假设我以某种方式从其他类获得了一个对象引用:
Object myObj = anObject;
现在我可以获得这个对象的类:
Class objClass = myObj.getClass();
现在，我可以获得这个类的所有构造函数:
Constructor[] constructors = objClass.getConstructors();
现在，我可以循环每个构造函数:
if (constructors.length > 0)
{
for (int i = 0; i < constructors.length; i++)
{
System.out.println(constructors[i]);
}
}
这已经给了我一个关于构造函数的很好的总结，例如构造函数 public Test(String paramName) 显示为 public Test(java.lang.String)
然而，我没有给我类类型，而是想获取参数的名称.. 在本例中为“paramName”。我该怎么做？我尝试了以下但没有成功:
if (constructors.length > 0)
{
for (int iCon = 0; iCon < constructors.length; iCon++)
{
Class[] params = constructors[iCon].getParameterTypes();
if (params.length > 0)
{
for (int iPar = 0; iPar < params.length; iPar++)
{
Field fields[] = params[iPar].getDeclaredFields();
for (int iFields = 0; iFields < fields.length; iFields++)
{
String fieldName = fields[i].getName();
System.out.println(fieldName);
}
}
}
}
}
不幸的是，这没有给我预期的结果。谁能告诉我我应该怎么做或者我做错了什么？谢谢!
如评论中所述 Roman's answer ，如果编译器包含调试符号，则参数名称可以被检索，尽管不是通过标准的 Java 反射 API。下面是一个示例，说明如何使用 ASM bytecode library 通过调试符号获取参数名称。 :
/**
* Returns a list containing one parameter name for each argument accepted
* by the given constructor. If the class was compiled with debugging
* symbols, the parameter names will match those provided in the Java source
* code. Otherwise, a generic "arg" parameter name is generated ("arg0" for
* the first argument, "arg1" for the second...).
*
* This method relies on the constructor's class loader to locate the
* bytecode resource that defined its class.
*
* @param constructor
* @return
* @throws IOException
*/
public static List<String> getParameterNames(Constructor<?> constructor) throws IOException {
Class<?> declaringClass = constructor.getDeclaringClass();
ClassLoader declaringClassLoader = declaringClass.getClassLoader();
Type declaringType = Type.getType(declaringClass);
String constructorDescriptor = Type.getConstructorDescriptor(constructor);
String url = declaringType.getInternalName() + ".class";
InputStream classFileInputStream = declaringClassLoader.getResourceAsStream(url);
if (classFileInputStream == null) {
throw new IllegalArgumentException("The constructor's class loader cannot find the bytecode that defined the constructor's class (URL: " + url + ")");
}
ClassNode classNode;
try {
classNode = new ClassNode();
ClassReader classReader = new ClassReader(classFileInputStream);
classReader.accept(classNode, 0);
} finally {
classFileInputStream.close();
}
@SuppressWarnings("unchecked")
List<MethodNode> methods = classNode.methods;
for (MethodNode method : methods) {
if (method.name.equals("<init>") && method.desc.equals(constructorDescriptor)) {
Type[] argumentTypes = Type.getArgumentTypes(method.desc);
List<String> parameterNames = new ArrayList<String>(argumentTypes.length);
@SuppressWarnings("unchecked")
List<LocalVariableNode> localVariables = method.localVariables;
for (int i = 0; i < argumentTypes.length; i++) {
// The first local variable actually represents the "this" object
parameterNames.add(localVariables.get(i + 1).name);
}
return parameterNames;
}
}
return null;
}
此示例使用 ASM 库的 tree API .如果速度和内存很宝贵，您可以重构示例以使用其 visitor API相反。