JDB - Java Debugger
JDB (Java Debugger) is a command-line tool provided with the Java Development Kit (JDK) that allows developers to debug Java applications. On z/OS, it is primarily used within the z/OS UNIX System Services (USS) environment to diagnose and troubleshoot Java programs, offering capabilities to set breakpoints, step through code, and inspect variables.
Key Characteristics
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- Command-Line Interface: JDB operates entirely from the z/OS UNIX command line, requiring users to issue text commands for all debugging operations, making it suitable for headless server environments.
- JDK Component: It is an integral part of the IBM Semeru Runtime Certified Edition for z/OS (or other JDK distributions), making it readily available wherever Java is installed on the mainframe.
- Standard Debugging Features: Supports essential debugging functionalities such as setting and clearing breakpoints, stepping into/over/out of methods, examining local variables and object fields, and inspecting the call stack.
- JVM Interaction: JDB communicates with a target Java Virtual Machine (JVM) using the Java Platform Debugger Architecture (JPDA), either by launching the JVM in debug mode or attaching to an already running JVM.
- Remote Debugging Capable: While JDB itself runs locally within a USS session, it can connect to a JVM running on the same or a different z/OS LPAR, provided the target JVM is started with appropriate debug options for remote attachment.
Use Cases
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- Debugging USS Java Applications: Troubleshooting Java programs that execute directly within the z/OS UNIX System Services environment, such as utilities, shell scripts, or batch jobs invoked via the
javacommand orBPXBATCH. - Diagnosing Java Components of Middleware: Debugging specific Java code paths within z/OS-based middleware like WebSphere Liberty Profile, Apache Tomcat on z/OS, or custom Java servlets/applications deployed in these environments when a GUI debugger is not feasible.
- Headless Server Debugging: Providing a lightweight option for debugging Java applications running on z/OS servers where a graphical user interface is not available or practical.
- Pre-production Environment Debugging: Performing quick diagnostics in test or pre-production z/OS environments where installing or configuring a full GUI debugger might be overly complex or restricted.
- Debugging USS Java Applications: Troubleshooting Java programs that execute directly within the z/OS UNIX System Services environment, such as utilities, shell scripts, or batch jobs invoked via the
Related Concepts
JDB is fundamentally tied to Java on z/OS and the z/OS UNIX System Services (USS) environment, as it operates within this POSIX-compliant layer. It interacts directly with the JVM (Java Virtual Machine), which executes the Java bytecode. While it provides basic debugging, it is often complemented or replaced by more sophisticated GUI debuggers like the IBM Debug Tool for z/OS (which supports Java, COBOL, PL/I, C/C++) or Eclipse-based debuggers (e.g., from an IDE running