如何在运行时发出和执行Java字节码？

I am writing an interpreter in Java for a domain-specific language with some scripting capabilities. I have already implemented a parser and now need to do a back end. To this end I am considering either to write my own interpreter (either working with abstract syntax trees or with some custom bytecodes) or target JVM (emit and execute Java bytecode at runtime).

我正在用Java编写一个解释器,用于具有某些脚本功能的特定于域的语言。我已经实现了一个解析器,现在需要做一个后端。为此,我正在考虑编写自己的解释器(使用抽象语法树或使用一些自定义字节码)或目标JVM(在运行时发出并执行Java字节码)。

Could someone with more experience in this area say how feasible is the approach of targeting JVM and what libraries would you recommend to use for emitting Java bytecode?

在这方面有更多经验的人是否可以说针对JVM的方法有多可行?您建议使用哪些库来发布Java字节码?

4 个解决方案

#1

Here is a working "hello world" made with ObjectWeb ASM (a library which I recommend):

这是一个使用ObjectWeb ASM(我推荐的库)制作的“hello world”:

package hello;

import java.lang.reflect.Method;

import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.Label;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

public class HelloWorldASM implements Opcodes {
    public static byte[] compile(String name) {
        ClassWriter cw = new ClassWriter(0);
        MethodVisitor mv;

        cw.visit(V1_6, ACC_PUBLIC + ACC_SUPER, "hello/HelloWorld", null,
                "java/lang/Object", null);

        cw.visitSource("HelloWorld.java", null);

        {
            mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
            mv.visitCode();
            Label l0 = new Label();
            mv.visitLabel(l0);
            mv.visitLineNumber(4, l0);
            mv.visitVarInsn(ALOAD, 0);
            mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>",
                    "()V");
            mv.visitInsn(RETURN);
            Label l1 = new Label();
            mv.visitLabel(l1);
            mv.visitLocalVariable("this", "Lhello/HelloWorld;", null, l0, l1,
                    0);
            mv.visitMaxs(1, 1);
            mv.visitEnd();
        }
        {
            mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC, "main",
                    "([Ljava/lang/String;)V", null, null);
            mv.visitCode();
            Label l0 = new Label();
            mv.visitLabel(l0);
            mv.visitLineNumber(7, l0);
            mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out",
                    "Ljava/io/PrintStream;");
            mv.visitLdcInsn(String.format("Hello, %s!", name));
            mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println",
                    "(Ljava/lang/String;)V");
            Label l1 = new Label();
            mv.visitLabel(l1);
            mv.visitLineNumber(8, l1);
            mv.visitInsn(RETURN);
            Label l2 = new Label();
            mv.visitLabel(l2);
            mv.visitLocalVariable("args", "[Ljava/lang/String;", null, l0, l2,
                    0);
            mv.visitMaxs(2, 1);
            mv.visitEnd();
        }
        cw.visitEnd();

        return cw.toByteArray();
    }

    public static class DynamicClassLoader extends ClassLoader {
        public Class<?> define(String className, byte[] bytecode) {
            return super.defineClass(className, bytecode, 0, bytecode.length);
        }
    };

    public static void main(String[] args) throws Exception {
        DynamicClassLoader loader = new DynamicClassLoader();
        Class<?> helloWorldClass = loader.define("hello.HelloWorld",
                compile("Test"));
        Method method = helloWorldClass.getMethod("main", String[].class);
        method.invoke(null, (Object) new String[] {});
    }
}

To generate the code, I found very useful Bytecode Outline for Eclipse plug-in. Although you could use the ASMifier (included with ASM) like this:

为了生成代码,我发现了非常有用的Bytecode Outline for Eclipse插件。虽然您可以使用ASMifier(包含在ASM中),如下所示:

ClassReader cr = new ClassReader(new FileInputStream("HelloWorld.class"));
cr.accept(new ASMifierClassVisitor(new PrintWriter(System.out)), 0);

At runtime, if you need to obtain the Class object for the created class, you can load your class by extending a class loader and publishing (through another method, for instance) the defineClass method and providing the class as a byte array, as listed in the example.

在运行时,如果需要获取已创建类的Class对象,可以通过扩展类加载器并发布(例如,通过另一个方法)defineClass方法并将类作为字节数组提供来加载类,如列出的那样在示例中。

You can also handle the created class with an interface, like in this example:

您还可以使用接口处理创建的类,如下例所示:

package hello;

import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.Label;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

public class HelloWorldPlugin implements Opcodes {
    public static interface Plugin {
        void sayHello(String name);
    }

    public static byte[] compile() {

        ClassWriter cw = new ClassWriter(0);
        MethodVisitor mv;

        cw.visit(V1_6, ACC_PUBLIC + ACC_SUPER, "hello/MyClass", null,
                "java/lang/Object",
                new String[] { "hello/HelloWorldPlugin$Plugin" });

        cw.visitInnerClass("hello/HelloWorldPlugin$Plugin",
                "hello/HelloWorldPlugin", "Plugin", ACC_PUBLIC + ACC_STATIC
                        + ACC_ABSTRACT + ACC_INTERFACE);

        {
            mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
            mv.visitCode();
            Label l0 = new Label();
            mv.visitLabel(l0);
            mv.visitLineNumber(5, l0);
            mv.visitVarInsn(ALOAD, 0);
            mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>",
                    "()V");
            mv.visitInsn(RETURN);
            Label l1 = new Label();
            mv.visitLabel(l1);
            mv.visitLocalVariable("this", "Lhello/MyClass;", null, l0, l1, 0);
            mv.visitMaxs(1, 1);
            mv.visitEnd();
        }
        {
            mv = cw.visitMethod(ACC_PUBLIC, "sayHello",
                    "(Ljava/lang/String;)V", null, null);
            mv.visitCode();
            Label l0 = new Label();
            mv.visitLabel(l0);
            mv.visitLineNumber(9, l0);
            mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out",
                    "Ljava/io/PrintStream;");
            mv.visitTypeInsn(NEW, "java/lang/StringBuilder");
            mv.visitInsn(DUP);
            mv.visitLdcInsn("Hello, ");
            mv.visitMethodInsn(INVOKESPECIAL, "java/lang/StringBuilder",
                    "<init>", "(Ljava/lang/String;)V");
            mv.visitVarInsn(ALOAD, 1);
            mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder",
                    "append", "(Ljava/lang/String;)Ljava/lang/StringBuilder;");
            mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/StringBuilder",
                    "toString", "()Ljava/lang/String;");
            mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println",
                    "(Ljava/lang/String;)V");
            Label l1 = new Label();
            mv.visitLabel(l1);
            mv.visitLineNumber(10, l1);
            mv.visitInsn(RETURN);
            Label l2 = new Label();
            mv.visitLabel(l2);
            mv.visitLocalVariable("this", "Lhello/MyClass;", null, l0, l2, 0);
            mv.visitLocalVariable("name", "Ljava/lang/String;", null, l0, l2,
                    1);
            mv.visitMaxs(4, 2);
            mv.visitEnd();
        }
        cw.visitEnd();

        return cw.toByteArray();
    }

    public static class DynamicClassLoader extends ClassLoader {
        public DynamicClassLoader(ClassLoader parent) {
            super(parent);
        }

        public Class<?> define(String className, byte[] bytecode) {
            return super.defineClass(className, bytecode, 0, bytecode.length);
        }
    };

    public static void main(String[] args) throws Exception {
        DynamicClassLoader loader = new DynamicClassLoader(Thread
                .currentThread().getContextClassLoader());
        Class<?> helloWorldClass = loader.define("hello.MyClass", compile());
        Plugin plugin = (Plugin) helloWorldClass.newInstance();
        plugin.sayHello("Test");
    }
}

Have fun.

PS: I can add comments to the code if not clear enough. I didn't because the answer is already too long. Nevertheless, my suggestion for you is to try debugging it.

PS:如果不够清楚,我可以在代码中添加注释。我没有,因为答案已经太长了。不过,我的建议是尝试调试它。

#2

I can suggest that you take a look at these libraries:

我建议你看看这些库:

#3

Check out Jetbrains MPS. Built by guys who brought us IDEA.

查看Jetbrains MPS。由带给我们IDEA的家伙建造。

#4

From a different perspective I ask if you considered to use XText. This is designed to enable you to create DSL, code editor with code completion, compiler, code generator and so on. I think it is real cool and have a nice documentation. Worth to take a look at it. You can create a compiler easily based on it for your DSL.

从不同的角度来看,我问你是否考虑过使用XText。这旨在使您能够创建DSL,代码编辑器与代码完成,编译器,代码生成器等。我认为这很酷,并且有很好的文档。值得一看。您可以根据它为DSL轻松创建编译器。

#1