金华哪里做网站,网站建设昆山博敏,办公空间设计尺寸标准,建立什么网站#来自ゾフィー#xff08;佐菲#xff09; 1 反射#xff08;Reflect#xff09; 运行期间#xff0c;获取类的信息#xff0c;进行一些操作。
运行时构造类的对象。运行时获取类的成员变量和方法。运行时调用对象的方法#xff08;属性#xff09;。
2 Class 类 Cla…#来自ゾフィー佐菲 1 反射Reflect 运行期间获取类的信息进行一些操作。
运行时构造类的对象。运行时获取类的成员变量和方法。运行时调用对象的方法属性。
2 Class 类 Class 类封装了类的所有信息。
//1.类名.class - Person.class
//2.对象.getClass() - person.getClass()
//3.Class.forName(类全名) - Class.forName(com.yoyiyi.test.Person)
3 Class 常用方法 Person.java
public class Person {String name;private int age;public Person(String name, int age) {super();this.name name;this.age age;System.out.println(有参数构造器);}public Person() {super();System.out.println(无参数构造器);}public String getName() {return name;}public void setName(String name) {this.name name;}public int getAge() {return age;}public void setAge(int age) {this.age age;}private void privateMethod() {System.out.println(私有方法);}
}
public class TestReflec {public static void main(String[] args) throws Exception {ClassPerson clazz (ClassPerson) Class.forName(demo02.Person);/***1.构造器**///获取所有的构造器ConstructorPerson[] constructors (ConstructorPerson[]) clazz.getConstructors();for (ConstructorPerson c : constructors) {System.out.println(c);}//获取某一个构造器ConstructorPerson constructor clazz.getConstructor(String.class, int.class);//创建对象constructor.newInstance(Jack, 89);/**2.方法**///获取类所有方法包括父类私有方法不能获取到Method[] methods clazz.getMethods();for (Method method : methods) {System.out.println(method.getName());}//获取当前类所有方法包括私有方法Method[] methods1 clazz.getDeclaredMethods();for (Method method : methods1) {System.out.println(method.getName());}//获取指定方法Method setName clazz.getDeclaredMethod(setName, String.class);Method setAge clazz.getDeclaredMethod(setAge, int.class);System.out.println(setName.getName());System.out.println(setAge.getName());//调用某一个方法Person person clazz.newInstance();setAge.invoke(person, 89);System.out.println(person.getAge());/**3.属性**///获取当前类的属性不包括父类Field[] fields clazz.getDeclaredFields();for (Field field : fields) {System.out.println(field.getName());}//获取当前类的指定属性Field name clazz.getDeclaredField(name);System.out.println(name.getName());//获取属性的值Person person1 new Person(Maria, 7);String s (String) name.get(person1);System.out.println(s);//设置对象的值Person person2 new Person();Field age clazz.getDeclaredField(age);age.setAccessible(true); //私有属性设置 setAccessible(true)age.set(person2, 5);System.out.println(person2.getAge());//获取当前类的指定私有属性Field age2 clazz.getDeclaredField(age);age2.setAccessible(true);System.out.println(age2.getName());}
}
4 代理模式 为其他对象提供一种代理以控制对这个对象的访问代理类相当于一个中介。 4.1 静态代理 //ISeller.java
public interface ISeller {void sell();
}//Factory.java
public class Factory implements ISeller {Overridepublic void sell() {System.out.println(厂家直销);}
}//Daigou.java
public class Daigou implements ISeller {private ISeller seller;public Daigou(ISeller seller) {this.seller seller;}Overridepublic void buy() {doBefore();//真正调用的持有的类的方法mSeller.sell();doAfter();}private void doBefore() {System.out.println(加价899);}private void doAfter() {System.out.println(提供售后);}
}//TestProxy.java
public class TestProxy {public static void main(String[] args) {Factory factory new Factory();Daigou daigou new Daigou(factory);daigou.buy();}
}//假如我们买一个面膜找到代购代购其实也是别处买的代购加价 899 元卖给你我们不直接和厂家发生关系这种就是一个代理模型
代理模式可以在不修改被代理对象的基础上通过扩展代理类进行一些功能的附加与增强。值得注意的是代理类和被代理类应该共同实现一个接口或者是共同继承某个类。
但是有弊端假如这人不仅不仅要面膜还要核导弹、航空母舰等等就创建了许多代理类。
4.2 动态代理 //ISeller.java
public interface ISeller {void sell();
}//SuperDaigou.java
public class SuperDaigou implements ISeller {Overridepublic void sell() {System.out.println(超级代购);}
}//ProxyHandler.java
public class ProxyHandler implements InvocationHandler {//声明目标对象private ISeller target;public ProxyHandler(ISeller target) {this.target target;}Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {doBefore();Object invoke method.invoke(target, args);doAfter();return invoke;}//得到代理对象public Object getProxyInstance() {return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), this);}private void doBefore() {System.out.println(加价899);}private void doAfter() {System.out.println(提供售后);}
}public class TestProxy {public static void main(String[] args) {SuperDaigou superDaigou new SuperDaigou();ProxyHandler handler new ProxyHandler(superDaigou);//增强原来的方法ISeller seller (ISeller) handler.getProxyInstance();seller.sell();}
}
由于使用了反射效率比较低。
5 动态代理原理解析 //Proxy.java
public static Object newProxyInstance(ClassLoader loader,Class?[] interfaces,InvocationHandler h)throws IllegalArgumentException{Objects.requireNonNull(h);final Class?[] intfs interfaces.clone();final SecurityManager sm System.getSecurityManager();if (sm ! null) {checkProxyAccess(Reflection.getCallerClass(), loader, intfs);}//1.动态生成 class 文件字节流然后通过 loader 加载此字节流创建代理类 classClass? cl getProxyClass0(loader, intfs);/** Invoke its constructor with the designated invocation handler.*/try {if (sm ! null) {checkNewProxyPermission(Reflection.getCallerClass(), cl);}final Constructor? cons cl.getConstructor(constructorParams);final InvocationHandler ih h;if (!Modifier.isPublic(cl.getModifiers())) {AccessController.doPrivileged(new PrivilegedActionVoid() {public Void run() {cons.setAccessible(true);return null;}});}//2.获取代理类的类构造对象return cons.newInstance(new Object[]{h});} catch (IllegalAccessException|InstantiationException e) {throw new InternalError(e.toString(), e);} catch (InvocationTargetException e) {Throwable t e.getCause();if (t instanceof RuntimeException) {throw (RuntimeException) t;} else {throw new InternalError(t.toString(), t);}} catch (NoSuchMethodException e) {throw new InternalError(e.toString(), e);}}//Proxy.java
private static Class? getProxyClass0(ClassLoader loader,Class?... interfaces) {if (interfaces.length 65535) {throw new IllegalArgumentException(interface limit exceeded);}// If the proxy class defined by the given loader implementing// the given interfaces exists, this will simply return the cached copy;// otherwise, it will create the proxy class via the ProxyClassFactoryreturn proxyClassCache.get(loader, interfaces);}// WeakCache.javapublic V get(K key, P parameter) {Objects.requireNonNull(parameter);expungeStaleEntries();Object cacheKey CacheKey.valueOf(key, refQueue);// 根据cachekey获取键值对valuesMap, valuesMap的key是接口列表的包装类value是动态生成代理类的包装类ConcurrentMapObject, SupplierV valuesMap map.get(cacheKey);if (valuesMap null) {ConcurrentMapObject, SupplierV oldValuesMap map.putIfAbsent(cacheKey,valuesMap new ConcurrentHashMap());if (oldValuesMap ! null) {valuesMap oldValuesMap;}}// create subKey and retrieve the possible SupplierV stored by that//核心获取代理类 ProxyClassFactory#applyObject subKey Objects.requireNonNull(subKeyFactory.apply(key, parameter));SupplierV supplier valuesMap.get(subKey);Factory factory null;while (true) {if (supplier ! null) {// supplier might be a Factory or a CacheValueV instanceV value supplier.get();if (value ! null) {return value;}}// else no supplier in cache// or a supplier that returned null (could be a cleared CacheValue// or a Factory that wasnt successful in installing the CacheValue)// 如果动态生成代理类的工厂类为空则创建新的工厂类if (factory null) {factory new Factory(key, parameter, subKey, valuesMap);}if (supplier null) {//工厂类的包装类为空则创建新的包装类supplier supplier valuesMap.putIfAbsent(subKey, factory);if (supplier null) {// successfully installed Factorysupplier factory;}// else retry with winning supplier} else {if (valuesMap.replace(subKey, supplier, factory)) {// successfully replaced// cleared CacheEntry / unsuccessful Factory// with our Factorysupplier factory;} else {// retry with current suppliersupplier valuesMap.get(subKey);}}}}
//以上代码通过 map 来存储动态生成的代理类其中 key 是接口的包装类value 是动态代理类的包装类//Proxy.java#ProxyClassFactoryprivate static final class ProxyClassFactoryimplements BiFunctionClassLoader, Class?[], Class?{// prefix for all proxy class namesprivate static final String proxyClassNamePrefix $Proxy;// next number to use for generation of unique proxy class namesprivate static final AtomicLong nextUniqueNumber new AtomicLong();Overridepublic Class? apply(ClassLoader loader, Class?[] interfaces) {MapClass?, Boolean interfaceSet new IdentityHashMap(interfaces.length);for (Class? intf : interfaces) {/** Verify that the class loader resolves the name of this* interface to the same Class object.*/Class? interfaceClass null;try {interfaceClass Class.forName(intf.getName(), false, loader);} catch (ClassNotFoundException e) {}if (interfaceClass ! intf) {throw new IllegalArgumentException(intf is not visible from class loader);}/** Verify that the Class object actually represents an* interface.*/if (!interfaceClass.isInterface()) {throw new IllegalArgumentException(interfaceClass.getName() is not an interface);}/** Verify that this interface is not a duplicate.*/if (interfaceSet.put(interfaceClass, Boolean.TRUE) ! null) {throw new IllegalArgumentException(repeated interface: interfaceClass.getName());}}String proxyPkg null; // package to define proxy class inint accessFlags Modifier.PUBLIC | Modifier.FINAL;/** Record the package of a non-public proxy interface so that the* proxy class will be defined in the same package. Verify that* all non-public proxy interfaces are in the same package.*/for (Class? intf : interfaces) {int flags intf.getModifiers();if (!Modifier.isPublic(flags)) {accessFlags Modifier.FINAL;String name intf.getName();int n name.lastIndexOf(.);String pkg ((n -1) ? : name.substring(0, n 1));if (proxyPkg null) {proxyPkg pkg;} else if (!pkg.equals(proxyPkg)) {throw new IllegalArgumentException(non-public interfaces from different packages);}}}if (proxyPkg null) {// if no non-public proxy interfaces, use com.sun.proxy packageproxyPkg ReflectUtil.PROXY_PACKAGE .;}/** Choose a name for the proxy class to generate.*/long num nextUniqueNumber.getAndIncrement();//代理类名称String proxyName proxyPkg proxyClassNamePrefix num;//代理类字节码byte[] proxyClassFile ProxyGenerator.generateProxyClass(proxyName, interfaces, accessFlags);try {//最终生成代理类的 class 对象是本地方法 defineClass0 方法//原理是根据类名、接口、类加载器、方法列表、异常列表按照 class 文件格式先生成字节流再生成动态代理类return defineClass0(loader, proxyName,proxyClassFile, 0, proxyClassFile.length);} catch (ClassFormatError e) {/** A ClassFormatError here means that (barring bugs in the* proxy class generation code) there was some other* invalid aspect of the arguments supplied to the proxy* class creation (such as virtual machine limitations* exceeded).*/throw new IllegalArgumentException(e.toString());}}}
