加静态标志位,构造方法通过synchronized修饰。或者枚举
举例1:不经过处理的单例类被JAVA反射机制攻击
Singleton.java 代码清单【1.1】
1 public class Singleton 2 { 3 private static boolean flag = true; 4 private static final Singleton INSTANCE = new Singleton(); 5 6 private Singleton() 7 { 8 } 9 10 public static Singleton newInstance() 11 { 12 return INSTANCE; 13 } 14 15 }
SingletonReflectAttack.java 代码清单【1.2】
1 /** 2 * 单例模式被java反射攻击 3 * @throws IllegalArgumentException 4 * @throws InstantiationException 5 * @throws IllegalAccessException 6 * @throws InvocationTargetException 7 * @throws SecurityException 8 * @throws NoSuchMethodException 9 */ 10 11 public static void attack() throws IllegalArgumentException, InstantiationException, IllegalAccessException, InvocationTargetException, SecurityException, NoSuchMethodException 12 { 13 Class<?> classType = Singleton.class; 14 Constructor<?> constructor = classType.getDeclaredConstructor(null); 15 constructor.setAccessible(true); 16 Singleton singleton = (Singleton) constructor.newInstance(); 17 Singleton singleton2 = Singleton.newInstance(); 18 System.out.println(singleton == singleton2); //false 19 }
测试结果:SingletonReflectAttackMain.java 代码清单【1.3】
1 /** 2 * 1.测试单例模式被java反射攻击 3 * @throws NoSuchMethodException 4 * @throws InvocationTargetException 5 * @throws IllegalAccessException 6 * @throws InstantiationException 7 * @throws SecurityException 8 * @throws IllegalArgumentException 9 */ 10 @Test 11 public void testSingletonReflectAttack() throws IllegalArgumentException, SecurityException, InstantiationException, IllegalAccessException, InvocationTargetException, NoSuchMethodException 12 { 13 System.out.println("-------------单例模式被java反射攻击测试--------------"); 14 SingletonReflectAttack.attack(); 15 System.out.println("--------------------------------------------------"); 16 } 17
运行结果:
返回结果为false,说明创建了两个不同的实例。通过反射获取构造函数,然后调用setAccessible(true)就可以调用私有的构造函数;所以创建出来的两个实例时不同的对象。
如果要抵御这种攻击,就要修改构造器,让他在被要求创建第二个实例的时候抛出异常。
下面,我们对饿汉式单例模式做修改。
举例2.经过处理的单例类,JAVA反射机制攻击测试
SingletonNotAttackByReflect.java 代码清单【2.1】
1 package com.lxf.singleton; 2 3 import javax.management.RuntimeErrorException; 4 5 public class SingletonNotAttackByReflect 6 { 7 private static boolean flag = false; 8 private static final SingletonNotAttackByReflect INSTANCE = new SingletonNotAttackByReflect(); 9 10 //保证其不被java反射攻击 11 private SingletonNotAttackByReflect() 12 { 13 synchronized (SingletonNotAttackByReflect.class) 14 { 15 if(false == flag) 16 { 17 flag = !flag; 18 } 19 else 20 { 21 throw new RuntimeException("单例模式正在被攻击"); 22 } 23 24 } 25 } 26 27 public static SingletonNotAttackByReflect getInstance() 28 { 29 return INSTANCE; 30 } 31 32 33 }
SingletonReflectAttack.java 代码清单【2.2】
1 public static void modifiedByAttack() 2 { 3 try 4 { 5 Class<SingletonNotAttackByReflect> classType = SingletonNotAttackByReflect.class; 6 Constructor<SingletonNotAttackByReflect> constructor = classType.getDeclaredConstructor(null); 7 constructor.setAccessible(true); 8 SingletonNotAttackByReflect singleton = (SingletonNotAttackByReflect) constructor.newInstance(); 9 SingletonNotAttackByReflect singleton2 = SingletonNotAttackByReflect.getInstance(); 10 11 System.out.println(singleton == singleton2); 12 } 13 catch (Exception e) 14 { 15 e.printStackTrace(); 16 } 17 18 }
SingletonReflectAttackMain.java 代码清单【2.3】
1 /** 2 * 2.修改后的单例模式被java反射攻击测试. 3 * 攻击失败 4 * @throws IllegalArgumentException 5 * @throws SecurityException 6 * @throws InstantiationException 7 * @throws IllegalAccessException 8 * @throws InvocationTargetException 9 * @throws NoSuchMethodException 10 */ 11 12 @Test 13 public void testModifiedByattack() throws IllegalArgumentException, SecurityException, InstantiationException, IllegalAccessException, InvocationTargetException, NoSuchMethodException 14 { 15 System.out.println("-------------修改后的单例模式被java反射攻击测试--------------"); 16 SingletonReflectAttack.modifiedByAttack(); 17 System.out.println("----------------------------------------------------------"); 18 }
运行结果:
在之前,我们也介绍过,枚举类型的单例模式也可以防止被JAVA反射攻击,这里我们简单测试一下。
举例3:枚举类型的单例模式被JAVA反射机制攻击测试
Singleton6.java 代码清单【3.1】
1 public enum Singleton6 2 { 3 INSTANCE; 4 5 private Resource instance; 6 7 Singleton6() 8 { 9 instance = new Resource(); 10 } 11 12 public Resource getInstance() 13 { 14 return instance; 15 } 16 17 18 }
SingletonReflectAttack.java 代码清单【3.2】
1 public static void enumAttack() throws SecurityException, NoSuchMethodException, IllegalArgumentException, InstantiationException, IllegalAccessException, InvocationTargetException 2 { 3 try 4 { 5 Class<Singleton6> classType = Singleton6.class; 6 Constructor<Singleton6> constructor =(Constructor<Singleton6>) classType.getDeclaredConstructor(); 7 constructor.setAccessible(true); 8 constructor.newInstance(); 9 10 } 11 catch (Exception e) 12 { 13 e.printStackTrace(); 14 }
SingletonReflectAttackMain.java 代码清单【3.3】
1 /** 2 * 枚举类型的单例模式被java反射攻击测试 3 * 攻击失败 4 * 5 * @throws IllegalArgumentException 6 * @throws SecurityException 7 * @throws InstantiationException 8 * @throws IllegalAccessException 9 * @throws InvocationTargetException 10 * @throws NoSuchMethodException 11 */ 12 13 @Test 14 public void testenumAttack() throws IllegalArgumentException, SecurityException, InstantiationException, IllegalAccessException, InvocationTargetException, NoSuchMethodException 15 { 16 System.out.println("-------------枚举类型的单例模式被java反射攻击测试--------------"); 17 SingletonReflectAttack.enumAttack(); 18 System.out.println("----------------------------------------------------------"); 19 }
运行结果:
原文:https://www.cnblogs.com/lthIU/p/6240128.html
原文地址:https://www.cnblogs.com/luquanjian/p/10886793.html
时间: 2024-10-12 02:07:30