最近有个需求，需要获取java方法参数的名称，网上查了下，然后自己也实践了下，总结出3点：

1.能不能获取方法参数的名称取决于class文件里是否含有LocalVariableTable。 2.javac编译生成的class文件不含有LocalVariableTable，但是eclipse编译生成的class文件却含有LocalVariableTable。 3.有2种方式可以获得，用Asm和Javassist，Asm的性能略高。 贴代码： maven依赖：

    			
     
      org.javassist
     			
     
      javassist
     			
     
      3.18.0-GA
     		
    		
    			
     
      org.ow2.asm
     			
     
      asm
     			
     
      4.1
     		
    

User类：

/** *  * @author yankai * @date 2013-7-17 */public class User {		String name;	String address;	int age;		public User(String name, String address, int age) {		this.name = name;		this.address = address;		this.age = age;	}		public static User newInstance(String name, String address, int age) {		return new User(name, address, age);	}		public User copy(String name, String address, int age) {		return new User(name, address, age);	}}

asm实现：

import java.lang.reflect.Method;import java.lang.reflect.Modifier;import org.objectweb.asm.ClassReader;import org.objectweb.asm.ClassVisitor;import org.objectweb.asm.Label;import org.objectweb.asm.MethodVisitor;import org.objectweb.asm.Opcodes;/** * @author yankai * @date 2013-7-17 */public class AsmTool {		private static boolean sameType(Type[] types, Class
    [] clazzes) {		if (types.length != clazzes.length) {			return false;		}		for (int i = 0; i < types.length; i++) {			if (!Type.getType(clazzes[i]).equals(types[i])) {				return false;			}		}		return true;	}		public static String[] getMethodParamNames(final Method m) throws Exception {		final String[] paramNames = new String[m.getParameterTypes().length];		String methodClass = m.getDeclaringClass().getName();		ClassReader cr = new ClassReader(methodClass);		cr.accept(new ClassVisitor(Opcodes.ASM4) {			@Override			public MethodVisitor visitMethod(final int access,					final String name, final String desc,					final String signature, final String[] exceptions) {				Type[] args = Type.getArgumentTypes(desc);				if (!name.equals(m.getName())						|| !sameType(args, m.getParameterTypes())) {					return null;				}				return new MethodVisitor(Opcodes.ASM4) {					@Override					public void visitLocalVariable(String name, String desc,							String signature, Label start, Label end, int index) {						int i = index - 1;						if (Modifier.isStatic(m.getModifiers())) {							i = index;						}						if (i >= 0 && i < paramNames.length) {							paramNames[i] = name;						}					}				};			}		}, 0);		return paramNames;	}}

asm测试：

import java.lang.reflect.Method;import java.util.Arrays;/** *  * @author yankai * @date 2013-7-17 */public class TestAsm {	public static void main(String[] args) throws Exception {		long start = System.currentTimeMillis();		final Method method = 				User.class.getMethod("newInstance", new Class
    []{String.class, String.class, int.class});		String[] s = AsmTool.getMethodParamNames(method);		System.out.println(Arrays.toString(s));		System.out.println(System.currentTimeMillis() - start);//40	}}

javassist实现：

import javassist.ClassPool;import javassist.CtClass;import javassist.CtMethod;import javassist.Modifier;import javassist.bytecode.CodeAttribute;import javassist.bytecode.LocalVariableAttribute;import javassist.bytecode.MethodInfo;/** *  * @author yankai * @date 2013-7-17 */public class JavassistTool {		// 
    
     	static final Map
     
       pool2map = 			new ConcurrentHashMap
      
       (); 		public static String[] getMethodParamNames(Method method)			throws Exception {		Class
        clazz = method.getDeclaringClass();		String methodName = method.getName();		ClassPool pool = ClassPool.getDefault();		CtClass cc = null;		try {			cc = pool.get(clazz.getName());		} catch (Exception e) {			if (e instanceof NotFoundException) {				pool = pool2map.get(clazz.getClassLoader());				if (pool == null) {					pool = new ClassPool(true);					pool.appendClassPath(new LoaderClassPath(clazz.getClassLoader()));					pool2map.put(clazz.getClassLoader(), pool);				}			}		}		cc = pool.get(clazz.getName());		CtMethod cm = cc.getDeclaredMethod(methodName);		MethodInfo methodInfo = cm.getMethodInfo();		CodeAttribute codeAttribute = methodInfo.getCodeAttribute();		LocalVariableAttribute attr = 				(LocalVariableAttribute) codeAttribute.getAttribute(LocalVariableAttribute.tag);						if (attr == null) {			throw new IllegalStateException("LocalVariableAttribute is null");		}		String[] paramNames = new String[cm.getParameterTypes().length];		int offset = Modifier.isStatic(cm.getModifiers()) ? 0 : 1;		for (int i = 0; i < paramNames.length; i++) {			paramNames[i] = attr.variableName(i + offset);		}		return paramNames;	}}
      
     
    

javassist测试：

import java.util.Arrays;/** *  * @author yankai * @date 2013-7-17 */public class TestJavassist {	public static void main(String[] args) throws Exception {		long start = System.currentTimeMillis();		String[] paramNames = JavassistTool.getMethodParamNames(User.class, "newInstance");		System.out.println(Arrays.toString(paramNames));		System.out.println(System.currentTimeMillis() - start);//90	}}