Reflection -- basic usage

because servlet No main method , Other procedures must be used ,tomcat

The static Cannot call directly , want new First generate the object of the class Through object call Non static methods

Any programming language There are traversal subdirectories and sub files （ route ） The ability of

tomcat I do not know! class Your name cannot pass new To get instances

Reflection ： adopt java The code gets all the information of the class （ What the human eye can see ）, Get the object of the class

Class information ： annotation , attribute , Method , Construction method , Attribute types , Attribute name , Attributes decorate （ Public and private ）, Method type , Method name , Input quantity , Input parameter type , Enter the name .....

（ a key ） How to get information

1. object .getclass

2. class .forName() Class path Call static methods forName Get the corresponding Class object .

tomcat adopt Reflection of the path The other two roads are impassable

3. class .class

calss x1=Person.class; //x1 obtain Person Class information class x2=Cat.class; //x2 obtain Cat Class information class x3=class.forName("Dog Path to class ");

Class information .newlnstance Get an instance of the class . take forName And newlnstance Use in conjunction with , You can create an object based on the class name stored in the string

Must recite v

getFields、 Returns the public Domain （ attribute ）

getMethods Return the method of the class

getConstructors Constructor array of class ,

printConstructors(Classcl) Printing construction method

printMethods(Class） Printing method

printFields(Classcl) Print properties ( Domain )

intgetModifiers() Returns a description of the constructor 、 The integer value of the modifier of a method or field . Use Modifier The method in the class can analyze the return value .

Field[ ]getFields()1

•Filed[ ]getDeclaredFie1ds()

getFields Method will return a containing Field An array of objects , These objects record the public domain of this class or its superclass .getDeclaredField Method will also return containing Field An array of objects , These objects record all fields of this class . If there are no fields in the class , perhaps Class Object describes a basic type or array type , These methods will return a length of 0 Array of .

•Method[] getMethods()

•Method[] getDeclareMethods()

Return contains Method An array of objects ：getMethods All public methods will be returned , Including public methods inherited from superclasses ;getDeclaredMethods Return all the methods of this class or interface , But it does not include methods inherited by superclasses .

•Constructor[ ] getConstructors()

•Constructor[ ] getDeclaredConstructors()

Return contains Constructor An array of objects , Which includes Class All public constructors of the class described by the object （getConstructors) Or all constructors （getDeclaredConstructors).

•Class getDeclaringClass()

Returns a constructor that describes the definition in the class 、 Method or domain Class object .

•Class[ ] getExceptionTypes() ( stay Constructor and Method Class ）

Returns a that describes the type of exception thrown by the method Class An array of objects .

•int getModifiers()

Returns a description of the constructor 、 The integer value of the modifier of a method or field . Use Modifier The method in the class can analyze the return value .

•String getName()

Returns a description of the constructor 、 Method or domain name string .

•Class[ ] getParameterTypes() ( stay Constructor and Method Class ）

Returns a... That describes the parameter type Class An array of objects .

•Class getReturnType()( stay Method Class ） To return a description of H Type of Class object .

Use cases ：

package com.qcby;

import java.lang.reflect.*;


public class ReflectionTest {
	public static void main(String[] args) {
		try{
			Class cl=Class.forName("com.qcby.Person");
			Class supercl=cl.getSuperclass();
			String modifiers=Modifier.toString(cl.getModifiers());
			if(modifiers.length()>0) System.out.print(modifiers+"");
			System.out.print("class"+"com.qcby.Person");
			if(supercl !=null&&supercl!=Object.class)System.out.print("extends"+supercl.getName());
			System.out.print("\n{\n");
			printConstructors(cl);
			System.out.println();
			printMethods(cl);
			System.out.println();
			printFields(cl);
			System.out.println("}");
			}catch(ClassNotFoundException e){
				e.printStackTrace();
				}System.exit(0);
	}
	public static void printConstructors(Class cl){
		Constructor[] constructors=cl.getDeclaredConstructors();
		for(Constructor c:constructors){
			String name=c.getName();
			System.out.print("");
			String modifiers=Modifier.toString(c.getModifiers());
			if(modifiers.length()>0) System.out.print(modifiers+"");
			System.out.print(name+"(");
			Class[] paramTypes=c.getParameterTypes();
			for(int j=0;j<paramTypes.length;j++){
				if(j>0)System.out.print(",");
				System.out.print(paramTypes[j].getName());
				}System.out.println(");");
		}
	}

	public static void printMethods(Class cl){
		Method[] methods=cl.getDeclaredMethods();
		for(Method m:methods){
			Class retType= m.getReturnType();
			String name=m.getName();
			System.out.print("");
			String modifiers=Modifier.toString(m.getModifiers());
			if(modifiers.length()>0)System.out.print(modifiers+"");
			System.out.print(retType.getName()+""+name+"(");

	Class[] paramTypes=m.getParameterTypes();
	for(int j=0;j<paramTypes.length;j++){
		if(j>0) System.out.print(",");
		System.out.print(paramTypes[j].getName());
		}System.out.println(");");
		}
	}
	public static void printFields(Class cl){
		Field[] fields=cl.getDeclaredFields();
		for(Field f:fields){
			Class type=f.getType();
			String name=f.getName();
			System.out.print("");
			String modifiers=Modifier.toString(f.getModifiers());
			if(modifiers.length()>0)System.out.print(modifiers+"");
			System.out.println(type.getName()+""+name+";");
			}
		}
}