A tool for Java developers who are curious about what really goes on inside the JRE (Java Runtime Environment). It provides a user-friendly view of such runtime activity such as system properties and thread activity. [Freeware]

Allows remote debugging inside a number servlet-engine. Zero installation. JSP linemapping. [Freeware]

Analyzes program execution and generates a trace and a visualizer. Supports JDK 1.1 and higher. For debugging, understanding, diagnosing. [Non-timeout eval copy]

A grafical user interface for the java.util.logging package. [Shareware]

By debugtools.com is Java debugger, built on top of the standard JPDA (Java Platform Debugger Architecture). It features an intuitive and graphical Java Swing GUI. [Shareware]

A Java monitoring platform. It attaches to Java application, using its own lightweight web server to let view log messages, threads, properties, and runtime statistics. It comes with its own logging API, plus it supports the log4j API and the Java Logging API. [Commercial]

A debugging tool similar to the Inspector in Smalltalk environments. [Freeware]

Graphical Java debugger. Requires Java 1.2 or higher. [Open Source, GPL]

Recursively dumps all fields of an object, using reflection. [Freeware, source included]

An experimental debugging tool written in Java which allows "rewinding" and seeing what the values of variables were in the past. Works by modifying bytecode. [Freeware]

Visual debugger with recall of operation history. [Commercial]

Assists in developing and debugging of Java GUI applications and applets. It shows a list of GUI components, allows viewing fields, execute methods, trace events, function calls and field accesses at run time. [Commercial]