java獲取參數名稱

javassist和asm都是動態建立、修改字節碼的類庫。我的感受主要區別是：asm的性能要好一些。javassist的主要優點是學習成本 低，能夠根據java源代碼生成字節碼，而沒必要直接和字節碼打交道。（本例不涉及生成字節碼的部分）發現javassist貌似不支持泛型。

基於javassist的實現

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">依賴javassit</font>的工具類，獲取方法的參數名
 * </p>
 * 
 * @author dixingxing
 * @date Apr 20, 2012
 */
public class Classes {
    private Classes() {}

    /**
     * 
     * <p>
     * 獲取方法參數名稱
     * </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;
    }

    /**
     * 獲取方法參數名稱，按給定的參數類型匹配方法
     * 
     * @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);
    }

    /**
     * 獲取方法參數名稱，匹配同名的某一個方法
     * 
     * @param clazz
     * @param method
     * @return
     * @throws NotFoundException
     *             若是類或者方法不存在
     * @throws MissingLVException
     *             若是最終編譯的class文件不包含局部變量表信息
     */
    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);
    }

}

基於asm的實現

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

    private Classes() {
    }

    /**
     * 
     * <p>比較參數類型是否一致</p>
     *
     * @param types asm的類型({@link Type})
     * @param clazzes java 類型({@link Class})
     * @return
     */
    private static boolean sameType(Type[] types, Class<?>[] clazzes) {
        // 個數不一樣
        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>獲取方法的參數名</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);
                // 方法名相同而且參數個數相同
                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;
                        // 若是是靜態方法，則第一就是參數
                        // 若是不是靜態方法，則第一個是"this"，而後纔是方法的參數
                        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));
    }

}