How to enter tomcat source?

Question

I want to learn tomcat internal operations 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 the search source directories and started the server in debug mode. Below is the stack trace when the 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 TestServlet initialization. If I exit this position, it will return to its original position, and then stop. However, I want to understand the basic logic of the server. What needs to be done to go to the org.apache.catalina.startup.Bootstrap class? (or some other class that runs in the main launch thread)

Answer 1

You can debug Tomcat as a remote Java application.

Here are the steps:

• Create a Java project and copy the Tomcat source files to the project source folder. (You can ignore compilation errors.)
• Open Bootstrap.java and set a breakpoint with the main method.

• Create the file CATALINA_BASE / bin / setenv.bat (or .sh) and put the following line in the file.

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

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

  catalina.bat jpda start

• In Eclipse, configure the debugging configuration under the remote Java application and connect to the Tomcat process. (Run → Debug Configurations → Remote Java Application.)

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