streams. Just add either String or byte[] content to the message.in.body.
The special stream:header URI is used for custom output streams. Just add a java.io.OutputStream object to message.in.header in the key header.
See samples for an example.

Samples

In the following sample we route messages from the direct:in endpoint to the System.out stream:

@Test
public void testStringContent() throws Exception {
    template.sendBody("direct:in", "Hello Text World\n");
}

@Test
public void testBinaryContent() {
    template.sendBody("direct:in", "Hello Bytes World\n".getBytes());
}

protected RouteBuilder createRouteBuilder() {
    return new RouteBuilder() {
        public void configure() {
            from("direct:in").to("stream:out");
        }
    };
}

The following sample demonstrates how the header type can be used to determine which stream to use. In the sample we use our own output stream, MyOutputStream.

private OutputStream mystream = new MyOutputStream();
private StringBuffer sb = new StringBuffer();

@Test
public void testStringContent() {
    template.sendBody("direct:in", "Hello");
    // StreamProducer appends \n in text mode
    assertEquals("Hello\n", sb.toString());
}

@Test
public void testBinaryContent() {
    template.sendBody("direct:in", "Hello".getBytes());
    // StreamProducer is in binary mode so no \n is appended
    assertEquals("Hello", sb.toString());
}

protected RouteBuilder createRouteBuilder() {
    return new RouteBuilder() {
        public void configure() {
            from("direct:in").setHeader("stream", constant(mystream)).
                to("stream:header");
        }
    };
}

private class MyOutputStream extends OutputStream {

    public void write(int b) throws IOException {
        sb.append((char)b);
    }
}

The following sample demonstrates how to continuously read a file stream (analogous to the UNIX tail command):

from("stream:file?fileName=/server/logs/server.log?scanStream=true&scanStreamDelay=1000").to("bean:logService?method=parseLogLine");

Stream Component

URI format

Options

Message content

Samples

See Also

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