How to Debug Source

Most Java IDEs support remote debugging. The IDE connects to miniJVM's debug port over TCP and starts a debugging session. miniJVM provides two options: enable debugging, and suspend on startup (wait for the IDE to attach before executing bytecode). Configure both options before initializing the VM. These options are defined in jvm.h:

struct _MiniJVM {
    ...
    s32 jdwp_enable; // 0: disable Java debug, 1: enable Java debug and disable JIT
    s32 jdwp_suspend_on_start;
    ...
};

1. Enable miniJVM debug mode. Desktop: Run mini_jvm with -Xdebug, add parameter if needed -Xjdwp:transport=dt_socket,server=y,suspend=n,address=5005, or set it in source before building. /minijvm/c/main.c: jvm->jdwp_enable = 1; iOS/Android: set it in source before building. /mobile/c/glfmapp/main.c: jvm->jdwp_enable = 1; For device debugging, check the device IP address in Settings -> Wi-Fi -> (i).

2. Run the VM with JARs, for example: mini_jvm.exe -Xdebug -bootclasspath ../lib/minijvm_rt.jar -cp ../libex/glfw_gui.jar org.mini.glfw.GlfwMain

3. Open a project in your IDE, for example: /mobile/java/ExApp IntelliJ IDEA: Run -> Edit Configurations -> + Remote; Transport: Socket; Debugger mode: Attach; host/port of your mini_jvm, for example 127.0.0.1:5005 or 192.168.0.32:5005. Eclipse: configure similarly. NetBeans: Debug -> Attach Debugger; Connector: SocketAttach; host/port of your mini_jvm, for example localhost:5005; Timeout: 10000.

4. Set breakpoints, pause the VM, and inspect variables.

Profiling

Use the built-in profiling page to monitor method execution cost in real time. The following methods also apply to all platforms, including iOS and Android devices or emulators.

1. Enable profiling in jvm.h:

   #define _JVM_DEBUG_METHOD_PROFILE 1
   

2. Rebuild miniJVM.

3. Run miniJVM, then open Settings -> Developer Options -> Enable LAN Web Server.

4. Your browser opens automatically at http://localhost:18088/.

5. On this web page:

   • You can upload plugin apps.
   • You can click VM infomation (VM Information) to open the profiling page.

Profiling Page Features

• View the top 200 methods by execution time.
• Click a method to set a call-time threshold. If a call exceeds this threshold, miniJVM saves a call snapshot.
• Open SlowCallTree to inspect saved snapshots and expand the call stack.
• Dump the current heap memory, download the dump file, and open it in VisualVM to analyze memory usage.
• View runtime VM information, including garbage collector activity; data refreshes every 5 seconds.

Projects Based on miniJVM

• Awtk-minijvm: AWTK cross-platform native UI bound to miniJVM.
• LWJGUI-Mobile: Java LWJGL UI library.
• BiBiX: Java instant messenger.
• miniJVM web demo: miniJVM web demo.

Referenced Projects and Technologies

• Oracle CLDC: CLDC API reference.
• OpenJDK: Java API reference.
• Miniz: Reads JAR files.
• Glfm: Cross-platform (Android/iOS) GUI.
• Nanovg: GUI rendering.
• Stb: GUI TrueType fonts and images.
• Glad: OpenGL/GLES header replacement.
• Glfw: Cross-platform desktop GUI.
• Dirent: Linux-style file and directory APIs on Windows VC.
• Tinycthread: Cross-platform threads.
• JRegex: Java string regex matching.
• Janino: Compiles Java source files.
• MiniAudio: Java audio playback and capture.
• Sljit: Platform-independent low-level JIT compiler.
• Mbedtls: HTTPS support via mbedtls.
• Avian: Java API reference.

Recommended Development IDEs

• C / ObjC: JetBrains CLion, Xcode, Visual Studio
• Swift: Xcode
• Java: JetBrains IntelliJ IDEA, NetBeans
• Android: Android Studio

Using miniJVM in a Project

Copy C sources from /minijvm/c into your project, and copy the built minijvm_rt.jar into your project's resource folder.

#include "jvm/jvm.h"

int main(int argc, char **argv) {
    char *bootclasspath = "../../binary/lib/minijvm_rt.jar";
    char *classpath = "../../binary/libex/minijvm_test.jar;./";
    char *main_name = "test.Foo3";

    s32 ret = 1;
    MiniJVM *jvm = jvm_create();
    if (jvm != NULL) {
        jvm->jdwp_enable = 0; // set to 1 to enable Java remote debugging
        jvm->jdwp_suspend_on_start = 0;
        jvm->max_heap_size = 25 * 1024 * 1024;

        ret = jvm_init(jvm, bootclasspath, classpath);
        if (ret) {
            printf("[ERROR] minijvm init error.\n");
        } else {
            ret = call_main(jvm, main_name, NULL);
        }
        jvm_destroy(jvm);
    }
    return ret;
}

Third-Party Libraries

Janino Java Compiler

• Project: Janino
• Janino is a very small and very fast Java compiler.
• Janino can compile source files to class files like javac, and it can also compile a Java expression, a block, a class body, one .java file, or multiple .java files in memory, then load and execute the generated bytecode directly in the same JVM. Janino is not a full Java compiler; see limitations, for example:

List<String> list = new ArrayList();
list.add("abc");
String s = (String) list.get(0); // cannot omit the (String) cast.

• Download JARs:
• janino.jar
• commons-compiler.jar

# compile /binary/res/BpDeepTest.java
mini_jvm -bootclasspath ../lib/minijvm_rt.jar -cp ../libex/janino.jar:../libex/commons-compiler.jar org.codehaus.janino.Compiler ../res/BpDeepTest.java

LuaJ

• Project: LuaJ
• miniJVM adaptation: Luaj minijvm
• LuaJ is a lightweight, fast, Java-centric Lua interpreter for JME and JSE. It includes string, table, package, math, io, os, debug, coroutine, and luajava libraries, plus JSR-223 bindings, full metatag support, weak tables, and direct Lua-to-Java bytecode compilation.
• Download JAR:
• luaj.jar

mini_jvm -bootclasspath ../lib/minijvm_rt.jar -cp ../libex/luaj.jar Sample

Screenshots

Windows mini_jvm GUI

macOS mini_jvm GUI

Linux mini_jvm GUI

Web mini_jvm GUI

Directory Structure

.
├── binary              miniJVM binaries for builds (win32/win64/mac/linux)
├── desktop
│   ├── awtk_gui        open-source AWTK GUI JNI bindings
│   └── glfw_gui        desktop OpenGL, GLFW, miniaudio, native module
├── j2c                 tools to translate miniJVM Java source to C
│   ├── app
│   └── translator
├── minijvm             core source
│   ├── c               miniJVM C source
│   └── java            miniJVM runtime library
├── mobile
│   ├── androidapp      Android launcher
│   ├── assets          app resources (fonts, JARs, images, audio, etc.)
│   ├── c               mobile native libs: OpenGLES, GLFM framework, GUI JNI, glfmapp
│   ├── iosapp          iOS launcher
│   └── java            mobile Java libs, GUI, AppManager, example app
├── doc
└── test                miniJVM test cases

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License

License: MIT

Gust, [email protected]