How to step into tomcat source?

Question

I want to learn the internals of tomcat operation and understand the flow.

For this I created a servlet -

public class TestServlet extends HttpServlet {
    //Breakpoint set on constructor
    public TestServlet() {
    }
}

I included the tomcat source code in source lookup directories and launched the server in debug mode. Following is the stack trace when debugger stops at my breakpoint -

Daemon Thread [localhost-startStop-1] (Suspended (entry into method <init> in TestServlet)) 
    owns: StandardWrapper  (id=39)  
    owns: StandardContext  (id=40)  
    TestServlet.<init>() line: 12   
    NativeConstructorAccessorImpl.newInstance0(Constructor, Object[]) line: not available [native method]   
    NativeConstructorAccessorImpl.newInstance(Object[]) line: 39    
    DelegatingConstructorAccessorImpl.newInstance(Object[]) line: 27    
    Constructor<T>.newInstance(Object...) line: 513 
    Class<T>.newInstance0() line: 355   
    Class<T>.newInstance() line: 308    
    DefaultInstanceManager.newInstance(String) line: 138    
    StandardWrapper.loadServlet() line: 1144    
    StandardWrapper.load() line: 1088   
    StandardContext.loadOnStartup(Container[]) line: 5123   
    StandardContext.startInternal() line: 5407  
    StandardContext(LifecycleBase).start() line: 150    
    ContainerBase$StartChild.call() line: 1559  
    ContainerBase$StartChild.call() line: 1549  
    FutureTask$Sync.innerRun() line: 303    
    FutureTask<V>.run() line: 138   
    ThreadPoolExecutor$Worker.runTask(Runnable) line: 886   
    ThreadPoolExecutor$Worker.run() line: 908   
    Thread.run() line: 662

As you can see tomcat initiates a new daemon thread to handle initialization of TestServlet. If I step out from this position it would backtrace upto run and then stop. However I want to understand main server logic. What should I do to step into the org.apache.catalina.startup.Bootstrap class? (or some other class that is run on main startup thread)

Answer 1

You can debug Tomcat as a remote Java application.

Here is the steps:

1. Create a Java project and copy Tomcat source files into project's source folder. (You can ignore compile errors.)
2. Open Bootstrap.java and set a breakpoint at main method.

3. Create a CATALINA_BASE/bin/setenv.bat(or .sh) file and put following line into the file.

   set JPDA_OPTS=-agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=y

4. Start the Tomcat in debug mode using catalina.bat (or .sh) from command line.

   catalina.bat jpda start

5. From Eclipse, set up a Debug Configuration under Remote Java Application and connect to the Tomcat process. (Run -> Debug Configurations -> Remote Java Application.)

Screenshot:

Answer 2

Don't go for any of the confusing solutions. Found this after lot of research.

• Simply setup your tomcat using eclipse.
• Later download tomcat source file and execute ant command.
• Nw go to your JavaEE setup => select new project => ava Project from Existing Ant Buildfile => point to tomcat source code and select build.xml
• Set your break-point accordingly, in my case, bootstrap.java's main() method.
• Go to your serverand selectdebug`
• This should open the class where you have set your breakPoint. If there is warning named Source not Found, click add source => java project => select the source project

There you go.