如何在运行时发出和执行 Java 字节码？
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How to emit and execute Java bytecode at runtime?
提问by vitaut
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 为具有一些脚本功能的域特定语言编写解释器。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（使用抽象语法树或一些自定义字节码）或目标 JVM（在运行时发出和执行 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能否说一下以 JVM 为目标的方法的可行性，以及您建议使用哪些库来发出 Java 字节码？
采纳答案by mschonaker
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 Eclipseplug-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。尽管您可以像这样使用 ASMifier（包含在 ASM 中）：
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 Classobject for the created class, you can load your class by extending a class loader and publishing (through another method, for instance) the defineClassmethod and providing the class as a byte array, as listed in the example.
在运行时，如果您需要Class为创建的类获取对象，您可以通过扩展类加载器并发布（例如通过另一种方法）该defineClass方法并将类作为字节数组提供，如例子。
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.
玩得开心。
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，我对您的建议是尝试调试它。
回答by Bozho
回答by Peter Knego
Check out Jetbrains MPS. Built by guys who brought us IDEA.
查看Jetbrains MPS。由给我们带来 IDEA 的人构建。
回答by Gábor Lipták
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.
从不同的角度我问你是否考虑使用XText。这旨在使您能够创建 DSL、具有代码完成功能的代码编辑器、编译器、代码生成器等。我认为它真的很酷并且有一个很好的文档。值得一看。您可以基于它为您的 DSL 轻松创建一个编译器。
