Java获取函数参数名称的另一种方法

亦凉 2022-05-31 07:14 214阅读 0赞

关于获取java 方法的参数名(这里指java 1.8以前的版本,java 1.8已经提供了相关的原生方法)，网上可以找到不少文章，这篇文章讲得比较全面了：[《Java获取函数参数名称的几种方法》][Java]，无外乎是借用asm,javasist等第三方库。

我的项目中也有此需求，看了这篇文章还是觉得比较麻烦，为了这个小小的需求，要多引入一系列依赖库，有点不划算。

我对[axis2][]比较熟悉，知道[axis2][]中在生成client代码时也需要获取方法的参数名，于是通过分析源码找到了[axis2][]的实现代码。  
[axis2][]获取java参数名的实现代码的package为`org.apache.axis2.description.java2wsdl.bytecode`，在axis2核心jar包[axis2-kernel-1.6.2.jar][]中(源码下载地址：[axis2-kernel-1.6.2-sources.jar][])  
好就好在这个package没有引用package之外的代码，所以可以单独提取出来独立调用。

于是我把这部分代码单独复制出来(完整代码参见gitee仓库：  
[https://gitee.com/l0km/common-java/tree/master/common-base/src/main/java/org/apache/bytecode][https_gitee.com_l0km_common-java_tree_master_common-base_src_main_java_org_apache_bytecode])，并在此基础上封装了一个类`ParameterNames`，方便调用：

ParameterNames.java

package net.gdface.utils;
    
    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 net.gdface.utils.Assert;
    
    import org.apache.bytecode.ChainedParamReader;
    
    /**
     * 获取构造函数或方法的参数名<br>
     * 当不能获取参数名的情况下,
     * {@link returnFakeNameIfFail}为{@code false}时返回{@code null},否则返回返回arg,arg2...格式的替代名<br>
     * {@link returnFakeNameIfFail}默认为{@code true}
     * @author guyadong
     *
     */
    public class ParameterNames {
        
        private final Map<Class<?>, ChainedParamReader> readers = new HashMap<Class<?>, ChainedParamReader>();
        private final Class<?> clazz;
        /** 当获取无法参数名时是否返回arg,arg2...格式的替代名字 */
        private boolean returnFakeNameIfFail = true;
        public ParameterNames setReturnFakeNameIfFail(boolean returnFakeNameIfFail) {
            this.returnFakeNameIfFail = returnFakeNameIfFail;
            return this;
        }
    
        /**
         * @param clazz 要构造函数或方法的参数名的类,为{@code null}时所有getParameterNames方法返回{@code null}
         */
        public ParameterNames(Class<?> clazz) {
            this.clazz = clazz;
            if(null != 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) {
            String [] parameterNames = null;
            int paramCount ;
            if (member instanceof Method){
                parameterNames = reader.getParameterNames((Method) member);
                paramCount = ((Method) member).getParameterTypes().length;
            } else if (member instanceof Constructor){
                parameterNames = reader.getParameterNames((Constructor<?>) member);
                paramCount = ((Constructor<?>) member).getParameterTypes().length;
            } else {
                throw new IllegalArgumentException("member type must be Method or Constructor");
            }
            if(this.returnFakeNameIfFail){
                if (null == parameterNames) {
                    parameterNames = new String[paramCount];
                    for (int i = 0; i < parameterNames.length; i++)
                        parameterNames[i] = String.format("arg%d", i);
                }
            }
            return parameterNames;
        }
    
        /**
         * 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) {
            if(null == clazz){
                return null;
            }
            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 #getParameterNames(String, Class)
         */
        public final String[] getParameterNames(String name, Class<?>[] parameterTypes) throws NoSuchMethodException {
            if(null == clazz){
                return null;
            }
            try {
                Member member = null == name ? clazz.getConstructor(parameterTypes) : clazz.getMethod(name, parameterTypes);
                return getParameterNames(member);
            } catch (SecurityException e) {
                throw new IllegalArgumentException(e);
            }
        }
    }

完整代码参见gitee仓库：[https://gitee.com/l0km/common-java/blob/master/common-base/src/main/java/net/gdface/utils/ParameterNames.java][https_gitee.com_l0km_common-java_blob_master_common-base_src_main_java_net_gdface_utils_ParameterNames.java]

调用示例：

private static void outputParameterNames(Method method){
            // 抽象方法不能正确获取参数名，只能用假名替代
            System.out.printf("%s abstract = %b\n parameter names:",
                    method.getName(),
                    Modifier.isAbstract(method.getModifiers()));
            ParameterNames pt = new ParameterNames(method.getDeclaringClass());
            String[] names = pt.getParameterNames(method);
            for(String name:names){
                System.out.print(name + ",");
            }
            System.out.println();
        }

完整的代码参见gitee仓库：  
[https://gitee.com/l0km/common-java/blob/master/common-base/src/test/java/net/gdface/common/ClassTest.java][https_gitee.com_l0km_common-java_blob_master_common-base_src_test_java_net_gdface_common_ClassTest.java]

[Java]: http://blog.csdn.net/wwwwenl/article/details/53427039
[axis2]: http://axis.apache.org/axis2/java/core/
[axis2-kernel-1.6.2.jar]: http://central.maven.org/maven2/org/apache/axis2/axis2-kernel/1.6.2/axis2-kernel-1.6.2.jar
[axis2-kernel-1.6.2-sources.jar]: http://central.maven.org/maven2/org/apache/axis2/axis2-kernel/1.6.2/axis2-kernel-1.6.2-sources.jar
[https_gitee.com_l0km_common-java_tree_master_common-base_src_main_java_org_apache_bytecode]: https://gitee.com/l0km/common-java/tree/master/common-base/src/main/java/org/apache/bytecode
[https_gitee.com_l0km_common-java_blob_master_common-base_src_main_java_net_gdface_utils_ParameterNames.java]: https://gitee.com/l0km/common-java/blob/master/common-base/src/main/java/net/gdface/utils/ParameterNames.java
[https_gitee.com_l0km_common-java_blob_master_common-base_src_test_java_net_gdface_common_ClassTest.java]: https://gitee.com/l0km/common-java/blob/master/common-base/src/test/java/net/gdface/common/ClassTest.java