java获取参数名称

摘要: java获取参数名称

javassist和asm都是动态创建、修改字节码的类库。个人感觉主要区别是：asm的性能要好一些。javassist的主要优势是学习成本 低，可以根据java源代码生成字节码，而不必直接和字节码打交道。（本例不涉及生成字节码的部分）发现javassist貌似不支持泛型。

基于javassist的实现

package org.cc.tx.aop.javassit;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;
import javassist.Modifier;
import javassist.NotFoundException;
import javassist.bytecode.CodeAttribute;
import javassist.bytecode.LocalVariableAttribute;
import javassist.bytecode.MethodInfo;

import org.cc.core.CcException;
import org.cc.core.common.Exceptions;

/**
* <p>
* <font color="red">依赖javassit</font>的工具类，获取方法的参数名
* </p>
*
* @author dixingxing
* @date Apr 20, 2012
*/
public class Classes {
private Classes() {}

/**
*
* <p>
* 获取方法参数名称
* </p>
*
* @param cm
* @return
*/
protected static String[] getMethodParamNames(CtMethod cm) {
CtClass cc = cm.getDeclaringClass();
MethodInfo methodInfo = cm.getMethodInfo();
CodeAttribute codeAttribute = methodInfo.getCodeAttribute();
LocalVariableAttribute attr = (LocalVariableAttribute) codeAttribute
.getAttribute(LocalVariableAttribute.tag);
if (attr == null) {
throw new CcException(cc.getName());
}

String[] paramNames = null;
try {
paramNames = new String[cm.getParameterTypes().length];
} catch (NotFoundException e) {
Exceptions.uncheck(e);
}
int pos = Modifier.isStatic(cm.getModifiers()) ? 0 : 1;
for (int i = 0; i < paramNames.length; i++) {
paramNames[i] = attr.variableName(i + pos);
}
return paramNames;
}

/**
* 获取方法参数名称，按给定的参数类型匹配方法
*
* @param clazz
* @param method
* @param paramTypes
* @return
*/
public static String[] getMethodParamNames(Class<?> clazz, String method,
Class<?>... paramTypes) {

ClassPool pool = ClassPool.getDefault();
CtClass cc = null;
CtMethod cm = null;
try {
cc = pool.get(clazz.getName());

String[] paramTypeNames = new String[paramTypes.length];
for (int i = 0; i < paramTypes.length; i++)
paramTypeNames[i] = paramTypes[i].getName();

cm = cc.getDeclaredMethod(method, pool.get(paramTypeNames));
} catch (NotFoundException e) {
Exceptions.uncheck(e);
}
return getMethodParamNames(cm);
}

/**
* 获取方法参数名称，匹配同名的某一个方法
*
* @param clazz
* @param method
* @return
* @throws NotFoundException
*             如果类或者方法不存在
* @throws MissingLVException
*             如果最终编译的class文件不包含局部变量表信息
*/
public static String[] getMethodParamNames(Class<?> clazz, String method) {

ClassPool pool = ClassPool.getDefault();
CtClass cc;
CtMethod cm = null;
try {
cc = pool.get(clazz.getName());
cm = cc.getDeclaredMethod(method);
} catch (NotFoundException e) {
Exceptions.uncheck(e);
}
return getMethodParamNames(cm);
}

}

基于asm的实现

/**
* Classes.java 9:22:44 AM Apr 23, 2012
*
* Copyright(c) 2000-2012 HC360.COM, All Rights Reserved.
*/
package org.cc.core.common;

import java.io.IOException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

import org.cc.core.asm.ClassReader;
import org.cc.core.asm.ClassVisitor;
import org.cc.core.asm.ClassWriter;
import org.cc.core.asm.Label;
import org.cc.core.asm.MethodVisitor;
import org.cc.core.asm.Opcodes;
import org.cc.core.asm.Type;

/**
* <p>
* 基于asm的工具类
* </p>
*
* @author dixingxing
* @date Apr 23, 2012
*/
public final class Classes {

private Classes() {
}

/**
*
* <p>比较参数类型是否一致</p>
*
* @param types asm的类型({@link Type})
* @param clazzes java 类型({@link Class})
* @return
*/
private static boolean sameType(Type[] types, Class<?>[] clazzes) {
// 个数不同
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;
}

/**
*
* <p>获取方法的参数名</p>
*
* @param m
* @return
*/
public static String[] getMethodParamNames(final Method m) {
final String[] paramNames = new String[m.getParameterTypes().length];
final String n = m.getDeclaringClass().getName();
final ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
ClassReader cr = null;
try {
cr = new ClassReader(n);
} catch (IOException e) {
e.printStackTrace();
Exceptions.uncheck(e);
}
cr.accept(new ClassVisitor(Opcodes.ASM4, cw) {
@Override
public MethodVisitor visitMethod(final int access,
final String name, final String desc,
final String signature, final String[] exceptions) {
final Type[] args = Type.getArgumentTypes(desc);
// 方法名相同并且参数个数相同
if (!name.equals(m.getName())
|| !sameType(args, m.getParameterTypes())) {
return super.visitMethod(access, name, desc, signature,
exceptions);
}
MethodVisitor v = cv.visitMethod(access, name, desc, signature,
exceptions);
return new MethodVisitor(Opcodes.ASM4, v) {
@Override
public void visitLocalVariable(String name, String desc,
String signature, Label start, Label end, int index) {
int i = index - 1;
// 如果是静态方法，则第一就是参数
// 如果不是静态方法，则第一个是"this"，然后才是方法的参数
if(Modifier.isStatic(m.getModifiers())) {
i = index;
}
if (i >= 0 && i < paramNames.length) {
paramNames[i] = name;
}
super.visitLocalVariable(name, desc, signature, start,
end, index);
}

};
}
}, 0);
return paramNames;
}

public static void main(String[] args) throws SecurityException,
NoSuchMethodException {
String[] s = getMethodParamNames(Dates.class.getMethod("parse",
String.class,String.class));
System.out.println(Strings.join(s));
s = getMethodParamNames(Dates.class.getMethod("parse",
String.class,String[].class));
System.out.println(Strings.join(s));
}

}