获取Java方法参数的名称

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：

<dependency>
<groupId>org.javassist</groupId>
<artifactId>javassist</artifactId>
<version>3.18.0-GA</version>
</dependency>
<dependency>
<groupId>org.ow2.asm</groupId>
<artifactId>asm</artifactId>
<version>4.1</version>
</dependency>

User类：

/**
*
* @author <a href="mailto:yankai913@gmail.com">yankai</a>
* @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 <a href="mailto:yankai913@gmail.com">yankai</a>
* @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 <a href="mailto:yankai913@gmail.com">yankai</a>
* @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 <a href="mailto:yankai913@gmail.com">yankai</a>
* @date 2013-7-17
*/
public class JavassistTool {
// <ClassLoader, ClassPool>
static final Map<ClassLoader, ClassPool> pool2map =
new ConcurrentHashMap<ClassLoader, ClassPool>();
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 <a href="mailto:yankai913@gmail.com">yankai</a>
* @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
}
}