这是一个工作的“你好世界”与
ObjectWeb ASM
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[] {});
}
}
为了生成代码,我发现非常有用
Bytecode Outline for Eclipse
插件。尽管您可以像这样使用asmier(包括在ASM中):
ClassReader cr = new ClassReader(new FileInputStream("HelloWorld.class"));
cr.accept(new ASMifierClassVisitor(new PrintWriter(System.out)), 0);
在运行时,如果需要获取
Class
对象。对于创建的类,可以通过扩展类加载器并发布(例如,通过另一个方法)来加载类
defineClass
方法,并将类作为字节数组提供,如示例中所列。
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");
}
}
玩得高兴。
