Java Call TracerYou can check the java call tracer tool on SourceForge

http://sourceforge.net/projects/javacalltracer

It is a very lightweight tool and you can control what you want to generate and see in the sequence diagram.

Together 2008 SP1 Although generating sequence diagrams from execution is cool, it is dependent upon the scenario under execution. Together offers the classic approach of reverse engineering the diagrams from Java source code. Together can generate a UML 2.0 sequence diagram (with frame blocks: e.g. alt, try, opt etc.) for any method specified in a class diagram, so you can get method level behavioral descriptions of your code. It does generate a sequence diagram log which you should check because this version of their code parser does have occasional trouble with expressions used in arguments which can prevent the sequence diagram from including all the detail. You can also tailor the generation detail to include depth of calls and whether you want to include invocations to java libraries in the diagram. MaintainJ generates sequence diagramsYou may want to check MaintainJ at http://maintainj.com .

Here is a brief description from the MaintainJ homepage:

MaintainJ, an Eclipse plug-in, generates runtime sequence and class diagrams for a given use case, helping the users to quickly understand a complex Java or J2EE application.

MaintainJ logs runtime method execution sequence to a file and uses that trace file to render sequence and class diagrams. MaintainJ Instrumentation Wizard instruments a Java/J2EE application and MaintainJ UML Editor renders sequence and class diagram from the trace file.

The following features make MaintainJ a unique and useful tool for Java developers.

a) Generated Diagrams - Runtime sequence and class diagrams for a given use case are generated on demand in a few minutes; no need to prepare and update UML diagrams.

b) Source Untouched - The application code is not changed in anyway; application is rebuilt using AspectJ compiler to capture the method execution sequence at runtime.

c) Collapsible Calls - Method calls in sequence diagram are collapsible. One can easily explore a complex sequence diagram by collapsing and expanding calls as necessary.

d) Focused Diagrams - Only application classes in specified packages are shown in diagrams. All repeat calls occurring in a loop and recursive calls are removed from sequence diagrams.

e) Runtime Diagrams - All classes shown in the diagrams are concrete runtime classes.

f) Eclipse Integration - Double clicking a call or class opens matching method or class in Eclipse.

g) Outline Views - Outline views in both diagrams make navigating a complex diagram easier.

h) Print or Export - Diagrams can be printed or exported as JPEG images.

jTracert can generate sequence diagrams from existing application runtimehttp://jtracert.googlecode.com

jTracert will allow you to generate sequence diagrams directly from your application runtime!

jTracert is implemented as a small javaagent, consisting from only one jar with no dependencies. In order to profile your application with jTracert, just add the following option to VM options: -javaagent:jTracert.jar

So your full command line will look like below: java -javaagent:jTracert.jar -jar yourApplicationJar.jar

Please note, that you're not limited to J2SE applications. Add this parameter to your J2EE App server options, and profile your J2EE application. It's also possible to profile applets, and almost all other types of java applications. This is a benefit of implementing jTracert in pure Java.

Note: as of 30 Mar 2010 jTracert has been replaced by jSonde (which is also free). See http://www.jsonde.com

Reverse Java (http://www.reversejava.com)Reverse Java is a dynamic reverse engineering application which generates UML Sequence diagram and view of Participating Class diagram for any Java Application at runtime.

Reverse java works with both any standalone Java application or a Web based J2EE application.