Tinyj2c

Tinyj2c transfer JAVA source to C source, build as standlone binary, and run without any class file. It's so small can be used to embedded device.

Feature

• A very very small java runtime
• Garbage collection
• Minimize memory footprint
• Exception stack trace
• Thread support
• Lambda support

Requirement

1. JDK 8+ (not only jre).
2. clang/gcc/vsc.
   win i686 download: https://github.com/digitalgust/mingw-w64/releases/download/release/i686-8.1.0-release-posix-dwarf-rt_v6-rev0.7z
   win x64 download: https://github.com/digitalgust/mingw-w64/releases/download/release/x86_64-8.1.0-release-posix-seh-rt_v6-rev0.7z

Steps

• run build script :
  /tinyj2c/posix_build.sh

Or

• git clone https://github.com/digitalgust/tinyj2c.git
• Idea open /tinyj2c/class2c , run translator.
• Clion/vs/xcode open /tinyj2c/app , compile c source and run .
• Run binary no java classes dependence.

Translated java file Example

• Java code:

package test;

public class HelloWorld {
    static String str = "Hello world!";

    void test() throws RuntimeException {
        try {
            System.out.println(str);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String args[]) {
        new HelloWorld().test();
    }
}

• converted C code:

// CLASS: test/HelloWorld extends java/lang/Object
#include "metadata.h"


// generation
// globals
//struct test_HelloWorld_static {struct java_lang_String* str_0;  };
struct test_HelloWorld_static static_var_test_HelloWorld = {NULL};


__refer arr_vmtable_test_HelloWorld_from_test_HelloWorld[] = {
    func_test_HelloWorld_test___V  //0
};
__refer arr_vmtable_test_HelloWorld_from_java_lang_Object[] = {
    func_java_lang_Object_toString___Ljava_lang_String_2,  //0
    func_java_lang_Object_wait___V,  //1
    func_java_lang_Object_finalize___V,  //2
    func_java_lang_Object_equals__Ljava_lang_Object_2_Z,  //3
    func_java_lang_Object_clone___Ljava_lang_Object_2,  //4
    func_java_lang_Object_getClass___Ljava_lang_Class_2,  //5
    func_java_lang_Object_wait__J_V,  //6
    func_java_lang_Object_notify___V,  //7
    func_java_lang_Object_notifyAll___V,  //8
    func_java_lang_Object_hashCode___I  //9
};
VMTable vmtable_test_HelloWorld[] = {
    {147, 1, arr_vmtable_test_HelloWorld_from_test_HelloWorld}, //0
    {5, 10, arr_vmtable_test_HelloWorld_from_java_lang_Object}, //1
};



// locals: 1
// stack: 1
// args: 1
void func_test_HelloWorld__init____V(JThreadRuntime *runtime, struct test_HelloWorld* p0){
    
    StackItem local[1] = {0};
    RStackItem rlocal[1] = {0};
    StackItem stack[2];
    RStackItem rstack[2];
    s32 sp = 0;
    StackFrame *__frame = method_enter(runtime, 1207, &rstack[0], &rlocal[0], &sp);
    rlocal[0].obj = p0;
    ; 
    //  line no 3 , L1842355195 , bytecode index = 0
    __frame->bytecodeIndex = 0; //first
    __frame->lineNo = 3;
    rstack[sp++].obj = rlocal[0].obj;
    // invokespecial java/lang/Object.<init>()V
    sp -= 1;  //pop para
    // it's a empty method
    method_exit(runtime);
    return;
    ; 
    __ExceptionHandler:
    switch (find_exception_handler_index(runtime)) {
        default: goto __ExceptionHandlerNotFound;
    }
    __ExceptionHandlerNotFound:
    method_exit(runtime);
    return ;
}

void bridge_test_HelloWorld__init____V(JThreadRuntime *runtime, __refer ins, ParaItem *para, ParaItem *ret) {
    func_test_HelloWorld__init____V(runtime, ins);
}

ExceptionItem arr_extable_func_test_HelloWorld_test___V[] = {
    { 0, 9, 130}
};
ExceptionTable extable_func_test_HelloWorld_test___V = {1, arr_extable_func_test_HelloWorld_test___V};

// locals: 2
// stack: 2
// args: 1
void func_test_HelloWorld_test___V(JThreadRuntime *runtime, struct test_HelloWorld* p0){
    
    StackItem local[2] = {0};
    RStackItem rlocal[2] = {0};
    StackItem stack[3];
    RStackItem rstack[3];
    s32 sp = 0;
    StackFrame *__frame = method_enter(runtime, 1208, &rstack[0], &rlocal[0], &sp);
    rlocal[0].obj = p0;
    // try catch :L389748355 L944266478 L1437243359 (0,9)->12
    L389748355:
    __frame->bytecodeIndex = 0; //try catch begin
    //  line no 8 , L389748355 , bytecode index = 0
    __frame->bytecodeIndex = 0; //first
    __frame->lineNo = 8;
    // getstatic java/lang/System out Ljava/io/PrintStream;
    rstack[sp].obj =static_var_java_lang_System.out_2;
    sp += 1;
    // getstatic test/HelloWorld str Ljava/lang/String;
    rstack[sp].obj =static_var_test_HelloWorld.str_0;
    sp += 1;
    // invokevirtual java/io/PrintStream.println(Ljava/lang/String;)V
    {
        sp -= 2;
        JObject *__ins = rstack[sp + 0].ins;
        if (!__ins) {
            rstack[sp++].obj = construct_and_throw_exception(runtime, 0, 0, 8);
            goto __ExceptionHandler;
        }
        void (*__func_p) (JThreadRuntime *,struct java_io_PrintStream*,struct java_lang_String*) = find_method(__ins->vm_table, 19, 4);
        __func_p(runtime, rstack[sp + 0].obj, rstack[sp + 1].obj);
        sp += 0;
        if (runtime->exception) {
            rstack[sp++].obj = runtime->exception;
            goto __ExceptionHandler;
        }
    }
    L944266478:
    __frame->bytecodeIndex = 9; //try catch end
    //  line no 11 , L944266478 , bytecode index = 9
    goto L1959940703;
    L1437243359:
    //  line no 9 , L1437243359 , bytecode index = 12
    rlocal[1].obj = rstack[--sp].obj;
    ; 
    //  line no 10 , L999480648 , bytecode index = 13
    rstack[sp++].obj = rlocal[1].obj;
    // invokevirtual java/lang/Exception.printStackTrace()V
    {
        sp -= 1;
        JObject *__ins = rstack[sp + 0].ins;
        if (!__ins) {
            rstack[sp++].obj = construct_and_throw_exception(runtime, 0, 13, 10);
            goto __ExceptionHandler;
        }
        void (*__func_p) (JThreadRuntime *,struct java_lang_Throwable*) = find_method(__ins->vm_table, 18, 4);
        __func_p(runtime, rstack[sp + 0].obj);
        sp += 0;
        if (runtime->exception) {
            rstack[sp++].obj = runtime->exception;
            goto __ExceptionHandler;
        }
    }
    L1959940703:
    //  line no 12 , L1959940703 , bytecode index = 17
    method_exit(runtime);
    return;
    ; 
    __ExceptionHandler:
    switch (find_exception_handler_index(runtime)) {
        case 0 : goto L1437243359;
        default: goto __ExceptionHandlerNotFound;
    }
    __ExceptionHandlerNotFound:
    method_exit(runtime);
    return ;
}

void bridge_test_HelloWorld_test___V(JThreadRuntime *runtime, __refer ins, ParaItem *para, ParaItem *ret) {
    func_test_HelloWorld_test___V(runtime, ins);
}


// locals: 1
// stack: 2
// args: 1
void func_test_HelloWorld_main___3Ljava_lang_String_2_V(JThreadRuntime *runtime, JArray * p0){
    
    StackItem local[1] = {0};
    RStackItem rlocal[1] = {0};
    StackItem stack[3];
    RStackItem rstack[3];
    s32 sp = 0;
    StackFrame *__frame = method_enter(runtime, 1209, &rstack[0], &rlocal[0], &sp);
    rlocal[0].obj = p0;
    ; 
    //  line no 15 , L1087515232 , bytecode index = 0
    __frame->bytecodeIndex = 0; //first
    __frame->lineNo = 15;
    // new test/HelloWorld
    rstack[sp++].obj = new_instance_with_classraw_index(runtime, 147);
    // dup
    stack[sp].j = stack[sp - 1].j; 
    rstack[sp].obj = rstack[sp - 1].obj; 
    ++sp;
    // invokespecial test/HelloWorld.<init>()V
    {
        sp -= 1;
        JObject *__ins = rstack[sp + 0].ins;
        if (!__ins) {
            rstack[sp++].obj = construct_and_throw_exception(runtime, 0, 0, 15);
            goto __ExceptionHandler;
        }
        func_test_HelloWorld__init____V(runtime, rstack[sp + 0].obj);
        sp += 0;
        if (runtime->exception) {
            rstack[sp++].obj = runtime->exception;
            goto __ExceptionHandler;
        }
    }
    // invokevirtual test/HelloWorld.test()V
    {
        sp -= 1;
        JObject *__ins = rstack[sp + 0].ins;
        if (!__ins) {
            rstack[sp++].obj = construct_and_throw_exception(runtime, 0, 0, 15);
            goto __ExceptionHandler;
        }
        void (*__func_p) (JThreadRuntime *,struct test_HelloWorld*) = find_method(__ins->vm_table, 147, 0);
        __func_p(runtime, rstack[sp + 0].obj);
        sp += 0;
        if (runtime->exception) {
            rstack[sp++].obj = runtime->exception;
            goto __ExceptionHandler;
        }
    }
    ; 
    //  line no 16 , L645187727 , bytecode index = 10
    method_exit(runtime);
    return;
    ; 
    __ExceptionHandler:
    switch (find_exception_handler_index(runtime)) {
        default: goto __ExceptionHandlerNotFound;
    }
    __ExceptionHandlerNotFound:
    method_exit(runtime);
    return ;
}

void bridge_test_HelloWorld_main___3Ljava_lang_String_2_V(JThreadRuntime *runtime, __refer ins, ParaItem *para, ParaItem *ret) {
    func_test_HelloWorld_main___3Ljava_lang_String_2_V(runtime, para[0].obj);
}


// locals: 0
// stack: 1
// args: 0
void func_test_HelloWorld__clinit____V(JThreadRuntime *runtime){
    
    StackItem stack[2];
    RStackItem rstack[2];
    s32 sp = 0;
    StackFrame *__frame = method_enter(runtime, 1210, &rstack[0], NULL, &sp);
    ; 
    //  line no 4 , L1892854145 , bytecode index = 0
    __frame->bytecodeIndex = 0; //first
    __frame->lineNo = 4;
    //  ldc 
    rstack[sp++].obj = construct_string_with_utfraw_index(runtime, 2092);
    // putstatic test/HelloWorld str Ljava/lang/String;
    sp -= 1;
    static_var_test_HelloWorld.str_0 = rstack[sp].obj;
    method_exit(runtime);
    return;
    __ExceptionHandler:
    switch (find_exception_handler_index(runtime)) {
        default: goto __ExceptionHandlerNotFound;
    }
    __ExceptionHandlerNotFound:
    method_exit(runtime);
    return ;
}

void bridge_test_HelloWorld__clinit____V(JThreadRuntime *runtime, __refer ins, ParaItem *para, ParaItem *ret) {
    func_test_HelloWor