Expect-for-Java

Pure Java implementation of the Expect tool

Introduction

Expect for Java is a pure Java implementation of the Unix Expect tool.
The target is robust, easy-to-maintain code, with only one class file.
In order to use this tool, you need to know Java regular expressions and have some basic ideas about the original Expect tool.

Dependencies

Expect.java:
log4j-1.2.X.jar

TestExpect.java:
junit-4.X.jar

How to Use

The JavaDoc explains how to use the class. You may find the following useful:
http://search.cpan.org/~rgiersig/Expect-1.15/Expect.pod
http://oreilly.com/catalog/expect/chapter/ch03.html

Note Expect does not provide a "forever" timeout, you may use a very large integer for that purpose, eg. 99999 or Integer.MAX_VALUE.

Expect can expect for a list of patterns/strings at one time. However there is no callback, because in Java the code does not look neat (refer to expect4j examples)

The expect() method can handle a mixture of regular expression Pattern and literal String: in fact it accepts arbitrary number of Object, then uses Pattern as regex and uses String as literal string.

Expect does NOT expect on more than one connection at a time (which IS a feature for Unix Expect/Perl Expect)

Those methods that end with "OrThrow" will throw checked exceptions when something goes wrong, for example timeout or lost connection(EOF), or IOException caused by alien invasion. This helps handling unexpected results.

Examples

Example that connects to an SSH server and send "ls" command. (assuming your prompt is $)

try {
	JSch jsch = new JSch();
	Session session = jsch.getSession(USER, HOST);
	session.setPassword(PASSWD);
	session.setConfig("StrictHostKeyChecking", "no");
	session.connect(60 * 1000);
	Channel channel = session.openChannel("shell");
	Expect expect = new Expect(channel.getInputStream(),
			channel.getOutputStream());
	channel.connect();
	expect.expect("$");
	System.out.println(expect.before + expect.match);
	expect.send("ls\n");
	expect.expect("$");
	System.out.println(expect.before + expect.match);
	expect.send("exit\n");
	expect.expectEOF();
	System.out.println(expect.before);
	expect.close();
	session.disconnect();
} catch (JSchException e) {
	e.printStackTrace();
} catch (IOException e) {
	e.printStackTrace();
}

You can substitute expect.expect("$"); with expect.expectOrThrow("$");, and add catch clauses in the end.

It is possible the prompt is either $, or # with/without a space:

	expect.expect("$", Pattern.compile("#\\s?"));

Related Work

Through Google, I found two Java-based Expect library: ExpectJ and Expect4j. Both of them are well-maintained and have quite a few users, and I learned a lot by looking at the source code. However, both libraries are very complex with a lot of multi-threading, making them hard to customize. Some functions from other expect packages are also missing.

ExpectJ
There is no regular expression matching, only plain text.

Expect4j
Expect4j is basically a "ported" version for the original Expect.
Cannot specify timeout at each expect call.
Uses glob regex or perl regex, not native Java regex.
In the source code there are too many unused classes.

Notes

Some advice if you want to implement Expect: avoid multi-threading as much as possible, you will find it not worth the efforts for such a program, where performance is not as important.

License

The use and distribution terms for this software are covered by the Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php). By using this software in any fashion, you are agreeing to be bound by the terms of this license. You must not remove this notice, or any other, from this software.