知识基础
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类
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对象
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构造方法
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重载
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单例模式
动态加载
JVM在执行的时候，并不是一次性把所有的class加载到内存中的，而是用到谁加载谁。
反射的概述
https://www.cnblogs.com/tech-bird/p/3525336.html
Reflection（反射）是Java被视为动态语言的关键，反射机制允许程序在执行期借助于Reflection API取得任何类的內部信息，并能直接操作任意对象的内部属性及方法
获取class对象的三种方式
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class.forName("全类名")
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类名.class
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对象.getClass()，如果上下文存在某个实例对象，可以通过getClass获取他的类
public class re {public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException, NoSuchMethodException, InvocationTargetException {Class cls1 = Class.forName("demo.Person");Class cls2 = Person.class;Person person = new Person();Class cls3 = person.getClass();System.out.println(cls1);System.out.println(cls2);System.out.println(cls3);System.out.println(cls1==cls2);System.out.println(cls3==cls2);}
类“初始化”执行顺序是什么
package demo;public class test {public static void main(String[] args) {Ref ref = new Ref();}}class Ref{static {System.out.println("最先执行rn");}{System.out.println("第二执行rn");}public Ref(){System.out.println("最后执行rn");}}
demo1
package demo;public class test {public static void main(String[] args) throws ClassNotFoundException {Class.forName("demo.CalcDemo");}}class CalcDemo {static {try {Runtime rt = Runtime.getRuntime();Process pc = rt.exec("calc");pc.waitFor();} catch (Exception e) {}}}
Class方法
获取变量
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Field getField(name)：根据字段名获取某个public的field（包括父类）
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Field getDeclaredField(name)：根据字段名获取当前类的某个field（不包括父类）
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Field[] getFields()：获取所有public的field（包括父类）
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Field[] getDeclaredFields()：获取当前类的所有field（不包括父类）
cls3.getField("aaa");//指定名称的public修饰的cls3.getFields();//获取所有public修饰的成员变量cls3.getDeclaredField("aaaa");//获取所有cls3.getDeclaredFields();
获取构造方法
cls3.getConstructors();cls3.getConstructor("aaa");cls3.getDeclaredConstructor("bbb");cls3.getDeclaredConstructors();
package demo;import java.lang.reflect.Constructor;import java.lang.reflect.InvocationTargetException;public class test {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {// Ref ref = new Ref();Class cls = Class.forName("demo.Person");Constructor constructor = cls.getConstructor();Constructor constructor1 = cls.getConstructor(String.class);constructor.newInstance();constructor1.newInstance("jl");}}
demo2
package demo;import java.lang.reflect.Constructor;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.Arrays;import java.util.List;public class test {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {Class cls = Class.forName("java.lang.ProcessBuilder");Method methodStart = cls.getMethod("start");Constructor constructor = cls.getConstructor(List.class);Object obj = constructor.newInstance(Arrays.asList("calc.exe"));methodStart.invoke(obj);}}
demo3-可变长参数
package demo;import java.lang.reflect.Constructor;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.Arrays;import java.util.List;public class test {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {Class cls = Class.forName("java.lang.ProcessBuilder");Method methodStart = cls.getMethod("start");Constructor constructor = cls.getConstructor(String[].class);Object obj = constructor.newInstance(new String[][]{{"calc.exe"}});methodStart.invoke(obj);}}
获取成员方法
cls3.getConstructors();cls3.getConstructor("aaa");cls3.getDeclaredConstructor("bbb");cls3.getDeclaredConstructors();
demo4
package demo;import java.lang.reflect.Constructor;import java.lang.reflect.InvocationTargetException;public class test {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {// Ref ref = new Ref();Class cls = Class.forName("demo.Person");Constructor constructor = cls.getConstructor();Constructor constructor1 = cls.getConstructor(String.class);constructor.newInstance();constructor1.newInstance("jl");}}
demo5
package demo;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;public class test {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {Class cls = Class.forName("java.lang.Runtime");Method method = cls.getMethod("exec", String.class);Method method1 = cls.getMethod("getRuntime");method.invoke(method1.invoke(cls),"calc.exe");}}
Runtime类就是单例模式，我们只能通过 Runtime.getRuntime() 来获取到 Runtime 对 象。
往期回顾
小程序测试流
ModSecurity 搭建web安全防火墙和流量检测
原文始发于微信公众号（雷石安全实验室）：Java安全-01反射
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