ASM ASMifierClassVisitor类应用
ASM是一个十分灵活高效的java字节码生成工具，他可以帮助我们动态的生成所需的字节码文件，也可以修改已存在的字节码使其满足我们新的需要，是一个功能强大的AOP工具。
ASM官网地址http://asm.ow2.org/，附件提供了官方guide很详细，以及ASM的api。
ASM本身功能强大灵活，为此付出的代价就是其功能函数粒度很细，写ASM代码有一种写汇编代码的感觉，不过开发者为此已经想好了解决办法，ASMifierClassVisitor类提供了:生成一个给定class文件的ASM代码的功能。
下面的代码就是利用ASM3.2中的ASMifierClassVisitor类生成 能够产生test类class文件的ASM代码 的代码。
package nihaokid.asm;
import org.objectweb.asm.*;import org.objectweb.asm.attrs.*;public class hhhhtestDump implements Opcodes {public static byte[] dump () throws Exception {ClassWriter cw = new ClassWriter(0);FieldVisitor fv;MethodVisitor mv;AnnotationVisitor av0;cw.visit(V1_6, ACC_PUBLIC + ACC_SUPER, "nihaokid/asm/hhhhtest", null, "java/lang/Object", null);cw.visitSource("hhhhtest.java", null);{mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);mv.visitCode();Label l0 = new Label();mv.visitLabel(l0);mv.visitLineNumber(3, 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", "Lnihaokid/asm/hhhhtest;", 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(9, l0);mv.visitTypeInsn(NEW, "nihaokid/asm/hhhhtest");mv.visitInsn(DUP);mv.visitMethodInsn(INVOKESPECIAL, "nihaokid/asm/hhhhtest", "<init>", "()V");mv.visitVarInsn(ASTORE, 1);Label l1 = new Label();mv.visitLabel(l1);mv.visitLineNumber(10, l1);mv.visitVarInsn(ALOAD, 1);mv.visitMethodInsn(INVOKEVIRTUAL, "nihaokid/asm/hhhhtest", "print", "()V");Label l2 = new Label();mv.visitLabel(l2);mv.visitLineNumber(12, l2);mv.visitInsn(RETURN);Label l3 = new Label();mv.visitLabel(l3);mv.visitLocalVariable("args", "[Ljava/lang/String;", null, l0, l3, 0);mv.visitLocalVariable("t", "Lnihaokid/asm/hhhhtest;", null, l1, l3, 1);mv.visitMaxs(2, 2);mv.visitEnd();}{mv = cw.visitMethod(ACC_PUBLIC, "print", "()V", null, null);mv.visitCode();Label l0 = new Label();mv.visitLabel(l0);mv.visitLineNumber(16, l0);mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");mv.visitLdcInsn("hello world!");mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V");Label l1 = new Label();mv.visitLabel(l1);mv.visitLineNumber(17, l1);mv.visitInsn(RETURN);Label l2 = new Label();mv.visitLabel(l2);mv.visitLocalVariable("this", "Lnihaokid/asm/hhhhtest;", null, l0, l2, 0);mv.visitMaxs(2, 1);mv.visitEnd();}cw.visitEnd();return cw.toByteArray();}}??