java本身提供的方法不能获取方法的参数名的，只能获取每个参数的类型 比如：
代码语言：javascript复制public String concatString(String param1,String param2){
return param1 param2;
}想获取”param1”,和”param2”这个参数名，肯定是不行的。关于获取方法的参数名字(不是参数类型)，一般的做法是借助第三方包javassist或asm来实现。参见下面的文章：
java反射：使用asm 获取方法的参数名 javassist:增强型的java反照工具,获取方法参数名
不过如果你的项目是基于axis2环境的，其实还有第三种方法： 我做基于axis2的项目时，需要获取方法的参数名字，当时也找到了上述的两种办法，都可以实现，没啥问题，但是系统要多一个jar包，感觉不爽。想到axis2在生成wsdl文件时需要获取方法的名字，所以我认为axis2的jar包中肯定有办法获取方法的参数名。于是研究了axis2 关于生成wsdl文件的相关代码，总算找到了，用法也很简单。 在axsi2生成wsdl文件时，使用了一个叫org.apache.axis2.description.java2wsdl.bytecode.MethodTable(axis2-kernel-1.6.2.jar)的类来获取方法的参数名，代码如下：
代码语言：javascript复制/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.axis2.description.java2wsdl.bytecode;
import java.lang.reflect.Method;
import java.util.HashMap;
public class MethodTable {
private HashMap nameToMethodMap;
//关键的实现都在这个类中
private ChainedParamReader cpr;
public MethodTable(Class cls) throws Exception {
cpr = new ChainedParamReader(cls);
nameToMethodMap = new HashMap();
loadMethods(cls);
}
/**
* To load all the methods in the given class by Java reflection
*
* @param cls
* @throws Exception
*/
private void loadMethods(Class cls) throws Exception {
Method [] methods = cls.getMethods();
for (int i = 0; i < methods.length; i ) {
Method method = methods[i];
if (method.isBridge()) {
continue;
}
nameToMethodMap.put(method.getName(), method);
}
}
public String [] getParameterNames(String methodName) {
Method method = (Method) nameToMethodMap.get(methodName);
if (method == null) {
return null;
}
return cpr.getParameterNames(method);
}
}看上面的代码，这个类其实很简单，实际实现获取参数名的工作都是在org.apache.axis2.description.java2wsdl.bytecode.ChainedParamReader下完成的
代码语言：javascript复制/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.axis2.description.java2wsdl.bytecode;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
/**
* Description: In ParamReader class, user cannot get inherited method parameter
* from the class they passed in for performance reasons This class
* is walks up the inheritance chain. If the method is not found in
* the derived class, search in super class. If not found in the immedidate super
* class, search super class's super class, until the root, which is java.lang.Object,
* is reached. This is not an eager load since it only start searching the super class
* when it is asked to.
*/
public class ChainedParamReader {
private List chain = new ArrayList();
private List clsChain = new ArrayList();
private Map methodToParamMap = new HashMap();
/**
* Processes a given class's parameter names.
*
* @param cls the class which user wants to get parameter info from
* @throws IOException
*/
public ChainedParamReader(Class cls) throws IOException {
//具体解析每个class文件是由这个ParamReader实现的
ParamReader reader = new ParamReader(cls);
chain.add(reader);
clsChain.add(cls);
}
//now I need to create deligate methods
/**
* Returns the names of the declared parameters for the given constructor.
* If we cannot determine the names, return null. The returned array will
* have one name per parameter. The length of the array will be the same
* as the length of the Class[] array returned by Constructor.getParameterTypes().
*
* @param ctor
* @return Returns array of names, one per parameter, or null
*/
public String[] getParameterNames(Constructor ctor) {
//there is no need for the constructor chaining.
return ((ParamReader) chain.get(0)).getParameterNames(ctor);
}
/**
* Returns the names of the declared parameters for the given method.
* If cannot determine the names in the current class, search its parent
* class until we reach java.lang.Object. If still can not find the method,
* returns null. The returned array has one name per parameter. The length
* of the array will be the same as the length of the Class[] array
* returned by Method.getParameterTypes().
*
* @param method
* @return String[] Returns array of names, one per parameter, or null
*/
public String[] getParameterNames(Method method) {
//go find the one from the cache first
if (methodToParamMap.containsKey(method)) {
return (String[]) methodToParamMap.get(method);
}
String[] ret = null;
//在当前类中寻找指定的方法，找到就返回
for (Iterator it = chain.iterator(); it.hasNext();) {
ParamReader reader = (ParamReader) it.next();
ret = reader.getParameterNames(method);
if (ret != null) {
methodToParamMap.put(method, ret);
return ret;
}
}
//if we here, it means we need to create new chain.
Class cls = (Class) clsChain.get(chain.size() - 1);
//如果在当前类中找不到指定的方法，就到父类中寻找，找不到就返回null
while (cls != null && cls != java.lang.Object.class && cls.getSuperclass() != null) {
Class superClass = cls.getSuperclass();
try {
ParamReader _reader = new ParamReader(superClass);
chain.add(_reader);
clsChain.add(cls);
ret = _reader.getParameterNames(method);
if (ret != null) { //we found it so just return it.
methodToParamMap.put(method, ret);
return ret;
}
} catch (IOException e) {
//can not find the super class in the class path, abort here
return null;
}
cls = superClass;
}
methodToParamMap.put(method, ret);
return null;
}
}仔细看代码，ChainedParamReader也只是一层级联封装，实现对父类的方法搜索，真正实现对每个class文件字节读取解析是在 org.apache.axis2.description.java2wsdl.bytecode.ParamReader(axis2-kernel-1.6.2.jar)里完成的，如果你想继续深入可以看axis2的源代码。
对于我来说，我只要关心org.apache.axis2.description.java2wsdl.bytecode.ChainedParamReader这个类就够了。
于是我根据自己的需要，基于ChainedParamReader写了这个下面这个类，来实现获取一般方法和构造方法的参数名。
代码语言：javascript复制import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
import org.apache.axis2.description.java2wsdl.bytecode.ChainedParamReader;
/**
* 获取构造函数或方法的参数名
* @author guyadong
*
*/
public class ParameterNames {
private final Map<Class<?>, ChainedParamReader> readers = new HashMap<Class<?>, ChainedParamReader>();
private final Class<?> clazz;
/**
* @param clazz 要构造函数或方法的参数名的类
*/
public ParameterNames(Class<?> clazz) {
this.clazz = clazz;
try {
Class<?> c = clazz;
do {
readers.put(c, new ChainedParamReader(c));
} while (null != (c = c.getSuperclass()));
} catch (IOException e) {
throw new RuntimeException(e);
}
}
/**
* 获取构造函数或方法的参数名
* @param reader
* @param member 构造函数或方法对象
* @return
*/
private final String[] getParameterNames(ChainedParamReader reader, Member member) {
if (member instanceof Method)
return reader.getParameterNames((Method) member);
else if (member instanceof Constructor)
return reader.getParameterNames((Constructor<?>) member);
else
throw new IllegalArgumentException("member type must be Method or Constructor");
}
/**
* 获取构造函数或方法的参数名
* @param member 构造函数或方法对象
* @return
* @see #getParameterNames(ChainedParamReader, Member)
*/
public final String[] getParameterNames(Member member) {
Assert.notNull(member, "member");
Class<?> declaringClass = member.getDeclaringClass();
ChainedParamReader reader;
if (null == (reader = readers.get(declaringClass))) {
throw new IllegalArgumentException(String.format("%s is not member of %s", member.toString(),
declaringClass.getName()));
}
return getParameterNames(reader, member);
}
/**
* 获取构造函数或方法的参数名<br>
* {@code name}为{@code null}时,获取构造函数的参数名
* @param name 方法名
* @param parameterTypes 构造函数或方法的参数类型
* @return
* @throws NoSuchMethodException
* @see {@link #getParameterNames(String, Class)}
*/
public final String[] getParameterNames(String name, Class<?>[] parameterTypes) throws NoSuchMethodException {
try {
Member member = null == name ? clazz.getConstructor(parameterTypes) : clazz.getMethod(name, parameterTypes);
return getParameterNames(member);
} catch (SecurityException e) {
throw new IllegalArgumentException(e);
}
}
}注意： 不论是使用asm，javassist，还是我上述的办法，都只能获取实体类中方法的参数名，对于抽象类或接口，是没有办法的。
