How to Debug Bytecode with Bytecode Visualizer

Have you seen this warning dialog?

Debug functionality is unavailable in this context.

Prerequisites

The debug-related functionality such as setting breakpoints and displaying classes from the stack in the debug view is available for classes which are both:

(i) included in the build path of a java project

and

(ii) opened using Package Explorer, Open Declaration (F3) or similar feature of Java Development Tools (JDT) plugin.

(ii) is normally impossible without (i).

How to Include Classes into Build Path

To achieve (i) the steps are different for the following 3 situations:

(a) Your .class files are in a JAR archive.
In Project Explorer, go to

bytecode-debug-project > context menu > Properties > Java Build Path > Libraries (Tab) > Add JARs... (Button)

and add your JAR (which is preferably located in the workspace)
(b) Your .class files are in a build output folder (usually called 'bin') of some Java project (call it 'project-1') in your Eclipse workspace.
You need to use project distinct from project-1 to debug the classes from project-1's build output folder. Create a new Java project, name it e.g. 'bytecode-debug-project' and copy recursively project-1/bin to bytecode-debug-project/classes. Proceed with (c/2)
(c) Your .class files are somewhere in your filesystem and (b) is not the case.
(1) Create a new Java project, name it e.g. 'bytecode-debug-project' and copy your .class files (together with their package folders) to bytecode-debug-project/classes.
(2) In Project Explorer, go to

bytecode-debug-project > context menu > Properties > Java Build Path > Libraries (Tab) > Add Class Folder (Button)

and add the bytecode-debug-project/classes folder.

After you have included your classes in build path of a Java project, they are visible in Package Explorer under bytecode-debug-project/Referenced Libraries/ If you open some of your classes now, you can set breakpoints and when you start a debug session, you see your bytecode upon suspend.

Setting Breakpoints

The following breakpoint types are supported in Bytecode Visualizer:

  • Class Load breakpoint
  • Field Watchpoint
  • Method Entry breakpoint

Breakpoints can be set by double clicking on the left ruler or through the context menu of the left ruler.

Adjust Preferences

You may want to adjust some preferences before you start your first debug session. Just go to

Window > Preferences > Dr. Garbage > Bytecode Visualizer > General

If you are debugging classes which are modified at runtime, you may consider activating the JDI class retrieval option; see also Visualizing Classes as they Appear in a Running JVM.

If Java bytecode is the only thing you want to see during your debug session, you probably want check the appropriate preference on

Window > Preferences > Dr. Garbage > Bytecode Visualizer > Source Code

Start Debug Session

Start debug session in the same way as you would start a debug session for debugging source code.

Bytecode Debugger will suspend when a breakpoint is reached and bytecode will be displayed in Bytecode Tab of Bytecode Viewer.

Use bytecode stepping buttons to step through bytecode instructions:

Step Into Bytecode Step Into Bytecode
Step Over Single Instruction Step Over Single Instruction