反射使用指南

反射

反射的作用：
在运行状态中，

• 对于任意一个类，都能够知道这个类的所有属性和方法
• 对于任意一个类，都能够调用它的任意一个属性和方法

当然，还可以获知类的父类、接口和包等信息。

反射还是比较重要的知识点，这里主要介绍反射的各个方法的使用，可以做工具参考。

实体类

import java.io.Serializable;
import java.util.List;

public class ReflectionEntity implements Cloneable, Serializable {
    private String str;
    private double d;
    public boolean b;
    public static short s;

    public ReflectionEntity() {

    }

    public ReflectionEntity(String str) {
        this.str = str;
    }

    public ReflectionEntity(String str, double d, boolean b) {
        this.str = str;
        this.b = b;
        this.d = d;
    }

    private void privateMethod() {

    }

    public String publicMethod(int i) {
        return null;
    }

    public String publicMethod(int i, double d, List<String> l) {
        return "Reflection.publicMethod(int i, double d, List<String> l), result: " + "i = " +
                i + ", d = " + d;
    }

    public static int returnOne() {
        return 1;
    }

    public String toString() {
        return "Str = " + str + ", d = " + d + ", b = " + b;
    }
}

测试类

import javafx.scene.effect.Reflection;

import java.awt.*;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;

public class ReflectionTest {
    public static void main(String[] args) throws Exception {
        Class<?> c = Class.forName("ReflectionEntity");
        ReflectionEntity re = (ReflectionEntity) c.newInstance();
        ReflectionEntity[] res = new ReflectionEntity[2];

        // -------------- Class and ClassLoader --------------
        System.out.println("Class.getClass(): " + c.getClass());
        System.out.println("Class.getClassLoader(): " + c.getClassLoader());
        System.out.println("Class.getSuperclass(): " + c.getSuperclass());
        // 获取类的接口列表，返回的是一个数组
        System.out.println("Class.getInterfaces(): " + c.getInterfaces()[0] + ", " + c.getInterfaces()[1]);
        // 获取该数组的 Class 对象
        System.out.println("Class.getComponentType(): " + res.getClass().getComponentType());

        // 默认调用无参构造方法实例化
        System.out.println("Class.newInstance(): " + re);

        // -------------- Method --------------
        Method method1 = c.getMethod("publicMethod", int.class, double.class, List.class);
        System.out.println("Method.getMethod(): " + method1);

        Method method2 = c.getDeclaredMethod("privateMethod");
        System.out.println("Method.getDeclareMethod(): " +method2);

        // 获取此类包括其父类中所有的 public 方法
        Method[] md1 = c.getMethods();
        System.out.println("Method.getMethods(): ");
        for (Method m : md1)
            System.out.println(m + "\n");

        // 返回此类中所有的方法(无访问权限限制),但不包括继承的方法
        Method[] md2 = c.getDeclaredMethods();
        System.out.println("Method.getDeclaredMethods(): ");
        for (Method m : md2)
            System.out.println(m + "\n");

        System.out.println("getName: " + method1.getName());
        System.out.println("isAccessible(): " + method1.isAccessible());
        System.out.println("isVarArgs(): " + method1.isVarArgs());
        System.out.println("getReturnType(): " + method1.getReturnType());
        // 获取方法的参数类型，数组形式
        System.out.println("getParameterTypes(): " + method1.getParameterTypes()[0] + ", " + method1.getParameterTypes()[1] + ", " + method1.getParameterTypes()[2]);
        // 获取方法的参数化（带泛型）类型，数组形式
        System.out.println("getGenericParameterTypes(): " + method1.getGenericParameterTypes()[0] + ", " + method1.getGenericParameterTypes()[1] + ", " + method1.getGenericParameterTypes()[2]);

        System.out.println(method1.invoke(re, 233, 666, new ArrayList<String>()));

        // -------------- Field --------------
        Field f1 = c.getField("b");
        Field f2 = c.getDeclaredField("d");
        System.out.println("getField(): " + f1);
        System.out.println("getDeclareField(): " + f2);

        Field[] fs1 = c.getFields();
        Field[] fs2 = c.getDeclaredFields();
        System.out.println("getFields(): ");
        for (Field f : fs1)
            System.out.println(f);
        System.out.println("getDeclareFields(): ");
        for (Field f : fs2)
            System.out.println(f);

        System.out.println("getName and getType: " + f1.getName() + ", " + f1.getType());
        System.out.println("getBoolean(): " + f1.getBoolean(re));

        // 由于 isAccessible 为 false 故会报异常
        //System.out.println("getDouble(): " + f2.getDouble(re));

        // 以整数形式返回此Field对象的Java语言修饰符，如public、static、final等
        System.out.println("getModifiers(): " + f1.getModifiers());

        // 返回Field的访问权限
        System.out.println("isAccessible(): " + f1.isAccessible());

        f2.setAccessible(true);
        System.out.println("getDouble(): " + f2.getDouble(re));
        System.out.println(re);
        f2.setDouble(re, 233.666);
        System.out.println(re);
        f2.setAccessible(false);

        // -------------- Constructor --------------
        Constructor<?> constructor = c.getConstructor(String.class);
        Constructor<?>[] constructors = c.getConstructors();
        System.out.println("constructor: " + constructor);
        System.out.println("constructors: ");
        for (Constructor cc : constructors)
            System.out.println(cc);

        System.out.println("getName: " + constructor.getName());
        System.out.println("isAccessible(): " + constructor.isAccessible());
        System.out.println("isVarArgs(): " + constructor.isVarArgs());
        System.out.println("getModifiers(): " + constructor.getModifiers());
        // 获取方法的参数类型，数组形式
        System.out.println("getParameterTypes(): " + constructor.getParameterTypes()[0]);

        ReflectionEntity r = (ReflectionEntity) constructor.newInstance("AE86");
        System.out.println("newInstance(): " + r);

        Field f3 = c.getField("s");
        System.out.println("f3.getModified :" + f3.getModifiers());
    }
}

也就是说如果一个方法是 "public static final synchronized" 的，那么这个方法的 getModifiers() 返回的应该是 1 + 8 + 16 + 32 = 57。可通过 “&” 运算反过来推算。